Environmental Sustainability

One of the challenges facing modern forest management is producing forest products, including bioenergy and bio-based products, from southern forests in a sustainable manner (Guldin and Kaiser 2004). Defining sustainability and sustainable forest management has been difficult because of complexity in relevant scientific concepts and the state of current technical progress that might have practical application for land managers. And, as stated by Shifley (2006), we need to improve the ability of the natural resource community to interpret a variety of performance indicator measurements with regard to sustainability. Definitions related to sustainability have also eluded precise clarity and consensus because of the highly politically charged atmosphere that characterizes ongoing debates about forest management practices and land tenure involving landowners, forest industry, environmental conservation organizations, aboriginal peoples, the general public, and public agencies at local to national and international levels. The discussions and debates over what sustainability means precisely are still vigorously continuing as of 2006 (Floyd 2002, Shifley 2006).

In spite of our collective difficulty in agreeing on precise definitions of sustainability and sustainable forest management, there has been very rapid progress in several important ways since the Rio Earth Summit in 1992. Examples of recent progress can be seen in the following three examples. First, The Dictionary of Forestry (Helms 1998) now includes definitions of sustainability and sustainable forest management and related concepts; and in the context of forests, sustainability has been defined as "...the capacity of forests, ranging from stands to ecoregions, to maintain their health, productivity, diversity, and overall integrity, in the long-run, in the context of human activity and use."

A second example of progress during the last decade is seen in international programs in which nations are voluntarily agreeing to document and report progress towards measurable sustainability goals. The United States participates in one such international program called the Montreal Process in which national trends are measured over time according to criteria and indicators (C&I) of sustainable forest management. The most recent national report, titled National Report on Sustainable Forests - 2003 (Guldin and Kaiser 2004), provides an analysis of data describing the condition of U.S. forests according to the Montreal Process C&I, and proposes alternatives for continued progress.

A third example is characterized by the development of certification schemes, such as the Forest Stewardship Council, that are designed to guarantee that specific performance standards related to sustainable forest management are achieved by forest managers. Certification programs vary with respect to regional applicability and standards to be achieved, but all require third-party audit, and therefore provide the general public and consumers the basis for objective, independent assessment and verification that management systems will achieve the principles of sustainability.

These examples provide evidence that sustainability concepts are emerging from theory to practice. They demonstrate that national policy and legislation are evolving and informed by a science-based understanding of sustainability. They clearly show that industry and the market place have incorporated concepts of sustainability into regular business practice. It is important to recognize that all parties engaged in development of the conceptual framework for sustainable forest management implicitly accept that, with proper forest management, it is possible to achieve sustainable forest management in practice. All parties should enter into negotiations leading to related international agreements with that in mind. Those involved in the business of financially supporting certification systems must have market-driven incentives to achieve sustainable forest management. In effect, all parties are committed to the principle that it is possible to maintain and enhance the site productivity, water quality, and biodiversity of forests managed with varying intensities over the long-term at stand and ecoregion levels of resolution by applying management systems that consider environmental, economic, and social criteria (Angelstam and others 2002; Burger 2002; Neary 2002; Shepard 2006; Environmental Benefits of Biomass, Forest Management and Silviculture for Bioenergy Production, and Carbon Displacement).

The primary purpose of this section on Environmental Sustainability is to introduce the concept of sustainable forest management; to develop an understanding of the scientific basis defining the sustainability of forest ecosystems from perspectives of soils, water, and biodiversity; and to summarize the policy framework and certification programs which enable forest landowners and managers to develop sustainable practice and maintain market access for both traditional forest products, as well as emerging bioenergy and bio-based products. This section will discuss the main issues affecting the sustainability of resources associated with forest ecosystems which require careful consideration and conservation, and which are considered valuable goods and services provided by forests, namely forest soils, water quality and quantity, and biodiversity; and provides guidance for designing low-impact, sustainable forest operations to protect and conserve soil, water, and biodiversity resources. Although most of the material in this section has been necessarily drawn from broad, national and international perspectives, specific information relevant to Southern conditions is provided wherever possible. Readers should be aware that concepts defining sustainable forest management are applicable to management systems designed to produce a wide array of good and services, including traditional forest products, wildlife, water, aesthetics, as well as biomass for renewable energy and bio-based products. Where necessary, special attention will be given to ways in which sustainability is differentially affected when forests are managed for bioenergy or new bio-based product feedstocks. Specific subsections include:

• Framework for Achieving Sustainable Forest Management
• Soil Values
• Hydrologic Values
• Biodiversity Values
• Designing Low-Impact Operations

Topics covered in this section of the Encyclopedia of Southern Bioenergy are complementary to topics covered from different perspectives in other sections of this encyclopedia titled Forest Management and Silviculture for Bioenergy Production, Introduction to Harvesting, Processing, Storage, and Delivery, and Economics.

Forest health and vitality and global carbon cycles are considered important criterion of sustainable forest management. However, scientific concepts and management practices related to these two Montreal Process criteria will not be covered in any depth by this section of the Encyclopedia. Topics related to insects, diseases, risk of wildfire, and invasive species will be covered where active management of Southern forests for bioenergy and bio-based products will reduce risk of decline or improve the health of Southern forests. Readers interested in issues related to Southern U.S. forest health are directed to summary documents by Hoffard and others (1995), Rauscher and Johnson (2004) and relevant materials found in other parts of the Forest Encyclopedia Network, such as Forest Environmental Threats and the Encyclopedia of Southern Pine Beetle. Readers interested in the relevance of bioenergy and bio-based products to global carbon cycles are directed to the section of the Encyclopedia titled Environmental Benefits of Biomass and associated resources. The Soil Values and Designing Low-Impact Operations sections of this Encyclopedia provide guidance for ways in which carbon sequestration benefits of forest management can be enhanced through practices which conserve soil and ecosystem organic matter.

"Sustainable forest management" implies that forest resources will be managed to supply goods and services to meet the current demands of society while conserving and renewing the availability, capacity, and quality of the resource, at least at some scale, if not on every site, for future generations. Internationally agreed definitions of sustainability involve social, environmental, and economic values. Different values are given variable weighting when applied to management planning at scales ranging from stands to ecoregions depending on the site characteristics, stakeholder interests, and local values. Sustaining the environmental values of forest resources requires consideration of such ecosystem attributes as vegetation, soils, water, biodiversity, the productive capacity of soils and forested regions, and forest health.

Each of the topics discussed in this section of the encyclopedia is considered part of the overall framework essential to achieve the intent of sustainable forest management. For example, Adaptive Forest Management provides a management planning framework within which forest managers can set environmental goals for their operations, monitor performance, and continually improve. International agreements and protocols have provided the voluntary policy framework for defining sustainable forest management and have contributed to the establishment of performance standards and criteria and indicators by which performance can be, and is, measured at national and local scales of resolution. Certification systems complete the framework necessary to achieve sustainable forest management by providing mechanisms for third pary audit of forest management systems, performance standards, and operational success. Each of these components of the overall framework is described in more detail in the following sections:

• Adaptive Forest Management
• International Agreements and Protocols
• Certification Systems

Adaptive Forest Management

Adaptive management is defined in The Dictionary of Forestry (Helms 1998) as "a dynamic approach to forest management in which the effects of treaments and decisions are continually monitored and used, along with research results, to modify management on a continuing basis to ensure that objectives are being met." As such, Adaptive Forest Management can be pictured as a procedural approach to management which has been developed to enable forest managers to improve the effectiveness of their management systems through formal commitment to performance evaluation procedures. This approach has been developed to ensure that management is consistent, structured, and involves auditable practices. The process of Adaptive Forest Management (above) includes steps for planning, developing operational guidelines, monitoring outcomes, evaluation, response, and reporting to stakeholders (Raison 2002). This type of system is based on the principles of openness, transparency, and accountability. All stakeholders are able to participate, there is clarity in decision-making, and specific individuals are responsible for carrying out the desired actions.

The planning process involves setting goals and objectives for the each resource to be managed, i.e. soils, water, vegetation, biodiversity. Openness and transparency are key to this part of the process and at all levels of the organization.

Operational guidelines are the implementation stage of adaptive forest management. Processes, resources, and responsible individuals are identified to carry out the goals and objectives identified in the planning process.

Standards and other appropriate information are necessary for the monitoring and evaluation stages. Independent auditing is becoming more and more acceptable during these stages. (International agreements, standards, and protocols are discussed in more detail in later sections.) Monitoring is performed to ensure compliance with the plans developed and an evaluation is conducted to ensure that practices are sustainable.

The agreed responses stage involves adapting plans based on the monitoring and evaluation conducted. Plans should be adapted based on advances in management techniques and site specific changes over time.

The final stage to complete the cycle is reporting to stakeholders. Reporting helps to ensure accountability and helps maintain the openness and transparency crucial to the entire adaptive forest management system.

While reporting to stakeholders is considered the last step in the process of adaptive forest management, it should be understood that the process does not stop at this point. Rather, Adaptive Forest Management is an ongoing process to promote continual maintenance and improvement in management practices and forest conditions.

Concepts and procedures embodied in Adaptive Forest Management are being applied throughout the world, and, for example, are reflected in position statements developed by the Society of American Foresters in the Inland Empire region of the Western U.S. This is another example where the theoretical concepts of sustainability are being applied on the ground and affecting day-to-day management of our nations forests.

Overall, forests are important to the health of the global environment and economy. In recognition of the global importance of forests, in 1992, at the Rio Earth Summit, The Statement of Forest Principles and Agenda 21 were adopted by world leaders to recognize the importance of forests to sustainable development (UN-DSD 2007). After the summit, several regional and international initiatives on criteria and indicators for sustainable forest management were developed.

The Montreal Process

The largest of these initiatives, The Montreal Process, relevant to most of the worlds temperate and boreal forests, began in 1994 and includes Argentina, Australia, Canada, Chile, China, Japan, Republic of Korea, Mexico, New Zealand, Russian Federation, United States, and Uruguay (MPCI 2005).

Representatives of the Montreal Process countries met in 1995 and drafted a set of seven national level criteria and 67 indicators to aid in the conservation and sustainable management of temperate and boreal forests. These criteria and indicators are used by forest managers, policymakers, and the general public. The national level criteria include:

1. Conservation of biological diversity
2. Maintenance of productive capacity of forest ecosystems
3. Maintenance of forest ecosystem health and vitality
4. Conservation and maintenance of soil and water resources
5. Maintenance of forest contribution to global carbon cycles
6. Maintenance and enhancement of long-term multiple socio-economic benefits
7. Legal, institutional, and economic framework for forest conservation and sustainable management

Each of the 67 indicators relates to one of the seven criteria categories. The indicators are both quantitative and qualitative and provide information relevant to present and future forest conditions (MPCI 2005). The criteria and indicators undergo continual review to ensure that new advances in research, technology, and measurement capabilities are incorporated into the process.

One requirement of the Montreal Process is the production of national reports to be available to the public. These reports provide information on the current and future state of a nations forest. Reports for each of the Montreal Process countries can be found on their website.

The many challenges to implementing the Montreal Process include involving all forest stakeholders in the process, collecting the appropriate data, interpreting trends, and making necessary changes. In response to these challenges, the implementation of the Montreal Process criteria and indicators signals a willingness on the part of governments and forest industry to manage forests in a sustainable manner. International agreements defining the criteria and indicators of sustainable forest management provide a framework for the development of certification systems, and provide specific indicators required for monitoring in Adaptive Forest Management.

Certification programs are intended to play a key role in ensuring consumers that the forest products they purchase are produced from forests that are managed in a sustainable manner. These forest products include lumber, paper, fiber board, strand board, and could include energy and other bio-based products. For example, eucalyptus plantations in Brazil, managed by Plantar SA to make charcoal for pig iron production, are certified by the Forest Stewardship Council (FSC Brazil). Another company in Brazil, Tramontina (www.tramontina.com.br) produces FSC certified wood products using Brazilian timbers, and uses manufacturing residues to supply the majority (60%) of their energy demand and reduce their net carbon dioxide emissions, since use of mill residues for energy reduces their demand for fossil fuels. There are many international, national, or regional certification programs that can be adhered to by industry today.

The four major certification programs under which most Southern forests are certified today are the Forest Stewardship Council (FSC US), the Sustainable Forestry Initiative Program (SFI) created by the American Forest and Paper Association, the American Tree Farm System, and ISO 14001.

• Forest Stewardship Council
• Sustainable Forestry Initiative Program
• American Tree Farm System
• ISO 14001

While these programs are currently used to certify forest management systems and traditional forest products, these standards could be applied to forest energy products in the Southern United States (Richardson and others 2005; Lewandowski and Faaij 2006). Energy product suppliers in the United States could certify that they were using raw materials from certified forests, as are Brazilian companies (e.g. Plantar SA and Tramontina). It should be recognized that many of these suppliers would be using materials from both certified and uncertified sources, and that type of mixed source could be accounted for within the chain of custody or labeling system. This would be one way to ensure that at least some forest biomass used to produce energy, whether it is heat, electricity, or fuel, is being produced under sustainable forest management practices.

The majority of forests (93%) that have been certified around the world are located in the Northern Hemisphere (Siry and others 2005; Taylor 2005), although a major driver was originally concern about tropical deforestation. Siry and others (2005) argue that forests which have been certified are typically well managed and that Northern forest resources are generally expanding. It appears that forest certification has developed as a market-oriented program designed to reduce global environmental degradation, maintain market access for certified producers, and possibly promote higher prices for wood products produced on certified land (Siry and others 2005).

As of 1999, non-industrial private forestland (NIPF) owners in the Southern U.S. had a relatively low level of involvement in the development of certification programs, as measured by a survey of landowners (Vlosky 1999). Furthermore, 62% of survey respondents felt that certification of NIPF land was not necessary, and that some combination of adherence to state guidelines, education of NIPF owners regarding sustainable management and harvesting practices, and "certification" of NIPF lands by professional foresters were preferred alternatives. These results indicate NIPF owners preferred to protect private landowner rights, as opposed to delegation of that authority to the federal government, non-governmental organizations (NGOs), and third-party certifiers.

The objective of this and related sections of the Encyclopedia of Southern Bioenergy is to inform landowners about the issues involved, certification programs currently being adopted in the South, and to educate them about sustainable forest management practices and guidelines available for their state. While it is not appropriate for this encyclopedia to direct landowners to certifying agencies, the information provided should be helpful in comparing certification programs which will be useful in discussing alternatives with professional foresters, including forestry extension specialists and agents. Readers interested in a comprehensive comparison among internationally recognized certification systems are encouraged to read the FERN report (Ozinga 2004).

Forest Stewardship Council

The Forest Stewardship Council (FSC) is an international non-profit group offering forest certification. The Council was founded in 1993 by representatives of 25 different countries. The Council currently consists of 600 members representing 70 countries. Membership includes environmental groups, forest products companies, forestry professionals, community forest groups, forest product certification organizations, and indigenous peoples organizations (FCRC 2005).

Ten principles and 57 criteria addressing legal aspects, labor rights, indigenous rights, multiple benefits and environmental impacts of forest management have been developed by the Council. While these criteria are applicable globally, the Council encourages national working groups to adapt the criteria and principles to their local conditions. In the United States, there are nine approved regional standards. Certification by FSC includes a pre-interview, documentation review, and field assessment to determine compliance with the approved standards.

The FSC program includes three tracking approaches. These approaches allow those companies that manufacture or trade certified products to assure the credibility of claims on products by tracking materials as they leave the forest and become products down stream. This "chain of custody" (COC) certification process is like any inventory control system. Chain of custody tracking allows products to be segregated and identified as having come from a particular source, as for example, from an FSC-certified forest. FSC tracking options include a physical separation model that involves separately storing and using certified material; a mixed model which allows the use of both certified and non-certified materials; and a batch model tracks on certified materials which are used in manufacturing during specific periods.

There are also three product labels under the FSC system. A FSC pure label is for products made with 100% certified materials. Materials that are made from 100% recycled content get the FSC recycled label. The FSC mixed label is reserved for products in which a minimum of 10% of the material is certified. These labels are only applied to products that do not include raw materials from controversial sources. Controversial sources include illegally obtained materials, genetically modified trees, ecologically significant forests, and forests where social conflicts exist.

The FSC logo identifies products which contain wood from well-managed forests certified in accordance with the rules of the Forest Stewardship Council.

For more information on the Forest Stewardship Council program in the United States, view their website at www.fscus.org.

Sustainable Forestry Initiative

In 1994, professional foresters, conservationists, scientists, landowners, the forest products industry, and other stakeholders developed the Sustainable Forestry Initiative (SFI) program. The Sustainable Forestry Board  (SFB), a non-profit organization, has management oversight over the SFI program. The SFB is comprised of 15 members that represent the environmental, economic, and social community. The SFB makes decisions on the SFI Standard and verification procedures, program quality control, the SFI label and chain of custody programs and dispute resolutions. In addition to the SFB, an 18-member independent External Review Panel serves in an advisory role to the SFB. This review panel works to ensure the programs scientific and technical accuracy (www.abouterp.org) (FCRC 2005).

The SFI Standard (SFIS) is based on nine principles addressing the cultural, legal, economic, and environmental issues surrounding sustainable forestry. A commitment  to continuously improve sustainable forest management systems is also part of the SFIS. Sustainable forest management, public reporting, procurement of wood and fiber, mitigating illegal logging, and continuous improvement are addressed by the 13 objectives of the SFIS. Third party auditing is required for certification processes to ensure conformance with SFIS. Annual surveillance audits are required and full recertification must occur every five years.

The SFI program also has a chain of custody (CoC) and labeling program. The CoC and labeling program include one label for primary producers and one label for secondary producers. Different claims are available to participants depending on the chain of custody system. Examples of claims include fiber sourcing and percent content. In this context, "labels" can be physically seen on the packaging or advertising of a product. The presence of such a label along with a claim indicates that a product produced by a company is independently certified as conforming to specific standards.

More information about the Sustainable Forestry Initiative program can be found by visiting their websites: www.aboutsfb.org and www.aboutsfi.org.

American Tree Farm System

The American Tree Farm System, under the umbrella of the American Forest Foundation, is a certification program aimed at private landowners. Its mission is to "promote the growing of renewable forest resources on private lands while protecting environmental benefits and increasing public understanding of all benefits of productive forestry." The program currently has 80,000 family forest owners with 33.2 million acres of forestland in 46 states.

To become a certified Tree Farmer, one must meet a set of guidelines that have been outlined by the American Tree Farm System. A management plan is required by these guidelines. Also required is an inspection by an American Tree Farm System volunteer forester every five years.

More information related to the American Tree Farm System can be found at their website, www.treefarmsystem.org, along with their Standards of Sustainability for Forest Certification.

The ISO 14000 certification program series of standards  are published and administered by the International Organization for Standardization. The ISO 14000 series of standards, particularly ISO 14001, relate to Environmental Management Systems (EMS). ISO 14001, first published in 1996, requires that an organization put in place and implement practices and procedures that, when combined, result in an environmental management system which guarantees that they are able to conform to performance standards established by the organization seeking certification. ISO 14001 is the only standard in the 14000 series against which an organization can be certified by an external certification authority.

The ISO 14001 standard requires that an organization:

• Implement, maintain, and improve an environmental management system
• Assure itself of its conformance with its own stated environmental policy
• Demonstrate conformance
• Ensure compliance with environmental laws and regulations
• Seek certification by an external third party organization
• Make a self-determination of conformance

This "plan-do-check-review" process lies at the heart of the ISO 14001 EMS, and incorporates the intent of Adaptive Forest Management in its certification requirements.

More information related to the ISO 14000 series can be found at the ISO website, the U. S. Environmental Protection Agencys website, and at http://www.iso14000-iso14001-environmental-management.com/.

Soil Profile

Soils are the biophysical foundation upon which forests thrive and grow. They contain and provide the nutrients, water, root-associated microbes (e.g. mycorrhizae and N-fixing symbionts), and support for tree growth. The productivity of forests is dependent upon the quality and health of the soils blanketing the landscape. Soils play a critical role in regulating water supplies which we depend on for recreation and drinking and irrigation water. The health and diversity of wildlife are affected indirectly by soil quality because of its relationship with plant-related habitat diversity, structure, and productivity and nutrition. Forest managers have direct control over silvicultural systems and harvesting operations which have the potential to directly affect soil quality in their forests. Conservation and improvement of soil resources are essential to sustainable forest management, and can only be done practically by landowners and foresters who have a working knowledge of the composition and functions of soils and how they are affected by forest management operations.

The objective of this section is to provide a basic understanding of soils and soil management which is essential to sustainably manage forests and harvesting operations.

Specific forest soils topics covered here include:

• Composition
• Function
• Productivity
• Forestry Practices That Can Affect Soils

Soil Composition

Soils are complex and dynamic systems consisting of mixtures of solids, pores, water and gases, and are often seen in several different horizons or layers (Fisher and Binkley 2000; Brady and Weil 2004). Horizons will vary in thickness, boundaries, and composition and generally are more or less parallel to the land surface. These layers contain organic material, pore space, water, and minerals. In an "ideal" soil, pore space makes up approximately 50% of soil volume (at right). Depending on the water content in a soil, different proportions of pore space are filled with air and water.

Soil Critters

Surface horizons are typically referred to as "topsoil." In forest ecosytems, this layer may be high in organic matter due to litter fall and incorporation of organic matter into mineral soil following litter decomposition and soil organism activity. Plants and animals (at left), including bacteria, tree roots, reptiles, and small mammals, live within this soil layer. Topsoil can be altered by adding amendments through either chemical or physical means. Soil amendments such as fertilizers, bedding or tilling can positively affect the fertility and productivity of a soil.

Soil Layers and Horizons

Lower horizons are called subsoil. These horizons (at right), not seen from the soil surface, can greatly influence land use. Some soils differ drastically between the topsoil and subsoil, while other soils have a gradual change from one layer to another. Although much of the water needed for plant growth is stored in the subsoil, the topsoil is generally more conducive to root proliferation. Therefore, the depth of the topsoil often correlates to a soils productivity.

These soil layers and associated physical, biological, and chemical properties are the result of five major factors that affect soil development: parent material, time since soil development was initiated, climatic factors such as temperature and rainfall, topography and landscape position, and vegetation and associated organisms. More detailed information related to Southern forest soils can be found in the introductory module under Soils.

The composition of a soil influences many soil properties that, in turn, affect the potential productivity of forest lands and should be considered for management objectives and operations. For example, water and nutrient movement and storage are affected by soil composition, and affect relatively basic forest management decisions such as crop tree species selection, site preparation and planting operations, fertilizer requirements, and timing of thinning and final harvest operations. Therefore, it is important to understand the composition of the soil on a particular site in order to plan forest management operations that will achieve short- and long-term landowner objectives. Much excellent information about soils is available in the various soil survey reports of the USDA-NRCS (Natural Resources Conservation Service) (http://www.nrcs.usda.gov).

Soil Function

The "function" of soils refers to the roles that soils play in the environment, e.g. supporting plants, transmitting water. Five main functions of soils characterize the relevance of soils to forest management (at right): 1) medium for plant growth, 2) recycling system, 3) water supply regulator, 4) soil organism habitat, and 5) engineering medium (Brady and Weil 2004).

Medium for Plant Growth

Medium for plant growth. Soils play a critical role in supporting the physical structure of plants, controlling water movement, providing essential nutrients, controlling temperature, and providing adequate aeration for living roots. Each of these roles are essential for normal plant growth and development, and many of these can be controlled by foresters and forestry activity.

Soils provide adequate support for trees when soil depth and physical structure allow strong, anchoring root systems to develop. Shallow and wet soils do not typically support trees during strong winds or heavy snowfall as well as deep and well-drained soils.

Soil moisture content and aeration levels must be balanced since plant roots require oxygen for normal respiration and must take up water to maintain normal plant growth and development. Soils that are too wet or dry are therefore not desireable for optimal tree growth and ecosystem health.

Soils are typically well buffered with respect to temperature fluctuations due to the insulating effects of surface forest floor organic matter and temperature regulating properties of soil moisture. Forested soils also have more moderate seasonal fluctuations than bare soil in similar ecosystems due to the temperature moderating effects of the stand of trees. Summer high temperatures and winter low temperatures are therefore more moderate under forests than in open areas. The temperature moderating effects of forests can contribute positively to root development and biological activity in soil organisms in temperate and tropical ecosystems. In boreal ecosystems, soil activity often increases when forests are cleared.

The majority of essential elements needed by trees for normal growth, reproduction, and development are taken up by roots from the soil. In addition to supplying essential nutrients, soils can also contain chemicals which are toxic to plants (phytotoxic) at certain concentrations. Soils that are a good medium for plants continuously supply trees with essential elements in the proportions necessary and appropriate for normal seasonal growth and development. It is common for Southern forest plantations to be fertilized to improve levels of available nutrients and forest growth rates.

Recycling System

Recycling system.The complex physical, chemical, and biological properties of forest soils are created and maintained by incorporation and decomposition of myriad organic compounds in leaf and branch fall, dead roots, and other organic matter. This "recycling" function is an important characteristic of soil productivity maintenance in both unmanaged and managed forests and must be recognized for sound forest management (see Productivity). Because of the great variety of organic matter in forests, e.g. herbaceous plants, tree bark, branches, cones, seeds and foliage, forest soil organism communities have evolved capacities to recycle these compounds. Because of these inherent characteristics soils have the capability to recycle some human waste materials such as wastewater treatment plant effluent, sludge (biosolids), vegetable processing residues, animal manures, some pulp and paper mill sludges and ash from combustion boilers. Such potential recycling systems must be carefully evaluated to ensure that wastes are applied in appropriate amounts and do not contain toxic and environmentally-harmful elements or compounds that could "poison" soils, waters, and plants.

Water Supply Regulator

Water supply regulator. Most water in streams, rivers, lakes, and ground-water aquifers enters the earth through soils. Rain or snow-melt penetrating a forest canopy and soil surface percolates through soil layers, often very slowly, and physically and chemically interacts with soil components resulting in chemically-altered water in streams and aquifers. Water from forested landscapes is slowed and delayed in its passage to streams, thus "regulating" stream flows. Removal of forest vegetation eliminates some or much of this regulating function and reduces time of water contact with soil components. Re-establishing forests restores these functions. Vegetated versus bare soils greatly reduce erosion and runoff rates and help protect many aquatic resource values. Soil management as part of forest management is clearly important to preserve water supplies.

Soil Organism Habitat

Soil organism habitat. Forest soils provide a great variety of habitats for numerous large-, small-, and microscopic-sized organisms. Tiny mites and insects, ants, centipedes, earthworms, and small mammals make their homes in soils where they plow, chop, shred, and move soil components. Bacteria and fungi proliferate in forest floor litter layers and within soils where they decompose organic residues. In these processes, organic matter and inorganic soil particles are intimately mixed and bound together to create plant-nurturing soil structure. Specialized fungi create mutually-beneficial structures with roots (mycorrhizae) that facilitate nutrient and water uptake by trees. Organism habitats are maintained by additions of organic matter and maintenance of soil structure and porosity, all of which can be influenced by forest management.

Engineering Medium

Engineering medium. Soils mediate flows of water and support roads, machines, and structures. Their composition, strength, porosity, and water content influence their utility in engineering functions. Appropriate designs and management of forest roads and machines are important to sustainable silvicultural and harvesting operations.

Soils must have adequate bearing strength to avoid rutting and compaction during harvesting and forwarding operations. Season moisture contents often range from dry to wet with corresponding bearing strengths ranging from high to very low or negligible. Forestry operations should take seasonal soil moisture levels into account, and also select machine and tire designs which provide adequate flotation and soil protection. Forest engineers constructing roads desire soils with adequate bearing strength, shear strength, compressibility, and stability to permit regular traffic of forwarding machinery with heavy loads. Soils not possessing these qualities require expensive engineering technological solutions to meet operational standards. Southern soil physical properties are highly variable across the landscape, so forest managers are encouraged to becom knowledgeable about their specific resources.

Forest Biomass Production Curve

The productivity of a forest ecosystem can be measured according to a variety of outputs or values. For example, productivity might be measured in units relevant to wildlife populations, carbon sequestration, water, or timber. In the context of managing forests for bioenergy feedstocks, it is essential to measure forest productivity by quantifying the accumulation of biomass over time in above- and below-ground components of trees. Tree biomass is typically sorted by material that can be harvested and utilized for various merchantable end-products and material that remains in the forest after harvesting. The productivity of specific forest sites is the result of the interaction of several factors, including climate, soil quality, crop management or silviculture practices, and tree genetic potential. The combination of soil and climatic factors contributing to plant growth and development is generally refered to as "site" productivity. It can be described as biomass accumulation as a function of time. The graphic above depicts a hypothetical forest biomass production curve (Burger 2002). As resources are readily available during early phases of stand development, plant biomass accumulation and generally stand production increases exponentially. A leveling off of the rate of accumulation and decrease in production rate typically occur as resources become limited and trees mature until the point at which the carrying capacity of the site is reached.

Forest Productivity

As characterized by Dyck and Cole (1990) (at left) there are generally three means of increasing the inherent biomass production capacity of a forested site including: (1) selecting plants that can more efficiently convert site resources into biomass; (2) increasing the availability of site resources to plants; and (3) controlling tree density per acre through time to maximize harvest yield. Genetically improved trees can be planted to increase the potential of the stand to efficiently utilize site resources. Fertilizer and weed control are effective for increasing the availability of site resources such as soil water and nutrients essential to crop plants. Soil tillage can also be used to increase the carrying capacity of waterlogged forest sites by increasing aeration in the rooting zone of the soil. Silvicultural systems have been developed for the major Southern forest types which control planting conditions, stand density, and spacing from plantation establishment to final harvest in order to achieve various stand management objectives, including high biomass yields. Many of these practices are described for Southern forests by Fox and others (2004) and Allen and others (2005).

Adhering to the principles of sustainable forest management implies that forest ecosystems will be managed to maintain environmental, economic, and social criteria or values. Environmental criteria for most international agreements, including the Montreal Process, include indicators for site productivity and soil quality (MPCI 2005). Therefore, it becomes essential to understand the biological and physical factors that affect soil and site productivity.

Soil productivity is the capacity of a soil to contribute to the production of a crop, whether it is agricultural crops or forest biomass. Physical, chemical, and biological properties of the soil all affect its productivity.

Different combinations of physical and chemical properties affect the productivity of soil. Some of these properties, including soil depth, parent material, and slope position, cannot be changed easily with management practices, although deep ripping can be accomplished mechanically to increase the effective rooting depth of a soil. Other properties including soil structure, organic matter content, nutrient content, and temperature can be modified by forest practices, which in turn can help to improve the productivity of the soil. Soil productivity is highly influenced by several factors including: soil temperature, water-air balance, and soil fertility (Burger 2002).

Soil temperature can be greatly affected by forest management practices (Burger 2002). Removing organic layers and exposing mineral soils can result in higher surface temperatures. In colder climates, root and shoot growth can be stimulated in this manner. In other climates, it may be necessary to retain or add organic layers to help reduce the soil temperature and stimulate growth. Harvesting has the potential to affect the distribution of organic soil horizons through machine movement and distribution of unutilized forest biomass.

Soil Field Capacity

The water-air balance of soil can also be manipulated through forest management practices. The balance between water and air in soil pore space affects water and nutrient uptake and root respiration (Burger 2002). Plant root function and health are optimal when soil moisture content is near "field capacity" (right), since there is both adequate water and air for root survival. The depth to saturated soil on forest sites is an important measure of the volume of soil in which the water-air balance is optimal for plant health. Water table depth can be affected by forest management activity. For example, the water table can rise in relatively low positions on the landscape after clear-cut harvesting as watershed foliage is removed and tree uptake of water is reduced during a period of revegetation. Alternatively, the water table can be lowered during periods of stand development when foliar surface area is high and water utilization by the crop is high. Water tables can also be lowered by installation of drainage ditches and drain tiles. However, such engineered solutions may be highly prohibitive in forest management operations in the Southern United States.

The term "soil fertility" is used generally to refer to the total availability, concentration, and amount of essential plant nutrients. The essential nutrients that tend to limit forest growth and development include nutrients needed in large quantities (macronutrients) such as nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), and magnesium (Mg), and those for which only trace amounts are necessary (micronutrients) such as boron (B), zinc (Zn), and copper (Cu).

The Nitrogen Cycle

Nitrogen availability often limits the growth of forests in the South (Brady and Weil 2004; Burger 2002; Fisher and Binkley 2000). Trees mostly absorb inorganic forms of nitrogen from the soil; however, the majority of forest ecosystem nitrogen is contained in soil organic matter. Therefore, sustaining the supply of nitrogen to plants requires consideration of the critical physical, chemical, and biological factors that convert organic forms of nitrogen to inorganic forms. The nitrogen cycle (at right) shows how nitrogen is transformed as it passes through the atmosphere, soil, and plant tissue.

Trees utilize nitrogen in the form of nitrate (NO₃^-) anions and ammonium (NH₄⁺) cations, and in some cases as organic compounds. Soil micro-organisms are responsible for converting organic forms of nitrogen to inorganic nitrate and ammonium (mineralization process), and so productive sites often have soil and climatic conditions which are conducive to high rates of biological activity. On sites with insufficient amounts of available nitrogen, chemical fertilizer containing nitrogen may be added, if economically feasible. In appropriate circumstances, other common ways of adding nitrogen to soils include amendment with animal manure, wastewater biosolids and effluent, and planting nitrogen-fixing plants such as those in the legume family; these methods require very specialized consideration and are not common in forestry. Careful management is required to avoid excessive loss of nitrogen due to leaching, which in some cases might be a source of water pollution (Brady and Weil 2004). Nitrogen deficiencies in trees can be identified by yellowish foliage, thin stems, and a stunted appearance.

The Phosphorous Cycle

Phosphorous is needed by plants to help supply energy for the completion of many biochemical processes, including uptake and transportation of plant nutrients. Phosphorous availability limits forest site productivity on some soils (Burger 2002). The phosphorous cycle (at left) shows the organic and inorganic forms of phosphorous and their relative availability for plant growth. Easily soluble inorganic soil phosphorous is the most readily available for plant use. Phosphorous deficiencies generally occur due to a low phosphorous content in very old, highly weathered soil parent materials, or where high levels of iron and aluminum oxides and hydroxides chemically bind with phosphate ions, and reduce phosphorous availability to plants. In general, only a small amount of phosphorous is found in soil parent materials and most phosphorous in forest soils is in organic forms. The application of chemical fertilizer to forests to increase phosphorous availability is relatively common in the South, is necessary for adequate forest growth on some soils (Fox and others 2004), and can be very effective at amending inherent site deficiencies. Poor yields, stunted growth, and plant mortality can be attributed to a lack of phosphorous.

For some forest sites, fertilizer additions of N and/or P or other essential elements may enhance forest growth where economically justified (Allen and others 2005; Fristoe and Gothard 1998; Fox and others 2004). When properly applied, fertilizer can greatly enhance the productivity of a forest site. Nutrients should be applied on the basis of diagnosed deficiencies identified at a specific site. Improper application of fertilizer can lead to negative environmental effects and may violate Best Management Practices and state environmental regulations for forest management (Shepard 2006). More information related to soil productivity and forest fertilization can be found at the Alabama Forestry Commission website and in the literature of the NCSU Forest Nutrition Cooperative (http://www.forestnutrition.org/history.htm).

Spectrum of Managed Systems

High intensity forest management systems affect forest soil through use of fertilizers, weed control chemicals, large machinery, and other potential mechanical impacts which may affect the environmental quality and sustainability of forest sites, as described by Burger (2002) (at right). Forest management systems that are designed to produce bioenergy feedstocks often may involve whole-tree harvesting to recover greater biomass than typically removed during stem-only harvesting systems. Increased biomass recovery and associated intensive silvicultural and mechanical harvesting increases the risk of negative site impacts, and therefore requires care to ensure that such operations can be certified as sustainable. Nutrient depletion and organic matter removal are of specific concern in such intensive biomass production systems, as is the potential for soil erosion and displacement, and soil compaction. Practices that may affect soil quality and sustainability include:

• Organic Matter Disturbance
• Nutrient Management
• Soil Displacement and Compaction

Root Raking

Soil organic matter moderates soil temperature, increases water infiltration and holding capacity, and serves as food and energy for soil organisms. Plant nutrients are also held within soil organic matter, which is the most important source of nitrogen in forest ecosystems. The removal or decrease of soil organic matter, especially forest litter layers on the soil surface, as a result of forest management practices, is generally thought to have negative consequences for environmental sustainability, and therefore should be carefully managed by those responsible for design of biomass production and harvesting systems. Site preparation operations, such as windrowing or root raking, which remove forest floor layers and harvesting residue (at right), have been shown to reduce nutrient availability and stand productivity in the following rotation, and therefore should be conducted in such a manner that minimizes forest site organic matter removal.

Conservation of site production potential requires careful consideration of the amounts of organic matter and nutrients removed with merchantable tree boles, branches and foliage during harvesting operations, and the amount of organic residues retained on site to return organic matter to the soil and to benefit successive rotations of trees. Research has shown that, while the branches, foliage, and unmerchantable tops potentially removed during whole-tree harvesting represent a relatively small proportion of the total biomass produced over the whole rotation, it may be large when compared to the amount of available nutrients on a site.

Nutrient Composition of Loblolly Pine Tree Parts

Tree crown biomass is relatively nutrient rich, and should be retained on site if nutrient deficiencies are predicted in the following rotation. For example, in young loblolly pine trees, the greatest percentage of nutrients is held within the needles, with a smaller percentage of nutrients in stembark, branches, and stemwood (Metz and Wells 1965) (at right). However, during a full rotation a greater amount of organic matter is returned to the soil through tree mortality, root turnover, and litterfall during a full rotation than is removed at harvest time. There is a greater concern for organic matter depletion when growing short rotation woody crops, yet these crops are generally grown on highly fertile soils, and crop nutrition management typically involves regular fertilizer additions (Shepard 2006).

In general, traditional forest harvesting including whole-tree harvesting has been shown by research to cause little or no detriment to site productivity potential in terms of soil organic removal unless followed by mechanical disturbance of forest floor layers, soil tilling, or intense burning (Johnson and Curtis 2001).

Fertilizer Addition

A second possible consequence of intensive management and whole-tree harvesting includes nutrient depletion. Factors that affect nutrient depletion include crop species nutrient demand and composition, orginal site condition, harvesting operations, and age of the stand. Site-specific assessments are required to evaluate the consequences of management system design on site nutrient capital and availability. However, the following generalizations appear applicable to most sites:

Adding Biosolids

1. Deciduous trees contain more nutrients in biomass than conifers, but can be harvested without leaves by either harvesting during winter or leaving felled trees on-site until foliage drops off.
2. Younger stands harvested using the whole-tree method are more likely to have site nutrients depleted, due to nutrient accumulation patterns which result in a greater percentage of nutrients in crowns than boles of young trees.
3. Stem-only extraction removes fewer nutrients than whole-tree harvesting.
4. Soil tillage increases the rate of soil organic matter decomposition and mineralization.
5. Harvesting and site preparation desynchronize nutrient supply and demand. Nutrient availability is very high immediately after harvesting and site preparation operations, but tree uptake demand is typically low and less than available nutrient supply until crown closure is achieved in young plantations.
6. Site preparation that removes harvesting residues associated with branches and foliage reduces the size of active nutrient pools.

The consequences of these practices on site fertility and stand productivity vary by site.

Wood Ash

Several comprehensive reviews of the literature on the long-term effects of intensive forest management of site productivity, including harvest machine traffic, site preparation operations, and intensified biomass utilization have been published (Leaf 1979; Morris and Miller 1994; Burger 2002; Powers and others 2005; papers following Vance and Sanchez 2006). These reviews have reported that, to date, few long-term studies have supported the hypothesis that soil productivity would decline with prolonged periods of intensive harvesting practices. However, trials conducted on sites with previously diagnosed nutrient deficiences (i.e. N and P) indicate that plantation productivity in succeeding rotations will decline if excessive organic matter removals (i.e. forest floor, foliage and tops of harvested trees) result in reduced nutrient availability to the developing crop. For example, loblolly pine productivity has been reduced by whole-tree harvesting on phosphorous deficient sites in the South that previously required fertilizer additions to maintain acceptable growth rates in the rotation before whole-tree harvesting (Scott and others 2004). In New Zealand, removal of the forest floor and whole-tree harvesting reduced productivity in the second rotation of radiata pine (Pinus radiata) planted on recent coastal sand dunes (Smith and others 2000).

Nutrient Management

Forest managers and landowners should practice site-specific nutrient management. This approach will allow identification of the relative level of risk associated with intensive management, and ensure that any proposed management practices and utilization levels are sustainable. Managing nutrient availability to trees may require fertilization (at right) of soils with deficient nutrients, just as done by farmers to maintain and improve the fertility of agricultural production systems.

Fertilizer (at right), wastewater biosolids (below left), and wood ash (below right) can be added to nutrient deficient forest soils to replenish nutrients removed during intensive harvesting operations.

A balanced nutrient management regime that includes nutrient replenishment, monitoring, and selection of appropriate harvesting and site preparation techniques (as described by Peter Clinton and others with the New Zealand Forest Research Institute, at right) will ensure the long-term sustainability of forest soil productivity.

Erosion

Soil erosion and displacement occur through the removal of topsoil by machinery. This can lead to reduced stream water quality through sedimentation. In forests, erosion (at right) is typically caused by surface or overland water flow on sloping terrain that has been cleared of organic matter. In many regions, chemical control of weeds has reduced the need for soil tillage and thus reduced the occurrence of erosion. Orienting site preparation operations and skid trails along slope contours can minimize the risk of soil erosion and displacement. Forest roads are also an important potential source of sedimentation in streams, yet such effects can be mitigated through the use of Best Management Practices developed by the USDA Forest Service and collaborators at such experimental watersheds as Coweeta Hydrologic Laboratory and the Fernow Timber and Watershed Laboratory (see Forest Roads; Stickney and others 1994).

Soil compaction may occur as a result of the use of heavy machinery during harvesting and site preparation operations. This also has the potential to decrease soil productivity, yet few, if any, long-term research trials have documented lasting decreases in forest productivity due to soil compaction across harvested land (e.g. site not located directly on skidder roads and landings) (Morris and Miller 1994; Burger 2002; Powers and others 2005; papers following Powers 2006).

East Texas Lake

Water and water supplies are among the worlds most threatened and precious natural resources. Forests play a key role in maintaining the quantity and quality of water supplied by watersheds throughout the South because such a large portion of the landscape is forested. Forest management operations directly affect many of the forest ecosystem components that in turn determine the amount and quality of water draining from forests, through such actions as the use of fertilizers and chemicals to control weeds, insects, and diseases, the number of trees per acre, harvesting equipment, and soil quality. Therefore, forest managers need to understand how forested watersheds function, and, in turn, how management operations have the potential to affect water that is critical habitat for fish and other wildlife, as well as important for supplying Southern rural and urban populations with drinking water.

Specific topics in this section include:

• Hydrologic Processes Affected by Harvesting
• Water Quantity and Quality

While the information presented in this section of the Encyclopedia of Southern Bioenergy is applicable across the Southern U.S., readers interested in finding out more about water resource management in the Southern Appalachain Mountain region of the Southeast should visit sections of the Encyclopedia of Southern Appalachian Forest Ecosystems. Relevant materials include Aquatic Resource Management and Aquatic Ecology. Readers interested in identifying how the U.S. Geological Survey (USGS) classifies the water resources associated with their land should visit the page on USGS Hydrologic Units. For further reading, we direct readers to a comprehensive summary of forest and wildland watershed research published by the Society of American Foresters (Ice and Stednick 2004).

The Hydrologic Cycle

Water is one of the basic necessities of life. It is needed by all organisms in all ecosystems. Quality and quantity can be affected by processes occurring in watersheds. Many of these watersheds are located in forest lands. The hydrologic cycle (at right) depicts the flow of water through an undisturbed forested watershed. Water flow is affected by climatic factors and other environmental factors and will vary from site to site (Neary 2002).

There are three major outputs of water from watersheds including streamflow, evaporation, and transpiration or evapotranspiration (ET). Streamflow refers to water located in and moving through the watershed in stream channels. Evapotranspiration is the water lost from soil, leaves, and stems of plants, while direct evaporation is from water bodies in the area. Inputs of water are generally from precipitation and include rain, fog, snow, and sleet.

Partitioning of Precipitation

Water movement is influenced by the various pathways precipitation follows en route to streams, such as those affected by plants, including interception, streamflow, and throughfall; those affected by soils including infiltration, surface runoff, interflow, baseflow, and by the intensity and duration of storms (Neary 2002). Interception refers to precipitation that is intercepted by leaves, branches, and stems of the forest canopy as it falls to the ground. In undisturbed forests, 91% of precipitation passes into the soil. Only 1% of watershed precipitation does not enter the soil and runs off as overland flow. The figure to the left shows how rainfall is partitioned as it falls into a forested watershed.

The forestlands in an area can affect the amount of precipitation that enters the water supply. For example, the forest canopy can influence the amount of water that is intercepted and water lost through evaporation and evapotranspiration. The condition of the forest floor can influence the amount of water that infiltrates the soil surface and it can influence the amount of water that is lost due to surface runoff. Healthier soils will allow for more infiltration, while more compacted and eroded soils will favor runoff and result in sediment transfers to surface water in streams and lakes. These factors are all influenced by forest management practices, so it is important to understand that soils, hydrologic processes, and forest management are all related.

Water quantity and water quality are major criteria for measuring the effects of forest management for bioenergy and bio-based products on water resources. Water quantity refers to the timing and total yield of water from a watershed, while water quality refers to the suitability of the water coming from ground and surface water supplies for drinking water, recreational uses, and as habitat for aquatic organisms and other wildlife (Neary 2002). Water quality is measured using chemicals, biological, and physical (i.e. temperature, color, clarity) indicators.

Hubbard Brook Stream Flow

Water quantity is measured in two ways: total yield and peak flow, both of which can be affected by forest management practices including harvesting and residue removal. Total yield is the total amount of available water that flows out of a watershed area. In general, water flow is increased in the first year after harvesting. Removing vegetation and litter from the watershed allows more water to fall and infiltrate the ground and streams. The actual increase in water yield resulting from forest management will depend upon the amount of precipitation, evapotranspiration, percent of cover removed, and other environmental factors including soil conditions (Neary 2002).

Peak flows, or flood peak flows, can also be affected by forest management. However, it is not a simple matter to predict how management will affect watershed responses to storms. For example, some areas will have declines in peak flows, while peak flows will increase in other areas. The effect of management on peak flows will be determined by site specific characteristics which affect the hydrological cycle directly, such as plant leaf area, soil water storage capacity, time of year, and slope and aspect. Sites should be evaluated by qualified professionals prior to any harvesting and production decisions so that watershed responses to management can be predicted reliably. While intensive management can create a risk for an increase in peak flows, severe wildfires produce a greater increase in peak flows than do harvesting operations. Therefore, in order to minimize the risk of adverse impacts on water resources due to active versus passive management, landowners and professional foresters must undertake risk assessment procedures which compare alternative management operations including harvesting biomass in order to reduce fuel loads and wildfire hazards. This is a good example of the ways in which biomass removal can provide a renewable energy source, reduce wildfire risk, and potentially improve water resources. In such situations, doing nothing results in loss of multiple values gained by active management.

Pennsylvania Stream

A second factor to consider when discussing water and biomass production is the effect on water quality. Water quality is measured by the amount of sediment, water temperature, the concentration of pollutants, and the level of nitrogen and other nutrients and chemicals in the water supply. The nitrate-nitrogen concentration in water is one indicator of water quality. High concentrations of nitrate-nitrogen in water can be harmful to human health. However, no long-lasting, harmful increases in stream water nitrate-nitrogen have been observed following harvesting operations (Neary 2002). Herbicide usage to suppress vegetation after fire, the use of chemical fertilizers during regeneration, and atmospheric deposition generally have a greater effect on stream nitrate levels than do harvesting operations.

Sediment yield from forested watersheds is variable and site specific, but generally negligible when compared with many other land uses. Much of the sediment movement is caused by disturbance of the soil during site preparation operations. Proper site preparation techniques, proper road construction, and other best management practices can lessen the potential for sediment movement and adverse effects of forest management on water quality. Readers interested in knowing more about the physical, ecological, and socio-economic effects of forest roads in the mountainous Southeastern U.S. should visit the section on Forest Roads in the Encyclopedia of Southern Appalachian Forest Ecosystems.

Theoretical Detail of a Streamside Management Zone

Forest canopies protect streams from solar radiation, thus reducing the variability in water temperatures. Therefore, harvesting operations can adversely affect stream temperatures. The effect of stream temperatures will depend upon the aquatic species located within the forest streams. Some species are able to survive post-harvest temperature changes better than others. Management practices designed to maintain effective buffer strips along streams and prevent adverse affects of harvesting on water quality have been developed for the major Southern physiographic regions, as for example the Southern Appalachians as a result of research conducted at Coweeta Hydrologic Laboratory (see Forest Roads; Stickney and others 1994), the Alto Watersheds in East Texas, and elsewhere. Managers typically incorporate recommendations for managing Streamside Management Zones (SMZs) into forest management plans, as described under Adaptive Forest Management. Streamside management zones (above right) take into account the area directly around the stream as well as the effects of any management practices that may affect the stream quality.

Recommendations for maintaining water quality in managed forests have been published for all states in the Southern United States. Many of these publications are available through forestry extension programs in each state.

• Alabama
• Arkansas
• Florida
• Georgia
• Kentucky
• Louisiana
• Mississippi
• North Carolina
• Oklahoma
• South Carolina
• Tennessee
• Texas
• Virginia
• Forestry BMP

A recent review by Shepard (2006) indicates that Best Management Practices developed to protect water quality in forests managed for a conventional mix of forest products should be applicable to bioenergy production systems.

Biodiversity Values

The forests of the Southern United States are home to a large number of species of fauna as a result of the warm, relatively humid climate and the diversity of habitats found from Virginia to Texas among the associated coastal plains, bottomlands, and uplands. Forests are valued by many purely for their wildlife populations which provide opportunities to pursue such pastimes as hunting and bird watching. Federal and state laws have been enacted which are intended to prevent species extinction and maintain adequate, critical habitat for rare, threatened, and endangered species. Forest managers are responsible for maintaining the habitat required by wildlife populations in their forests. Therefore, as forests in the South are managed more intensively, and as population growth and urban expansion put greater pressure on forests and result in fragmentation of forest ecosystems, it is critical that foresters and landowners be knowledgeable about the ways in which forest management can affect biodiversity.

This section will provide an explanation of biodiversity, its place in sustainable forest management, and management options to help maintain diversity. Specific topics include:

• Understanding Biodiversity
• Forest Biodiversity Conservation Tools

Readers interested in additional sources of information about biodiversity conservation in our National Forests might consult Norse and others (1986), Linder (2004), and other papers in Rauscher and Johnson (2004) for material related to the South.

Conservation of biodiversity in forest ecosystems is an essential criterion of sustainable forest management. Although definitions of biodiversity are many and diverse (e.g. http://ceres.ca.gov/biodiv/Biodiversity/biodiv_def2.html), biodiversity is defined here as the diversity of species, genes, ecosystem function, and habitats (Angelstam and others 2002). Habitat plays the largest role in maintaining ecological diversity. Habitat is characterized in terms of size, quality, total area, distance between habitat areas, and the nature of the terrain between habitats.

Species need a critical amount of habitat in order to survive, maintain health, and maintain a stable population size. Critical habitat size varies by species, in that some require smaller habitat areas, while other species require larger areas.

Habitat quality also affects the biodiversity of a forest ecosystem. Vegetation quality, water quality, and those factors that affect the amount of shelter and food available throughout the year define habitat quality.

Maintaining biodiversity requires a large number of habitat areas or a large overall habitat area. Small areas can result in problems such as inbreeding depression and may not be adequate to sustain large populations. Also, if the distance between suitable habitats is large, species may not be able to move freely and could overpopulate an isolated habitat area. Habitat areas should be connected in a way that allows for easy travel from one area to another. If the travel route is difficult to traverse, species may not move from area to area.

Ensuring adequate habitat area and connectivity is one way to mitigate extinction and cultivate ecological biodiversity. It is important to understand the concept of habitat because the loss of acceptable habitat is the leading cause of extinction among species. According to Websters online dictionary, extinction is the loss of an animal or plant species from a landscape area. The conservation of habitat will be the most important method of maintaining biodiversity in intensely managed forest landscapes.

Stream Management Zones

Conservation tools have been developed to enable managers to maintain and improve forest biodiversity. Conservation tools can be used in both natural and intensely managed forest landscapes. In the case of intensely managed landscapes, the key is to use the conservation tools in conjunction with the principles of Adaptive Forest Management.

By examining forest stands from a landscape perspective, forest managers can gain a holistic perspective of how a particular stand relates to the larger regional context. Using this approach, one can examine an entire geographical area and estimate the amount of habitat available for various species. For species requiring large habitat areas, this is an especially important conservation tool. The landscape perspective (at right) also allows for the management of habitat over a larger area, rather than just one particular forested stand (Angelstam and others 2002). The Adaptive Forest Management approach taken in forest management certification systems, which intends to guarantee that management practices conform to performance standards which include biodiversity, and involves an opportunity for stakeholder input in planning and standards formulation by conservation groups and non-governmental agencies, can contribute to successful habitat conservation.

Umbrella Species

Another technique employed in biodiversity management is the "umbrella" species concept (Angelstam and others 2002). This technique involves wildlife biologists and forest managers choosing one species, such as the red cockaded woodpecker or flying squirrel (at left), that typically requires a relatively large habitat area that includes large trees and standing dead wood. Other species would then be identified that appear to co-occur with the "umbrella" species in the same habitat area. This allows forest managers to manage the landscape for one species, yet maintain habitat for several species at one time.

Stand structure and spatial configuration can also be manipulated in such a way as to conserve biodiversity in the forest landscape. The maintenance of a structurally complex stand is of utmost importance (Lindenmayer and Franklin 2002). There are three main strategies to managing stands for biodiversity. These strategies include:

1. Structural retention at the time of regeneration harvest
2. Management for creation and/or maintenance of structural complexity
3. Long rotation periods

A Complex Stand

Structural retention at time of regeneration harvest. At the time of harvest, forest managers should decide if certain types and quantities of structures should be retained as potential habitat. These structures include large trees, snags, and dead trees. Other structures, such as trees of varying sizes and ages (at right), would be retained to provide adequate habitat for the conservation of species in the landscape (Lindenmayer and Franklin 2002).

Nest Box

Managing stands for biodiversity. Managing stands for biodiversity includes several different techniques. The most obvious technique is the use of thinning and harvesting to produce stands with a complex structure. According to Lindenmayer and Franklin (2002), other techniques for stand management include creating suitable habitat, installing nest boxes (at left), planting desired plant species, prescribed burning, and introducing or enriching the population of animal species.

Suitable habitat can be created by maintaining buffer zones in intensely managed forest stands. These buffer zones are typically areas that are not harvested and are located in areas between harvested areas. Buffer zones can be along streamsides to protect aquatic life or along forest edge to protect terrestrial species (Russell and others 2004). This has been a proven method of conserving biodiversity in managed stands.

Long rotations

Long rotations. Long rotations allow for the development of structurally complex stands over long periods of time (at right). Lindenmayer and Franklin (2002) define long rotations as rotations significantly longer than the economic rotation of a stand. Rotation times could be extended from 50-300%. This requirement may make this conservation tool less attractive to a large number of forest managers; however it could be applied in streamside management zones and other conservation zones on managed landscapes.

While the same biodiversity conservation tools can be used for both timber operations and bioenergy feedstock production, there are specific challenges with regards to increased utilization of biomass in harvested forests. These challenges include the retention of adequate amounts of dead wood and large and old trees as habitat (Angelstam and others 2002).

Dead Wood

Many species are dependent upon deadwood (at right) for their habitat, yet the harvesting of this type of wood might intensify with increased demand for bioenergy and other bio-based products. This could decrease the amount of deadwood in the forests. It will be imperative that forest managers are keenly aware of the amount of deadwood available and retained in the forest for biodiversity conservation. The removal of some deadwood will be acceptable, but total removal will not be a long-term option.

Old and large trees are also desirable habitat for many species. While these trees may be ideal candidates for removal for bioenergy, they should be left on site for the purpose of biodiversity conservation. These trees, which tend to be in short supply, provide suitable habitat for many different species (Angelstam and others 2002).

If standards for bioenergy feedstocks quality prohibit incorporation of rotten wood, this may reduce the potential for habitat loss associated with dead and downed trees in forests that are managed for bioenergy supply.

Using appropriate stand techniques and the principles of Adaptive Forest Management, forest stands can be managed for both biological diversity and biomass production. Careful consideration of habitat conservation will ensure that species are maintained for future generations while providing raw materials for the production of bioenergy and other bio-based products.

The key to maintaining environmentally sustainable biomass production operations is to design low-impact operations. These forest operations would have minimal impacts on soil, water, and biodiversity, and have high potential for improving the health and productivity of managed forest ecosystems. Many of the techniques for creating low impact operations have been discussed in the previous sections on soil values, hydrologic values, and biodiversity values. This section provides a management-oriented summary of these techniques which draws from materials summarized by Angelstam and others (2002), Burger (2002), Neary (2002), and Hakkila (2002), and provides specific focus on conserving the following three environmental resources.

• Soils
• Water
• Biodiversity

It is possible to maintain and enhance the site productivity of intensely managed forests in the long-term (Burger, 2002). Through the use of Adaptive Forest Management, forest management systems can be designed for plantations and naturally regenerated forests which adhere to the principles of sustainable forest management and gain certification under international protocols involving third party audits. These procedures will enable landowners and professional foresters to achieve sustainable forest management which will conserve soil, water, and biological values and ensure sustainability of Southern forests for future generations.

Best Management Practices have been formulated to enable forest managers to maintain and improve the environmental values of forests associated with soils, water, and biological diversity. Handbooks have been published for each of the 13 southern states. Following these guidelines is essential to maintaining and improving the quality of soil, water, and biodiversity in the Southern United States. The following list contains links for each of the Southern states Best Management Practices handbooks. These resources should be useful for landowners and professional foresters in developing sustainable forest management practices.

• Alabama
• Arkansas
• Florida
• Georgia
• Kentucky
• Louisiana
• Mississippi
• North Carolina
• Oklahoma
  
• South Carolina
• Tennessee
  
• Texas
  
• Virginia
  

For a collection of the water quality guidelines check out the Forestry BMP website.

Topics covered in this section of the Encyclopedia of Southern Bioenergy are complementary to topics covered from different perspectives in other sections of this encyclopedia titled Forest Management and Silviculture for Bioenergy Production, Introduction to Harvesting, Processing, Storage, and Delivery, and Economics.

The key to maintaining soil productivity includes the following practices. Bioenergy harvesting has a number of potential environmental impacts on soils. There are also mitigating practices for these impacts (Table:Potential Environmental Impacts of Bioenergy Harvesting on Soils).

Conserving Organic Matter

Root Raking

Soil organic matter can be conserved by reducing the impact of those operations with high probability of removing the forest floor and generally disturbing the soil surface, such as machine traffic and disturbances associated with harvesting and site preparation operations (at right). Conserving organic surface horizons in managed forests will help maintain the single most important source of plant-available managing nutrients in forest soils (the forest floor), and reduce the need for fertilizer amendment to correct future nutrient deficiencies. Managers can train machine operators to reduce soil disturbances from machine traffic and schedule operations during seasons when soil moisture conditions contribute to resisting machine ruttings and scarification. Allowing machine traffic and performing certain operations during adverse soil conditions can lead to a loss of organic matter.

Conserving or Improving Soil Physical Properties

Machine traffic across harvesting blocks can be kept to a minimum in order to reduce the potential for adverse changes to soil physical properties from compaction or displacement (below left). Managers also need to consider scheduling machine work for times when moisture conditions are not high and therefore the potential for machine damage is relatively low on some sites. The use of specialized equipment, such as high flotation tires or advanced techniques such as boom-forwarding, can be adapted to prevent machine damage. Should soils be damaged, they should be repaired using appropriate techniques for the site. For example, on some sites compaction can be partially reversed by ripping and cultivation. Scarified soils can be amended by spreading harvest residues. Soils with high water tables can be mounded and bedded (below right).

Bedding

Skidder Rutting

Managing Nutrients

Fertilization

Nutrient management is essential for maintaining or improving the availability of essential nutrients to trees and therefore to maintaining soil productivity. The foliage of harvested trees should be left on site in order to retain the relatively high proportion of nutrients contained in this part of the tree. This practice may not significantly reduce the availability of high-quality biomass for bioenergy feedstocks, since foliage is of less value than woody tree components. If foliage retention is not possible, forest managers should consider the application of fertilizer (at right) or wood ash to sites that have been diagnosed as requiring nutrient amendments for specific deficiencies. Elements of special concern include nitrogen, phosphorous, and basic cations (Ca, Mg, K). Wood ash amendment is also recommended on soils which have become acidified by acid rain and associated air pollution.

Preventing erosion

Erosion

The potential for overland flow of rainfall and soil erosion (at left) can be reduced by minimizing compaction and the amount of bare soil exposed during harvesting and forwarding operations. Forest managers and logging supervisors must take special care to minimize soil scarification on sites with slope greater than 10%. Extra caution should be employed when considering tillage and road construction operations on erosion-prone sites.

While these guidelines can be generally applied in all areas, each site should be evaluated and managed with site-specific goals for maintaining or improving soil quality in mind. To find out more about the soils at a specific location, go to Web Soil Survey, a service of the Natural Resources Conservation Service.

Streamside Management Zone

High standards for water quantity and water quality can be achieved in managed forests.

Bioenergy harvesting has a number of potential environmental impacts on water. There are also mitigating practices for these impacts (Table:Potential Environmental Impacts of Bioenergy Harvesting on Water).

Stream and water table response to management and harvesting typically is dependent on the percentage reduction in stocking (ie. trees per acre), but is strongly dependent on the vegetation and climate of a specified watershed. At this time, there has been no significant evidence of adverse effects of harvesting on water quality. Best Management Practices have been formulated that provide guidelines for ensuring water quality and these standards have been effective in maintaining water quality throughout the Southern United States (Shepard 2006). The use of streamside management zones (SMZs) (at right), in which cover is retained in riparian areas adjacent to surface water and aquatic habitats, is essential for maintaining high standards of water quality. Site-specific management is required to conserve water resources.

Appalachian Mixed Hardwoods

Biodiversity is directly related to the amount of species-critical habitat in a forested area. There are potential environmental impacts of bioenergy harvesting on biodiversity. Mitigating practices can also be practiced to reduce these impacts (Table:Potential Environmental Impacts of Bioenergy Harvesting on Biodiversity)

Habitat, and thus biodiversity, can be conserved by employing several techniques in stand and landscape management. These include the following:

Creating structurally complex stands - Structurally complex stands (at right) can be created by harvesting patches of adjacent stands over time, and deciding before harvest if large old trees, snags, and deadwood will be retained. The resulting mixture of stand ages and deadwood are critical for maintaining habitat for diverse species.

Longleaf Pine

Creating habitat - The creation of habitat includes introducing animal and plant species (such as long leaf pine - at left), installing nest boxes, and providing the food and shelter needs for species across the landscape. Buffer zones and streamside management zones can be used to create areas of habitat adjacent to more intensively managed areas or highly sensitive landscape elements.

The use of long rotations - Managing stands over relatively long rotations (below left) would allow the development of more structurally complex stands over time due to the effects of biotic and abiotic stresses associated with natural disturbances such as fire, wind, insect and disease attacks, and tree mortality. While this may not be feasible for all stands in a management area due to a variety of management objectives and constraints, this technique can be used in buffer zones and streamside management zones to create ideal habitat.

Special attention must be given to the conservation of deadwood and large old trees (below right). These structures, while possibly attractive for bioenergy feedstocks, must be maintained in adequate quantities on a landscape basis due to their biodiversity value.

Old Growth Forest

Large Tree