Root and Butt Rot/Wood Decay Fungi
Root and butt rots are the most serious cause of lumber cull and degrade in southern forests. All southern hardwood species are affected, and the loss in terms of hardwood timber volume amounts to millions of board feet annually. The lower bole has always been of most concern to hardwood forest managers because these are the most valuable logs in the tree and the logs most likely to be wounded by harvest equipment, by logs pulled on skidder tracks, and by falling trees. During most of the 20th century, forest managers have tried to suppress root and butt rots in southern hardwood stands by preventing the creation of wound scars by which most decay fungi gain entry into the tree. During the first half of the last century, much effort went into controlling wounds caused by fires. At least 80 percent of lower bole decays in bottomland hardwoods were attributed to fire scars during that period (Toole 1960). Protection of the lower bole is still of prime concern in avoiding wounding. However, because fires are rarely a problem in hardwood forests today, this concern has largely shifted from fire wound management to management of logging wounds in residual trees caused by heavy harvesting equipment during precommercial thinning and partial commercial cuts. As demand for hardwood lumber volume increases in the future, management of root and butt rots in hardwoods will slowly begin to move away from the tolerance approach, or a willingness to live with and allow for a certain amount of cull losses by increasing cut volume, to a more preemptive approach based on detecting these microbes in standing trees and adjusting harvest schedules to reduce losses. This approach will require the capability of detecting incipient decay in standing trees and determining the specific causes of decay. However, new technology and decay models will have to be developed to provide the necessary knowledge and detection capabilities before this approach becomes feasible.
At least 30 fungi are known to contribute to root and butt rots in southern hardwoods, but only a relatively few species cause most of the damage. The root and butt rot fungi most frequently encountered in most southern hardwood stands include Pleurotus ostreatus (Jacq.:Fr.); Ganoderma lucidum (W. Curt.:Fr.); Hericium erinaceus (Bull.:Fr.) P.; Armillaria tabescens (Scop.) Den.; Inonotus dryadeus (Pers.:Fr.) Mu.; and Laetiporus sulphureus (Bull.:Fr.) Mu. Other species that are important to a lesser extent in individual hardwood species include Inonotus hispidus (Bull.:Fr.) P. and Tyromyces fissilis (Berk. & Curt.) Donk, Lentinus tigrinus (Bull.:Fr.) Fr., Phellinus igniarius (L.:Fr.) Quél, Trametes versicolor (L.:Fr.) Pil., Rigidoporus lineatus (Pers.) Ryv., R. ulmarius (Sowerby:Fr.) Imazeki in Ito, Tomentella spp. (Pat.), and the ascomycete Kretzschmaria deusta (Hoffm.:Fr.) P. Martin (= Hypoxylon deustum (Hoffm.:Fr.) Grev.). The rate of decay development within hardwoods varies with the specific wood decay fungus present and the host species involved (Toole 1959).
Thus, decay volume models must account for host species, decay fungi, and log taper equations of individual hardwood species when predicting future lumber volume losses. This information would be necessary for making stand harvesting decisions. Also, a portable, inexpensive, easily used detection device would be necessary to identify the presence and extent of damage by specific decay fungi in standing trees during routine stand evaluations by timber cruisers for the purpose of planning future harvest schedules.
The development of new technologies and methodologies for mitigating losses by wood decay fungi and other microbes causing defect losses in standing timber has been an active field of interest in recent years (Wilson and Lester 1997). Forest managers and cruisers responsible for monitoring forest stands are primarily interested in methods and criteria for minimizing losses in lumber volume and optimizing production in commercial forests. A major challenge facing forest managers is that of establishing policies and procedures for making management decisions to deal with defect losses including decay, discoloration, and structural alterations in the properties of wood caused by microorganisms in the sapwood and heartwood of standing timber. Most estimates indicate that at least 30 percent of the total lumber volume available in many southern hardwood stands is degraded or rendered unmerchantable by lumber defects caused by these pests. Defects in logs of standing trees can lead to significant economic losses ranging from reduced lumber production volume per acre to reduced lumber value (grade), degrade to pulpwood status with no merchantable lumber, and total loss with no commercial value available for salvage. The most significant challenges to be addressed in relation to defect volume losses in lumber production are to find ways of detecting defect in logs of standing trees and to determine when to cut individual trees that have log defects in order to optimize production on an individual tree basis. The methods used over the past 50 years to detect the presence of log defects in standing trees by cruisers of most commercial lumber producers have involved sounding the wood (butt log) by striking it with a hard object to locate hollows in the lower bole. This archaic method is useful only to detect advanced defect in standing trees because trees with incipient or even intermediate stages of defect usually cannot be distinguished from healthy trees. Unfortunately, detecting advanced defect is of little value, because it only serves to identify unmerchantable trees. Also, it occurs long after the decision should have been made to harvest the tree and avoid the high level of cull losses associated with the development of defect to advanced stages.
Previous strategies for managing defects in southern hardwoods involved simply accepting the defect losses caused by microbes and insects by removing the cull volume as the logs were processed at the mill. With the growing demand for quality lumber volume in the United States, new technologies are now needed with the capability of detecting defects in logs of standing trees at incipient stages before significant damage reduces the resulting lumber value in individual trees. New methods and technologies under development, such as electronic aroma detection by conductive polymer analysis (CPA) of volatile metabolites from microbial log-degrading pests, will allow preharvest field detection of log defects using a portable detector (Wilson and Lester 1997). This will be much more effective than older methods in optimizing lumber yields because it will prevent cull losses by allowing detection and control of the problem long before significant damage occurs. Early detection of these defect-causing microbes in standing trees is useful for predicting future potential damage because the damage potential is species-specific and thus the future depreciated value of individual trees can be estimated by using decay models coupled with fungi-specific decay expansion constants in different hosts. An integral part of this early detection system is the identification of the specific microbe(s) present, because the rate of development, type of damage, and location of defect volume depends on the particular pest present. Several applications of this technology are being developed. For example, CPA recently was used to distinguish the aroma signatures of sapwood cores from southern hardwood species. Technology also has been developed to identify forest pathogens and wood decay fungi in vitro and in wood samples, and to distinguish between different Armillaria species for disease diagnosis. Host- and fungi-specific decay-volume models based on log-taper equations of individual hardwood species also are under development with the objective of predicting future lumber volume losses for planning and establishing future harvest schedules for individual hardwood stands.
Encyclopedia ID: p984
