Oak Regeneration Potential

The first step in planning for oak regeneration is to evaluate its regeneration potential. It is the number, size, and spatial distribution of all three forms of reproduction that largely express the total oak regeneration potential of a stand (Sander and others 1984). The choice of which regeneration method to use must be based on the outcome of this regeneration potential analysis, the basic ecology of the forest region in which the stand is located, and the overall management objective.

Oak seedlings and sprouts cannot grow into the overstory as long as they are heavily shaded (Johnson, 1993). Therefore, clearcutting, shelterwood, group selection, or other methods that substantially reduce overstory density are usually used to regenerate oak stands (Hannah 1987, Sander and Clark 1971). The choice of appropriate regeneration methods depends upon whether the oak reproduction potential is:

• adequate: oaks present and tall enough (4.5 ft.) to respond after removal of the overstory;
• marginal: some oaks present but not tall enough to repond to release;
• poor: oak seedlings or saplings not present.

A brief discussion of what may be some appropriate choices in each of these cases is provided in the above links. Oak regeneration potential can be assessed using predictive models.

Regeneration potential and site quality

There is a general relation between site moisture and oak regeneration success: the better the site the more difficult it is to regenerate oaks (Johnson, 1993). For example, oak regeneration in the Central States is more abundant on average to poor sites than on good sites ((Table:Advance Production in Central States); Sander and Graney, 1993). Therefore, estimates of site quality are important factors in determining oak regeneration potential as well as for growth prediction and modelling. Site quality evaluation for oaks can employ either site index or ecological classification.

Following is a summary of what can be expected to regenerate on different sites.

Poor-to-fair sites: On drier, poor-to-fair sites, where mature oak trees occur, oaks can be reproduced through clearcutting or any other form of even-aged silviculture. These sites are often auto-accumulators of oak seedling sprouts and have sufficient light available to the seedlings for survival and some growth. On poor-to-fair sites, chestnut and scarlet oaks may dominate (C. Smith, 1993). (See Oak regeneration stategies on xeric Sites)

Fair-to-medium sites: On the moist, fair-to-medium sites, it has been difficult to reproduce oak from mature oak stands. With change in site quality, there is a change in species composition and the species differ in their ability to sprout. Sprouting is a function of size, age, growth rate, etc. On fair-to-medium sites, scarlet, chestnut, black, and white oaks may be dominant (C. Smith, 1993).

Good-to-best sites: On good-to-best sites, northern red, white, and black oaks will occur on the good sites and on the best sites, northern red oak is usually the only one that will compete (David W. Smith, personal communication). (C. Smith, 1993) For most of the Appalachians, a realistic objective for reproducing of oaks on the good-to-excellent growing sites is to reproduce some oak in the next stand. Thus, guidelines will be less stringent than those recommended for reproducing a fully stocked oak stand (C. Smith, 1993). (See Oak regeneration strategies on mesic sites)

Hydric sites: Matching appropriate species to suitable sites is especially important considering the wide variety of landforms (bars, levees, ridges, flats, sloughs, terraces) found in bottomlands and the different species of oak, each with specific silvical characteristics and site requirements (McKnight and others 1981). Slight, nearly undetectable elevational changes in bottomlands alter species-site suitabilities (Hodges and Switzer 1979). Other factors affecting regeneration are the frequency, depth, timing, and duration of flooding and the species tolerance to flooding. Baker and Broadfoot (1979) published a site evaluation guide for commercially important bottomland hardwoods. Typical species compositions for particular landforms have been developed for the major bottoms of the lower Mississippi alluvial plain and the minor bottoms of the Gulf coastal plain

(Hodges and Switzer 1979) and the red river and black river bottoms of the Atlantic coastal plain (Kellison and others 1988). (Clatterbuck and Meadows, 1993)

Along with flood tolerance, shade tolerance is another variable in the regeneration equation. Bottomland oaks range from intolerant to intermediate in their tolerance of shaded conditions (Putnam and others 1960) and most require some direct overhead sunlight to survive and grow (Johnson 1979). Even though oak seedlings will become established in almost any size of opening, continued growth and development require large openings. In small openings, sunlight becomes a limiting factor, especially as canopies close, and actually favors the more tolerant species. Consequently, bottomland oaks are managed most successfully by implementing an even-aged silvicultural system (Kellison and others 1988). (Clatterbuck and Meadows, 1993) (See: Oak regeneration strategies on hydric sites)

On many sites in the areas east of the Mississippi River it is not realistic to expect to be able to naturally regenerate essentially pure oak stands even though the current stand is dominated by oak. The ecological trends due to effective wildfire control, and results of past regeneration efforts, indicate many future stands will be mixtures of a number of species especially on high-quality sites. An oak component can be retained readily on average sites, but on good sites the stands will most likely be dominated by species other than oaks. (Sander and Graney, 1993)