Rating Degraded Stands

For timber-related goals, McGee (1982) suggests the following stand rating system to aid evaluation of individual stands and provide a means for ranking several stands. 

STEP 1. Identify, delineate, inspect, and inventory the stand. Determine causes for the poor condition.

STEP 2. Evaluate the following factors:

Site Quality. Site quality is a primary determinant of stand quality with hardwood species. In most site quality evaluations, three classes are recognized: (1) poor or below average, (2) average, (3) above average. Return on investment will generally decrease as site quality decreases, therefore it is important to evaluate site quality before starting any management activities. Conversely, the intensity of forest management should increase as site quality increases (Ezell 1992).

The principal measure of site quality has historically been site index-- the height of the tree of a given species at a specific age (usually 50 years in the eastern United States). However, a major problem with using site index in high-graded stands is the tendency to underestimate a sites true productive potential due to the lack of site index trees that have not been suppressed or wounded.  Therefore, if site index is used for evaluating site quality, it is important to carefully select trees that are in the main canopy and show no signs of growth suppression. Site index can also be obtained from soil surveys.  Another method for determining site quality is to use a physiographic site rating system based on landforms where available. These systems are dependable and well-suited to managing degraded stands (McGee 1982).  Where available, an ecological classification system may also be used to estimate site quality.  Ecological classification systems are similar to physiographic rating systems except that they place more emphasis on vegetation.

Manageable Trees. An important step in evaluating a degraded stand is to inventory manageable trees. Manageable trees include all sound trees of acceptable species. Acceptable growing stock includes trees that can be expected to increase in value, although the definitions of desirable and acceptable growing stock will vary substantially by ownership and site quality.

The number, species, distribution, and basal area of manageable trees are key factors when prescribing regeneration, cultural treatment, or postponement of action in degraded stands. If the basal area of manageable trees is less than 50 square feet per acre, the stand can be treated as a degraded stand. Stands with more than 50 square feet of manageable trees per acre are not considered degraded (McGee 1982).  A simple rule of thumb is: 50 small-sawlog-size trees per acre is the minimum number for a manageable stand. However, this minimum number can be expected to vary according to landowner objectives (McGee 1982).

Cull Trees. Cull trees, poor quality stems of desirable species, are often the most predominant component of a low quality stand. Cull trees represent less problems for future management than undesirable species, primarily because these trees have the potential to produce good sprouts if they are cut. Cull trees should be inventoried, both by the number of stems and by the basal area per acre. Hollow trees should be identified and their location noted as den trees if wildlife habitat is a management consideration (McGee 1982).

Undesirable Trees. Undesirable trees may include poorly formed trees of desirable species (usually too young or small to be classed as culls) as well as undesirable species. Repeated high-grading and diameter limit cuts have led to a large number of stems per acre of undesirable, typically shade-tolerant, species. Individually, undesirable trees may not have much impact on decisionmaking for a degraded stand, but collectively they are important due to their large numbers. Some stands may contain 400 or more undesirable trees per acre but most will have 150 to 250 (McGee 1982).

Advance Regeneration. Some degraded stands have large numbers of desirable small saplings and seedlings that should be inventoried during stand evaluation. The number and distribution of stems by species should be noted, accounting for "clumps" so as to not distort densities expressed on a per acre basis. Timing of the stand evaluation relative to recent harvests should also be considered. Although there may be a large number of desirable species stems in a recently cut stand, these stems usually will lose their vigor when the canopy closes (McGee 1982).

Age of Manageable Trees. Tree age should be determined for manageable trees only. Age affects the potential for release response and is needed for site index determination. With training and practice, tree age can be reliably estimated. Age estimates within 20 percent are accurate enough for most decisions (McGee 1982). Tree ages can also be estimated by ring counts of increment cores. Removing cores from the stump (6 to 8 inches of the ground), reinserting it in the hole, and sealing over the exterior wound can prevent damage to the merchantable portions of stems. A third option for determining age is to count annual rings on similar nearby harvested stems (if such stems exist). The underlying assumption from this type of evaluation is that the harvested stem and the remaining stem are about the same age, which is more likely in even-aged stands (Ezell 1992).

Collecting Information. A systematic approach is best for evaluating high-graded stands. Ezell (1992) suggests locating a series of plots spaced evenly across the area so that 5-10 percent of the area is sampled. At each plot, construct two subplots, with a small plot (0.001acre or 3.72 ft radius) nested within a larger plot (0.1 acre or 37.2 ft radius). Evaluate advanced regeneration in the small plot: record number of stems by species and size class ( <1 ft,1-3 ft, > 3 ft tall). Evaluate the midstory and overstory in the larger plot: record stems by size and classify them as desirable, undesirable, or cull (Ezell 1992).

STEP 3. Consider treatment options. There are essentially three broad options available for treatment of degraded stands: regeneration, intermediate management, or postponement of action (McGee 1982).

Regeneration. The need for complete harvest and natural regeneration will increase as: (1) number and basal area of manageable trees decrease, (2) number and basal area of culls and undesirable trees increase, (3) site index increases, (4) age of manageable trees increases, and (5) desirable advance regeneration increases. If conversion to pine is a management option, the weighting in favor of complete harvest and conversion will increase when: (1) site index for pine ranges between 70 and 85, (2) sources of desirable natural hardwood regeneration decrease, and (3) number of intermediate and smaller hardwoods decreases.

Intermediate Management. Opportunities for intermediate management will increase as: (1) basal area of immature manageable trees increases, (2) age of manageable trees in relation to size decreases, (3) number of undesirable plus cull trees increases, and (4) site index increases. Consider the advantages of crop tree management.

Postponement of Action. Postponement will be favored as: (1) site index decreases, (2) number of large manageable trees increases, (3) number of small undesirable trees increases, (4) out-of-pocket costs for treatment increase, and (5) desirable advance regeneration decreases.

STEP 4. Develop stand recommendations.

A. Based on the stand profile and the preceding treatment options, list the three major treatment options in order as they seem to apply to the stand. If only one stand is involved, the major recommendation has been made.

B. When more than one stand is involved, a stand ranking by treatment is needed so that priorities for treatment can be established and compared. A simple but highly subjective ranking system can be used where each treatment for each stand can be assigned a numerical value from 1 to 10.

C. Stand evaluations and treatment ranking must, where appropriate, take into account multiple use needs and values. Rankings can be adapted to consider needs for mast, browse, diversity, etc.

STEP 5. Compare stand priorities. After the stands in a forest property have been evaluated and rated, they can be ranked for treatment priority. If the priority ratings do not establish clear differences between stands, then stand profiles can be reviewed and rankings revised. A simplistic rating system should not be substituted for common sense and experience. Factors such as accessibility, markets, need for regulation, and multiple-use values should always be considered.