666 - XXX
Natural Resources Conservation Service
Conservation Practice Standard
FOREST STAND IMPROVEMENT
(Ac.)
Code 666
NRCS, NHCP
June, 1994
666 - 7
DEFINITION
The manipulation of species composition, stand structure and stocking by cutting or killing selected trees and understory vegetation.
PURPOSE
· Increase the quantity and quality of forest products by manipulating stand density and structure.
· Harvest forest products.
· Initiate forest stand regeneration.
· Reduce wildfire hazard.
· Improve forest health reducing the potential of damage from pests and moisture stress.
· Restore natural plant communities.
· Achieve or maintain a desired native understory plant community for special forest products, grazing, and browsing.
· Improve aesthetic and recreation, values.
· Improve wildlife habitat.
· Alter water yield.
· Increase carbon storage in selected trees.
CONDITIonS WHERE PRACTICE APPLIES
All forest land where improvement of natural resources associated with forest land is needed.
This standard is not applicable for Alley Cropping, 311; Multi-story Cropping, 379, Windbreak/Shelterbelt Establishment (operation and maintenance), 380, and Windbreak/Shelterbelt Renovation, 650.
CRITERIA
Use the following criteria in planning and applying this practice. The general criteria apply to all forest stand improvement. Additional criteria may apply based on the intended purpose(s) of the practice.
General Criteria Applicable to All Purposes
The extent or size and orientation of treatment area(s) shall be identified as part of practice design.
Preferred tree and understory species are identified and retained to achieve all planned purposes.
Spacing, density, size class, number and amounts of trees and understory species to be retained will follow established guidelines for the intended purposes.
Stocking guidelines shall contain stocking in terms of basal area, spacing or trees per acre by species and size class distribution.
The method, felling direction and timing of tree cutting for harvesting shall protect site resources, e.g., residual trees, wetlands, cultural resources, improvements and utilities. Time tree cutting to avoid buildup of insect or disease populations. Felling direction must be compatible with trail layout as specified by Forest Trails and Landings, 655.Forest stand improvement activities shall be performed to minimize soil erosion, compaction, rutting, and damage to remaining vegetation and maintain hydrologic conditions.
Slash and debris will be treated such that they do not present an unacceptable fire, safety, environmental, or pest hazard. Such remaining material will not interfere with the intended purpose or other management activities. Refer to burning of slash and other debris on-site shall follow the standard Prescribed Burning, 338.
Additional Criteria to Increase the Quantity and Quality of Forest Products
Increasing the merchantable volume and quality of a stand of trees requires management of tree spacing (stocking) and release from competition. The greatest gains occur when improvements are applied to young stands of trees. Where a stand is overstocked, or crowded by competing vegetation, tree spacing after improvement should be wide enough to achieve the intended intermediate and /or final forest products. Where production of fiber and timber products is the goal, tree spacing after improvement should permit fast growth until trees can reach sufficient merchantable size for an intermediate, commercial thinning.
Additional Criteria to Harvest Forest Products
Merchantable trees can be removed at intermediate times from a stand to create space for remaining trees to grow before final harvest. Intermediate tree improvement operations should regulate/maintain spacing and stocking that allows trees to reach economic and /or biological maturity sooner.
Commercial intermediate cuttings can begin at the earliest age that will provide sufficient wood products to make a profitable operation. Based on management objectives, select and leave desirable trees (form, condition, vigor) that are best suited to the site, and will yield the greatest return/benefit in the shortest time: poorer quality trees should be removed.
Criteria for Thinning
A. Trees to Leave: The selection of trees to leave in intermediate cuttings should be based on management objectives, adaptability of species to certain soils, the condition of individual trees as related to insects and diseases, and the form and vigor of individual trees. Tree species to favor on various soils are located in the NRCS Soils Data Mart in the Forestland Productivity Report. Merchantable dead trees and trees which are likely to die should be harvested during periodic thinnings.
B. Stocking: Stand density is a measure of the stocking of a stand of trees. Basal area is the common method used by foresters to measure stand density. Proper stocking is a term commonly used but as difficult to apply as to define. First of all, proper stocking is the number of trees per acre that fully utilizes the site's potential to grow trees. It follows that a high-quality site has a higher carrying capacity and, if properly stocked, would carry more trees per acre than a low-quality site. Second, a given site may be properly stocked, once the carrying capacity is reached, with an initial spacing as low as 450 trees/acre or as high as 1,000 or more trees/acre. Third, the rate of diameter growth on individual stems and of stand development differs considerably with spacing. Both the rate of diameter growth and the age at which carrying capacity, in basal area, is reached are greater at a wide spacing than at a narrow spacing.
Stands should be thinned to the desired basal area or spacing according to the species and DBH.
Desired StockingAve DBH / Spacing (Ft.) / BA** / # Trees **per Ac
Hardwoods
4 / 7-9 / 50-80 / 575-920
6 / 10-12 / 60-90 / 307-460
8 / 12-16 / 60-110 / 172-315
10 / 14-18 / 70-120 / 129-221
12 / 19-25 / 75-125 / 71-117
16 / 21-27 / 80-135 / 58-97
Pine
4 / 7-9 / 50-80 / 573-917
6 / 9-11 / 70-95 / 357-485
8 / 12-15 / 70-110 / 201-315
10 / 15-18 / 70-110 / 128-202
12 / 17-22 / 70-120 / 89-153
14 / 20-26 / 70-120 / 66-112
16 / 22-30 / 70-130 / 50-93
The smallest number is the “thin to” criteria under basal area (BA) and # of trees per ac. Where pine savanna (e.g. bobwhite quail ) is the objective thin so as to maintain 50 to 70 BA**
And the largest number indicates when the stand needs to be thinned. For wildlife habitat in pine stands greater than 6” dbh, lower the BA by less than or equal to 50 BA on the low end and at 70BA on the high end..
Additional Criteria to Initiate Forest Stand Regeneration
This is harvesting merchantable trees that are either financially or biologically mature and ensure that the forest is regenerated for both soil protection and the production of wood products and other uses.
The harvest-regeneration strategy will be identified for all planned forest improvement harvesting. These include:
· Even-aged management (e.g., clear-cut, seed-tree, shelterwood, coppice)
· Uneven-aged management systems (e.g., single-tree selection, group selection, coppice selection)
Site preparation is very important to insure that management objectives are met. See 490-Forest Site Preparation.
C. Pine:
1. Seed Tree Cut: This is a method in which a new age class develops from seeds that germinate in fully exposed sunlight after removal of the entire previous stand, except for a small number of trees left to provide seed. Seed trees should be dominant trees of good quality that are at least 9 to 10 inches in diameter. Seed trees should be removed within 3 to 5 years to reduce damage to seedlings.
Advantages of Seed Tree
· Seed is available on each acre,
· Delayed removal of seed trees is a safeguard against catastrophic loss of regeneration,
· Regeneration is established without high cost.
Disadvantages of Seed Tree
· Seed trees may limit site preparation techniques and operations,
· Natural regeneration from even the best phenotype seed trees may not offer the growth advantages and disease resistance of genetically improved seedlings,
· Precommercial thinning, a cost not revenue, may be necessary.
Minimum Recommended Number of Seed Trees (per acre)9 / 10 / 12 / 14 / 16
Shortleaf / 20 / 14 / 12 / 12
Loblolly / 12 / 9 / 6 / 4
Slash / 12 / 9 / 6 / 4
Longleaf** / 55 / 38 / 28 / 21
Virginia / 6 / 5 / 4 / 4 / 4
** Shelterwood cut of 30 sq. ft. of basal area.
2. Shelterwood Cut: A shelterwood cut involves leaving a large number of seed trees per acre. The trees are thinned to approximately 30 to 60 sq. feet of basal area depending on species. The residual stand of trees should be removed within 3 to 5 years to reduce damage to seedlings. This can be accomplished with more than one harvest that allows for best selection of seed trees.
Advantages of Shelterwood Cut
· Residual trees are higher quality,
· More aesthetical.
Disadvantages of Shelterwood Cut
· Established regeneration is subject to logging damage from seedtree removal,
· Increasing canopy cover may hinder regeneration establishment and growth.
3. Clearcutting: All merchantable trees are removed. Site preparation is usually needed to enhance regeneration. Natural regeneration methods such as seed-in-place, seedlings in place and seeding from the side may be used with clearcuts.
Tree planting and direct seeding are artificial regeneration options. Improved seedlings and improved seed should be used when possible. See 612-Tree/Shrub Planting.
· Regeneration may be too thick and necessitate precommerical thinning,
Advantages of Clearcutting
· Management areas are easily defined and treated,
· Neither high-value trees nor poorly formed culls are left on site,
· Plant genetically improved seedlings.
Disadvantages of Clearcutting
· Large amounts of residual debris on site,
· Planting costs,
· Poor visual quality.
4. Uneven-aged Management): The removal of trees individually or in small clumps. This type of harvesting creates an uneven-aged stand of timber. The stand is regulated by periodic volume removal. Regeneration occurs either continuously or periodically.
Advantages of Uneven-aged
· A less disturbed appearance,
· Habitat is maintained for wildlife,
· Seed sources always on site.
Disadvantages of Uneven-aged
· Shade tolerant species will dominate,
· Large volumes of high-quality timber are difficult to produce,
· More roads are necessary,
· Difficult to prescribe burn.
D. Hardwood:
1. Clearcutting: Clearcutting is one method of regenerating hardwoods. All merchantable trees should be harvested and small trees should be removed either mechanically or by the use of herbicides.
Seedlings and sprouts of shade intolerant pioneer species – yellow poplar, green ash, sweetgum, and sycamore- become established in great numbers, grow rapidly, usually produce repeated growth flushes in a growing season, and soon dominate the site. Seedlings of midtolerant species, such as oaks, grow more slowly and often are severely retarded or crowded out by intolerant pioneer species.
If midtorlerant species are the target species, it will necessary to release individual trees from competition either mechanically or with herbicides.
For bottomland sites or cove sites, yellow-poplar is a species which is easily managed by clearcutting if a seed source has been present for 3 to 5 years. Yellow-poplar seeds remain viable in the forest litter for up to 8 years. Normal harvesting operations will expose mineral soil and allow adequate germination of yellow-poplar seeds.
2. Shelterwood Cut: The shelterwood system can be used to obtain oak regeneration. The shelterwood system is preferable from a wildlife perspective. Stand density is reduced to 60% stocking to allow seedling establishment. When a stand of 500 or more seedlings per acre is 4.5 feet or higher, the overstory stand should be removed. It may take as long as 15 to 20 years to obtain the desired reproduction once stand density is reduced.
Criteria for Precommercial Thinning
Precommercial thinning is needed 1) where stands of desirable trees are of unmerchantable size and are overstocked, thereby preventing satisfactory growth, and 2) where thinning will either increase the growth of remaining trees or enhance the beauty of the stand.
A- Pines
Pre-commercial thinning is most cost effective when completed within 5-8 years of establishment because equipment such as disks, choppers or brush mowers can be used. Larger trees may require chain-saws. Leave 300-500 stems “free-to-grow” per acre.
Pre-commercial thinning can shorten the time interval to the first commercial thinning. The need for thinning varies by site, species, density, and uniformity of tree heights.
B-Hardwoods
Pre-commercial thinning is best preformed in the sapling stage (1-5 inches in diameter) and at least 12-15 years old. Trees should have started to show height dominance and be about 25 feet tall. Leave 100-150 stems “free-to-grow” per acre.
Additional Criteria to Reduce Wildfire Hazard
Reduce stocking rates of trees to minimize crown-to-crown spread of fire.
Remove “ladder” fuels to minimize the occurrence of crown fires.
Further treat or eliminate slash accumulations next to roads and trails.
Reduce or eliminate species with high volatility but not to a level that would compromise other intended purposes.
Additional Criteria to Improve Forest Health-Reducing the Potential of Damage from Pests and Moisture Stress
A well managed, actively growing stand of trees is the best defense against pest and/or moisture stress. Inspect trees periodically for insect and moisture stress problems. Remove or treat hot spots of insect infestation or dead/diseased trees.
Additional Criteria to Restore Natural Plant Communities
Select trees to leave that are indigenous or native to the site and will reflect species composition of the desired stand. If trying to develop the understory and native ground cover, provide sufficient sunlight to reach the forest flow to develop desired conditions. This can be controlled my manipulating tree spacing or density. Additional understory manipulations can be made with fire, and mechanical or chemical treatment. Consult a provisional forester or biologist for trees to select during forest stand improvements.
Additional Criteria to Achieve and Maintain a Desired Native Understory Plant Community for Special Forest Products, Grazing or Browsing.
Planned tree spacing and required understory manipulation will be determined based on intended use, and the expected native understory plant community for the site.