Good Forestry in the Granite State:
Recommended Voluntary Forest Management Practices for New Hampshire
Table of Contents >> 2.2 Forest Structure << 2.3 Regeneration Methods >> 2.4 Managing for High-Value Trees

2.3 REGENERATION METHODS

BACKGROUND

Carefully designed regeneration practices help perpetuate desired tree species.

Regeneration refers to the seedlings and saplings that develop beneath a forest stand, in openings within a stand, or following the removal of a stand (grouping of trees similar in species, age and site). In younger stands with potentially valuable trees, the immediate goal may be to manage the existing trees for timber as described in 2.4 Managing for High-Quality Trees. If the stand is older or contains an abundance of poor-quality trees, the emphasis can shift to a regeneration harvest using the techniques described in this section.

Successful regeneration involves analyzing the condition of the existing trees, advanced regeneration and seed source, and the site capability, then choosing a harvest practice that will regenerate the species best meeting your objectives. Regeneration is one of the most important factors affecting the long-term value and productivity of a forest property.

Silviculture is the art and science of establishing and tending trees and forests. Controlling the composition, health, structure, and growth of forest stands to help meet the landowner's objectives lies at its foundation. Landowner objectives may include timber products, wildlife, aesthetics, recreation, or overall health and stability. Some owners may wish to develop a forest that appears completely natural or untouched. Landowner objectives play a predominant role when choosing a silvicultural.

Financial and Biological Maturity

The need for income, promoting wildlife habitat or creating special aesthetics are but a few reasons to regenerate a stand. Financial maturity is one indication of whether or not to harvest. A tree is financially mature when its rate of return becomes less than what other financial investments (such as stock or bonds) can yield. Trees growing on better sites become financially mature at larger diameters than the same species growing on average or poor sites, since they grow faster and are able to deliver a higher rate of return for a longer period. Likewise, poor-quality trees mature financially at much smaller sizes than high-quality ones. Approximate diameters for financially mature, high-quality trees are given below. Maturity varies depending on tree condition, site quality, and markets.

Except for short-lived species such as paper birch and balsam fir, financial maturity isn't highly correlated with biological maturity. Most tree species can live for decades or centuries past their financial maturity. Biological maturity occurs when a tree begins to decline. Biological maturity may trigger a regeneration harvest, but these older trees provide benefits described in other chapters. Approximate ages are listed below.

Financial Maturity by DBH and Biological Maturity by Age

Species

Financial Maturity

(DBH) inches

Biological Maturity
years

Sugar maple, white ash, yellow birch, red oak

18-24

150-200

Red maple, beech

14-18

120-150

Paper birch, aspen

12-14

80-100

White pine

18-24

150-200

Red spruce

12-16

200-300

Balsam fir

10-14

   60-80

Hemlock

16 18

200-300

Site Capability

Analysis of site capability gives insight into which species are best adapted to grow on a particular site. Some general guidelines are:

Species

Preferred Site and Soil Conditions

White ash, sugar maple

Moderately well-drained and enriched fine-textured soils, especially with low acidity (higher pH soils)

Beech

Sandy tills, but common on a wide variety of soils

Red oak *

Sandy tills and outwash (where red oak may be poorly formed and defective)

White pine*

Outwash and, to a lesser extent, sandy tills

Yellow birch

Moderately well-drained, fine-textured soils; also on somewhat poorly drained pan soils in mixture with softwood

Red spruce, hemlock, balsam fir

Shallow pan soils and lakebed sediments often somewhat poorly drained; outwash; or shallow-to-bedrock

Paper birch, aspen,
red maple

Adapted to a variety of soils, but often on sites that supported shade-tolerant softwoods.

*Currently found growing on a variety of soils due to agricultural history and generally difficult to regenerate on the better soils.

New Hampshire soils are complex and highly variable, primarily due to their glacial origins. The Natural Resources Conservation Service (NRCS) categorizes site capability to correlate with county soil survey maps. Referred to as Important Forest Soil Groups, these categories can be used to evaluate the relative productivity of soils and better understand patterns of plant succession and the ways soil and site interactions influence management decisions. All soils are grouped into one of six categories. For a more complete treatment see the appendix. NRCS field offices can provide more information.

Site index is another way to categorize site quality. It is expressed as the height of a species at a given age, usually at age 50. The higher the site index, the taller the tree will grow in the given amount of time, and the better the site is for that species. A poor site for one species may be adequate for another. In New England, a site index of 45 or lower is poor, 55 to 65 is average, and 80 is excellent.

Tolerance

Shade tolerance, a species' ability to thrive and prosper depending on the amount of available light and competition from others, influences what will regenerate.

Sugar maple, American beech, red spruce, hemlock, and balsam fir are shade-tolerant. They can survive under heavy shade, including shade from the species itself, although growth is usually more rapid in the open.

White ash, red oak, white pine, and yellow birch are intermediate and can survive under partial shade or in small openings. Red maple is intermediate to tolerant.

Paper birch and aspen are shade-intolerant and survive best with full sunlight. They are called pioneer or early successional species, because often they are the first to inhabit openings after a disturbance.

In the absence of advanced regeneration, tree tolerance provides guidance as to which species may regenerate from a given harvest technique.

Advanced Regeneration

Seedlings or saplings established naturally without the influence of harvesting under a forest canopy are called advanced regeneration. Often it will determine what species will regenerate.

Some hardwoods such as beech and red maple are aggressive as advanced regeneration on certain sites. When crushed during timber harvesting, they sprout profusely. Other hardwoods aren't as aggressive and may sprout from small stumps but their survival and future in the stand is less certain.

Other species including most softwoods, may be persistent as advanced regeneration but may be eliminated from a stand from crushing if harvesting practices don't protect them. Most softwoods don't sprout. If advanced regeneration is destroyed during a timber harvest, new stems must start over from seed. Many softwood species are slow starters, giving hardwoods a head start.

Lack of advanced regeneration may provide opportunities to establish desired species suitable to the site. Measures may be taken to establish the desired species as advanced regeneration, or harvest practices may encourage regeneration at the time of harvest.

Seed Source

During all phases of management, it's important to maintain or increase a source of seed for the several species of most interest. The best seed producers are sawlog-sized trees with well-developed crowns. However, there is great variation among individual trees and seed crops vary greatly from year to year. If the desired species aren't present as advanced regeneration, harvest during the fall or winter of a good seed year. Most seeds fall within a couple hundred feet of the seed tree, but some seeds, notably red and white oak, may be moved (and eaten) by birds and small mammals such as squirrels. Both red and white oak are heavily consumed by wildlife.

Seeding Characteristics of Selected Trees

Species

Seeding Interval
(good years)

Other Seeding Characteristics

Birches

1-2

wide dispersal on snow

Sugar maple

3-7

Red maple

1-2

Beech

2-5

occasional animal dispersal

White ash

2-5

most germination second year after dispersal

Red oak

3-5

two years to mature; look closely for small one-year acorns

White oak

3-5

one year to develop

White pine

3-10

two years to mature; look for one-year cones

Red spruce

3-8

Eastern hemlock

2-4

Regeneration Harvest Methods

Knowing landowner objectives, site capability, advanced regeneration and seed sources helps to choose an optimum regeneration harvest method. Regeneration practices are applied in even-aged stands at the end of the rotation when the stand is mature and ready for final harvest. In uneven-aged stands, regeneration takes place after every harvest cut. The methods described below cover a wide range of disturbance levels, some approximating natural disturbances:

Practices Not Recommended

OBJECTIVE

Select a harvest practice that regenerates desired species rapidly and economically, consistent with landowner objectives and site capability.

CONSIDERATIONS

RECOMMENDED PRACTICES

Species

Harvest Method

Beech, sugar maple, red spruce*, balsam fir*, hemlock*

Single tree/small group selection (< ¼ acre) or narrow strips (< 50 feet wide)

White ash, yellow birch, red oak, white pine

Group selection (¼-2 acres) or medium strips (50-100 feet wide)

Aspen, paper birch

Group selection (> 2/3-2 acres) or medium strips (50-100 feet wide)

Red oak, white pine, red spruce, balsam fir, hemlock

Shelterwood (natural or planned)**

Aspen, paper birch, yellow birch

Clearcut or wide strips (> 100 feet)

* On wet and shallow soils, windthrow can be a problem if using single tree selection.
**A natural shelterwood is a removal cut where advanced regeneration is present.

Species

Special Feature

Red oak, white pine, red spruce, hemlock, balsam fir, sugar maple

Advanced regeneration important

Red oak, white pine

Important to bury the seed through harvesting activity or site preparation

Aspen, beech

Sprout from roots of trees present in the stand

Red maple, red oak

Prolific sprouters from stumps of poletimber or small sawlog trees

Sugar maple, red oak, red maple, yellow birch

Browsed heavily by deer

Paper birch, aspen

Short-lived species that typify early succession with pin cherry and Rubus sp.

CROSS REFERENCES

2.2 Forest Structure; 2.4 Managing for High-Quality Trees; 3.1 Timber Harvesting Systems; 3.2 Logging Aesthetics; 3.5 Soil Productivity; 4.1 Water Quality; 4.2 Wetlands; 4.3 Forest Management in Riparian Areas; 5.4 Logging Damage; 6.1 Mast; 6.2 Cavity Trees, Dens and Snags; 6.3 Dead and Down Woody Material; 6.7 Aspen Management; 7.2 Seeps; 7.3 Vernal Pools; Appendix: Important Forest Soils Group.

ADDITIONAL INFORMATION

Beattie, M., C. Thompson, and L. Levine. 1993. Working with Your Woodland: A Landowner's Guide (2nd ed.). University of New England Press, Hanover, N.H. 279 pp.

Bennett, K.P., and K. Desmarais (eds.). 2003. Managing white pine in a new millennium: 2003 workshop proceedings. UNH Cooperative Extension, Durham, N.H. 78 p.

Ward, J.S., T.E. Worthley, P.J. Smallidge and K.P. Bennett. 2006. Northeastern Forest Regeneration Handbook: A Guide for Forest Owners, Harvesting Practitioners, and Public Officials. USDA For. Serv. NA—State and Private Forestry, NA-TP-03-06. 66 p.

2.2 Forest Structure << 2.3 Regeneration Methods >> 2.4 Managing for High-Value Trees

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