Today's powerpoint file

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We've talked about a wide range of tools used to manage vegetation. Today, we'll discuss harvest-regeneration methods used in forestry. Our objectives for the next 3 days are to (1) create a vocabulary and (2) introduce concepts regarding stand replacement of forest stands

Until the 1700s, common practice was to go into a stand of trees every few years and remove trees

--> development of silviculture, specifically clearcutting as a system of harvest and subsequent regeneration

Clearcutting was the first silvicultural system; it was developed to replace degraded stands

Produces even-aged stands

Clearcut: removal of all merchantable material in a stand; see image here

Some states have laws or regulations governing maximum size of clearcut units--Arizona has no such regulations (defers to NFMA, which has no arbitrary size constraint)


Can easily handle stands in any condition

Can artificially introduce appropriate trees in a single step

Can realize large genetic gains with artificial regeneration


Can maintain high-quality trees via natural regeneration from adjacent stands

Relatively low skill level; easy to administer

Low costs for harvesting, management, administration

No damage to residual stand

High quantity and availability of herbs, browse (at least initially)

High water yield


Minimal site protection:

High erosion potential

Regeneration uncertain

Leaves large amount of slash, which must be removed

Non-continuous cash flow

Windthrow in adjacent areas

Aesthetically unappealing

Generally decreased biological diversity


Best-adapted for intolerant early-seral trees, especially those with easily disseminated seeds

In arid or semi-arid regions, northeastern aspects preferred (cooler, moister microclimate)



Natural regeneration into harvested strips from "leave" strips

Harvest "leave" strips after trees in harvested strips are reproductively mature, or artificially regenerate them

Provides "landscape corridors"


Prevailing winds blow across residual stand --> waves of regeneration

Less windthrow than with alternate-strip method

Coppice (synonymous with natural asexual reproduction)

Simplest harvest-regeneration system

Usually clearcut --> even-aged stand (aboveground)

Reproduction accomplished by sprouting from stumps and roots (within 1-2 years)

Advantages and Disadvantages similar to clearcut except:

(+) Excellent re-occupation of site

(+) Rapid volume growth --> short rotations

(-) Must have market for small material (i.e., fuelwood or fiber production)

(-) Limited to tree species that sprout profusely (few conifers, most angiosperms)

(-) Reduced vigor late in rotation, or after multiple rotations (roots are old, so each coppice --> decline in vigor earlier in rotation)

(-) No potential for genetic improvement (no change in genetic composition)


Use relatively small diameter trees (for evenly distributed site occupancy); this is consistent with fiber production or fuelwood production

Cut when dormant --> more vigorous sprouting

Cut stumps at an angle, to reduce water collection --> decay

Good species: fast-growing species with minimal rot

If there is uneven site occupancy (i.e., widely spaced trees in some areas) due to large trees in previous stand--or if you want to introduce new genetic material

plant seedlings ("standards") in these gaps (this is called "coppice with standards")

Partial harvests (i.e., do not remove all merchantable trees in one visit)

Seed-Tree Method

Produces even-aged stands

Harvest all trees except 10-25 trees/ha for natural regeneration ("seed" trees); see image here

Residual stand should have "best" characteristics and should have potential for good seed production (e.g., full crowns)

Seed trees usually (but not always) are harvested after next stand is established (usually 5-15 yr after initial harvest)

Best adapted for intolerant trees with easily disseminated seeds; best adapted for northerly aspects, in SW US (~ clearcut)

Beware: there is usually considerable pressure to cut good trees and leave poor-quality trees --> successively poorer stands

Advantages and Disadvantages similar to clearcut except:

Uniform distribution of seed (contrast with naturally regenerated clearcuts)

Windthrow to seed trees (or in adjacent areas, sensu clearcut) can be high

Harvesting seed trees may damage regeneration (consider harvesting on snow), and is more expensive than single entry per rotation

Site prep is challenging, especially with fire

Shelterwood Method

Goal: regenerate site under shade and protection of existing trees

Produces even-aged stands

Application: series of cuts are made toward the end of the rotation

Preparatory cut (1-several, removing 25-40% of stand); see image here

"Prepares" trees, with respect to seed production capability or windfirmness

Seed cut (1, removing 25-50% of stand)

Open canopy to favor regeneration of desired species

Removal cut (1-few, all within 20% of rotation age, removing remainder of stand)

Remove what foresters call "crop" trees, in a manner which will minimize environmental stress to regeneration

All within 20% of rotation age

Advantages and Disadvantages are "intermediate" between harvest-regeneration strategies with higher or lower harvest levels

Selection Methods

Produces uneven-aged stands

Harvest individual trees or groups of trees (preferably of similar age and size within a group) and rely on remaining trees for protection and regeneration

Single-tree selection is best adapted for tolerant species (usually no site prep); common in intensively managed German forests

Group selection is suitable for tolerant or intermediate species (usually mechanical site prep)


Continuous cash flow --> popular for small woodlot owners

Continuous tree cover --> high aesthetic, conservation values

Also --> excellent site protection from invasion of off-site species, erosion

High biological diversity (generally)

Minimal slash disposal (especially if decomposition is rapid)

Well-adapted for all aspects



High degree of skill required, time-consuming to administer

Difficult to monitor inventory, growth (most mensurational techniques were developed for even-aged stands)

Difficult to protect young age classes

Site prep limited to mechanical only (herbicide drift, fire may damage adj. trees)

Although our focus has been on conventional harvest-regeneration systems, you should recognize that these systems are merely points on a continuum of removing all overstory to removing none

Intermediate treatments

Definition:any manipulation in a stand that occurs between two regeneration periods
Note:definition does not consider uneven-aged mgmt. (in which regeneration is ± constant), but the concept does
Objectives:control species composition, spacing, growth form, and growth rate

Release Cuttings

Applied early in stand development {saplings (< 15 cm DBH) or smaller}

Designed to control species composition and size structure

Rarely yield merchantable material (treated as a "cost" in economic analysis)

Primary types of release cuttings: cleaning, weeding, liberation

Improvement Cuts

Release trees are pole size (15-30 cm) or larger

Therefore, harvested material is often merchantable

Purpose: release trees that will improve composition, form, and/or growth of residual stand

Often initial cuts in previously unmanaged (or poorly managed) stands --> better condition for subsequent management

In practice, locate and favor desirable trees rather than locating and removing undesirable trees

Removing trees is expensive

If removing a tree doesn't favor a desirable tree, it's not worth removing


Objectives:density control (not composition control)

capture volume that would otherwise be lost to mortality

Total volume in thinned stands < unthinned stands @ end of rotation

Thinning may increase yield of merchantable volume (i.e., increase value); may also provide early return on investment

Thinnings are classified based on economic criteria (pre-commercial vs. commercial) or biological criteria (based on relative position of crowns: low, high, selection, mechanical, free)

When released, young trees respond much more quickly and vigorously than old trees


Artificial removal of branches from selected portions of the stem, to increase quality and value of trees and/or to alter vertical structure

17' pruning height is common

Sanitation and Salvage Cutting

Sanitation:removal of trees that have been attacked or appear likely to be attacked by insects and/or disease to prevent spread to other trees (often not economic)
Salvage:removal of dead or dying trees for economic gain (death is usually by means other than "normal" competition-induced mortality, e.g., fire, insects, disease, lightning)

Of course, it is not always desirable to remove damaged trees, with respect to habitat requirements for some animal species

Additional Information (also see assigned readings):

Burns, R.M. and Honkala, B.H. (technical coordinators). 1990. Silvics of North America (Volume 1, Conifers; Volume 2, Hardwoods). USDA Agriculture Handbook 654, Washington, D.C.

Daniel, T.W., Helms, J.A., and Baker, F.S. 1979. Principles of Silviculture, 2nd edition. McGraw-Hill, New York.

Ffolliott, P.F. and Gottfried, G.J. 1991. Mixed conifer and aspen regeneration in small clearcuts within a partially harvested Arizona mixed conifer forest. USDA Forest Service Rocky Mountain Experiment Station Research Paper RM-294, Fort Collins, Colorado.

ForestyImages, online catalog of forest management images.

Gottfried, G.J. 1992. Growth and development in an old-growth Arizona mixed conifer stand following initial harvesting. Forest Ecology and Management 54:1-26.

Jones, J.R. 1974. Silviculture of southwestern mixed conifers and aspen: the status of our knowledge. USDA Forest Service Rocky Mountain Experiment Station Research Paper RM-122, Fort Collins, Colorado.

Smith, D.W. 1986. The Practice of Silviculture, 8th edition. John Wiley & Sons, New York.

Young, J.A. and Young, C.G. 1992. Seeds of Woody Plants in North America. Dioscorides Press, Portland, Oregon.