Common Even-Aged Systems

Seed Tree

Shelterwood

Clearcut

Clearcutting

• Clearcutting: A method of regenerating an even aged stand in which a new age class develops in a fully exposed microclimate after removal, in a single cutting, of all trees in the previous stand.

– Regeneration is from natural seeding, direct seeding, planted seedlings, and/or advance reproduction.

• Silvicultural clearcuts differ from ‘commercial clearcuts’

– The first removes all trees, the second only merchantable trees

How Clearcutting Changes the Microenvironment

• Full sunlight conditions• Air and soil temperature near the surface increases• Humidity decreases and surface evaporation increases• Soil moisture increases because transpiration decreases• Precipitation interception decreases, more water reaches the surface• Water infiltration and percolation increases; subsurface flow increases• Decomposition increases (warmer and wetter), releasing more nutrients• Nutrients not taken up or bound to soil leach out of system

Clearcutting

• Edge effect– Moisture increases on a gradient for 30-40 feet into a clearing and then

levels off– Shade (in the northern hemisphere) is more pronounced on the south

edge of the clearing. East to west shade depends on time of day.

Clearcutting

• Alternate clearcutting arrangements

– Strip clearcut

– Block clearcut

– Patch clearcut

• Use of alternative methods:

– Ensure good seed rain

– Manage shade patterns

– Protect against wind or ice/snow

– Improve aesthetics or meet policy-based constraints

Alternative Clearcutting Approaches

Block clearcutting• All trees are removed in a single operation

• Size limitations are based on policy and site conditions, not on regeneration constraints

Alternative Clearcutting Approaches

Alternate strip clearcut

Strip clearcuts, alternate or otherwise, are best oriented at right angles to prevailing winds. The width of the strips will depend on seedfall distances for the preferred species, wind hazard, and other factors

Progressive strip clearcut

Alternative Clearcutting Approaches

Patch clearcutting• Stand is regenerated in a series of clearcuttings made in patches

• Patch size influences light availability within the patch and should be chosen to match species silvics

Other considerations when using even-aged methods

• Stream Side Management Zones (SMZ’s)– Typically leave an unharvested or partially harvest buffer

• Legacy trees

• Travel corridors for wildlife

• Management of viewscapes– Orientation on landscape

– Aesthetic buffers

• Alter shapes, adjacencies– Avoid straight edges and square corners

• Limit harvest size

Clearcutting and Site Preparation

• Site preparation considerations for natural regeneration

– Some important questions• Is it needed or would it be detrimental? • Do you need it for a desired species?

– Does species need a mineral seedbed

Site preparation and clearcutting: Considerations for natural regeneration

– Scarification → mineral seedbed

– Control slash residues• Partial shade or browse protection afforded by slash• Control slash cover to manage seed eating mammals

– Mechanical or chemical vegetation control• Competing vegetation that may inhibit or delay regeneration and

effect subsequent growth rates

Advantages Clearcutting with Natural Regeneration

• Good method for most shade intolerant species

• Commercially attractive

• Ease of administration and implementation of regulated forest

• Clean site eases site preparation

• Easy machine access eases harvesting

• Total overstory removal reduces some pests (e.g. dwarf mistletoe)• Facilitates regeneration of species with serrotinous cones• Precludes blow down• Increases herbaceous cover (browse and cover for many wildlife species)

Shortcomings of Clearcutting with Natural Regeneration

• Problems with dependable seed sources and seedling establishment– Seed shortage limits regeneration to light seeded species– Poor seed years may lead to regeneration failure or irregular stocking– Overstory removal limits within stand seed production following harvest– Density and uniformity of a species is difficult to control

• Issues associated with no high forest cover and high light environment– Lack of cover may adversely impact some tree species and may increase

competition by herbaceous and shrubs– Dense competition may require costly site preparation– Cold air drainage may damage reproduction– Dry sites may not have sufficient surface moisture to support germination

• Reduced chance for genetic improvement

Shortcomings of Clearcutting with Natural Regeneration

• Impacts on soils and hydrology– Wet sites may become wetter– Wet soils may become unstable on steep slopes– Mineral soil exposure may increase soil erosion– Increased decomposition rates and potential nutrient leaching

• Decreased visual aesthetics

• Increased fuel loading and fire danger

• Decreased wildlife habitat for some species

Coppice Silviculture

Coppice

• The term "coppice" is commonly applied to any regeneration arising from sprouts or suckers—typically hardwoods of young to moderate age

• As a method, it is where regeneration is solely from sprouts or root-suckers

• Associated with short rotation production of pulpwood or fuelwood

– Historically associated with charcoal iron production

Coppice

• Some coppice principles:

– Low stumps produce better quality sprouts • Best sprouts originate from the root collar

– Sprouting vigor tends to decline with age and size of stems

• smaller stems, better sprouting

– Sprouting is most vigorous from dormant season cutting• Least vigorous from late spring cutting

Coppice

• Coppice for energy, bioremediation, environmental cleanup– Repeated crops without replanting

– Vegetative propagation maintains genetic integrity of plantation

– Increased growth rates allow large volume production on limited land base

– Short cycle provides quick return on investment

– Second and third rotation often produces greater biomass in shorter time frame due to multiple stems from sprouts

Coppice

• The cutting cycle is set by when the MAI intersects PAI

• General shortcomings of coppice systems– Financial success depends on access to markets for small diameter wood

– Serve limited set of management goals

– Frequent entry requires extra caution to minimize soil disturbance and may increase loss of soil nutrients after repeated harvests

– Coppices susceptible to freezing and browse

– It takes time to convert from coppice to high forest methods

– Coppice stands have limited non-market values

• General shortcomings of short-rotation biomass plantations– Require guaranteed markets

– Require fertile soils with abundant moisture as well as fertilization to maintain critical nutrients

– May require protection from browse

– Mechanized systems needed for efficient harvesting require fairly level sites with uniform surfaces and highly trafficable soils.

Coppice with standards: scattered, individual stems allowed to grow on through several coppice cycles

Seed Tree Method

• Definition: even-aged method retaining widely spaced, uniformly distributed seed bearing trees

• Reproduction source: from seeds disseminated from trees left after harvest

Seed Tree Method

• Remaining seed trees may be removed after suitable regeneration is established, but this is not necessary to the method's application

• Produces an even-aged stand

• Inherently works well for wind dispersed species, but not hard seeded trees such as oaks and hickories

• The method removes size constraints on the regeneration area (also shape and orientation issues)

Seed Tree Regeneration Method

• Regeneration must be established in a short period of years, or else the site will be occupied by other plants

• Produces early successional conditions on the site (the same as a clearcut):

• High light levels, high exposure to wind, and extremes in temperature at ground level.

• Retained trees do not provide enough canopy cover to alter the stands microenvironment in comparison to open condition

– Density of retained trees that would alter microenvironment is species-specific

Number and spacing of seed trees depends on:

– Size and species of seed trees

– Amount of viable seed per tree

– Percent of seed trees that may survive

– Percent of seed that produces an established seedling

Key considerations for the seed tree method

Considerations for number and spacing:

• Distance to which seed from desired species can be dispersed to fully stock an area– Do not exceed maximum dispersal distances

• Nature of the seedbed– If unfavorable (e.g., heavy duff or sandy topsoil), leave more seed trees (but,

better to prepare it by fire or disking)

• Anticipated competition level– Increase the number of seed trees if there will be a high competition level with

no or inadequate competition control

Above all, know the silvics of species to be retained

Considerations for number and spacing:

• Light seeded trees can disseminate 2 to 5 times their height

• Amount of viable seed is usually limiting factor

• Influence of spacing on pollination alter total seed production

• Because of year-to-year variation in seed production, it is best to ensure enough reserve trees to restock area in one moderate seed year

• Usually, 4 to 20 trees per acre retained

8 seed trees per acre in a loblolly-shortleaf pine stand. Arkansas.

Recommended minimum number of seed trees for major southern pines, by DBH class. Number per acre. (Average distance between trees, in ft, shown in parentheses). Will provide value for commercial removal

Species

DBH (inches)

Loblolly Shortleaf Slash Virginia

910121416+

NA12 (60)9 (69)6 (85)4 (104)

NA20 (47)14 (56)12 (60)12 (60)

NA12 (60)9 (69)6 (85)4 (104)

6 (85)5 (93)4 (104)4 (104)4 (104)

Characteristics of Quality Leave Trees

• Windfirmness– Shallow rooted trees or species with weak wood are not

desirable

• Wide, deep crowns, with high live crown ratio– Indicators of vigorously growing trees

– Dominant or better codominant crown class

– Seed production is linked to crown area

• Height– Height can influence distance of seed dispersion

• Age– Must be old enough to produce seed

Cutting Strategies – Seed Tree System

• Preparatory Cut: Optional initial treatment to increase tree vigor and seed production

• Establishment Cut: Treatment to establish seedling reproduction within the stand

• Removal Cut: Removal of final overwood to release established seedlings

– Multiple cuttings can be used and are the same as for a shelterwood except for the density of the establishement cut (i.e. can have a preparatory cut and a removal cut)

Cutting Strategies – Seed Tree System

• Additional Management Options:– Reserve Cutting: Retain seed trees to help make an early thinning of

the next stand more economically feasible

– Not competing removal cut and retaining seed tree through next rotation to meet multiple-use objectives

Seedtree Reserve Cutting Considerations

• Do economic gains out-weight positives to retention?

• Damage to established reproduction

• Is area fully stock with reproduction?

• Additional site preparation may be necessary if reproduction does not develop

• If removal is chosen and growth of established reproduction is your primary objective…– Implement removal cut when site is fully stocked with seedlings of desired

height

– Level of stocking and seedling height required is species-specific

Site Conditions: An adequate seedbed and low level of competition are required

• Some well-distributed exposed soil is desirable, since seeds are small – Best case: thin, discontinuous litter, with some mineral soil exposed

• Dispersed skidding during logging may be sufficient, particularly if the stand has been burned regularly

• Consider a prescribed burn (for pines) if a heavy litter layer exists – Best if before harvest, and not between seedfall and a winter/early spring

harvest

• Mechanical site preparation– provides some density/distribution control

Site Preparation Considerations for Seed Tree Method

Reduce anticipated competition, if needed• Logging operations can damage competition vegetation

present at time of harvest

• Pre- or post-harvest chemical control

• A burning regime prior to harvest– Involves planning many years ahead – May be part of your silvicultural system for pines– May need to include one or more summer burns just before the

anticipated harvest

Site Preparation Considerations for Seed Tree Method

• Advantages to Seed Tree Method:

– Allows for the control of species and phenotypic characteristics of seed source

– Seed source abundant and uniformly spaced

– Provides full sun growth conditions

• Disadvantages: – Exposes seed source to increased risk of premature destruction.

– Does not provide protection to reproduction on harsh sites

• Application of Seed Tree Method:– Southern Pines: slash, shortleaf, loblolly, sand

– Hardwoods: yellow-poplar, cottonwood, willow, ash

– Western Conifers

Shortleaf Pine Ponderosa Pine

Slash Pine

• Definition: an even-aged silvicultural system where the reproduction method removes mature community in two or more successive cuttings, temporary leaving some old trees to serve as seed source and to protect the regeneration.

• Characteristics:1. Relatively low density stand left of vigorous seed-bearing trees

2. Residual overstory provides sufficient canopy to mitigate sensitive environmental conditions.

• Especially important on harsh or exposed sites.

3. Residual trees are removed once new reproduction reaches adequate size (i.e. height) and density

Shelterwood System

Uniform Shelterwood Components

1. Preparatory Cut

An optional initial treatment to:

– Increase tree vigor and seed production in mature stand

– Remove undesirable seed sources

– Alter understory environment to promote development of advance reproduction

2. Establishment Cut– Artificially moves stand into understory reinitiation phase

of stand development– Promotes seed germination and establishment by creating

permanent openings in main canopy – Opens the canopy for sufficient light availability to allow

regeneration– Maintains some control (“shelter”) of understory vegetation

– Generally, 25-60 ft2/ac residual basal area• 30-40 ft2/ac southern pines, 50-60 ft2/ac for oak

– Should retain dominant, vigorous trees of favorable phenotypes

Uniform Shelterwood Components (continued)

2. Establishment Cut

Considerations for success:

– Appreciably modify the understory environment

– Retain sufficient residual cover to create conditions that favor target species and seed supply

– Understory environment must promote seedling development of desired species

Uniform Shelterwood Components (continued)

Tradeoffs Between Overstory Retention, Light Environment, and Understory Competition

*Optimal level is dependant on species, site productivity, and stand history

3. Removal Cut

• A harvest to take away the overwood, so the reproduction can develop uninhibited

– Conducted only after satisfactory establishment of reproduction based on density, height, and distribution of seedlings

– Will impact (i.e. damage) established reproduction

– Remove the overwood before suppression of regeneration

Uniform Shelterwood Components (continued)

Applicability of the Shelterwood Method

• Most flexible even-aged method

• A good method for heavy-seeded species

• A good method where the seed supply is irregular

• Obtain rapid increment of high quality wood

• Increase mast production

• Maintain aesthetics

Uniform Shelterwood Methods

• Three-cut Method: Preparatory, Establishment, and Removal cut are used

• Two-cut Method: Establishment and Removal cut only

Other Types of Shelterwood Systems

Irregular or Reserve Shelterwood:

• Leaves residual overstory for an extended period of time into new rotation – creates two-aged stand

• Has ecological/aesthetic vs. economic/operational tradeoffs

Other Types of Shelterwood Systems

Group Shelterwood:• Takes advantage of existing patches of reproduction• Removal cuttings done in patches containing reproduction• Preparatory and establishment cuts done in areas lacking

favorable reproduction

Group Shelterwood

Strip Shelterwood:

• Removal of mature age classes over a series of entries by cutting narrow strips not exceeding the height of adjacent standing trees

• Residual strips provide seed and partial shade to openings

• Strip Orientation:

– Long axis of strips at right angles to prevailing winds to reduce blow-down

– Alignment in relation to sun’s path influences proportion of direct and diffuse radiation

Other Types of Shelterwood Systems

Strip Shelterwood

Application of the Shelterwood System

• Upland and bottomland oak forests

• Eastern pines: red pine, eastern white pine

• Southern pines: longleaf pine

• Rocky mountain conifers: western white pine, ponderosa pine, Douglas-fir (Rocky Mountain variety), western larch (on harsh sites).

• Cascade and coastal range regions: western hemlock/Sitka spruce type and Douglas-fir

Upland Oak Shelterwood

Shelterwood in longleaf pine

Brief Comparison: Clearcut, Seed Tree, and Shelterwood

Clearcut:

• Entire canopy removed in one operation

• Seedlings grow under open field conditions

Seed Tree:

• Canopy removed in 2 to 3 stand entries

• Residual trees retained to provide a seed source

• Seedlings grow under essentially open field conditions

Shelterwood:

• Residual trees retained to provide a seed source and modify understory microenvironment

• Canopy removed in 2 to 3 stand entries