Silviculture

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SILVICULTURE (Chapter 13) : 

SILVICULTURE (Chapter 13) Application of knowledge of physical & biological sciences to achieve desired outcomes

DEFINITIONS : 

DEFINITIONS SILVICULTURE: “Manipulation of forest stands to accomplish a specified set of objectives” ROTATION AGE: “Age at which a harvest is planned”

OUR TOPICS : 

OUR TOPICS General silvicultural goals A premise on which silviculture rests Natural processes in forest stands Specific goals of silviculture Silvicultural systems Environmental effects of silvicultural practices

SILVICULTURE:GENERAL GOALS : 

ENHANCEMENT OF: Timber quality & productivity Wildlife habitat Streamflow & water quality Recreation Range quality & productivity Aesthetic qualities SILVICULTURE:GENERAL GOALS

SILVICULTURE: PREMISE : 

SILVICULTURE: PREMISE We can predict forest responses to forest management operations if we: Understand natural stand development processes Operate in ways that mimic natural processes

NATURAL PROCESSES: EVEN-AGED STANDS : 

NATURAL PROCESSES: EVEN-AGED STANDS Sudden canopy removal ? wave of seedling establishment, followed by stand development Stand stages Seedling (< 1 m tall) Sapling (> 1 m tall, < 4” diameter) Pole (4-10” diameter) Mature (adults, sizes vary) Overmature (mortality > growth; decay)

NATURAL PROCESSES: EVEN-AGED STANDS : 

NATURAL PROCESSES: EVEN-AGED STANDS Crown closure ? competition Competition ? Self-thinning Vertical stratification Small trees may be as old as canopy trees

VERTICAL STRATIFICATION: TREE CLASSIFICATION : 

VERTICAL STRATIFICATION: TREE CLASSIFICATION Dominant: above general canopy level Codominant: average canopy-level trees Intermediate: crowns crowded; only top of crown in direct sun; destined to become “suppressed” Suppressed: overtopped; little or no direct sun; mortality high; little chance of regaining dominant/codominant position

NATURAL PROCESSES: UNEVEN-AGED STANDS : 

NATURAL PROCESSES: UNEVEN-AGED STANDS DEFINITION: Uneven-aged stand has 3 or more tree age classes Even-aged stands become uneven-aged in absence of catastrophic disturbance Shade-tolerant understory develops Broad age range Fills gaps as canopy trees die May eventually become dominant/codominant

NATURAL PROCESSES: PURE- vs. MIXED-SPECIES STANDS : 

NATURAL PROCESSES: PURE- vs. MIXED-SPECIES STANDS PURE-SPECIES STANDS Often follow catastrophe Often even-aged Often more valuable economically MIXED-SPECIES STANDS May be more aesthetic Often favor wildlife May be more resistant to insects & disease

SILVICULTURE:SPECIFIC GOALS : 

SILVICULTURE:SPECIFIC GOALS STAND IMPROVEMENT REGENERATION THESE SPECIFIC GOALS ARE USED TO ACCOMPLISH LANDOWNER’S MANAGEMENT OBJECTIVE(S)

SILVICULTURAL GOAL: STAND IMPROVEMENT : 

SILVICULTURAL GOAL: STAND IMPROVEMENT Goal is to improve stand in one or more of: Species composition Growth rate Wood quality

SILVICULTURAL GOAL: STAND IMPROVEMENT : 

INTERMEDIATE TREATMENTS (BETWEEN STAND ESTABLISHMENT & HARVEST): Release cutting, herbicide treatment to change species composition Thinning, fertilizing to improve growth rate Improvement cut, pruning, salvage to improve wood quality SILVICULTURAL GOAL: STAND IMPROVEMENT

Slide 14: 

DOUGLAS-FIR, OREGON, HERBICIDE

Slide 15: 

4 YEAR OLD LOBLOLLY PINE, HERBICIDED OAKS

Slide 16: 

THINNING, SIERRA NEVADA, CALIFORNIA

Slide 17: 

PRUNING MONTEREY PINE, NEW ZEALAND

SILVICULTURAL GOAL: REGENERATION : 

SILVICULTURAL GOAL: REGENERATION SUCCESS OR FAILURE DEPENDS ON Harvest method Germination & seedling growth requirements Threshold stocking density Hastens self-thinning Discourages low forks Improves hardwood log quality Removal of low-quality trees (if in a partial cut) Natural vs. artificial regeneration

NATURAL REGENERATION : 

NATURAL REGENERATION SOURCES OF NATURAL REGENERATION Seeds carried by wind or animals “Advance regeneration” already on site Stump sprouts (many hardwoods) Seed bank (seeds in soil) INEXPENSIVE MAY RESULT IN SPECIES CHANGE

NATURAL REGENERATION : 

NATURAL REGENERATION SUCCESS DEPENDS ON MANY FACTORS Seed crop Weather Microclimate Seedbed condition Vegetative competition Seed & seedling herbivores

ARTIFICIAL REGENERATION : 

ACCOMPLISHED BY Direct seeding (an uncommon method) Planting nursery- or greenhouse-grown seedlings Bare-root Containerized SITE PREPARATION ESSENTIAL!!!!! Mechanical Prescribed fire ARTIFICIAL REGENERATION

Slide 22: 

LONGLEAF PINE CONTAINER SEEDLINGS

Slide 23: 

SITE PREP (PRESCRIBED BURN), SHORTLEAF PINE

ARTIFICIAL REGENERATION : 

ARTIFICIAL REGENERATION ADVANTAGES Stand establishment more reliable? Prompt reforestation? Can be timed with favorable weather Control of species composition Control of spacing Control of genotypes DISADVANTAGES Costly Facilitates monoculture

ARTIFICIAL REGENERATION : 

ARTIFICIAL REGENERATION INTENSIVE MANAGEMENT TENDS TO RELY ON ARTIFICIAL REGEN Usually creates pure stands (monocultures) Easier to manage Silvicultural treatment costs lower Harvest costs lower Value can be higher

SILVICULTURAL SYSTEMS : 

SILVICULTURAL SYSTEMS Long-term sustainable schemes to optimize: Growth Quality Regeneration of desirable species Silvicultural systems incorporate Harvest method Site preparation Regeneration plan Schedule of intermediate treatments

SILVICULTURAL SYSTEMS : 

SILVICULTURAL SYSTEMS TWO CATEGORIES OF SYSTEMS 1. Even-aged systems 2. Uneven-aged systems

EVEN-AGED SILVICULTURAL SYSTEMS : 

EVEN-AGED SILVICULTURAL SYSTEMS Essential for shade-intolerant species Four systems: Clearcutting Seed tree Shelterwood Coppice

EVEN-AGED SILVICULTURAL SYSTEMS: CLEARCUTTING : 

Removes all stems Regeneration may be natural or artificial If natural seeding, use small cuts Larger cuts if advanced regen or sprouting Hastens succession if tolerant understory EVEN-AGED SILVICULTURAL SYSTEMS: CLEARCUTTING

Slide 30: 

DOUGLAS-FIR CLEARCUTS, WASHINGTON

EVEN-AGED SILVICULTURAL SYSTEMS: SEED TREE : 

EVEN-AGED SILVICULTURAL SYSTEMS: SEED TREE Scattered mature “leave trees” not cut Tree seedlings may have competition Poor for shallow-rooted trees (windthrow) Reasonable if Site preparation feasible Species is wind-firm

Slide 32: 

SHORTLEAF PINE SEED TREE HARVEST

EVEN-AGED SILVICULTURAL SYSTEMS: SHELTERWOOD : 

EVEN-AGED SILVICULTURAL SYSTEMS: SHELTERWOOD More leave trees than seed tree method Ideally 30% - 80% of ground surface shaded Prescriptions written in terms of residual basal area (sq. ft. per acre) Residual trees cut after regen established Less visual impact than clearcuts May reduce erosion

Slide 34: 

SHELTERWOOD: MIXED HARDWOODS, VIRGINIA

EVEN-AGED SILVICULTURAL SYSTEMS: COPPICE : 

EVEN-AGED SILVICULTURAL SYSTEMS: COPPICE Regeneration is by stump or root sprouts Short rotations Usually for pulpwood, fuelwood

Slide 36: 

ASPEN COPPICE 2 YEARS AFTER CLEARCUT, COLORADO

Slide 37: 

30-YEAR-OLD ASPEN COPPICE

UNEVEN-AGED SILVICULTURAL SYSTEMS : 

UNEVEN-AGED SILVICULTURAL SYSTEMS “SELECTION METHOD” of harvesting: Individual selection: cut scattered individuals Group selection: cut scattered tree groups

UNEVEN-AGED SILVICULTURAL SYSTEMS : 

ADVANTAGES Site prep & planting unnecessary Sustained yield possible for single stand Manipulation less evident (canopy intact) Erosion minimal Fire hazard low (debris less concentrated) UNEVEN-AGED SILVICULTURAL SYSTEMS

UNEVEN-AGED SILVICULTURAL SYSTEMS : 

UNEVEN-AGED SILVICULTURAL SYSTEMS LIMITATIONS Unsuitable for shade-intolerant species Unfavorable for some wildlife Harvest may injure or damage uncut trees BEWARE TEMPTATION to “high grade”! GROUP SELECTION can mitigate limitations of individual selection system

Slide 41: 

SINGLE-TREE SELECTION, RED SPRUCE & EASTERN HEMLOCK

Slide 42: 

SINGLE-TREE & GROUP SELECTION -- RED SPRUCE, EASTERN HEMLOCK & BALSAM FIR

Slide 43: 

GROUP SELECTION (90-FOOT PATCH), MIXED CONIFERS, SIERRA NEVADA, CALIFORNIA

EVEN-AGED OR UNEVEN-AGED: HOW TO CHOOSE? : 

EVEN-AGED OR UNEVEN-AGED: HOW TO CHOOSE? Some reasons for even-aged prescription Many high-demand species are shade-intolerant Shade-tolerant species usually slow growing Shade-tolerant species may be less valuable (e.g., beech, eastern hemlock) Harvest may be expensive (e.g., cable logging in Pacific Northwest) Some wildlife requires early-successional stage Watershed management Recreation management

EVEN-AGED OR UNEVEN-AGED: HOW TO CHOOSE? : 

EVEN-AGED OR UNEVEN-AGED: HOW TO CHOOSE? Some reasons for uneven-aged prescription Some shade-tolerant species are valuable & in demand (e.g., sugar maple in Midwest) Lower risk of loss to insects and diseases Some wildlife requires mature forests Less erosion on slopes Recreation management Aesthetics

EFFECTS OF SILVICULTURE: GROWTH : 

EFFECTS OF SILVICULTURE: GROWTH Diameter growth models are often used to make silvicultural forecasts, e.g.: ?D = 0.0716 + 0.0129D + 0.0157SI + 2.03 { 1 / (1 + BA) } - 0.0117BA ?D = diameter growth, cm D = current diameter, cm SI = site index BA = stand basal area, m2/ha Predicts growth effects of thinning

EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES : 

EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES Soil erosion Nutrient loss Chemical use Aesthetics

EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES : 

EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES Soil Erosion Potential erosion problems include: Soil loss Stream sedimentation Stream temperature changes Roads & skid trails are the prime culprits Erosion reduced by Good road design & implementation Use of appropriate equipment Skylines, balloons, helicopters minimize erosion

EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES : 

Nutrient Loss Nutrients can leach from forest operations sites Nutrient loss accelerated by: Short rotations Even-aged silvicultural systems Whole-tree harvest Nutrient loss mitigated by: Long rotations Uneven-aged silvicultural systems Net effects unclear -- need more research EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES

EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES : 

EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES Chemical Use (herbicides, fertilizers) Impact is largely on water quality Some aquatic life has low tolerance Chemical levels in water generally “safe”?

EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES : 

Aesthetics Visual landscape quality is a resource Some considerations: In visually sensitive zones: use selection method For even-aged cuts: Use narrow cut blocks Design cut blocks to follow natural contours Leave “islands” of uncut vegetation screens EFFECTS OF SILVICULTURE: ENVIRONMENTAL ISSUES

SILVICULTURE: MIMICSNATURAL PROCESSES? : 

SILVICULTURE: MIMICSNATURAL PROCESSES? Natural tree death (selection method) Huge natural windfalls, e.g., 600,000 acres following hurricane (even-aged systems, including clearcut) Mount Saint Helens (even-aged systems) Insect epidemics & fire (even-aged systems)

SILVICULTURE: MIMICSNATURAL PROCESSES? : 

SILVICULTURE: MIMICSNATURAL PROCESSES? In some areas: most stands are naturally even-aged In other areas: most stands are naturally uneven-aged ? IDEAL: diversity of silvicultural systems to mimic the mosaic of cover types & age classes that occurs naturally

Slide 54: 

NATURAL JACK PINE & ASPEN REGENERATION FOLLOWING FIRE, MANITOBA

Slide 55: 

CLEARCUT TO MIMIC FIRE PATTERNS, JACK PINE & ASPEN, MANITOBA