Biomass Harvesting and Forest Site Productivity

Eric D. VanceNational Council for Air and Stream Improvement

(NCASI)Biomass/Bioenergy Workshop

February 24-25, Houston, TX

Biomass Harvesting

• Emerging markets for bioenergy

• Removal of biomass previously left on site

• Shorter rotations• Concerns over site

productivity, water, wildlife

Sustaining Site Productivity by Manipulating Site Resources

• Water, nutrients, sunlight• Allocation of existing site resources

– Competing vegetation, root growth• Increasing site resources

– Artificially removing biomass and nutrients– Cannot always rely on natural replacement

Management Intensity and Site Resources

ResourceCapital

Extensive

AvailableResources

Intensive

Intensive Utilization of Harvest Residues in Southern Pine PlantationsM.H. Eisenbies, E.D. Vance, W.M. Aust, J.R. Seiler

Bioenergy Research (2009) 2:90-98

• 32 million Mg yr-1 residues available in the South

• 50-85 Mg ha-1 on site after stem-only harvest

• 45-60% increase in mid-rotation fertilization may be needed to replace nutrients if residues removed

South Carolina Wet/Dry Harvest Study

(Virginia Tech, MeadWestvaco, NCASI)

Residue-Soil Disturbance MatrixBedded

Flat Planted

MinimalHeavy Moderate

Soil Physical Disturbance

Har

vest

ing

Res

idue

Dis

turb

ance

Cla

ss II

IC

lass

IC

lass

II

Hypoth

esize

d Inc

reasin

g Prod

uctiv

ity

Bedded

Flat Planted

MinimalHeavy Moderate

Soil Physical Disturbance

Har

vest

ing

Res

idue

Dis

turb

ance

Cla

ss II

IC

lass

IC

lass

II

Hypoth

esize

d Inc

reasin

g Prod

uctiv

ity

Ten-Year Effects of Harvest Residue Removal on Relative Rank of Stand

Biomass

Fall River Long-Term Soil Productivity Project

Univ. of Washington, Weyerhaeuser, USFS, NCASI

• Conventional bole-only removal

• Total stem (bole-only to a 5cm top)

• Total-tree removal• Total-tree + legacy-

wood removal • All cable-yarded

Fall River StudyDouglas-fir Age 5 Tree Volume Index

SVO

L (c

m3 /1

000)

0

5

10

15

20

25

30

BO BO BO BO5 TT+ TT BOnoVC C C T

Forest Service Long-Term Soil Productivity Network

Core SitesAffiliated Sites

Competing Vegetation: A Critical Factor

Lake States AspenNutrient Depletion and Rotation Length

• Deficiencies rare• Older studies

– Multiple, short-rotation cycles

– Concluded 10-15 yr rotations sustainable

• Reduced soil/foliar Ca on some sites

• Indices underdeveloped

Aspen in the Lake StatesNutrient Budgets for Whole-tree

Harvesting over 50 years(Mineral soils (lb/ac); Minnesota GEIS, Grigal 2004))

0500

1000150020002500300035004000

N P K Ca Mg

InputsOutputsCapital

Ca capital = 15,125

Short Rotation Aspen on Sandy Soils: A Worst-Case Scenario?

• < 1% Ca drain– (Grigal, 2004)

• Three 20-yr rotations– < 5% Ca removed

• 1 ton/ac wood ash

The Forest Calcium Cycle(Likens et al. 1998)

Over a Century of Forest Nutrition Management in Scandinavia

• Science-based• Forest productivity• Forest health• Nutrient imbalances

– Foliar, soil analysis• Biomass harvesting

Intensive Harvest and Site Productivity: What Do We Know?

• Many sites remarkably resilient

• Little evidence for productivity declines

• Preconceived notions often incorrect

• Managers often know best

But, More Work is Needed!

• Sensitive sites• Fundamental impacts• Long-term, repeated

removals• Indicators• Prevention, mitigation

A Range of Management Intensities to Meet Society’s Needs