Can Clearcutting Replace Stand-Replacing Fire?

Impacts on soil characteristics over time and future management

implicationsKerry MalmGEOG 5401 Soils Geography

Fall 2007 – Univ of Colorado, Boulder

Why clearcut instead of letting it burn?

• Timber harvesting – Emulation silviculture– More money– Better for the soil?

• OM for decomposition• Nitrogen and Carbon availability

– Faster regeneration

• Fire is detrimental– High costs to put out– Volatilization of compounds– Impenetrable layers

Wildfire vs. Clearcutting:Impacts on Soil

• Increase in pH• Temperature rise• Reduced SOM• NO and NH4+ losses to

atm– ~10% total N of some sites

• N deposition from ppt• Short term increase in

ammonium• Increased nitrate, returns

to normal ~10-12 yrs• Loss of microbial

populations

• Increased soil temperature

• Increased soil compaction

• Churning of soils• Less reduction in SOM• Decreased soil porosity• Increased rate of

mineralization

WILDFIRE CLEARCUTTING

Why care about nitrogen?

• Important for growth and development– Amino acids

• Proteins• Enzymes

• Commonly limits growth of many forest trees, like lodgepole and jack pines

• Wildfire can cause N to go back into atm– No longer available to plants– Acid rain, air pollution, respiration issues

Effects of Clearcutting

Nitrogen Availability

0

2

4

6

8

10

12

14

Unburned Unburned Clearcut Burned Burned Clearcut

Stand Character

ug

N/g

so

il

NH4+

NO3-

(Adapted from Giardina and Rhoades 2001)

Seedling Biomass

0

0.05

0.1

0.15

0.2

0.25

Clearcut Burnt Clearcut Forest Burnt Forest

Stand Character

See

dlin

g B

iom

ass

(g)

(Adapted from Giardina and Rhoades 2001)

Benefits of Clearcutting• Boreal soils – 12 year

old clearcuts increased inorganic-N production vs. more recently cut and uncut stands

(Hazlett et al. 2007)

Net Nitrification • Net nitrification

highest in clearcut• Downsides?

– Leaching– Water quality– Nutrient loss

(LeDuc and Rothstein 2007)

X Burned

Clear cut

Mature

Pulse in nitrification

N Mineralization

• Net N Mineralized was the highest in mature stands, but higher in clearcut than burned, which is consistent with other studies

(LeDuc and Rothstein 2007)

X Burned

Clear cut

Mature

Pulse in mineralization

N Immobilization

0

0.5

1

1.5

2

2.5

3

Burned Clearcut Mature

Stand Character

ug/N

/day

NH4+

NO3-

(Adapted from LeDuc and Rothstein 2007)

So, what are you getting at?

• Both cutting and fire produce short-lived pulses of increased N

• Significantly lower total N, labile N, and nitrification in wildfire soils vs. clearcut

• Vegetation community repercussions– Ecosystem functioning– Biodiversity

(McRae et al. 2001, Hazlett et al. 2007, Yermakov and Rothstein 2007)

Potential Issues

• Different methodologies between studies– Incubated soils vs. on site measurements– Different horizons

• Fire variation– Severity– Extent – Return interval/ frequency– Location: Slope, aspect, orientation

• Time since disturbance is important to realize• Need long term studies (>4 yrs)

Can Timber Harvesting Replace Fire in Fire Dependent

Ecosystems?

•Clearcutting does not REPLACE fire, but it may work with fire

•Too many other aspects to fire that harvesting doesn’t mimic well

•Clearcutting can be beneficial when economic value is considered

•Clearcutting is not as detrimental as one might believe

Just to note:

• Timber harvesting and ecosystem restoration are potentially compatible ideas

• Understanding soil processes for specific sites is extremely important to accomplish management goals

• Emulation silviculture is a balance between ecology, economics, and social values

(Simmard et al. 2001, McRae et al. 2001)

Works Cited• Giardina, C.P. and C.C. Rhoades. 2001. Clear cutting and burning affect nitrogen

supply, phosphorous fractions and seedling growth in soils from a Wyoming lodgepole pine forest. Forest Ecology and Management 140:19-28.

• Hazlett, P.W., A.M. Gordon, R.P. Voroney, and P.K. Sibley. 2007. Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario. Soil Biology & Biochemistry 39:43-57.

• McRae, D.J., L.C. Duchesne, B. Freedman, T.J. Lynham, and S. Woodley. 2001. Comparisons between wildfire and forest harvesting and their implications in forest management. Environemntal Review 9:223-260.

• LeDuc, S.D. and D.E. Rothstein. 2007. Initial recovery of soil carbon and nitrogen pools and dynamics following disturbance in jack pine forests: a comparison of wildfire and clearcut harvesting. Soil Biology & Biochemistry 39:2865-2876.

• Simmard, D.G., J.W. Fyles, D. Pare, and T. Nguyen. 2001. Impacts of clearcut harvesting and wildifre on soil nutrients in the Quebec boreal forest. Canadian Journal of Soil Science 81:229-237.

• Yermakov, Z. and D.E. Rothstein. 2006. Changes in soil carbon and nitrogen cycling along a 72-year wildfire chronosequence in Michigan jack pine forests. Oecologica 149:690-700.