The Effect of Harvest on Forest Soil Carbon

The Effect of Harvest
on Forest Soil Carbon
Rob Harrison
&
Jason James
University of Washington, Seattle, WA, USA

Forest Soils in Context
• Forests represent ~80% of terrestrial
aboveground biomass
• As much as 70% of global SOC in forest soils
• Net balance of forest SOC:
• Detrital inputs: 61.4 Pg C yr-1
• Respiratory losses: 60.0 Pg C yr-1
• Forests viewed as key sink for atmospheric C

Climate Change & Deep Soils
Hicks Pries et al.
Science (2017)
• Coniferous
temperate forest
on Alfisols
• 34-37% respiration
increase
• Subsoil (>30 cm)
contributed 20-25%
of respiration
• 10% of warming
response
Warm (+4°C)
Control

Climate Change & Deep Soils
Mobley et al. (2014)
• Reforestation of
agricultural land
• Began 1957
• Ultisol soils

Main Questions
1. What is the effect of harvesting on SOC?
2. How does this effect change with depth?
3. Is the response soil type specific?
4. Do particular management practices curtail
or exacerbate SOC change?
5. How long for SOC to recover?

Meta-analysis Methods
Dataset
• 112 publications
• 1979 – 2016
• 945 Response Ratios
• Meta-data:
• Depth
• Time since harvest
• Treatment intensity
• Soil Order
• Forest Type
Statistical Methods
• ln 𝑅 = ln
𝑋 𝑇
𝑋 𝐶
• 𝑋 𝑇 = Mean Treatment Soil C
• 𝑋 𝐶 = Mean Control Soil C
• Back-transform:
• 𝑒(ln 𝑅 ) − 1) × 100
• Expressed as %
change relative to
control
• Bootstrapped 95%
CI’s

14% loss of
SOC
33% loss of
SOC
3% loss of SOC
17% loss of
SOC

Significant
Difference
Significant loss in
hardwoods, not in
conifer forests
• No observations
deeper than 60
cm in Hardwoods
* p < 0.05
*
*
*
*

*
*
*
*
*
*
*
*
**
Alfisol
Andisol
Entisol
Inceptisol
Mollisol
Oxisol
Spodosol
Ultisol
Not Specified
12% loss of O horizon SOC
24% gain in SOC
* *
*
19% loss of SOC
Overall 21% SOC loss driven by
O horizon, not mineral soil
18% loss of SOC overall
31% loss of SOC
Substantial loss in both organic
and mineral soil
• -19% overall in Spodosols
• -25% overall in Ultisols
* p < 0.05

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Spodosol Ultisol
Alfisol Inceptisol
0 25 50 75 100 125 0 25 50 75 100 125
−100
0
100
200
−150
−100
−50
0
50
100
150
−100
0
100
200
300
−100
0
100
200
Time Since Harvest (Years)
%ChangeRelativetoControl
● Mineral Soil O Horizon

Less SOC loss in
mineral soil
Less SOC loss in
mineral soil
Large additional
loss of SOC
Additional loss in
mineral soil

USDA Forest Service
Uinta-Wasatch National Forest

Lack of Deep Sampling
Global Data Deficiency
• Across 112 publications
• Ave. depth: 24 cm
• Ave. max depth: 34 cm
• Global SOC (Pg C)
(Jobbagy & Jackson, 2000)
• 0 to 1 m: 1502
• 1 to 2 m: 491
• 2 to 3 m: 351

Potential Policy Implications
1. Response to management is soil/site specific
• One-size-fits-all policy not appropriate
2. Slash burning exacerbates SOC loss after
harvest
3. Deep soils must be monitored
• Considerable stocks
• Sensitive to warming
• Subsurface can react differently than surface soil

Questions?
Acknowledgements
• USDA McIntyre-Stennis
Program
• National Council for Air and
Stream Improvement
• Northwest Advanced
Renewables Alliance
• NSF Center for Advanced
Forest Systems
• Stand Management
Cooperative
• University of Washington

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