Carbon storage in silvopastoral systems
Farm Woodland Forum Annual Meeting
13 June 2013
Matthew Upson and Paul Burgess
Centre for Environmental Risk and Futures,
Department of Environmental Science and Technology.
p.burgess@cranfield.ac.uk
What effect does planting trees have on
soil carbon storage?
Soil: an important carbon sink
Reproduced from Lal (2008). 1 Pg = 1,000,000,000,000,000 g
Scientific consensus?
• Heavily dependent on previous land use.
• Planting on arable = large gains in soil carbon
• Planting on pasture = small gains OR losses in soil
carbon
Guo & Gifford (2002), Paul & Polglase (2002), Laganiere et al. (2010)
Research gaps
• Few UK studies in the literature.
• Even fewer relating to agroforestry.
• Fewer still that sample to any great depth (>50 cm).
Silvoarable
Agroforestry
• 19 year old poplar system
• Compared arable control with
two silvoarable treatments.
Silvoarable
Agroforestry
350
Cropped-Silvoarable
Fallow-Silvoarable
Arable Control
Cumulative SOC t C ha
1
300
• No differences at 0-20 cm.
250
• More carbon stored in agroforestry for
0-40, 0-60, 0-105 cm.
200
150
• No difference when 150 cm considered.
100
50
0
0
25
50
75
100
125
150
Depth (cm)
Error bars indicate standard error of the mean.
Reproduced from: Upson & Burgess (2013).
Silvopastoral
Agroforestry
• 14 year old silvopastoral site in Bedfordshire.
• Established as part of an EC funded project in 1998 (Burgess et al.,
2000).
• Parkland/pasture since 1880s.
• Most recent usage (since 1990s): grazing for beef-suckler herd.
Silvopastoral system (7. 98 ha)
• 34 groups of trees
• Native broadleaf mix (30% ash)
• Area under trees: c. 0.45 ha
Farm woodland (6.11 ha)
• Native broadleaf mix (60%),
shrub mixture (20%), open
ground – rides, footpaths (20%).
• Fenced.
• 80 stratified sampling points.
• >1000 samples.
• Soil bulk density.
• Organic carbon content.
Soil bulk density
3
0.0
Bulk density g cm
0.4
0.8
1.2
1.6
g
g
0-10
f
Sampling depth (cm)
• Tree planting often associated
with reduced soil bulk density.
• Bulk density in tree treatments as
high, if not higher than pasture at
all depths.
e
e
10-20
e
bc
• Probably a results of changes in
clay volume.
d
20-40
c
a
40-60
• Similar to findings in silvoarable.
b
a
FW
PA
SP
Error bars indicate standard error of the mean.
Similar letters indicates no significant difference.
Soil organic carbon
Organic carbon content g 100 g
0
1
2
3
4
5
6
1
7
c
0-10
a
b
Sampling depth (cm)
e
10-20
d
d
• Pro-rata reduction?
f
20-40
• Tree planting resulted in carbon losses
at 0-10 cm and 10-20 cm increments.
f
f
40-60
g
g
g
60-105
gh
h
gh
105-150
gh
h
gh
• Below 40 cm carbon contents broadly
similar, but further analysis needed.
FW
PA
SP
Error bars indicate standard error of the mean.
Similar letters indicates no significant difference.
Soil organic carbon (SOC)
350
Cropped-Silvoarable
Fallow-Silvoarable
Arable Control
Cumulative SOC t C ha
1
300
Farm Woodland
Silvopastoral blocks
Pastoral Control
250
200
150
80
100
60
50
40
0
0
25
50
75
Depth (cm)
100
125
150
0
25
50
75
100
125
Depth (cm)
Cumulative soil organic carbon (t C ha-1) for the silvoarable experiment (left) and silvopastoral (right).
Error bars indicate standard error of the mean. Inset shows differences at 0-10 cm increment.
150
Biomass carbon
• Assumption that ash data can be
generalised.
• Ash trees in silvopasture and farm
woodland sampled (diameter, height,
form, n=198)
• Destructive sampling of aboveground
biomass (n=38, belowground to follow).
• Creation of allometric biomass
equation.
Biomass carbon
Total Carbon t C ha
1
0-10
0-20
0-40
0-60
150
100
50
0
FW
PA
SP
FW
PA
SP
FW
PA
Treatment
Soil_carbon
Error bars indicate standard error of the mean.
Biomass_carbon
SP
FW
PA
SP
Biomass carbon
Differences between the pasture and the farm woodland (FW),
and silvopastoral (SP) treatment (t C ha-1) over 0-60 cm
SOC
Biomass C
Final
FW
-20.2
34.4
14.2
SP
-1.1
1.9
0.8
Longevity
• Carbon pools not created equal.
• Biomass generally considered a ‘labile’ pool.
• Some loss of shallow particulate organic matter
expected after planting, but…
• …could also be long lived (recalcitrant) carbon.
Longevity
80
Stored Carbon t C ha
1
Crop
Harvest
Trees
Woody Products
60
40
20
0
1992
2001
2011
2021
2031
2051
2061
2071
2081
2091
80
Stored Carbon t C ha
1
Crop
Harvest
Trees
Woody Products
60
40
20
0
1992
2001
2011
2021
2031
2041
Year
2041
Year
2051
2061
2071
2081
2091
Summary
• Tree planting on pasture can cause losses of soil
carbon…
• …but only if shallow depths are considered.
• Tree planting should aim to produce quality timber to
sequester carbon in durable woody products…
• …preferably displace more carbon intensive materials.
References
•
Burgess PJ, Graves AR, Goodall GR, Brierly EDR (2000) Bedfordshire Farm Woodland
Demonstration Project: Final Report to the European Commission. Cranfield, Bedfordshire
•
Guo LB, Gifford RM (2002) Soil carbon stocks and land use change: a meta analysis. Global
Change Biology 8:345–360.
•
Laganiere J, Angers D, Para, D (2010) Carbon accumulation in agricultural soils after afforestation: a
meta-analysis. Global Change Biology 16:439–453.
•
Lal R (2008) Sequestration of atmospheric CO2 in global carbon pools. Energy & Environmental
Science 1:86.
•
Paul K, Polglase P (2002) Change in soil carbon following afforestation. Forest Ecology and
Management 168:241–257.
•
Upson MA, Burgess PJ (2013) Soil organic carbon and root distribution in a temperate arable
agroforestry system. Plant and Soil. doi: 10.1007/s11104-013-1733-x