Transcript Land-use changes in the temperate forest biome

Land-use changes in the
temperate forest biome:
Implications for carbon-cycling
Dave Egan
Emilie Grossmann
Jeanine Rhemtulla
Temperate Forests:
Small in area but important
biologically & politically
•
•
•
•
•
Smallest forest biome
Lowest carbon content of all forest biomes
Longest history of intensive land-use
The missing sink?
Politically powerful
Small in area
Small amount of stored carbon
C-storage
Soils
C-storage
Vegetation
Forest Area
High
25%
High
33%
Low
27%
Low
42%
Low
59%
Mid
16%
Mid
13%
High
60%
Mid
25%
(Dixon et al 1994)
Longest history of intensive
land-use
• Much longer history of intensive land-use than
either the tropics or boreal biomes
• Remaining old-growth:
–
–
–
–
< 1% Europe
2-3% Australia (temperate eucalypt forests)
~ 25% New Zealand
3 – 5 % United States
(Norton 1996 & WWF 1997)
Land-use II
• China: Temperate forests are known
primarily from the fossil record – most
forest was cleared for intensive
agriculture 4000 years ago.
• Eastern United States: Clearing for
timber and agriculture started in 1750’s
and swept westward thereafter.
Land Clearing in Harvard Forest, Fisher Museum Dioramas
The missing sink?
Figure credit: Woods Hole Research Center
Missing sink II
• Forests are generally increasing in area throughout
the temperate biome:
•
– Forest aggradation in eastern U.S.
– Forest restoration in China
– Plantations in New Zealand
“the coterminous United States, Europe, China, and small
Eurasian countries contained one-third of the [northern
hemisphere’s] forest and woodland area, but accounted for
at least 80% of the observed C-sink. This disproportionate
sink in temperate regions relative to boreal regions likely
reflects the temperate zone’s legacy of large-scale land-use
management and change over the last century, and firesuppression policies in recent decades.” (Goodale et al. 2002)
Figure credit: Woods Hole Research Center
Politically powerful
• The G8 nations (with the exception of
Canada and Russia) contain primarily
temperate forest.
• Much of the world’s political and financial
power resides in these nations.
• Is there a policy bias that favours nations of
the temperate biome?
Types of temperate forest biome
• Two major types:
– Broadleaf deciduous forest
– Evergreen forest
Broadleaf deciduous forest
• Most temperate forests are deciduous
• These forests occur in:
– Eastern United States & adjacent Canada
– Western & Central Europe
– Eastern Asia, including Korea, Japan, parts
of China and Russia
Hopkins Memorial Forest, Williamstown, MA
Coniferous and broadleaf
evergreen temperate forest
• Mixed evergreen forests are
a much smaller component
of the temperate forest
biome
• They are found primarily in
western North America,
Chile, New Zealand, and
Australia
Working definitions of
“temperate”
• Biological issues:
– Ecotone between boreal and temperate forests
• Geographic issues:
– Europe often includes Nordic countries
– China is not usually split
– US & Canada are often lumped
• Consistency issues:
– “mid-latitude” (Dixon et al. 1994)
– re-interpreted as “temperate” (Mahli et al. 1999)
Definitions of “forest” and
“woodland”
• A forest is defined as “A plant community
composed of trees the crowns of which touch,
forming a continuous canopy.”
• A woodland is defined as “A plant community that
includes widely spaced, mature trees the crowns of
which do not touch and generally have a canopy
closure of 40 percent or less.”
(The Concise Oxford Dictionary of Ecology, 1996)
Temperate Forest Area
450
400
Area (106 ha)
350
300
250
200
150
100
50
0
US
China
New
Zealand
Europe
Australia
Other
Data from Dixon et al.(1994), Goodale et al. (2002), & Fang et al. (2001)
Carbon storage in the temperate
biome: State of the knowledge
• Complementary approaches:
– Global/continental/regional
• Atmospheric studies
• Land-use studies
• Forest inventory/allometry
• Meta-analysis
– Local
• Eddy flux
• Stand measurements
Continental-scale C storage
C-content (Pg)
Region
Continental US
China
New Zealand
References
Total
vegetation
Soils2
15
26
15.3
18.9
17
16
Dixon et al. 1994
5.5
21
Goodale et al 2002
9.4 x 10 -4
Dixon et al . 1994
Goodale et al 2002
Tate et al. 2000
9
25
Dixon et al . 1994
9.4
13
Goodale et al 2002
Australia
18
33
Dixon et al . 1994
Other3
Total
4.7
-
52 - 64
81 - 105
Europe
Goodale et al 2002
Forest area vs C storage
Forest Area
Other
9%
C-content
Vegetation
US
23%
Australia
37%
China
11%
Other
8%
US
27%
Other
n/a
Australia
36%
US
24%
Australia
33%
China
20%
China
16%
New Zealand
1%
Europe
19%
C-content
Soil
Europe
16%
New Zealand
0%
Europe
20%
New Zealand
n/a
C-flux
Region
Continental US
China
C-flux
(Pg/year)
0.10 - 0.25
Australia
Other 3
Dixon et al. 1994
0.22
Goodale et al. 2002
-0.02
Dixon et al. 1994
0.04
Goodale et al. 2002
0.026
Fang et al. 2001
New Zealand
Europe
References
Tate et al. 2000
0.09 - 0.12
Dixon et al. 1994
0.13
Goodale et al. 2002
trace
Dixon et al. 1994
0.04
Goodale et al. 2002
Local controls on carbon fixation
• There has been a lot of mechanistic work
done at this scale
– Patterns seen at larger scales are a composite of
local phenomena
– We ultimately manage, and use land at a local
scale
Controls on carbon fixation at a
small scale
• Many things limit carbon fixation:
–
–
–
–
–
–
Forest age (Klopatek 2002)
Water limitations (Irvine et al. 2002)
Carbon dioxide limitations
Nitrogen limitations (Nadelhoffer et al. 1999)
Ozone pollution (Ollinger et al. 2002)
Forest type
CO2 fertilization hypothesis
• FACE Experiment, Duke Forest
• NPP increased by 25%
– (measurements included roots!)
• This study was done on a young,
aggrading, temperate deciduous
forest.
• This should be considered a
maximum response.
(DeLucia et al 1999)
Missing pieces: Below-ground
• We understand the general processes that limit soil
C storage in undisturbed soil reasonably well.
• We also understand the trends of how land use
change influences soil C storage, but need more
field measurements.
• Moving to a larger scale requires modeling.
• We also need to synthesize this information with
the data we have above-ground.
Modeled SOC
Amundson 2001: Regression derived from Post et al.’s 1982 data
Table 1. Ecosystem-based distribution of global soil C pools and fluxes a
Life zone
Area
(1012 m 2)
Mean soil C
content (kg m -2)
MAP
(mm)
MAT
(C)
C Inputs
Residence
-2 -1 b
time (y)
(kg m y )
Boreal forest—moist
4.2
11.6
375
4.5
0.19
61
Boreal forest—wet
6.9
19.3
1250
4.5
0.681
28
Temperate forest—cool
3.4
12.7
2250
9
0.912
14
Temperate forest—warm
8.6
7.1
4250
14.5
0.826
9
Tropical forest—moist
5.3
11.4
2500
23.5
2.491
5
129.6
10.8
0.585
18.5
Globed
a
All data except C inputs are from Table 2 in Post et al (1982). MAP, mean average precipitation. MAT,
mean average temperature.
b
C input data are from Table 1 in Jenkinson et al (1991).
d
Total global soil also includes the estimates for cultivated lands and wetlands.
Amundson 2001
Missing pieces: Below-ground
• We understand the general processes that limit soil
C storage in undisturbed soil reasonably well.
• We also understand the trends of how land use
change influences soil C storage, but need more
field measurements.
• Moving to a larger scale requires modeling.
• We also need to synthesize this information with
the data we have above-ground.
From Guo &Gifford 2002
Land Use Transitions & Soil C
agriculture has released 70 Gt of C to the atmosphere
Uncertainty in Transitions
Paul et al. 2002
From Guo &Gifford 2002
Pasture to Plantation
This type of transition is common in New Zealand,
where Pinus radiata plantations are common.
Missing pieces: Below-ground
• We understand the general processes that limit soil
C storage in undisturbed soil reasonably well.
• We also understand the trends of how land use
change influences soil C storage, but need more
field measurements.
• Moving to a larger scale requires modeling.
• We also need to synthesize this information with
the data we have above-ground.
Scaling back up: Using models
• Models have been used to link our small
scale mechanistic understanding of carbon
cycling to larger scale patterns.
• Model development needs more work:
“Whether models are parameterized by
biome or plant life form (or neither), use
single or multiple soil layers, or include
N and water limitation will all affect
predicted outcomes.” (Jackson et al. 2000)
Soil C models
• Used primarily to scale up, or to feed in to
carbon budget models
– One such model is the Century Model, a
process-based model of soil nutrient dynamics.
(Parton et al. 1994).
– It was created based on agricultural soils
Missing pieces: Below-ground
• We understand the general processes that limit soil
C storage in undisturbed soil reasonably well.
• We also understand the trends of how land use
change influences soil C storage, but need more
field measurements.
• Moving to a larger scale requires modeling.
• We also need to synthesize this information with
the data we have above-ground.
Carbon flux over time
(from data in Houghton & Hackler 2002)
500
300
200
100
0
-100
-200
-300
18
50
18
60
18
70
18
80
18
90
19
00
19
10
19
20
19
30
19
40
19
50
19
60
19
70
19
80
19
90
20
00
Carbon Flux (Tg C/yr)
400
Year
United States
Europe
China
Land use trends
• In the U.S., much of the carbon sink is due
to changing land uses and subtle
management effects, such as reduced fire
frequency that leads to woody
encroachment
(Schimel et al. 2001)
• In Europe, the carbon sink is the result of
both land-use changes and increased tree
growth due to CO2 fertilization & Ndeposition (Schimel et al. 2001)
Land-use trends II
• China
– 1949: new social system established, resulting in
rapidly increasing population, economic development
and, therefore, forest exploitation
– 1970’s to present: Chinese government has implemented
several extensive forest restoration projects
(Fang et al. 2001)
5.2
Total Forest C (Pg)
5
4.8
4.6
4.4
4.2
4
1949
1950-62
1973-76
1977-81
1984-88
1989-93
1994-98
Land-use trends III
• New Zealand:
– Increased planting of exotic forests (primarily
Pinus radiata) is the biggest land-use change in
New Zealand – 84 000 ha in 1996
– Organic C in the surface mineral-soil layers is
17-40% lower under plantation forests than
pasture, although this may be offset by Caccumulation in the forest floor
(Tate et al. 2000)
Future carbon trends
• Limitations to the US carbon sink?
– How long will it last?
– How much C will it suck out of the atmosphere?
– What policies could limit or enhance the US carbon
sink?
• Will agricultural abandonment & forest regrowth
create another sink somewhere else? Or not?
Future social trends
“Landsat photos showing that China is losing cultivated
land to development two and one-half times faster than
previously assumed have moved the Politburo into
ordering tough new measures.” US Embassy, Beijing,
June 1997