ELU WP6
Publishable executive summary
The carbon cycle related impact study (D 6.7) pointed out that air pollution has to be
taken into account when we try to estimate the future changes in the land carbon sink
and productivity of ecosystems. The possible feedback between climate change and
carbon cycle depends heavily on the biome type and the human decisions made in
relation with managed ecosystems (agriculture, forestry). The results suggest that
there can be positive feedback between climate change and carbon cycle for low land
deciduous forests, and there can be negative feedback between climate change and
carbon cycle for managed grassland ecosystems. Agricultural productivity might be
modulated in the future which might be beneficial for winter crops. The results
suggest that climate change and air pollution will act together in the future in a
complex manner.
Section 1 of PAR
Carbon cycle impact analysis by ELU was completed as the high resolution
climate scenarios became available from WP2. Based on the carbon cycle related
simulations performed with the BIOME-BGC model we could estimate the joint
impact of climate change and air pollution on the carbon cycle of two forest
ecosystems located in Poland and Slovakia, a managed grassland and a mixed
cropland ecosystem located in the Western part of Hungary. The results suggest that
climate change and air pollution will act together in a complex manner.
The main aim was to try to find relationship between the carbon cycle and
climate change. If the carbon sequestration capacity of an ecosystem is decreasing, it
means that atmospheric CO2 concentration will increase, which causes stronger
greenhouse effect of the atmosphere, which increases the mean temperatures even
further.
Based on the simulation results we could not detect any feedback mechanism
between climate change and carbon cycle of the Kampinos forest. Kampinos forest
will likely remain carbon sink in the future. For the Čifáre Turkey oak forest we
found positive feedback between changes in the carbon cycle and climate change.
This feedback has implications on timber production. In case of the managed
grassland we found negative feedback between carbon cycle and climate change.
Assuming unchanged management, due to the increasing ambient CO2 concentration
the grassland will be a lower source of CO2 to the atmosphere than it is currently. For
croplands because of the lack of information on management and fate of carbon we
were not able to detect any feedback mechanism. According to our results the annual
cycle of agricultural productivity will be modulated in the future, mainly because of
the CO2 fertilization effect. The changes might be beneficial as productivity might
increase in the first half of the growing season (i.e. winter wheat production might
increase).
Section 2 of PAR
Regarding the carbon cycle related impact study the main aim was to simulate
the carbon cycle of forest and agriculture ecosystems using high resolution climate
data provided by WP2 and to estimate the possible feedback between carbon cycle
and climate change taking into account the effects of air pollution as well.
Deliverable D 6.7 “Integrated assessment of climate change and air pollution
impacts on C-cycle in agriculture and on forest ecosystems” was completed during the
third reporting period. The deliverable was submitted in due time of the project
lifetime. The contractors involved were ELU, FRI and WUT.
The Polish target area was the Kampinos National Park, which is located in
Central Poland not far from Warsaw (Pine forest). The Slovak target area is the
forested region near Čifáre (Turkey oak forest). In this reporting period ELU
synthesized the forest related measurement data provided by FRI and WUT. Using the
measurement data from both sites ELU calibrated BIOME-BGC using the
methodology of Cienciala and Tatarinov (2006). During the previous reporting
periods ELU calibrated BIOME-BGC for the simulation of grassland and cropland
related carbon cycle to be performed in Hungary.
Using the output of different high resolution climate models provided by WP2
of the CECILIA project ELU performed model simulations to estimate present and
future evolution of the carbon cycle components at the Hegyhátsál agricultural region
(Hungary), at the Kampinos National Park and at the Čifare forest. The modelling
design, the calibration procedure and the ancillary data used for the simulations are
described in Deliverable D 6.7 in detail.
For the forest related carbon cycle impact study ELU analyzed the evolution
of the carbon content of the IPCC pools and also the evolution of exchange of carbon
dioxide between the biosphere and the atmosphere.
BIOME-BGC based model simulation results for Kampinos forest (Poland)
show that there can be large differences between the results obtained with the
different of ecophysiological parameterizations but the tendencies in evolution of
carbon pools, increments and carbon fluxes are almost the same. Carbon content of
IPCC pools is increasing continuously during the simulation period (1935-2100). This
means that Kampinos forest will likely remain carbon sink in the future. Biomass
(stem and root) increments are remaining at the same level (or showing a slight
increasing tendency) until 2050, but decreasing tendency is expected afterwards. We
could not detect any feedback mechanism between climate change and carbon cycle
of the Kampinos forest.
Nitrogen deposition has a significantly bigger impact on plants’ growth and
carbon uptake than elevated atmospheric CO2-concentration, though its effect differs
between the parameterizations. In case of Kampinos forest this increased uptake can
partly compensate the negative impacts of climate change so as the resulting effect is
unchanged carbon sequestration capacity of the forest in the future relative to the
present day conditions.
The Čifáre forest (Slovakia) related simulations suggest that carbon content of
IPCC pools might increase continuously, thus the unmanaged temperate oak forest
Čifáre will likely remain a net carbon sink in the future. This finding is corroborated
by the simulated net ecosystem exchange (NEE) data. We found a negative impact of
climate change on plant increments: higher mean annual air temperatures strongly
decrease stem and root increments. This latter might have a serious impact on timber
production, if the results are representative to managed forests.
Climate change and air pollution have a joint impact on the
biosphere/atmosphere CO2-exchange: the magnitude of both gross primary production
(GPP) and total ecosystem respiration (Reco) are increasing. The net effect is a slight
decrease in the magnitude of NEE (i.e. less carbon is sequestered by the forest in the
future as compared to the present day conditions) which may be interpreted as a
positive feedback for climate change: with less increment plants can uptake less CO2
from the atmosphere. The result is increasing atmospheric CO2 concentration which
causes stronger greenhouse effect of the atmosphere, which increases the mean
temperatures even further.
We found that the increasing nitrogen deposition has a significant impact on
the forest carbon cycle: N stimulates plants’ growth so they can take up more CO2
from the atmosphere. This reduces the positive feedback caused by increasing mean
annual temperature.
For the agriculture related carbon cycle impact study ELU analyzed the
evolution of the carbon dioxide flux between the atmosphere and the vegetation. For
managed grassland carbon stock changes were also estimated.
Simulations related to the managed grassland (Hungary) suggest that the
increasing CO2 concentration and increasing nitrogen deposition caused by air
pollution increase both the carbon release (total ecosystem respiration) and the
carbon-fixing (gross primary production). These two effects compensate each other,
therefore the net biospheric carbon uptake (NEE) will not change significantly in the
examined period (we predict a slight increase in the magnitude of carbon uptake). The
effect of increasing CO2 concentration is proved to be higher than the effect of
increasing nitrogen deposition.
Grass mowing decreases the soil carbon and therefore the total carbon content
of the ecosystem. Examining the separated effects of increasing CO2 concentration
and nitrogen deposition it was found that the increasing CO2 concentration can
compensate a certain part of the carbon loss caused by harvesting. After taking into
account the carbon content of the mowed grass it was found that net biome production
(NBP) will change in the future toward lower emission of CO2. This NBP change
means that the ecosystem will be a carbon source to the atmosphere, but the source
intensity is mitigated to some extent by the joint impact of increasing air pollution and
climate change. This means a small negative feedback to climate change if we
compare the results to the present day situation when the CO2 release is higher.
The cropland related simulations (Hungary) show that although the net
biospheric carbon exchange (NEE) seems to be unchanged in the future, the two large
carbon fluxes (GPP and Reco) and also net primary production (NPP) will increase in
magnitude as the consequence of climate change and increasing air pollution.
Increasing nitrogen deposition and CO2 concentration will amplify the changes, but
there is no simple answer about the importance of the two pollutants. Taking into
account both the unchanged NEE (biospheric carbon balance from the atmospheric
point of view) and the increasing NPP (which causes increasing anthropogenic CO2
emission caused by human and animal consumption) we were not able to estimate the
direction and magnitude of the carbon cycle related feedback to climate change and
air pollution. Human intervention substantially alters the carbon cycle of croplands,
and at present we do not have enough information to estimate the fate of cropland
carbon cycle in the future. Definitely more research is needed in this topic.
According to our results the annual cycle of agricultural NEE will be
modulated in the future, mainly because of the CO2 fertilization effect. The changes
might be beneficial as productivity might increase in the first half of the growing
season. Some models indicate that without the air pollution effect there can be
decrease in productivity and by 2100 crop growth might even decrease.
References
Cienciala, E., Tatarinov, F.A., 2006. Application of BIOME-BGC model to managed
forests. 2. Comparison with long-term observations of stand production for major tree
species. For. Ecol. Manage. 237, 252-266.