Title: and nitrogen pools. The simulation was set to

Title:
Modelling climate change impacts on terrestrial ecosystems using Biome BGC
model.

 

1.    
Introduction:

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Carbon and nitrogen
cycles are tightly coupled with each other owing to the metabolic needs of
organisms (IPCC Fifth Assessment Report (AR5),
2013).Terrestrial ecosystems are an integral
constituent of the global carbon cycle (Cramer
et al., 2001). The global carbon cycle is a series of reservoirs of
carbon in the Earth system which are connected by changes in fluxes of carbon (IPCC Fifth Assessment Report (AR5), 2013). This
study involves the use of Biome BGC model (Thornton, 2000) to examine the
possible impacts of climate change on the carbon and nitrogen cycling. It is a
computer model that simulates the storage and fluxes of water, carbon and nitrogen
within the vegetation, litter and soil components (Thornton, 2000).

2.    
Analysis:

Vegetation type

Nitrogen (sminn)

C veg

C litter

C soil

C total

Forest

0.000017

8.090982

2.333099

7.305681

17.72975

Grassland

0.000008

0.048715

0.097631

2.681498

2.827843

2.1

 

 

 

 

 

The Biome-BGC model (Thornton,
2000) calculated the values of the carbon and
nitrogen pools. The simulation was set to run through the 44 years of
meteorological data. No changes were made in the default values which were set
for both of the ecosystem types. Hence, these values were referred as the base
case to predict future scenarios in the world of high atmospheric CO2.

2.2  Residence time:

The average time that carbon resides
in a given reservoir or pool is often termed as the residence time (Friend et al., 2013).  

Residence time = Carbon pool / Carbon
flux (Schlesinger and Bernhardt, n.d.).

The Net Primary Productivity is
considered to be the most important carbon flux in any biome (Schlesinger
and Bernhardt, n.d.). The residence time was calculated by the formula;

Residence time = Total carbon (kg/m2)
at the end of 44 year/ NPP at the end of 44 year.

Type of Biome

Residence Time (Years)

Evergreen Needle-leaf
 
Grassland

126.7 Years
 
43.3Years

2.3 Single changes were made in few
parameters in the model which brought about new values for carbon pools for needle-leaf
forest ecosystem.

 

 

    
CO2 (ppm)

Prec (mm H2O)

  
Temperature(K)

  N deposition
(mg N m-2 yr-1)

 

-150 ppm

+150ppm

  
-15%

  
+15%

     
+1

  
+5

   
-50

    
+50

C veg

-17.9%
 

+5.57
%
 

-6.55
%
 

+6.64
%
 

+1.62%
 

+7.4%
 

-0.139%
 

+0.13%
 

C litter

-44.6
%
 

+8.75
%
 

+1.78
%
 

-1.59
%
 

-3.52%
 

-18.65%
 

-0.074%
 

+0.09
%
 

C soil

-12.47
%
 

+1.33
%
 

-0.38
%
 

+0.25
%
 

-0.39%
 

-2.81%
 

-0.07%
 

+0.06
%
 

C total

-19.19
%
 

+4.24
%
 

-2.91
%
 

+2.93
%
 

+0.11%

-0.26%
 

-0.101%
 

+0.098%
 

 

 

 

2.4 Variations were observed in the three carbon pools
which contained carbon in organic compounds, like the vegetation living
biomass, the dead organic matter in litter and soils when climatic factors like
precipitation, temperature and CO2 concentrations of the atmosphere
were changed in the model (IPCC Fifth Assessment
Report (AR5), 2013). The increasing
concentration of atmospheric CO2 increases plant photosynthesis and
plant growth, this led to an increase in the carbon storage in the pools (IPCC
Fifth Assessment Report (AR5), 2013). An increase of +4.24% was observed in the
total carbon when the amount of CO2 was increased. The vegetation
pool increased by +5.57%. The solubility of CO2 decreases with
higher temperature, which is also believed to affect the carbon storage (IPCC
Fifth Assessment Report (AR5), 2013). Decrease of -0.26% of total carbon was
observed with a 5° rise in temperature. Water availability due to precipitation
steers carbon accumulation through primary production, hence an enhanced total
carbon level was observed with higher rate of precipitation (Rohr et al., 2013).
Although, precipitation also affects the carbon loss through respiration which
can balance long-term soil carbon storage (Rohr et al., 2013). The
output results (Fig.2.2) show the fluctuations in the carbon pools and their
response to the changes in N deposition. As the change in availability of
carbon or nitrogen influenced the biological productivity, requirements for
both the elements were observed in the storages. (IPCC
Fifth Assessment Report (AR5), 2013). Nitrogen is said to affect the net
CO2 uptake from the atmosphere in terrestrial ecosystems in a
positive direction by increasing the productivity or reducing the rate of
organic matter breakdown or in a negative direction where it accelerates the
organic matter breakdown (IPCC Fifth Assessment
Report (AR5), 2013).  When there was
reduction in the nitrogen availability, the carbon pools had limited storage
(IPCC Fifth Assessment Report (AR5), 2013). Temperature and water
interact with each other to force complicated and changing limitations on vegetation
activity (Nemani, 2003).

 

 

 

3.    
Effect
of climate change on grassland and forest ecosystems:

3.1

 

 

 

 

3.2

 

3.3
      

% Increase in carbon

Type of ecosystem

+11.479 %
+0.25%
 

Needle-leaf forest
Grassland

        

          

 

The response of both the land ecosystems showed
increase in the total carbon pools due to higher concentrations of CO2 and
nitrogen deposition. The grassland with C3 species responses rapidly
with  increased temperature level and
higher availability of water(Jones, 1997). The evergreen needle-leaf forest
includes leaf habits that retain at least some of their foliage year-round.
Therefore, it was capable of retaining more carbon unlike the non-woody
grassland (Thornton, 2000). Nitrogen increase due to litter decomposition was a
strong feedback for the development of soil and plant carbon pools (Thornton et al., 2002). Excess of nitrogen
deposition causes changes in plant physiology in the grassland ecosystem (Stevens, 2004). Therefore, increase in dead
organic matter could be taken into account for the increase in total carbon
level. The net growth of the trees over the years in a forest was also responsible
for assimilation of higher amount of carbon contrary to the grasslands which
usually have an annual cycle (Canadell and
Raupach, 2008).

 

 

 

 

4.
 Effect of climate change on global
forest cover:

4.1

Type

Total Carbon (kg/m2)

Total Carbon (PgC) for global forest cover
(area=4×107 km2)
 

Difference in Total carbon
(PgC)

Normal forest
 
Forest in case of climate change

17.72953
 
19.714403

709.1812
 
788.57612
 

 
79.39
 
 

 

 

 

 

5.    
Estimation
of net change of carbon in the atmosphere due to change in land-cover:

5.1 Estimated net flux of carbon in the atmosphere
when 20% of the global forest area was changed into grassland accounts to 1.443 PgC yr-1.

Total carbon net flux (PgC)

Total global forest
area (km2)

1.803
 
1.443

40,000,000
 
32,000,000

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6.    
Role
of forests in climate change:

It is essential to identify the potential of terrestrial
sinks to mitigate climate change (Bonan, 2008).
Summarizing the variability and trends in the climatic conditions, a clear
change was seen in the future scenario when it came to the carbon uptake by
terrestrial sinks. The forest biome had the potential to accumulate 788.5 PgC
in the case of rising CO2. When forested area was decreased, ~20%
decrease was measured in carbon assimilation potential. It could be estimated
that 0.36 PgC of carbon still existed in the atmosphere due to lack of forest area
cover and the carbon store remained in the atmosphere. Thus, it can be implied
that strong land-use policies regarding deforestation are the key aspect for
preservation of forests, which are the crucial carbon sinks (Bonan, 2008). Afforestation and reforestation
have the physical potential to remove 40-70 PgC carbon in a century (IPCC Fifth Assessment Report (AR5), 2013). Thus,
forests have the ability to mitigate global warming (Bonan, 2008).  In this
conducted study, the terrestrial sinks tend to take in large amount of carbon
with high CO2 levels, although, soil respiration and plant
maintenance tend to increase with warmer temperature. Thus, there is a
possibility of these sinks to turn into carbon sources (Cox et al., 2000).  

 

 

 

 

 

 

 

 

 

 

 

 

7.    
Discussion:

The current version of Biome BGC (version 4.1.1) fulfilled
the purpose of studying the influences of climate, disturbances and management
history and the atmospheric chemistry along with plant ecophysiological
characteristics on the terrestrial components of the carbon, nitrogen and water
cycles (Thornton et al., 2002). It helped
in estimating the state and the fluxes of carbon, nitrogen and water in and out
of an ecosystem (Thornton et al., 2002). It
modelled the primary physiological processes like photosysnthesis,
evapotranspiration, respiration (autotrophic and heterotrophic), decomposition,
final allocation of photosynthetic assimilate and mortality. However, the model
posed a few limitations on this study. The type of the grassland and
needle-leaf species was not specified which limited the knowledge of the physiological
characters of the plant, hence it put restrictions on a few conclusions of the
review. The model did not consider the possibility of retranslocation of carbon
out of the leaves prior to the litterfall. It assumed that there is no retranslocation
of nitrogen (Thornton, 2000). The review was focused more on the total
terrestrial carbon sink, therefore, the discussion of the three individual
carbon pools was limited. The seasonal changes in the carbon sinks were
neglected as annual carbon storages were measured. Uncertainties continue to
remain as the potential conversion of the global terrestrial carbon sink to a
source is dependent upon the long-term sensitivity of soil respiration to
global warming (Cox et al., 2000). Although,
this numerical model indicated the significance of climate and carbon cycle
feedbacks, the magnitude of this in the real Earth system is highly uncertain (Cox et al., 2000).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References

 

Bonan, G. (2008). Forests and Climate
Change: Forcings, Feedbacks, and the Climate Benefits of Forests. Science,
320(5882), pp.1444-1449.

Canadell, J. and Raupach, M. (2008).
Managing Forests for Climate Change Mitigation. Science, 320(5882),
pp.1456-1457.

Cox, P., Betts, R., Jones, C., Spall,
S. and Totterdell, I. (2000). Erratum: Acceleration of global warming due to
carbon-cycle feedbacks in a coupled climate model. Nature,
408(6809), pp.184-187.

Cramer, W., Bondeau, A., Woodward,
F., Prentice, I., Betts, R., Brovkin, V., Cox, P., Fisher, V., Foley, J.,
Friend, A., Kucharik, C., Lomas, M., Ramankutty, N., Sitch, S., Smith, B.,
White, A. and Young-Molling, C. (2001). Global response of terrestrial
ecosystem structure and function to CO2and climate change: results from six
dynamic global vegetation models. Global Change Biology, 7(4),
pp.357-373.

Friend, A., Lucht, W., Rademacher,
T., Keribin, R., Betts, R., Cadule, P., Ciais, P., Clark, D., Dankers, R.,
Falloon, P., Ito, A., Kahana, R., Kleidon, A., Lomas, M., Nishina, K., Ostberg,
S., Pavlick, R., Peylin, P., Schaphoff, S., Vuichard, N., Warszawski, L.,
Wiltshire, A. and Woodward, F. (2013). Carbon residence time dominates
uncertainty in terrestrial vegetation responses to future climate and
atmospheric CO2. Proceedings of the National Academy of Sciences,
111(9), pp.3280-3285.

M.B.Jones The impacts of global climate change on
grassland ecosystems. Climate Change: Implications and role of grasslands.
Botany department, Trinity college, University of Dublin.

Nemani, R. (2003). Climate-Driven
Increases in Global Terrestrial Net Primary Production from 1982 to 1999. Science,
300(5625), pp.1560-1563.

Numerical Terradynamic Simulation Group, University of
Montana,Biome BGC version 4.2: Theoretical Framework of Biome-BGC January, 2010

Peter E. Thornton User’s Guide for Biome-BGC, Version
4.1.1 Numerical Terradynamic Simulation Group School of Forestry, University of
Montana Missoula, MT 59812 USA.

Rohr, T., Manzoni, S., Feng, X.,
Menezes, R. and Porporato, A. (2013). Effect of rainfall seasonality on carbon
storage in tropical dry ecosystems. Journal of Geophysical Research:
Biogeosciences, 118(3), pp.1156-1167.

Schlesinger,
W. and Bernhardt, E. (n.d.). Biogeochemistry.

Stevens, C. (2004). Impact of
Nitrogen Deposition on the Species Richness of Grasslands. Science,
303(5665), pp.1876-1879.

Thornton, P., Law, B., Gholz, H.,
Clark, K., Falge, E., Ellsworth, D., Goldstein, A., Monson, R., Hollinger, D.,
Falk, M., Chen, J. and Sparks, J. (2002). Modeling and measuring the effects of
disturbance history and climate on carbon and water budgets in evergreen
needleleaf forests. Agricultural and Forest Meteorology, 113(1-4),
pp.185-222.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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