Geography Reference
In-Depth Information
1.2.2 Impacts on the Biogeochemical Process
The influence of the land use change on the biogeochemical process, especially the
discharge or absorption of the greenhouse gases such as CO
2
in the atmosphere
due to the land use change, can alter the concentration of the greenhouse gases in
the atmosphere and consequently influence the climate. The historical accumula-
tive carbon loss due to the land use change was estimated to be 180-200 PgC
(House et al.
2002
), and the land use change contributed to 10-30 % of the carbon
discharge due to human activities. The deforestation, afforestation, forest resto-
ration and agricultural activities are the major approaches through which the land
use influences the carbon cycle. There are many researches on the influence of the
land use change on the carbon cycle, most of which focused on the deforestation,
especially the deforestation in the tropic rainforest. Since the 1850s, the global
forest area decreased by 20 %, and the carbon emission due to the deforestation
accounted for 90 % of the carbon emission caused by the land use change and
33 % of the man-made carbon emission (including the discharge from the fossil
fuel burning and land use change).
The influence of the afforestation and forest restoration on the carbon cycle has
also gradually become the hot issue in the relevant researches. Although the
reforestation has not significantly influenced the terrestrial carbon sink at the global
scale, it has played an important role in the carbon sink at the regional scale. For
example, the man-made forests in China has stored over 0.45 Gt carbon since the
1970s (Fang et al.
2001
). Some researches indicated the forest restoration played a
key role in the carbon sink resulting from the land use (Pacala et al.
2001
).
The productivity of the forest and decomposition of organic matters in the soil
both influence the change of CO
2
in the atmosphere and the climate pattern, and
consequently influence the terrestrial carbon sink). When the photosynthesis rate is
bigger than the respiration rate, and discharge rate of the biogenic volatile organic
compounds (BVOC), and the decomposition rate of organic carbon, the forest
plays a role as the carbon sink (Heimann and Reichstein
2008
). Besides, the
deforestation will reduce the potential carbon sequestration (House et al.
2002
). In
addition, the higher temperature and higher CO
2
concentration will increase the
NPP, which will lead to the negative feedback and make more CO
2
in the
atmosphere sequestrated. The radiative forcing due to the carbon emission
resulting and the accelerated respiration due to the higher temperature will lead the
positive feedback, in which the organic matters will decompose more rapidly
(Friedlingstein et al.
2006
). For example, there is an extreme example in the
climate-carbon cycle, i.e., the tropic rainforest in Amazon will gradually succeed
into other vegetation if the temperature continuously increases and the precipita-
tion continuously decreases.
