economic benefits they bring and the associated risks, as confirmed by several
participatory workshops held with the study area rice farmers. This would mean
that for those irrigated paddy fields in the study with a low flood risk, farmers will
be willing to reduce fertilizer consumption if the current system is proven to be
sustainable and if severe drought risks are not present. In contrast, for fields prone to
flooding, farmers will tend to reduce the risk of yield losses and; therefore, be
hesitant to adopt innovative fertilizer management strategies. The continuous
decrease of organic C and total N content in flooded fields is likely to become a
serious threat to the sustainability of the system, and so the negative impact on
lowland soil fertility and productivity clearly demands for adequate soil conservation practices to be put in place in the uplands, those which will positively influence
sediment reallocation to the lowlands. However, due to a lack of intrinsic motivation among local farmers, there is a need for policy makers to raise farmers’
awareness levels regarding upland-lowland linkages and the crucial role of soil
conservation practices (Saint-Macary et al. 2010; Schad et al. 2012).
3.5 Dynamics of Carbon Stocks in Upland Areas
5
Why bother about C stocks in upland areas? According to Craswell and Lefroy
(2001), C serves many functions as a part of SOM. SOM is a reserve of N and other
nutrients required by plants. It also forms stable aggregates, protects the soil surface
and maintains a vast array of biological functions, including the immobilization and
release of nutrients, the provision of ion exchange capacity and the storage of
terrestrial C. Lal et al. (2007) indicated that soil C not only functions to mitigate
climate change, but is also important in advancing food security; therefore, its
depletion always leads to a degradation in soil quality and a decline in agronomic/
biomass productivity.
Lal (2004) estimated the global C pool as 46,850 Pg, of which the biotic and soil
C pools make up 1.2 % and 5.3 % respectively. Forests play an important role in the
global C cycle, and according to the FAO (2006), global forest cover is approximately 3,952 million ha, or 30 % of the world’s land area. In Southeast Asia alone,
the current total biomass C stock in forests amounts to approximately 64.2 Gt, of
which 22 % is stored below-ground and 78 % above-ground (Saatchi et al. 2011).
The conversion of forest land to non-forest land; however, causes a relatively
large loss of C stocks per deforested area above-ground, with negative consequences on both the global and local scales (DeFries et al. 2007; Ellison et al.
2012). Between 2000 and 2005, gross deforestation was 12.9 million ha year
À1 ,
mainly as a result of the conversion of forests to agricultural land (FAO 2006; MEA
2005). The global contribution of deforestation and the decay of biomass to C in the
atmosphere is estimated to be 8.5 Gt year
À1 , or 17.4 % of the total anthropogenic
5 Written by Thomas Hilger.
3 Water and Matter Flows in Mountainous Watersheds of Southeast Asia:. . .
133
participatory workshops held with the study area rice farmers. This would mean
that for those irrigated paddy fields in the study with a low flood risk, farmers will
be willing to reduce fertilizer consumption if the current system is proven to be
sustainable and if severe drought risks are not present. In contrast, for fields prone to
flooding, farmers will tend to reduce the risk of yield losses and; therefore, be
hesitant to adopt innovative fertilizer management strategies. The continuous
decrease of organic C and total N content in flooded fields is likely to become a
serious threat to the sustainability of the system, and so the negative impact on
lowland soil fertility and productivity clearly demands for adequate soil conservation practices to be put in place in the uplands, those which will positively influence
sediment reallocation to the lowlands. However, due to a lack of intrinsic motivation among local farmers, there is a need for policy makers to raise farmers’
awareness levels regarding upland-lowland linkages and the crucial role of soil
conservation practices (Saint-Macary et al. 2010; Schad et al. 2012).
3.5 Dynamics of Carbon Stocks in Upland Areas
5
Why bother about C stocks in upland areas? According to Craswell and Lefroy
(2001), C serves many functions as a part of SOM. SOM is a reserve of N and other
nutrients required by plants. It also forms stable aggregates, protects the soil surface
and maintains a vast array of biological functions, including the immobilization and
release of nutrients, the provision of ion exchange capacity and the storage of
terrestrial C. Lal et al. (2007) indicated that soil C not only functions to mitigate
climate change, but is also important in advancing food security; therefore, its
depletion always leads to a degradation in soil quality and a decline in agronomic/
biomass productivity.
Lal (2004) estimated the global C pool as 46,850 Pg, of which the biotic and soil
C pools make up 1.2 % and 5.3 % respectively. Forests play an important role in the
global C cycle, and according to the FAO (2006), global forest cover is approximately 3,952 million ha, or 30 % of the world’s land area. In Southeast Asia alone,
the current total biomass C stock in forests amounts to approximately 64.2 Gt, of
which 22 % is stored below-ground and 78 % above-ground (Saatchi et al. 2011).
The conversion of forest land to non-forest land; however, causes a relatively
large loss of C stocks per deforested area above-ground, with negative consequences on both the global and local scales (DeFries et al. 2007; Ellison et al.
2012). Between 2000 and 2005, gross deforestation was 12.9 million ha year
À1 ,
mainly as a result of the conversion of forests to agricultural land (FAO 2006; MEA
2005). The global contribution of deforestation and the decay of biomass to C in the
atmosphere is estimated to be 8.5 Gt year
À1 , or 17.4 % of the total anthropogenic
5 Written by Thomas Hilger.
3 Water and Matter Flows in Mountainous Watersheds of Southeast Asia:. . .
133