Agriculture Reference
In-Depth Information
Gmelina and other fast-growing timber tree species was between eight to 10 years.
Thus, an optimal rotation interval of 10 years was specified in the model for timber
trees. Simulations were run for two cycles of tree growth or 20 years in all land use
systems. The analysis was based on a 1-ha system since SCUAF determines plant
growth and soil changes on a per hectare basis.
14.2.5
Model Parameterization, Economic
Data and Assumptions
The default values of biophysical parameters used in SCUAF model are based on the
characteristics of the physical environment inputted in the model such as climate, slope
class, soil drainage, parent material, soil texture, soil reaction and organic matter status.
The physical environment used in SCUAF model for Claveria has the following char-
acteristics: lowland humid class of Koppen climate classification, moderate slope class,
free soil drainage, intermediate parent material, clayey soil texture, strongly acid soil
reaction, and intermediate organic matter status. The plant growth, nutrient composi-
tion, soil properties and erosion parameters were specified in the model for each land
use system. A detailed discussion of these parameters can be found in Predo (2002).
Data and assumptions used in the economic analysis were derived from SCUAF
simulations, primary data (survey and key informant interviews), and secondary
sources. The base parameter values used in calculating the net present value of each
system are presented in Appendix 2. These parameters include the following eco-
nomic data and assumptions: labor requirements, wage or labor costs, material input
requirements, input and output prices, cost of capital and other data (Predo 2002).
14.2.6 Economic Analysis
The economic component of the model was linked to SCUAF with specification of
production and conservation inputs and outputs for harvest, including other bio-
physical impacts of modeled land use systems. These outputs from SCUAF were
subjected to economic analysis through the BCA framework. Two decision criteria
were used in evaluating each land use system: (i) net present value (NPV) and (ii)
annualized net benefits (ANB). The discount rates used in the analysis were based
on existing cost of capital to upland farmers (25 percent) and the social cost of capi-
tal of 10 percent (Medalla et al. 1990).
The NPV of the land use systems over a period of time was computed as:
(
)
BC
r
T
=
t
t
t
NPV
=
(
)
1
+
t
0
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