Agriculture Reference
In-Depth Information
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site had to be surveyed to help characterize the available grazing area,
water resources, animal numbers, livestock movement rules (e.g., where
the animals can move during the grazing year), herd density, and estimates
of other households who share the same grazing resource. This information
was needed to parameterize the forage production model for those points.
The households in each site were asked to designate the most probable area
of migration should drought set in and force them to move. Locating both
the primary and likely migration points allowed the forage conditions in
both locations to be captured for the system. Both the household and the
migration areas were geo-referenced using inexpensive, handheld global
positioning system (GPS) units. The number of points was dictated by the
analytical technique used. The minimum number of points per zone within
the region was set at 30. As of this writing, there are eight 30,000-50,000-
km
2
zones activated in East Africa, with 30 or more monitoring points
located in each zone (figure 22.1). Five additional zones are at various
stages of development.
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Norm
PgEn
Bi
ophysical Modeling
Once a monitoring site was selected, the sampling protocol was largely
driven by the input needs of the biophysical model used for the analysis.
Point-based biophysical modeling is a mechanism to capture complex re-
lationships at key localities (e.g., Bouman, 1995). In the case of LEWS, the
Phytomass Growth Simulator model (PHYGROW;
http://cnrit.tamu.edu/
phygrow/;
Rowan, 1995) was selected as the primary analytical engine for
the monitoring program and was designed by our research team. PHY-
GROW is a hydrologic-based plant growth model that uses multiple plant
species, soil, weather, and multiple grazer parameters to simulate daily
plant production and water dynamics under grazing pressure for a spec-
ified ecological site or a designated plant community. Parameters required
by the PHYGROW model include the physical and hydrologic character-
istics of soils, physical response and competitive potential of plant species,
and forage preferences and forage demand of grazers.
PHYGROW requires that the following major attributes be measured
for each site: (1) grass basal cover by species or species group using a
modified point method, (2) forb frequency, by species or species group,
(3) woody plant effective canopy cover, by species or species group, (4) the
name of soil and the depth and texture of each soil layer, slope, degree of
rockiness, and (5) the estimates of the temporal density for each kind of
livestock (this can be derived from discussions with pastoralists or individ-
ual landholders).
[286
M
odel Analysis and Verification
Results obtained from the PHYGROW simulations include quantity and
relative quality of daily forage production, changes in stocking rates, and a
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