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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
1.- Low NDVI - Low Variability
2.- Low NDVI - Medium Variability
3.- Low NDVI - High Variability
4.- Medium NDVI - Low Variability
5.- Medium NDVI - Medium Variability
6.- Medium NDVI - High Variability
7.- Hhg NDVI - High Variability
8.- High NDVI - Medium Variability
9.- High NDVI - Low Variability
IBBEBH
0080
Figure 3.- Spatial homogeneity index (SHT) which relates
the mean maximum values and the variation coefficient. As
a general norm, increased NDVI means better ecosystem
quality, and increased variability means an increase in the
ecosystem instability.
[—1-—2 3—4—5 —$ —7 —8 9
Figure 4.- Monthly evolution of the NDVI for each class of
the SHI in the time series of NOAA-AVHRR images.
4. VEGETATION DYNAMICS
In the study area a great ground diversity exists such as those of
alluvial type of fine and heavy textures, "depresionals",
“graniticos of lomajes" and hills (mountain range of the coast),
alluvial of marine terraces, "pumicíticos" and "trumaos
granítico"s (Honorato, 2000). In this atmosphere, the most
important forages resources are the spinal ones. This vegetal
formation is defined as a pseudo-savannah (Ovalle et al., 1990),
in which two layers are clearly distinguished: one of shrubs
type, dominated Acacia digs Mol. (hawthorn) and a herbaceous
layer, composed by “Poéaceas” (gramineas) mainly of annual
winter growth. Among these last ones, species pertaining to the
sorts Oats, Aira, Bromus, Hordeum, Vulpia and Lolium are
emphasised. They are common in the herbaceous layer, species
of the Composite family, in special of the Hypochoeris sorts,
Cynara and Chartamus, in addition to species of the Fabaceae
family (leguminosas) Papilionoideae subfamily, pertaining to
the Medicago sorts and Trifolium, mainly (Castellaro et al.,
1994; Ovalle and Squella, 1996).
0.40 4
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ii NZ ,
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0.10 +
0.05 +
0.00
4
m
MOY
[+1—2 3—4—5—6 —7 —8 -9|
Figure 5.- Mean monthly evolution of the NDVI for each SHI
class
4.0 4
3.5 4
3.0 4
2.5 4
2.0 4
1.5 4
Acummulated NDVI
1.0 4
054
0.0
[2-1 2 3-—-4--5--6 —7 —8 9
Figure 6.- Accumulated NDVI month by month.
The zone presents habitually a low natural fertility in its
grounds, which entails to low yields. However, these prairies
are the base of sustentation of the production systems animal,
which are predominantly of extensive type, where it stands out
the raising of smaller ruminates (ovine and goat) and the raising
of meat cattle, being the load animal average of the order of 0.2
animals has! year" units (Ovalle and Squella, 1996). In spite of
the shown antecedents, a complete study of the dynamics of the
vegetation in the zone does not exist, for that reason it is
necessary to resort to computational models that describe
quantitatively his behaviour. Most of the models related to
prairies have been developed by interdisciplinary equipment of
university centres, specifically by the schools of Science Range
(handling of natural prairies) of the United States (Innis, 1978;
Pendleton et al., 1983. Parton et al., 1993; Laurenroth et al.,
1993; Hanson et al., 1994). Its main intention is the research
and are complex, as much of the conceptual points of view such
the computational ones, which causes that their use is restricted.
Nevertheless, there are someone, thanks to its simplicity, can be
implemented by fast and simple way (Smith and Williams,
1973; White et al; 1983). Despite the previous notes, a previous
process of validation is required, to evaluate its behaviour and
the behaviour to its reformulation, by means of the calculation
of suitable parameters (Silva, 1993).
