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amount of information from the MODIS image time series
(Freitas et al., 2011).
Historical monthly precipitation data from the Tropical Rainfall
Measuring Mission (TRMM) and information from the Google
Maps API digital elevation model over two concentric circles
with adjustable radii around the pixel are also available for each
MODIS pixel of the time series (Freitas et al., 2011). To locate
the selected polygon of interest in the Google Maps Virtual
Globe it is sufficient to indicate the coordinates (latitude and
longitude).
3.1 Classification of the EVI2 temporal profile
The LUC classification using the EVI2 profiles is conducted
based on the previous knowledge of the temporal patterns of the
main targets within the deforested polygons. Figure 2 presents
some typical EVI2 profiles for the region, which allows
identifying some of the LUC patterns and transitions.
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2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011
Figure 2. EVI2 temporal profile for two deforested polygons:
(a) Forest from 2000 to 2006, transition from forest to pasture
in 2007 and 2008, and pasture after 2009; and (b) Forest from
2000 to 2007, transition from forest to bare soil in 2008 and
2009 followed by agriculture use in 2010 and soy in 2011.
Abbreviations: for. (forest); degrad. (degradation); clear. (total
clearing of the area); past. (pasture); agric. (agriculture).
Previous works such as Galford et al. (2008), Freitas et al.
(2011), and Adami et al. (2012) presented some examples of
typical temporal behavior of MODIS vegetation indices for
pasture and agriculture land. A common characteristic of these
targets is the pronounced seasonality. The amplitude is more
evident for annual crops, while the duration of the cycle is
longer for pasture. These characteristics allow the
differentiation of forest, which has low seasonal variation
throughout the year (Figure 2).
In the off-season the dominant spectral response for agriculture
is bare soil/dry straw with low EVI2 values. During the crop
growth period a rapid increase of green vegetation causes the
EVD to peak reaching values as high as 0.9 at maximum
canopy development, especially on soy crops . Furthermore, the
agricultural areas tend to have a rapid increase in EVI2 values
during the crop development period, followed by a strong drop,
creating a more narrow profile, aiding in its identification. In
this work, areas with high seasonal variation, narrow profiles
and EVI2 peaks lower than 0.7 were classified as agriculture.
This class tends to include rice (predominantly), corn (more
common in Parä), and in some instances less developed soy
fields. Profiles with EVI2 20.7 will be classified as soy. The
threshold of 0.7 was established after a detailed evaluation of
the 194 polygons with soy in crop year 2010/11. Several of the
aerial surveyed polygons presented corn and rice fields, which
were used to define the threshold.
For pasture land, there is less increase in EVI2 values because
the canopy tends to be less homogeneous and the soil cover, in
the majority of cases, is not complete. This is further enhanced
by the low investments in pasture renewal, typical for extensive
cattle production zones. The presence of cattle herd, which
consumes green biomass before the maximum pasture
vegetative peak, also contributes to the heterogeneity of the
spectral response. In addition, the predominance of grass with
erect leaf geometry lowers the EVI2 values. Therefore,
agriculture and pasture land are easily identified in the temporal
EVI2 profiles, as can be seen in Figure 2.
In some isolated cases of rice cultivation amid piles of trunks
and above ground roots, during one to three crop years after the
clearing of a former forested land, the temporal profile of the
EVI2 can be similar to pasture.
The degraded forest pattern is observed under selective logging
and/or fire occurrence. This pattern is observed during the
deforestation process before the area has been totally cleared.
When the clearing of the area is not completed an intensive
vegetation regrowth can be observed in the rainy season (Lima
et al, 2012). In this work, these areas will be classified as
regrowth. Although they are less common, some areas classified
by PRODES as deforested may present regrowth after the total
clearing of the area.
Eventually, the LUC trajectories will be traced and the most
frequent patterns of transition after the deforestation process
will be indicated for the polygons with and without soy
plantations. For the soy polygons the average time between
deforestation and soy plantation will also be evaluated to
characterizing the most common trajectories of the soy
polygons that are not in agreement with the Soy Moratorium.
4. RESULTS AND DISCUSSION
Areas without soy in crop year 2010/11
The 50 selected polygons without soy in crop year 2010/11
were classified according to the year of deforestation detected
by PRODES. Twelve polygons (24%) were from deforestation
detected in 2007; 32 polygons (64%) from 2008; 4 polygons
(8%) from 2009; and 2 polygons (4%) from 2010. Most of the
polygons (68%) were from Mato Grosso, followed by Pará
(26%) and Rondönia (6%). Forty polygons (80%) presented
significant degradation prior to the deforestation process. This
finding agrees with Uhl et al. (1991), Nepstad et al. (1999) and
Sorrensen (2004), which report that the forest degradation in the
Amazon region is a common practice prior to the deforestation
process, either by selective logging or fire.
Figure 3 shows that 38 polygons (76%) presented indications of
regrowth in 2011. For 19 of these polygons the information
from the temporal profiles was not enough to distinguish
regrowth from pasture. Despite the evidence of regrowth, the
identification of small seasonal cycles could be associated with
fire occurrence in the dry season, a common practice in the
region for pasture renewal (Lima et al., 2012). Nevertheless, if