Land Degradation
and Deforestation in Southwest Madagascar
Analysis of Forest Cover Change Through Satellite Images
Analysis of Forest Cover Change Through Satellite Images
Joo Yung Seo*
Dr. Thomas W. Gillespie
* Department of Geography, University of California, Los
Angeles
14 December 2012
 |
| Figure 1: Physical land cover of Madagascar |
Introduction
Madagascar,
the fourth largest island in the world, is located off the southeastern coast
of Africa. The land consists of different ecosystems, ranging from tropical,
desert, high mountain ranges, spiny desert, rain forest, and dry and wet
forest. Madagascar is also home to some of the world’s most diverse forests
(Clark, 2010). These unique ecosystems host a tremendous number of diverse and
exotic species with a high level of endemism. However, the island has been
heavily affected by the arrival of humans, who caused the rapid disappearance
of the forests due to unsustainable practices. According to 2005 World Bank
figures, Madagascar is among the world’s poorest countries, with a gross
national income per capita at about US $290 (Gorenflo et al., 2011). Consequently,
people have depleted the country’s natural resources in an attempt to make
profits.
The
most active resource extraction in Madagascar is deforestation. According to
the World Wildlife Fund, after humans arrived 2,000 years ago, 90% of the
Madagascar forest cover was lost (“Madagascar Forests”). Additionally,
deforestation is still ongoing. Some of the main causes of deforestation
include expansion of cropland (agricultural conversion), cattle grazing, timber
wood export, fuel wood collection, and pasture land (Casse, 2004). The problem
with continuing land degradation and deforestation is that it destroys the whole
ecosystem, fragments species habitat, destroys the natural food chain,
increases erosion and flooding, increases greenhouse gases, and decreases
oxygen. Therefore, it is important to keep the forest healthy to avoid
catastrophic consequences.
Study Area
The
study area is in Madagascar, an island off the southeastern coast of Africa,
which is separated by the Indian Ocean. The study will specifically look at the
southwest part of Madagascar, a region called Atsimo Andrefana. This region is
around 24°6' S and 44°3' E (lat/long). Atsimo Andrefana’s area is about 25,574
square miles (“Atsimo Andrefana”). There are many dry forests and arid areas in
that region. The study area seems to have gone through major vegetation change
(Figure 1).
Method
The
first step of the analysis was downloading the raw data from the Internet.
Landsat satellite images were used to examine the problems and examine the change
in the forest’s greenness over a period of time. I went to glovis.usgs.gov/ to
download the Landsat data. I chose an area from the southwestern part of
Madagascar and came up with the point of 24° 6' S and 44° 3' E. I went through
different time series to finalize two sets of data from the same time period with
which to run the comparison of deforested areas. Geotiff files of the year 1993
(L4-5 TM) and 2007 (L7 ETM+ SLC-off) from April were chosen to be
analyzed.
After
downloading the data, a remote sensing program called “Environment for
Visualizing Images” (ENVI) was used to put the raw data all together. I used
the “layer stacking” function to import the bands to combine the data, and I used
the “data manager” to choose bands upon which to work. I chose visible bands,
3-4-3, to see the greenness of each year’s data. Two maps (year 1993 and 2007)
were then created, showing green where there was vegetation and pink where
there was none. After that, I found the greenness and vegetation amount of
each year (1993 and 2007) through the Normalized Difference Vegetation Index
(NDVI), which gave values from -1 to 1 to show how much vegetation was in a
certain area (Figure 2). I made two NDVI files by clicking on “spectral” and
then “vegetation” to get to NDVI function in order to see the vegetation
greenness of each image. I selected the layer-stacked file of each year,
changed the NDVI bands of red to 1 and near-IR to 2, and saved it as a new
file.
After
completing this step to make two NDVI images of year 1993 and year 2007, I combined
those two images to see the actual greenness change. I clicked on “change
detection” and then clicked on “change detection difference map” to compute the
differences in the maps and then clicked on data manager to display it. This
resulted in one image that combined the two images of year 1993 and 2007 to
show the change of greenness over time. I changed the color of the difference
of change to the green color series to show the decreased level of vegetation (from
a 1%-5%
decrease, including “no change” of vegetation as well.
In
order to make a more complete analysis, I used the ArcGIS program to make maps
of Madagascar to relate it to satellite imagery outcomes. I downloaded polygon
data of Madagascar, nature reserves (protected areas), and fire data to explain
how deforestation is related to human activity. A natural reserve shapefile
could be found through protectedplanet.net, a website that offers information
on all protected areas around the world. I chose a suitable protected area that
matched my satellite image information. The fire data were downloaded from NASA
Earth data, (EOSDIS), which gives access to the most recent active fire data of
Madagascar. After organizing all the ENVI and ArcGIS images, I pulled out 20
locations from the change detection result of the years 1993 and 2007
(excluding the areas in the Tsimanampetsotse nature reserve) to make a line
graph. I also pulled out 20 locations inside the Tsimanampetsotse nature
reserve to see how the vegetation has changed inside the park, where a high
level of biodiversity is concentrated. After pulling out the 20 points, I made
a chart and graphs through Excel. Last, I took images from Google Earth to see
forest change through different time ranges.
Results
 | |
| Figure 3:Greenness and NDVI of year 1993 and 2007 |
In
Figure 3, Image 1 is almost all covered in green, but image 2 is partially
covered with green vegetation and largely covered with pink, meaning that
vegetation has gone from that part. This result shows how the greenness of the
vegetation cover has declined dramatically from 1993 to 2007. Images 3 and 4
show the greenness of the vegetation value from -1 to 1. If the color is
whiter, it means that there is more greenness in the vegetation (towards value
of 1), and if the color is towards black, it means that the greenness value is
very low (close to value of -1). Images 3 and 4 show how the greenness has
decreased from 1993 to 2007.
 |
| Figure 4: Change detection result of years 1993 and 2007 (decrease of forest from 1%-5%) |
Figure
4 shows the decrease of greenness from 1% to 5%, which resulted from change
detection of years 1993 and 2007. It shows how a 1% change made a dramatic
change on the forest cover in southwest Madagascar. The result shows that the
forest has changed distinctively from 1993 to 2007. Also, it shows how a 5%
decrease of forest is significantly critical for the ecosystem and the environment
of forests in southwest Madagascar.
 |
| Figure 5: Close up- change detection result |
Figure
5 is similar to Figure 4, but it is a more close up image of the area. This
result particularly looks at the Tsimanampetsotse nature reserve and its
surroundings in order to assess the greenness value change. The result shows that
greenness has significantly decreased inside the park, showing how
deforestation happens in the nature reserves, potentially affecting animal
species as well.
 |
| Table 1: Greenness value difference |
In
Table 1, the numbers ranging between -1 and 1 are the outcome of NDVI change
detection; the higher the greenness, the closer the NDVI change will be to 1,
and the lower the greenness, the closer it will be to -1. The table shows the
20 locations inside and outside the Tsimanampetsotse nature reserve. The result
shows that the greenness value in 1993 was higher than it was in 2007 in all
places.
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| Figure 6: Deforested area in Southwest Madagascar |
Figure
6 shows the results for a selected area in southwest Madagascar. The four
images show the greenness change through NDVI, an actual satellite image, and
the past satellite image. The area had been forested and green, but the forest was
eradicated due to cutting. The line graph is the result of the table (Table 1),
showing that each point had more greenness in 1993, but as time passed, the amount
of vegetation dropped.
 | ||
| Figure 7: Deforested area matching with recent fire, table- greenness difference in Tsimanampetsotse Park |
Figure 7 shows the result of the recent fire that occurred near the Tsimanampetsotse nature reserve. This is to show how fire is related to decrease forest cover. The next image shows how the NDVI results for 1993 and 2007 match the recent fire data, showing that there was fire in the past as well. In fact, the satellite image in the bottom shows how the forest is cleared due to fire and clear-cutting.
Discussion
Deforestation
in southwest Madagascar was evident in most of the areas. The results showed that
the decrease of forest cover was still occurring due to clear-cutting and fires
caused by human activity. The results also showed that the value of greenness
dropped significantly from 1993 to 2007, suggesting that the continuing
deforestation will expand and will be a threat to nature and the surrounding
environment. Using the ENVI program and doing NDVI processes helped to
determine the forest reduction rate in southwest Madagascar and whether it was caused
by human activity. The change detection process allowed assessment of the real
changes in the forest and analysis of the rate of greenness inside and outside
the Tsimanampetsotse nature reserve. In addition, combining my work with Google
Earth worked well to show that the particular study area was correlated with
humans cutting the forest.
What
did not really work was combining the recent fire data, because I needed older
fire data to compare with the exact time frame, which was year 1993 and 2007,
but the data were not available. It would have been more helpful to have older
fire data to match with years 1993 and 2007 to compare with the NDVI results
for both years.
Southwest Madagascar is known for deforestation
issues; however, this issue was not examined by using satellite imagery. Thus,
it was interesting to interpret satellite imagery to examine the forest cover
change in this area, to compare the time series data, and to combine GIS
knowledge and Google earth to get more accurate result. As the work
"Causes of Deforestation in Southwestern Madagascar: What Do We
Know?" (Casse, 2004) suggests, deforestation rate and its causes can be
studied and be learned; however, if there are visible images, it can be much
helpful to understand and apply our knowledge unto the real life. Therefore, in
the future, more satellite images will aid to conduct researches in subjects
such as deforestation, especially using higher resolution satellite images.
People in Madagascar realize that cutting down
trees and taking down the forest is bad for the environment and the ecosystem;
however, they cannot stop this action because they highly depend on the forest
for economical reasons. Deforestation continues because of people’s demand, but
it is important for them to realize that forest won’t last long if
deforestation continues, leading into a serious challenge to solve in the
future.
References
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(2012, September 12). Retrieved November 11, 2012, from
http://en.wikipedia.org/wiki/Atsimo-Andrefana
Casse,
T. Milhoj, A., Ranaivoson, S., & Randriamanarivo, J. R. (2004). Causes of deforestation
in Southwestern Madagascar: What do we know? Forest Policy and Economics,
6(1),
33-48.
Gorenflo,
L. J., Corson, C., Chomitz, K. M., Harper, G., Honzak, M., & Ozler, B.
(2011). Human population: Its influences on biological diversity.
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