Landscapes Forest and Global Change - ESA - Escola Superior ...

H.R. Ratsimba et al. 2010. Multi-scale analysis of carbon stocks and deforestation monitoring
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ecosystem and land use conditions as well as the range of approaches to carbon credit
accounting (Holmgren et al., 2008).
This study is carried out in the tropical humid forest of Madagascar which is located in the
eastern part of the island. The objective is to propose a methodology of upscaling process in
deforestation and degradation assessment through satellite images (different resolutions)
analysis and biomass inventory in the field. A spatial modelling approach is applied to search
specific factors correlated to biomass stock, to identify vegetation indices in order to simulate
the forest area across large regions, and to estimate the deforestation trend.
2. Methodology
2.1. Study area
Madagascar should be considered among the highest conservation priorities (Myers, 1988;
McNeely et al., 1990; Mittermeier et al., 1992). However, the poverty remains one of the main
causes of deforestation and degradation. The average income is around $200 per year
(Population Reference Bureau, 1992). Moreover, more than 70 % are from the rural regions
which are facing low agricultural productivity (CIA, 2009). These situations have led to a
continuous deforestation and degradation process in the whole country.
The eastern part of Madagascar is characterized by a tropical humid climate with over 2000 mm
mean rainfall per year and about 26°C annual mean temperature. The vegetation of this region is
divided into three primary categories corresponding to elevation bands: "lowland rain forest" (0
to 800 m), "moist montane forest" (800 to 1,300 m), and "sclerophyllous montane forest" (1,300
to 2,300 m) (White, 1983). The third category is not considered in this study due to its limited
repartition (the patches are to small to be evaluated in a 232 m * 232 m pixel of MODIS).
There are some general trends in forest characteristics with increasing elevation: decreasing
stature, fewer straight unbranched and boled trees, less stratification, more epiphytes, more
bryophytes and lichens, a better developed and more diverse herb layer, and floristic changes
(Lewis et al. 1996). Dense evergreen trees characterize the lowland forest up to 800 m, with a
canopy exceeding 30 m. The mid-altitude moist forest is as rich in species as the lowland forest,
but tends to have a shorter canopy of 20 to 25 m.
The main threat is from subsistence agriculture through slash and burn activities (“tavy”) and
illegal logging which are the main causes of deforestation and degradation (Humbert, 1927;
Rauh, 1979; Jolly and Jolly, 1984; Sussman et al., 1985; Jenkins, 1987).
All of these aspects make REDD monitoring, reporting and verification very important for the
country by creating clear and simple methods and tools to evaluate deforestation threat across a
landscape especially for policy makers and forest managers.
2.2. Biomass and forest carbon accounting
Biomass is defined as “organic material both above-ground and below-ground, and both living
and dead, e.g., trees, crops, grass, tree litter, roots etc.” (Samalca et al., 2007). The IPCC
(Intergovernmental Panel on Climate Change, 2003, 2006), has defined five different carbon
pools for Greenhouse Gas (GHG) inventory : (1) living above-ground biomass (AGB), (2)
living below-ground biomass (BGB), (3) dead organic matter in wood (DOM), (4) dead organic
matter in litter (DOM), and (5) soil organic matter (SOM). Biomass is converted into carbon by
multiplying its weight with a carbon fraction of dry matter which is usually 0.5 (IPCC, 2006).
Many biomass estimation researches are focused on above-ground forest biomass (Aboal et al.,
2005; Kraenzel et al., 2003; Laclau, 2003; Losi et al., 2003; Rakoto Ratsimba et al., 2010)
because it represents the majority of the total biomass.
This study focuses on the link between the assessment of above-ground forest biomass based on
Rakoto Ratsimba et al. methods (2010) and recorded vegetation indices on satellite images.
2.3. Stratification and randomized plot based sampling
Rakoto Ratsimba et al. (2010) in their study on deforestation and degradation show that the
differentiation between “low degraded forest” and “degraded forest” is possible in tropical
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.