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

F.M. Rabenilalana et al. 2010. Multi-temporal analysis of forest landscape fragmentation in the North East of Madagascar
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For this computation, a 3 by 3 kernel (majority filter) was used so that c equalled 9.This interval
choice was linked to the importance of reflectance. A reflectance of 100% means that the
surface reflects all solar energy in the atmosphere. This corresponds to a fragmentation index of
0. When the reflectance is 0%, the fragmentation index equals 1.
2.1.3 Change analysis
Land cover maps from two different dates, 2004 and 2009, were used to make land cover
predictions for 2010. Using Land Change Modeler (Eastman 2006), this was done in two major
stages: the transition potential sub-model, which is developed in this paper, stage and the
change prediction model stage. A transition sub-model consists of a single land cover transition
or a group of transitions that are thought to have the same underlying driver variables. In the
first stage, particular transitions of interest for the sub-model and the variables which are
assumed to drive the transitions taking place were specified. Variables considered as drivers of
deforestation were distance to rivers and streams, paths, villages and to topographic parameters.
Using Cramer’s V or Phi statistic the strength, association or dependency between two variables
(Agresti 2002) was analyzed. The closer V is to 0 when the smaller ie the association between
the categorical variables X and Y. On the other hand, V being close to 1 is an indication of a
strong association between two variables.
Afterward, gain and loss of fragmentation (forests cover) area were calculated between two
periods with the aim to determine the rate of fragmentation in the study area.
3. Results
3.1 Fragmentation Index
The fragmentation was classified in two groups depending on the fragmentation index: a) a
forest fragment was considered to have a low level of fragmentation when the index was
between [0; 0.1[, b) a forest fragment was considered to have a high level of fragmentation
when the index was within the interval [0.1; 1].
Table 1 shows the fragmentation index. In 2004, the index ranged from 0 to 0.875 while in 2009
the values were between 0 and 0.25. The reasons for this difference could be either a) the
luminosity at the time when the images were taken was not the same or b) the forest fragments
of 2004 have been converted into less fragments in 2009, which is not evident in the short
period. In terms of patch numbers, there is a large difference between 2004 and 2009. 17 % of
forests cover with low fragmentation in 2004 shows a high level of fragmentation or has been
converted into other land uses in 2009.
Table 1: Fragmentation index characteristics
Period
Total
area
Count Minimum Maximum Mean
Standard
deviation
Low
fragmented
class
Patches number
2004 30487 18918482 0 0.875 0.054 0.01 65535 5633
2009 22472 18918482 0 0.25 0.017 0.01 11231 6442
Fragmented
class
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.