Mediterranean land abandonment and associated biomass variation
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Biomass is an important factor in environmental processes, such as erosion, carbon storage, climate change and land degradation. Human-induced changes in plant community systems and increased tourism and recreation result in more biomass stress and pressure on the water recourses, which have strong effects on ecosystems. This study investigated biomass variation, biomass change over a time span of 24 years and the causal factors for a Mediterranean area. The study was performed in the Peyne area, South France. For detecting the biomass variation and change a descriptive biomass model was made, which involved a linear regression model, based on the spectral bands of the Hymap image of 2008 and the biomass of 2009 which was measured in the field. The descriptive biomass model was applied on the Hymap image of 2008 and the Landsat TM image of 1984, which resulted in a biomass image of 2008 and 1984 and (after subtracting these two maps of each other) a biomass change image between 1984 and 2008. The biomass in 2008 ranged between 37 and 653 ton/ha with an average of 245 ton/ha and a standard deviation of 80 ton/ha. The results for the biomass in 1984 was very unreliable with biomass ranging between 168 and 173 ton/ha. The absence in variation could be attributed to the absence in variation in reflectance values. Since, the biomass change was unreliable, the causal factors were mainly discussed for the biomass variation in 2009. The variation in biomass was discussed in terms of different factors: geology, soils, elevation, slope, aspect and human influence. Geology and soils were found to be important factors in determining biomass variation. This variation was mainly caused by variation in available soil moisture and soil thickness. Also environmental factors, such as elevation, aspect and slope were proved to be related to biomass variation. Elevation was found to positive related to biomass, while slope was negative correlated to biomass. Biomass varied also per aspect class. Humans had an influence on the biomass too: areas under the influence of reforestation had a larger biomass in 2009 than areas without influence. Furthermore, other human influences, such as paths, walls and other kind of influences, were proven to have no large influence on the biomass variation in 2009.