Abstract
Many studies have identified drivers of deforestation throughout the tropics and, in most cases, have recognised differences in the level of threat. However, only a few have also looked at the temporal and spatial dynamics by which those drivers act, which is critical for assessing the conservation of biodiversity as well as for landscape planning. In this study, we analyse land cover change between 2000 and 2009 in north-western Colombian Amazonia to identify the interactions between the use of fire, cultivation of illicit crops and establishment of pastures, and their impacts on the loss of forest in the region. Yearly analyses were undertaken at randomly selected sample areas to quantify the average areas of transition of land cover types under different landscape compositions: forest-dominated mosaics, pasture mosaics, fire mosaics, and illicit crop mosaics. Our results indicate that despite the fact that forest areas were well-preserved, deforestation occurred at a low annual rate (0.06%). Conversion to pasture was the main factor responsible for forest loss (the area of pastures tripled within forest mosaics over 8 years), and this process was independent of the landscape matrix in which the forests were located. In fire mosaics, burning is a common tool for forest clearing and conversion to pasture. Thus, forests in fire mosaics were highly disturbed and frequently transformed from primary to secondary forests. The use of fire for illicit cropping was not detected, partly due to the small size of common illicit crops. Forest regeneration from pastures and secondary vegetation was observed in areas with large amounts of natural forest. Overall, assuming the continuation of the observed pasture conversion trend and the use of forest fire, we suggest that our results should be incorporated into a spatially explicit and integrated decision support tool to target and focus land-planning activities and policies.
Highlights
Rates of forest loss are currently being reported at 0.6% per year at the global level [1], and deforestation remains a prime environmental problem all over the planet
Few pixels changed on an annual basis, and year-to-year persistence was high in all categories, with the lowest rate of persistence being illicit crops at 87.7%
The average distance of coca crops from San Jose de Guaviare did not show the expected pattern of increasing distance over time following the expansion of the colonist frontier, but the distance tended to decrease over time, indicating that, on average, illicit crops were being cultivated closer to the urban centre (Figure 3B)
Summary
Rates of forest loss are currently being reported at 0.6% per year at the global level [1], and deforestation remains a prime environmental problem all over the planet. Forest fires related to slash-and-burn practices, traditionally used for the conversion of forests into agricultural lands and pastures, have been highlighted as a significant factor that degrades and erodes forests and alters their composition and structure [5], [6]. Forest clearance results in forest fragmentation, increasing the number of forest edges and altering sub-canopy humidity conditions, which in turn, increases the susceptibility of the remaining fragments to fire [5]. Grazing area has increased over recent decades at the expense of forested area, in tropical Latin America [7]. The extensive and expanding production of livestock, spurred by a demand for meat and milk production, which is expected to continue to increase until 2015 [7], [8], is considered another great driver of land use change and deforestation in Latin America
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