Application of fractal analysis to assess land use changes on woody cover and landscape fragmentation in the Orinoco savannas

摘要

The effect of land use changes on the woody cover and patchiness of the Orinoco lowlands was analyzed from 1951 to 1997 by using a stretched exponential model in terms of the patch size distribution. We selected five production systems on the basis of the following components: policy option, technology and environment. They are: (a) high-input pasture in deep soil, (b) low-input cropping in deep soil, (c) high-input cropping in deep soil, (d) low-input cropping in shallow soil and (e) extensive cattle grazing in shallow soil. For comparison, stands with similar soil depth and woody density were selected at the protected Biological Reserve in the Calabozo region. Results indicate that the distribution of the patches was described by the stretched exponential distribution model with c as the exponent distribution. The magnitude of c reflected the effect of land use changes over time. Thus, the parameter c for human impacted stands was higher than that for the fallow stands. The stretched exponential model implies that the human impact had a multiscalar effect on the Orinoco mosaic, in terms of the multiplicative processes. There is a generic mechanism exhibiting an anomalous distribution of the patches such as has been proposed for physical systems. Therefore, the number of generation of the multiplicative processes (i.e. inverse of c) for impacted stands was lower than that in the fallow stands. As the time from fallow establishment proceeded, there was a tendency to patch re-organization by biotic effects.