Ecological fragmentation two years after a major landslide: Correlations between vegetation indices and geo-environmental factors

Abstract

This study was carried out about two years after a major landslide took place in Aranayake, Sri Lanka to evaluate geo-ecological status quo (spatial variation of vegetation and geo-environmental variables, and the correlations between them), and to identify spatially explicit landscape units (ecotopes). Sampling was done continuously based on a mesh covering visual landslide patch (disturbed area) and its surrounding (undisturbed area). When overlaid with the visual landslide patch, the contours of tree diversity, above ground herb dead biomass, and soil toughness (resistance to penetration) showed a good spatial match or a responsiveness. In contrast, herb diversity and landslide patch did not spatially match. As expected, soil physio-chemistry (soil moisture, organic content, soil toughness, etc.) of the disturbed and undisturbed areas showed significant differences. In contrast to many past studies the disturbed areas showed a better herb diversity, yet in agreement they were mostly nonnative or invasive species. Detrended correspondence analyses revealed the fragmentation was more than a mere separation as disturbed and undisturbed; the disturbed area showed a further fragmentation based on the terrain as hilly and flat. Therefore, the single ecotope existed before the landslide, changed into three. The correlations between vegetative indices and geo-environmental variables in general, varied with the ecotope, elucidating the need of different management strategies. Soil toughness of disturbed areas was significantly lesser than the undisturbed. However, force required to uproot herbs were similar in disturbed and undisturbed areas, indicating adaptation and/or colonization of stress tolerant plants. While agreeing that the area is not suitable for human settlements, we propose to use the area for controlled agriculture, fire wood collection, tourism activities and biodiversity studies, instead of total abandonment. This study gave important baseline data on dynamics of biotic and abiotic factors of a landslide in a tropical environment. Further studies should be continued in the long run to evaluate succession of flora and to identify temporal trajectories of biotic and abiotic factors.