TEXTURE MEASURES FOR THE QUANTIFICATION OF SPATIAL VARIABILITY OF VEGETATION IN SAVANNA LANDSCAPES

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Year:
2017
Type of Publication:
Article
Keywords:
Texture, SAVI, spatial variability, heterogeneity, diversity
Authors:
Tony Rajan Mathew,
Abstract:
If biodiversity can be considered as the total variability of life on earth, vegetation variability plays a significant part in its sustenance. Vegetation at any given location changes over time and space. Reliable information in this regard is key to identifying sources of ecosystem stress and devising adequate management strategies. Conservation efforts traditionally have focused on changes at the local scale and at species levels. Limitations of space and time did not enable such studies to adequately explain the processes that are in operation and their interrelationships across hierarchic levels. Spatial analysis of vegetation index images derived from medium resolution sensors such as Landsat could be a possible source of this information at broader spatial and temporal scales. The present study analyses the spatial dynamics of savanna vegetation in Kruger National Park, South Africa using Landsat derived Soil Adjusted Vegetation Index images. Spatial variability is assessed through its constituent elements of heterogeneity and diversity. Changes in vegetation conditions while contributing to spectral changes will also induce changes in the spatial structure of the image. Texture measures operating within local neighborhoods will be able to quantify this change in local image variance and hence spatial variability. Texture measures of mean, variance, skewness and kurtosis were calculated for quadrats of size 2*2 km using moving windows of size 3*3, 31*31 and 61*61 corresponding to local, patch and landscape scales for the four years considered in the study - 1984, 1990, 1996 and 2002. Results indicate that the park is a constantly changing and evolving ecosystem. Seasonality is the primary contributor to intra-year vegetation variability. Differences in geology plays the dominant role in deciding inter-year variability though at coarser spatial scales the effect is negligible. Spatial heterogeneity and diversity as measured by skewness and kurtosis show a declining trend from 1984 to 2002
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