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Conférence (01/04/2014)

Trends in vegetation productivity and seasonality for Namaqualand, South Africa between 1986 and 2011: an approach combining remote sensing and repeat photography

par Claire Davis, Climate Studies, Modelling and Environmental Change, Natural Resources and Environment, CSIR – Stellenbosch, South Africa

Understanding the rate and extent of historical vegetation change in Namaqualand in response to local drivers, such as livestock grazing and climatic variability, is required as it provides the necessary benchmarks against which future changes can be assessed. An accurate determination of the extent of vegetation change in Namaqualand over time remains a challenge. Not only does the region cover a large, bio-climatically diverse area but the lack of long-term observations and scientific data makes reliable reconstruction difficult. Remotely sensed vegetation indices in combination with historical repeat photography are utilised in this study in order to effectively determine the critical pathways of vegetation change in Namaqualand. This study presents a unique approach in the sense that it employs multi-source and multi-temporal data to assess vegetation change over time. A comprehensive set of archival images taken since 1876 (Hoffman & Rohde 2010) was utilised in order to understand vegetation change in Namaqualand over long time scales from decades to centuries. Spatially-explicit time series analysis of remotely sensed vegetation indices and satellite-derived vegetation phenology were used to assess more recent changes in vegetation cover over the last 25 years. This study offers new insights into the spatial patterns and inter-annual variability of vegetation productivity and seasonality of Namaqualand. The results demonstrate a trend towards improved vegetation cover and composition with a clear shift in dominance from annual to perennial cover. Furthermore, combining information from both repeat photographs and remote sensing provide the best description and interpretation of landscape-scale vegetation change.

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