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Impact of communal land use and conservation on woody vegetation structure in the Lowveld savannas of South Africa

by K. J. Wessels, R. Mathieu, B. F N Erasmus, G. P. Asner, I. P J Smit, J. A N van Aardt, R. Main, J. Fisher, W. Marais, T. Kennedy-Bowdoin, D. E. Knapp, R. Emerson, J. Jacobson show all authors
Forest Ecology and Management ()

Abstract

Millions of people rely on savannas for ecosystem services, such as the provision of grazing and fuel wood, so it is important to determine the extent to which utilization affects woody vegetation resources. Using airborne LiDAR from the Carnegie Airborne Observatory (CAO), we quantified and compared tree canopy cover and height distributions between areas of contrasting management in the Lowveld savanna region of South Africa - a region connecting communal landscapes with heavy utilization (especially fuel wood harvesting) to fully protected public (Kruger National Park - KNP) and private reserves (SabiSand Game Reserve - SSGR) that conserve biodiversity. Differences in total woody vegetation cover and cover within functional height classes (1-2. m, 2-3. m, 3-5. m, 5-7. m and >7. m) were investigated between 7 sites located within (i) conservation areas (in KNP, SSGR), (ii) communal rangelands or (iii) cultivated fields in communal areas. The impact of human utilization on wood resources in the communal areas varied widely between sites. Heavy utilization on gabbro substrate greatly reduced total woody cover of the rangelands, while two other communal rangelands that were presumably less intensively utilised had double the total woody cover of conservation areas. Rangelands and fields in most of the communal sites had more vegetation cover in the 5-7. m and >7. m classes than most of the conservation sites, presumably due to the absence of elephants in communal rangelands and the active preservation of large fruiting trees. On granite substrates, which account for the majority of the study area, there was a 50% reduction in woody cover below 5. m in communal rangelands. Although large trees were clearly being conserved in communal rangelands and fields, there was a relatively low cover of vegetation below 5. m, which raise doubts about recruitment and long-term sustainability of the tree resources. These results in conjunction with other studies based on the CAO LiDAR data for experimental burn plots and large mammal exclosures in KNP, suggest that communal land use on granite substrates have a higher impact on the woody cover below 5. m than both elephants and fire. ?? 2010 Elsevier B.V.

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