Track 1-13: Monitoring and Managing Grass and Forage Biomass Resources at the Landscape Level
Description
Rangelands are a major global resource, and there is an urgency to improve the assessment of landscape performance to capture carbon, produce biomass, and improve water use. Effective monitoring necessitates the collection of high quality rangeland condition data using repeatable techniques. Despite much effort, there are few comprehensive data sets that allow confident detection of landscape change. Data are lacking for several reasons, including high cost of data collection, conflicting methodologies, and loss of archival data. Satellite imagery provides the basis for trend and pattern analysis of rangeland in different conditions classes and this paper presents some examples of the analysis and interpretation of selected imagery from southern African rangelands. One approach to understanding rangeland change is to identify models that use functional concepts to describe landscape performance. Rangeland water use has being equated to that of more thirsty crops, resulting in further pressure to convert rangeland to dryland cultivation. Water use efficiency (WUE) is of considerable value in defining functionality. Here, WUE defines the ability of an ecosystem to produce above-ground biomass (kg DM) per unit of actual evapotranspiration (mm). It been calculated for several condition classes at sites in arid and semi-arid rangelands. In the past, estimates of WUE have been hampered by the scarcity of reliable net primary production (NPP) and evapotranspiration data. With the availability of spatially explicit estimates of actual evapotranspiration (ETa) from the MODIS programme, it is now possible to validate annual ETa surfaces at a spatial resolution of 1 km. We have validated these ETa surfaces for southern Africa using a range of instruments and approaches. In addition, a global annual net primary production (MOD17) surface is available from MODIS. By combining these products, we have prepared an estimate of WUE (WUE = NPP/ ETa) for natural rangelands in southern Africa for 2009. WUE varies spatially, with values ranging from 0.1 kg DM mm/ha/y in the arid western regions to > 8 kg DM/mm/ha/y in the forests and grasslands of the eastern region. Using data from several ground-based measurements of WUE, this surface has been validated, and demonstrates that this is a useful product for comparing landscape management strategies and condition classes. I show how this product, and other remote sensing products, can be used to evaluate different land management strategies.
Included in
Monitoring Landscape Changes Using Remote Sensing Technology in Southern Africa
Rangelands are a major global resource, and there is an urgency to improve the assessment of landscape performance to capture carbon, produce biomass, and improve water use. Effective monitoring necessitates the collection of high quality rangeland condition data using repeatable techniques. Despite much effort, there are few comprehensive data sets that allow confident detection of landscape change. Data are lacking for several reasons, including high cost of data collection, conflicting methodologies, and loss of archival data. Satellite imagery provides the basis for trend and pattern analysis of rangeland in different conditions classes and this paper presents some examples of the analysis and interpretation of selected imagery from southern African rangelands. One approach to understanding rangeland change is to identify models that use functional concepts to describe landscape performance. Rangeland water use has being equated to that of more thirsty crops, resulting in further pressure to convert rangeland to dryland cultivation. Water use efficiency (WUE) is of considerable value in defining functionality. Here, WUE defines the ability of an ecosystem to produce above-ground biomass (kg DM) per unit of actual evapotranspiration (mm). It been calculated for several condition classes at sites in arid and semi-arid rangelands. In the past, estimates of WUE have been hampered by the scarcity of reliable net primary production (NPP) and evapotranspiration data. With the availability of spatially explicit estimates of actual evapotranspiration (ETa) from the MODIS programme, it is now possible to validate annual ETa surfaces at a spatial resolution of 1 km. We have validated these ETa surfaces for southern Africa using a range of instruments and approaches. In addition, a global annual net primary production (MOD17) surface is available from MODIS. By combining these products, we have prepared an estimate of WUE (WUE = NPP/ ETa) for natural rangelands in southern Africa for 2009. WUE varies spatially, with values ranging from 0.1 kg DM mm/ha/y in the arid western regions to > 8 kg DM/mm/ha/y in the forests and grasslands of the eastern region. Using data from several ground-based measurements of WUE, this surface has been validated, and demonstrates that this is a useful product for comparing landscape management strategies and condition classes. I show how this product, and other remote sensing products, can be used to evaluate different land management strategies.
