Theme 5: Drought--Oral Sessions

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Monitoring changes in carbon and water vapour fluxes over a landscape helps in understanding ecosystem functioning and improves vegetation management. To understand potential shifts in ecosystem functioning, MoDerate Resolution Imaging Spectroradiometer (MODIS) evapotranspiration (ET), net photosynthesis, gross primary production and net primary production data were explored in Sikumi forest dominated by three species clusters (Teak forest woodland, Miombo woodland and savannah, and Vachellia). Measures of ecosystem stability including water use efficiency (WUE), rainfall use efficiency (RUE), evaporative index, and carbon use efficiency (CUE) were assessed for trends and step changes together with rainfall and evapotranspiration data. Miombo woodland and savannah had significantly higher actual ET and production compared to Vachellia and Teak clusters. Ecosystem production was strongly coupled with precipitation as the Vachellia and Teak clusters became sources of carbon during the dry season. High production in the Miombo cluster even during the dry season could be linked to xylem rehydration and convergent evolution to harvest additional water and nutrients. Annual net primary production in Sikumi forest was 632±189 g C m-2. Despite relatively small spatial coverage (12%), the Vachellia cluster contributed production similar to the Teak and Miombo woodlands clusters that covered 63 and 25% respectively of the forest area possibly due to soil fertility. Teak had the highest CUE (62%) but lowest NPP, possibly due to high respiration. The relationship between rainfall, NPP and measures of ecosystem stability was unimodal. This provided insights into the likely trajectory of these indices within the purview of climate change. The low RUE of the Teak cluster suggests that this cluster was more sensitive to disturbance. The study area was water limited as shown by a low ETa/PET ratio. Monitoring carbon and water flux dynamics help to identify the onset of ecosystem change and may inform requisite interventions to improve ecosystem functioning.

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Exploring Water Use and Production Dynamics of Indigenous Protected Sikumi Forest in South Western Zimbabwe

Monitoring changes in carbon and water vapour fluxes over a landscape helps in understanding ecosystem functioning and improves vegetation management. To understand potential shifts in ecosystem functioning, MoDerate Resolution Imaging Spectroradiometer (MODIS) evapotranspiration (ET), net photosynthesis, gross primary production and net primary production data were explored in Sikumi forest dominated by three species clusters (Teak forest woodland, Miombo woodland and savannah, and Vachellia). Measures of ecosystem stability including water use efficiency (WUE), rainfall use efficiency (RUE), evaporative index, and carbon use efficiency (CUE) were assessed for trends and step changes together with rainfall and evapotranspiration data. Miombo woodland and savannah had significantly higher actual ET and production compared to Vachellia and Teak clusters. Ecosystem production was strongly coupled with precipitation as the Vachellia and Teak clusters became sources of carbon during the dry season. High production in the Miombo cluster even during the dry season could be linked to xylem rehydration and convergent evolution to harvest additional water and nutrients. Annual net primary production in Sikumi forest was 632±189 g C m-2. Despite relatively small spatial coverage (12%), the Vachellia cluster contributed production similar to the Teak and Miombo woodlands clusters that covered 63 and 25% respectively of the forest area possibly due to soil fertility. Teak had the highest CUE (62%) but lowest NPP, possibly due to high respiration. The relationship between rainfall, NPP and measures of ecosystem stability was unimodal. This provided insights into the likely trajectory of these indices within the purview of climate change. The low RUE of the Teak cluster suggests that this cluster was more sensitive to disturbance. The study area was water limited as shown by a low ETa/PET ratio. Monitoring carbon and water flux dynamics help to identify the onset of ecosystem change and may inform requisite interventions to improve ecosystem functioning.