Browsing by Author "Bukombe, John"

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    Comparative Assessment of UAV and Sentinel-2 NDVI and GNDVI for Preliminary Diagnosis of Habitat Conditions in Burunge Wildlife Management Area, Tanzania
    (MDPI, 2022-06-28) Mangewa, Lazaro; Ndakidemi, Patrick; Alward, Richard; Kija, Hamza; Bukombe, John; Nasolwa, Emmanuel; Munishi, Linus
    Habitat condition is a vital ecological attribute in wildlife conservation and management in protected areas, including the Burunge wildlife management areas in Tanzania. Traditional techniques, including satellite remote sensing and ground-based techniques used to assess habitat condition, have limitations in terms of costs and low resolution of satellite platforms. The Normalized Difference Vegetation Index (NDVI) and Green NDVI (GNDVI) have potential for assessing habitat condition, e.g., forage quantity and quality, vegetation cover and degradation, soil erosion and salinization, fire, and pollution of vegetation cover. We, therefore, examined how the recently emerged Unmanned Aerial Vehicle (UAV) platform and the traditional Sentinel-2 differs in indications of habitat condition using NDVI and GNDVI. We assigned 13 survey plots to random locations in the major land cover types: three survey plots in grasslands, shrublands, and woodlands, and two in riverine and mosaics cover types. We used a UAV-mounted, multi-spectral sensor and obtained Sentinel-2 imagery between February and March 2020. We categorized NDVI and GNDVI values into habitat condition classes (very good, good, poor, and very poor). We analyzed data using descriptive statistics and linear regression model in R-software. The results revealed higher sensitivity and ability of UAV to provide the necessary preliminary diagnostic indications of habitat condition. The UAV-based NDVI and GNDVI maps showed more details of all classes of habitat conditions than the Sentinel-2 maps. The linear regressions results showed strong positive correlations between the two platforms (p < 0.001). The differences were attributed primarily to spatial resolution and minor atmospheric effects. We recommend further studies to test other vegetation indices.
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    Savannah trees buffer herbaceous plant biomass against wild and domestic herbivores
    (John Wiley & Sons Ltd, 2019-11-30) Smith, Stuart William; Graae, Bente Jessen; Bukombe, John; Hassan, Shombe Ntaraluka; Lyamuya, Richard Daniel; Mtweve, Philipo Jacob; Treydte, Anna C.; Speed, James David Mervyn
    Questions: Given the growing abundance and dominance of domestic herbivores in savannah ecosystems, can trees maintain plant herbaceous standing biomass under increasing herbivore pressure? Are there differences in the capacity of leguminous and non-leguminous trees in sustaining understory herbaceous biomass? And finally, to what extent does plant community composition underneath trees modulate the effects of herbivore assemblage and abundance on herbaceous biomass? Location: Pasturelands and protected areas along the borders of the Serengeti National Park, Tanzania, East Africa. Method: Monthly herbaceous biomass was monitored non-destructively using a calibrated pasture disc. Measurements were taken within a network of paired exclosures and open plots, underneath large leguminous and non-leguminous tree canopies and outside canopies. Herbivore community assemblage compositions and abundances were characterised using monthly dung counts, and herbaceous plant community composition was surveyed annually every wet season over two years. Results: Overall, we found that trees promote herbaceous standing biomass, particularly in the presence of moderate herbivory rather than under herbivore exclusion. Greater herbivore abundance and livestock dominance reduced herbaceous plant biomass, but trees, particularly leguminous trees, limited these negative effects. This capacity for trees to limit the effect of herbivores was related to herbaceous plant species composition. Understory plant communities that were compositionally typical of protected areas sustained the highest plant biomass when found in pasturelands with high herbivore pressure. Conclusion: Our findings give greater credence to the importance of preserving large trees in savannah landscapes increasingly dominated by high abundances of livestock. Moreover, our results highlight that park managers and pastoralists need to maintain the specialist herbaceous understory community beneath trees in order to benefit from facilitative tree–understory interactions.