Abstract
Phenological properties are critical in understanding global environmental change patterns. This study analyzed phenological dynamics in a savannah dominated semi-arid environment of Uganda. We used moderate-resolution imaging spectroradiometer normalized difference vegetation index (MODIS NDVI) imagery. TIMESAT program was used to analyse the imagery to determine key phenological metrics; onset of greenness (OGT), onset of greenness value, end of greenness time (EGT), end of greenness value, maximum NDVI, time of maximum NDVI, duration of greenup (DOG) and range of normalized difference vegetation index (RNDVI). Results showed that thicket and shrubs had the earliest OGT on day 85 ± 14, EGT on day 244 ± 32 and a DOG of 158 ± 25 days. Woodland had the highest NDVI value for maximum NDVI, OGT, EGT, and RNDVI. In the bushland, OGT occurs on average around day 90 ± 11, EGT on day 255 ± 33 with a DOG of 163 ± 36 days. The grassland showed that OGT occurs on day 96 ± 13, EGT on day 252 ± 36 with a total DOG of 156 ± 33 days. Early photosynthesis activity was observed in central to eastern Karamoja in the districts of Moroto and Kotido. There was a positive relationship between rainfall and NDVI across all vegetation cover types as well as between phenological parameters and season dynamics. Vegetation senescence in the sub-region occurs around August to mid-September (day 244–253). The varied phenophases observed in the sub-region reveal an inherent landscape heterogeneity that is beneficial to extensive pastoral livestock production. Continuous monitoring of savannah phenological patterns in the sub-region is required to decipher landscape ecosystem processes and functioning.
Highlights
Global environmental change, including climate change, is undoubtedly a pressing issue of global concern in recent times (Naeem et al, 2009; Bulkeley and Newell, 2010; Hussein, 2011)
We considered time of onset of greenness (OGT), end of greenness time (EGT) and duration of greenness (DOG) from the four major vegetation types: bushland, grassland, woodland and thicket and shrub
We analyzed the phenological dynamics of the Karamoja subregion using a suit of phenological metrics across four vegetation types
Summary
Global environmental change, including climate change, is undoubtedly a pressing issue of global concern in recent times (Naeem et al, 2009; Bulkeley and Newell, 2010; Hussein, 2011) This in part is due to a rise in extreme events and associated threats to humanity, species and habitats (Birkmann et al, 2014; Allen and Allen, 2017; Ma et al, 2018). Plant reproduction, population-level interactions, community dynamics and plant evolution and adaptations often influence ecosystem functions and services (Isbell et al, 2011; Maestre et al, 2012) These can, be altered by shifts in plant phenology (Peñuelas et al, 2013; Suonan et al, 2019)
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