Understanding seasonal variations of vegetation greening and senescence in the Southern African savannas

From the article: Response of Land Surface Phenology to Variation in Tree Cover during Green-Up and Senescence Periods in the Semi-Arid Savanna of Southern Africa

Moses A. Cho, Abel Ramoelo and Luthando Dziba

Natural Resources and Environment, Council for Scientific and Industrial Research (CSIR), PO. Box 395, Pretoria, South Africa 0001, Remote Sensing 9(7), p. 689 (2017). doi:10.3390/rs9070689

Figure: Tree dominated regions show longer growing seasons than grass dominated systems.

The African savanna is characterised by a mixture of grasses and trees in varying proportions and serve as a habitat for millions of people and wildlife. The annual cycle of vegetation greening and senescence in the savanna plays an important role in the functioning of the biosphere e.g. carbon and water cycles, migration of wildlife, spread of fire etc. This allows African savannas to provide numerous ecosystem services that are of high social and economic importance such as wildlife tourism, provision of food (e.g mopane worms, marula fruits, honey) and grazing land for livestock production. The periods corresponding to the start and end of the growing season, and indeed the length of the growing season (i.e. the phenological periods) determine the availability of the above ecosystem services both in space and time.

Furthermore, understanding the relative contribution of grasses and trees to the various phenological periods would enhance our ability to manage the savanna for optimal benefits to people and wildlife. This has become even more critical in the advent of climate change and variability characterised by erratic rainfall patterns in Southern Africa. The study on the response of land surface phenology on variation in tree cover during green-up and senescence periods in the semi-arid savanna of Southern Africa reveals that rainfall is the predominant factor that explains the inter-annual variability of the day corresponding to the start of the growing season in the region for areas dominated by grasses (< 20% tree cover) while tree cover is the predominant factor that explains the variability in the day corresponding to end of the growing season. In fact, the length of the growing season increases with increasing tree cover.   Quantifying the day of the year corresponding to end of growing season could be important in assessing the risk of fire spread both in space and time.