Savanna woody encroachment is widespread across three continents

Abstract

Tropical savannas are a globally extensive biome prone to rapid vegetation change in response to changing environmental conditions. Via a meta-analysis, we quantified savanna woody vegetation change spanning the last century. We found a global trend of woody encroachment that was established prior the 1980s. However, there is critical regional variation in the magnitude of encroachment. Woody cover is increasing most rapidly in the remaining uncleared savannas of South America, most likely due to fire suppression and land fragmentation. In contrast, Australia has experienced low rates of encroachment. When accounting for land use, African savannas have a mean rate annual woody cover increase two and a half times that of Australian savannas. In Africa, encroachment occurs across multiple land uses and is accelerating over time. In Africa and Australia, rising atmospheric CO , changing land management and rainfall are likely causes. We argue that the functional traits of each woody flora, specifically the N-fixing ability and architecture of woody plants, are critical to predicting encroachment over the next century and that African savannas are at high risk of widespread vegetation change.

Woody Vegetation Die off and Regeneration in Response to Rainfall Variability in the West African Sahel

“…The encroachment of woody vegetation in African savannas has been studied at continental scale [28,29] and in more detail in southern Africa [30][31][32][33], but there is still a lack of research in Sahel. After a serious reduction in canopy cover was reported in the 1990s [6], recent studies report that woody vegetation in Sahelian regions with a sparse human population shown signs of increase [11,34].…”

Tropical grassy biomes: linking ecology, human use and conservation

“…The degree to which this dynamism will influence trajectories of vegetation change in grassy biomes into the future is unresolved. However, it is apparent that many intact savannahs are now on a trajectory of increasing woody biomass, although the degree of gain varies regionally, with Australian savannahs most stable over time [4].…”

“…The extent of these vast biomes has shifted with glacial -inter-glacial cycles in response to changing atmospheric CO 2 concentrations, rainfall, rainfall seasonality, temperature and fire [19,21]. Given that all of these aspects of our environment are now changing, and generally at rates not previously observed, extensive alterations in the distribution and dynamics of TGBs over the coming century are inevitable and are likely already being observed ( [1,4,22], see the analysis provided by Stevens et al [23]). …”

Impact of bush encroachment management on plant response and animal distribution

“…The consequence of this transformation is a reduced grazing capacity of herbivores including livestock, which might also lead to enhanced soil erosion and desertifi cation Stevens et al, 2017). Furthermore, due to the limitation of sight, the visibility of wild herbivores is reduced which might lead to negative consequences for tourism.…”