Data for: Precipitation gradients drive high tree species turnover in the woodlands of eastern and southern Africa

Savannas cover one-fifth of the Earth’s surface, harbour substantial
biodiversity, and provide a broad range of ecosystem services to hundreds
of millions of people. The community composition of trees in tropical
moist forests varies with climate, but whether the same processes
structure communities in disturbance-driven savannas remains relatively
unknown. We investigate how biodiversity is structured over large
environmental and disturbance gradients in woodlands of eastern and
southern Africa. We use tree inventory data from the Socio-Ecological
Observatory for Studying African Woodlands (SEOSAW) network, covering 755
ha in a total of 6780 plots across nine countries of eastern and southern
Africa, to investigate how alpha, beta, and phylogenetic diversity vary
across environmental and disturbance gradients. We find strong
climate-richness patterns, with precipitation playing a primary
role in determining patterns of tree richness and high turnover across
these savannas. Savannas with greater rainfall contain more tree species,
suggesting that low water availability places distributional limits on
species, creating the observed climate-richness patterns. Both fire and
herbivory have minimal effects on tree diversity, despite their role in
determining savanna distribution and structure. High turnover of tree
species, genera, and families is similar to turnover in seasonally dry
tropical forests of the Americas, suggesting this is a feature of semiarid
tree floras. The greater richness and phylogenetic diversity of wetter
plots show that broad-scale ecological patterns apply to
disturbance-driven savanna systems. High taxonomic turnover suggests that
savannas from across the regional rainfall gradient should be protected if
we are to maximise the conservation of unique tree communities.