The Contribution of Hydric Habitats to the Richness of the Cape Fynbos Flora

Aim

The Cape Fold Belt Mountains, underlying the Cape fynbos flora, facilitate widespread moisture collection and groundwater availability across the region, with importance for maintaining hydric habitat niches. We assessed the contribution of hydric habitat-associated species (HH species) to the richness of this flora, and how this varies phylogenetically and spatially.

Location

The Cape Floristic Region (CFR), South Africa.

Methods

We compiled data describing habitat preference and distributions for 3114 species in 23 fynbos clades. We used published habitat descriptions to identify putative HH species and tested how hydric habitat association is structured phylogenetically using both Ornstein-Uhlenbeck models and measures of phylogenetic signal. We used species' distribution data to identify regional hotspots of HH species and boosted regression trees (BRTs) to identify associated environmental drivers.

Results

Preference for hydric habitats is associated with nearly a fifth of the species in our study, being most strongly represented in monocot clades. HH species are most strongly concentrated in the southwestern CFR, where they contribute to high overall richness. BRTs indicated that hotspots of HH species are generally associated with saturating, winter precipitation and/or elevated levels of groundwater discharge.

Main Conclusions

Our findings indicate that the unique climate, topography and hydrology of the CFR facilitate the formation and maintenance of important hydric habitats, which play host to a large fraction of the flora despite much of the region being semi- or seasonally arid. These findings highlight the threat of climate change and underscore the need for extreme caution regarding activities like groundwater abstraction, which could disrupt the hydrological processes essential to sustaining these habitats and their unique flora.