Projecting Podocarpaceae response to climate change: we are not out of the woods yet

Abstract

Under the changing climate, the persistence of Afrotemperate taxa may be threatened as suitable habitat availability decreases. The unique disjunct ranges of podocarps in southern Africa raise questions about the persistence of these species under climate change. Here, we identified likely environmental drivers of these distributions, characterized the current and future (2070) environmental niches, and projected distributions of four podocarp species in South Africa. Species distribution models were conducted using species locality data for Afrocarpus falcatus, Podocarpus latifolius, Pseudotropheus elongatus and Podocarpus henkelii and both historical climate data (1970–2000) and future climate scenarios (Representative Concentration Pathway [RCP] 4.5 and 8.5, 2061–2080) to estimate the current and future distributions. We also used this opportunity to identify the most important climatic variables that likely govern each species’ distribution. Using niche overlap estimates, a similarity test, and indices of niche expansion, stability and unfilling, we explored how niches change under different climate scenarios. The distribution of the study species was governed by the maximum temperature of the warmest month, temperature annual range, mean temperature of the wettest quarter, and precipitation of the wettest, driest and warmest quarters. The current distribution of A. falcatus was predicted to expand to higher elevations under RCP 4.5 and RCP 8.5. Podocarpus henkelii was predicted to lose most of its suitable habitat under RCP 4.5 and expand under RCP 8.5; however, this was the opposite for P. elongatus and P. latifolius. Interestingly, P. elongatus, which had the smallest geographic distribution, showed the most vulnerability to climate change in comparison to the other podocarps. Mapping the distribution of podocarps and understanding the differences in their current and future climate niches provide insight into potential climate drivers of podocarp persistence and the potential for adaptation of these species. Overall, these results suggest that P. elongatus and P. henkelii may expand to novel environmental niches.

Abstract

South African podocarps' distribution and response to climate change are primarily influenced by seasonal drought and physiological constraints. Total rainfall during the summer and winter months was identified as a crucial factor influencing podocarp distribution in South Africa. Podocarps are predicted to maintain their environmental niche under climate change. Furthermore, temperature annual range and mean temperature during the wettest quarter were found to limit the future distribution of some podocarps. The study highlights the importance of understanding environmental variables that shape and maintain species' geographic distributions for conservation purposes. It provides valuable insights into conservation actions and the re-introduction of South African podocarps in suitable habitats. The findings also underscore the need for physiologically oriented distribution models to consider the role of physiological thresholds in determining podocarp distribution.