Mudappa, D. | Search bioRxiv

bioRxiv2024

Distribution models predict climate-related range alteration or extinction of eleven threatened tropical rainforest trees in the Western Ghats

Evidence for climate-change related alteration in distributions and ranges of forest trees is accumulating, but information from Asian tropical forests, particularly for threatened and endemic species, remains limited. Here, we examine landscape-level distribution-abundance patterns of 11 endemic and threatened tropical rainforest tree species in the Anamalai Hills and model their distribution and responses to future climate scenarios in the Southern Western Ghats (SWG), India. Six of the primarily low- and mid-elevation species were more abundant in protected reserves than forest fragments. Occurrence data from the Anamalais and SWG (N = 3004, range: 41 - 706 per species) were used to model distributions using maximum entropy (maxent) species distribution modelling in R. Maxent model performances indicated excellent fits for 9 of 11 species (AUC>0.90) with precipitation and temperature variables showing higher permutation importance. There was high interspecies variability in range size (197 - 12,221 km2) and niche width (0.04 - 0.50). Models of distribution under future climate in 2061 - 2080 predict range reductions in six species (including near-extinction for two species), increases for three species, and no substantial change for two species. Predicted southward and westward shifts in ranges and persistence in parts of the SWG indicate the importance of identifying and conserving micro-climatic zones or refugia to ensure the persistence of tree species under anticipated climate change.

ecology↗

bioRxiv2023

Structure and dynamics of secondary and mature rainforests: insights from South Asian long-term monitoring plots

We assessed tree community and carbon dynamics over 5 years in two 1-ha long-term ecosystem monitoring plots, one each in mature tropical rainforests (MR) and 10-year post-agroforestry secondary rainforests (SR) in Indias Western Ghats mountains. Both plots were established in 2017 and monitored annually six times. We expected (1) higher tree diversity, distinct species composition, and greater carbon stock in MR; (2) higher carbon sequestration rates in SR; and (3) carbon dynamics shaped by growth and mortality in SR and MR, respectively. The SR plot had fewer species (67 vs. 84), stored substantially less carbon (76 vs. 193 Mg), and comprised a distinct community with fewer late-successional species than MR. SR gained 5.8 Mg carbon, due to tree growth exceeding losses from mortality, while in MR mortality exceeded growth and recruitment resulting in a 3.3 Mg carbon decline over five years. While MR had higher tree diversity, carbon stocks and relatively intact composition, the high rates of biodiversity and carbon accrual in SR highlight the conservation and climate significance of post-agroforestry secondary forests. Moderate carbon losses noted here in MR, as in other mature South Asian tropical forests, is a cause for concern under ongoing climate change.

ecology↗