Range contraction to a higher elevation: the likely future of the montane vegetation in South Africa and Lesotho

Abstract

AcknowledgmentsWe are grateful to three anonymous reviewers for their comments on this manuscript. We also thank Dr. V. R. Clark for the use of his plant occurrence database to provide independent evaluation occurrence records. AbstractGlobal climate change is a major challenge for the future with serious potential impacts on biodiversity. Biodiversity in mountains is particularly vulnerable as many montane species are adapted to narrow microhabitats, making them less able to adjust to a climatic change. It is considered important to investigate range changes in the South African Great Escarpment because of the high levels of biodiversity in these mountains, as well as their importance for water provision in South Africa. The current and future ranges of 46 montane plant species in South Africa and Lesotho were therefore modelled using biomod in R, using presence points and predictor variables which included rainfall and temperature worldclim layers. The performance of distribution models produced was evaluated using the Area under the Receiver Operating Curve (AUC), True Skill Statistic (TSS), Sensitivity and Specificity. We calculated beta diversity and species richness changes between current and future climates for the group of 46 species, as well as shifts of the predicted presence region boundaries and centroids. We also analysed shifts in minimum, median and maximum elevations. Results show a contraction in species' ranges towards higher elevation as has been documented from other mountain regions around the world. These results are a cause for concern as a warming climate is decreasing the potential regions of occurrence of montane species in South Africa and Lesotho's mountainous regions of high biodiversity. This region is under a diverse range of conservation and land use management practises, and our results suggest a coordinated response to climate change is needed.

Repeated surveying over 6 years reveals that fine-scale habitat variables are key to tropical mountain ant assemblage composition and functional diversity

“…In addition to ant assemblages varying with both altitude and aspect, horizontal vegetation cover also influenced species composition ( Table 2). We observed that the primary driver of species assemblages is altitude, which may be unsurprising, given that ectothermic species are more vulnerable to temperature fluctuations than endotherms, and species found at higher elevations occur in naturally isolated altitudinal niches 4,63 . Elsewhere, ant species occurring at higher altitudes have been found to occur at those elevations because they can tolerate cold temperatures better than more dominant species found at lower elevations either through physiology or behaviour 3,21 .…”

“…For example, the median altitudinal range change is 11 m upwards per decade 1 . Mountain-dwelling assemblages often include many endemics adapted to narrow niches, isolated in a landscape matrix that limits dispersal 2 – 4 . These assemblages are particularly susceptible to climate change, as high-altitude zones should experience faster rates of warming 5 .…”

“…The region is vulnerable to global change, currently experiencing reduced summer rainfall, elevated surface temperatures, and widespread, more frequent droughts 23 , 30 . Recent models reveal contraction of species’ ranges at higher elevation from montane regions in two southern African countries 4 . In our study site, ants show a decrease in species diversity with increasing altitude 18 , and at higher altitude sites, diversity over time seems to be more variable 31 .…”

Festuca drakensbergensis (Poaceae): A common new species in the F. caprina complex from the Drakensberg Mountain Centre of Floristic Endemism, southern Africa, with key and notes on taxa in the complex including the overlooked F. exaristata

“…and Helichrysum spp.). Future projections of global climate change are also of concern for high-elevation species in southern Africa ( Bentley et al 2019 ). Accordingly, we propose the IUCN conservation status of Near Threatened ( NT ) until further population studies can be undertaken.…”

Limits to resilience of Afroalpine vegetation to grazing and burning: a case study of grasses from the Drakensberg Mountain Centre, southern Africa

“…and entrenches poverty cycles (Adelabu et al, 2020;Carbutt, 2020;Turpie et al, 2021). Added to this is the threat of global warming, with projected range contraction of montane vegetation to higher elevations and subsequent biodiversity loss (Bentley et al, 2019). Despite these threats, Afroalpine grasslands of the DMC remain understudied regarding their response to human influence, with most ecological, paleoecological and floristic research focused on lower-elevation Afromontane grasslands of southern Africa (e.g.…”