Climate change drives plant diversity attrition at the summit of Mount Kenya

Abstract

Introduction

Mountains play crucial roles in sustaining biodiversity by simultaneously serving as cradles, museums, or graves (Rangel et al., 2018; Rahbek et al., 2019), and are vital for the survival and sustainable development of human societies (Perrigo et al., 2020). The long-term changes in temperature and precipitation regimes driven by global warming have the potential to cause significant shifts in the elevational distributions of mountain species, thereby increasing the exposure of mountain biota to extinction risks with important consequences on human societies (Lenoir et al., 2008; Moritz et al., 2008; Lenoir & Svenning, 2015; Pecl et al., 2017).

Over the past century, numerous studies have investigated species elevational range shifts for terrestrial plants, animals, and even fungi, reporting upslope range shifts in response to anthropogenic climate change (Lenoir & Svenning, 2013; Freeman et al., 2018; Vitasse et al., 2021; Zu et al., 2021). Temperature has long been recognized as the primary factor limiting the distributions of plants and animals along elevational gradients in mountain systems (Chan et al., 2024). However, the widely held and oversimplified hypothesis that increasing temperature is the main driving force behind species range shifts overlooks the potential compounding impact of changes in precipitation regimes (Crimmins et al., 2011; Zu et al., 2022) and other abiotic as well as biotic factors (Lenoir et al., 2010). For instance, notable downslope shifts of mountain plants in California have been explained by species' niche tracking of regional changes in climatic water balance rather than temperature (Crimmins et al., 2011). Simultaneously, the substantial decrease in precipitation in the high-elevation regions of Mount Jinfo in China has caused native plants to migrate downslope (Zu et al., 2022). We speculate that the increase in temperature caused by climate warming generally promotes the migration of plants towards higher elevations, but a concomitant decrease in precipitation caused by climate warming at high elevations in mountainous regions could have the opposite effect, prompting plants to migrate downslope. Here, we used plant distribution data sourced from herbarium records of a tropical African mountain (i.e. Mount Kenya) to explore the effects of climate change, specifically the contrasting changes in temperature and precipitation regimes between upland (> 3100 m above sea level, asl) and lowland (≤ 3100 m asl) vegetation belts, on the migration patterns of seed plants.