Plant ecology of tropical and subtropical karst ecosystems

Abstract

Substantial areas of tropical forests, including those within nine tropical biodiversity hotspots, contain karst landscapes that have developed on soluble carbonate rocks. Here, we review how the ecology of karst forest trees is influenced by hydrological, edaphic, and topographic factors that exhibit fine spatial heterogeneity. Comparative analysis of drought tolerance traits including wood density contributes to the assessment of whether karst tree species are more drought‐tolerant compared to non‐karst trees. Although karst ecosystems are generally considered to have low phosphorus availability, foliar nitrogen‐to‐phosphorus ratios exhibit wide variation across karst regions without a clear difference from non‐karst ecosystems. According to the analyses of leaf phenology, stem water storage, and isotopic signatures from xylem sap, water use strategies of karst trees can be classified into five types: (a) soil water dependent, (b) epikarst water dependent (mainly use water stored in fine pores and gaps within the epikarst rock during the dry season), (c) groundwater dependent, (d) fog water dependent, and (e) drought‐deciduous (shed leaves during the dry season). Overall, published data suggest that only a subset of karst tree species are exclusively distributed within karst hilltops where water availability is limited. The diverse resource acquisition and utilization strategies of karst plants across edaphic habitats must be considered when developing effective strategies to conserve and restore biodiversity in karst landscapes, which are under increasing anthropogenic pressure.

Topography strongly affects drought stress and xylem embolism resistance in woody plants from a karst forest in Southwest China

“…In this way, our results are consistent with previous studies, showing that topography can lead to soil water availability and fertility gradients from valleys to hilltops, so that shape the distribution and performance of species (Fortunel et al., 2018; Muscarella et al., 2020). The tropical and subtropical karst forests in Southwest China are at a global biodiversity hotspot with many endemic species (Geekiyanage et al., 2019), and are expected to encounter more severe water stress than other terrestrial ecosystems (Liu et al., 2016). Since the woody species studied showed a large variation in HSM, the karst forests in this region may be able to buffer increasing severity of future drought events due to their high hydraulic diversity (Anderegg et al., 2018).…”

What We Know and What We Do Not Know about Dragon Trees?

“…The southeast Asian Dracaena species belonging into the dragon tree group grow in tropical or subtropical areas with higher rainfall than the previous groups, but they are usually associated with cliffs and the tops of limestone rocks in karstic landscapes [9,10,202,203], where water availability is reduced due to relief and edaphic constraints [204].…”

“…The few studies mentioned above which focus on the population status and structure of dragon trees clearly indicate the high level of threat faced by these iconic species. Overgrazing [23][24][25][26]113,208], drought and aridification [20,31], global climate changes [11,18,181], long-term climate oscillation [209], the cutting of leaves, inflorescences, and fruits as fodder for livestock [14,17], longtime resin harvesting [27,32,203], and extraction of recruitment from the wild for use in horticulture [204] are all mentioned as the main factors in the decline of the population of dragon trees. Natural regeneration is mostly absent [11,14,17,26,112,181,207] and populations are overmature [20,56,207].…”

Water uptake depth is coordinated with leaf water potential, water‐use efficiency and drought vulnerability in karst vegetation

“…The shallow skeletal rocky soils typical of karst regions have very low water holding capacity, so rainfall water rapidly infiltrates into the deeper karst unsaturated (vadose) and saturated phreatic zones that can be reached by deep‐rooted plant species. The subtropical karst area of South China covers more than 0.54 million km 2 and has experienced rapid and intensive land use change and ecosystem degradation in recent times (Geekiyanage et al ., 2019; Green et al ., 2019). Abandonment of agriculture in steeply sloping terrain has led to extensive unmanaged regeneration of natural plant communities throughout degraded karst areas since the 1990s (Liu et al ., 2008; Brandt et al ., 2018).…”