Variation in CSR plant strategies along soil and climate gradients: A comparison between rocky outcrops and nearby rangelands

Question

Rocky outcrops in mountains represent unique ecosystems characterized by a series of stress-inducing features on living organisms. Despite numerous studies focusing on plant diversity and species community composition in these ecosystems, less attention has been given to understanding plant strategies in response to their challenging environment. This is essential, especially considering the existence of numerous endemic species facing climate change and human disturbances.

Location

The study was conducted in six sites located in rocky outcrops and their nearby rangelands across a rainfall gradient (160–910 mm) and under different soil fertility levels in northern Iran.

Methods

We used competitor, stress tolerator and ruderal (CSR) strategies as functional groups to examine the responses of plant communities to environmental variation. The composition of plant species and functional traits were evaluated in ninety 1-m² plots. The influence of 10 soil and 5 bioclimatic factors on CSR plant strategies was examined along the rainfall gradient.

Results

Our results showed changes in CSR strategies from stress-tolerant species (S) in rocky outcrops toward intermediate strategies (S/CSR) in rangelands. Soil organic carbon, electrical conductivity and sand were consistently correlated with shifts from S towards C and R strategies in rangelands. Silt and sodium (Na) affected the presence of S strategies in outcrops. The stressful conditions induced by a fine soil texture and Na in outcrops were particularly effective in establishing the dominance of the S strategy.

Conclusions

We identified patterns of shifts in CSR plant strategies that align with changes in environmental gradients. Although stress-tolerant species (S) were the dominant strategy in most cases, this shifted towards intermediate strategies (SR and CSR) under more benign environmental conditions. In outcrops, these changes were primarily aligned with soil parameters, whereas in rangelands, both soil and climate variables were correlative. However, these correlations varied between soil and climate factors, as well as between outcrop and rangeland landscapes.