Plant community distribution induced by microtopography due to soil cracks developed in overgrazed alpine meadows on the Tibetan Plateau

Microtopographic variation is a common feature of natural ecosystems. On the Tibetan Plateau, this variation includes soil cracking that influences the dynamics of soil nutrients and seed trapping, which further affect species distributions. Despite their importance, cracks in alpine meadows have rarely been reported, and the effects of cracks on soil properties and plant distribution are poorly understood. Therefore, we investigated the effects of microtopography induced by cracking on the soil properties, seed trapping, and plant community composition of crack mosaics in alpine meadows. The study focused on healed cracks that can recover from winter cracking and have not yet become irreversibly degraded. The results showed that the number of seeds in the healed cracks was significantly greater than that in the raised areas, by 2.37-times. The soil chemical parameters in the healed cracks were significantly higher than those in the raised areas. There were also significant differences in the soil physical parameters between these two positions of the mosaic. Differences in species richness and importance values, and their dynamics (2013-2018), were correlated with these two spatial positions in the crack mosaics. Soil physical and chemical parameters together explained 71% of the plant community composition on the crack mosaics, and the interaction effect explained 52.4%. To some extent, crack mosaics composed of microtopography units favour the conservation of water and nutrients in the healed-crack portion of the mosaic. We propose that cutting kobresia lawns will facilitate the repair of ecological processes and initiate a natural recovery in overgrazed alpine meadows.