A new model for secondary plant succession based on the herbaceous communities of soil mounds on the Tibetan Plateau

Zokors (Myospalax baileyi), small rodents on the Tibetan Plateau, create fresh soil mounds through burrowing in herbaceous plant communities. Secondary succession on these soil mounds is likely structured by both stochastic processes and deterministic environmental changes. However, existing models have not explicitly integrated their interaction to simulate secondary succession in herbaceous communities. Here we introduce a cohort-based succession (CBS) model that incorporates patch dynamics (including the creation and aging of patches) and environmental changes (e.g. soil compaction) within patches as they age. Our model incorporates plant reproduction and growth on soil mounds, with resource consumption depending on the environmental conditions within the patch. Besides these deterministic processes, the regenerating plant communities experience stochastic demographic processes. Field data validated the CBS model, confirming accurate predictions of multiple aspects of succession on the soil mounds: it reproduced hump-shaped trends in the proportions of mounds with successional stage, and generated positive trends in plant species richness, biomass, and evenness, and negative trends in plant species dissimilarity with successional stage. These patterns emerged from the combined effects of environmental changes and stochastic processes. Many dominant plant species were replaced during succession as a result of environmental changes, but a few species such as Potentilla anserina Linn were able to adapt and therefore persist. Our model also predicts declining biomass with increased disturbance during succession. This is the first time that a cohort-based model has been applied to plant succession, highlighting the importance of both stochastic process and environmental changes in structuring herbaceous plant communities.