Positive heterospecific interactions can increase long-term diversity of plant communities more than negative conspecific interactions alone

1. Negative conspecific interactions have been shown to promote diversity in plant communities, as have some heterospecific interactions such as intransitive competition and facilitation. However, it is unclear whether combinations of conspecific and other heterospecific interactions can also promote diversity in plant communities. We therefore investigated the effects of heterospecific plant interaction network architecture with and without conspecific interactions on alpha diversity, beta diversity and long-term diversity. 2. We simulated long-term plant community dynamics for theoretical plant interaction scenarios with modular, ring and nested networks of positive or negative heterospecific interactions and conspecific interactions, using a spatially explicit cellular automaton model that accounted for stochastic effects. Throughout the simulations several measures of diversity were recorded. 3. The way that heterospecific interactions affected diversity depended strongly on various characteristics of the architecture of the interaction network. Negative conspecific interactions generally promoted alpha diversity and reduced beta diversity, with a few key exceptions. Positive heterospecific ring interactions that resulted in cyclic appearance and disappearance of species groups led to the greatest long-term diversity (a measure of the total diversity over time). 4. This study provides new theoretical insights into how the network architecture of heterospecific plant interactions can affect the diversity of plant communities over time and provides the first evidence that heterospecific plant interactions can increase long-term diversity more than negative conspecific interactions alone.