| A mathematical model for interacting plant communities in water-limited systems is introduced and studied. Two positive feedbacks between biomass and water are found to be of crucial importance for understanding interspecific interactions: water uptake by plants' roots and increased water infiltration at vegetation patches. The former depletes the soil water resource under a vegetation patch and induces interspecific competition and species exclusion. The latter concentrates the soil-water resource under the patch and induces facilitation and coexistence. The actual patch structure is determined by the relative strength of the two feedbacks, which in turn is affected by species traits, environmental conditions and spatial patterning. The model sheds new light on recent observations of plant interactions along aridity gradients which are apparently in conflict, and predicts the possible emergence of facilitation as a result of patch grouping. The model further highlights mechanisms by which vegetation pattern formation, at the landscape level, affects species exclusion or coexistence. |
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