The effects of global changes on tropical forests and savannas are manifested primarily at their boundaries. The dynamics at these forest-savanna boundaries depend on their shapes, which influence the spread of fires through the savanna landscape. How these boundaries are shaped depends on tree recruitment patterns, which differ between trees dispersed by wind and those dispersed by birds. Therefore, tree dispersal modes may have large effects on fire spread and subsequently on forest-savanna resilience. To study these effects, we developed a novel individual-based model of seed dispersal in savanna-forest ecosystems, and investigated the interactions among tree seed dispersal modes, spatial patterns of tree cover, and fire spread. We study forest resilience by measuring the maximum loss of tree cover from which the forest can recover. We find that forest recruitment rate and resilience are more sensitive to forest pattern morphology when trees are dispersed by birds than by wind. In addition, these effects are more pronounced for larger forest patches that are spaced further apart. Moreover, recruitment and resilience in bird-dispersed forests display high sensitivity to bird behavioral parameters, suggesting that the community composition of frugivorous birds may be an important indirect driver of forest resilience. Our findings demonstrate for the first time that interactions between spatial patterns of tree cover and tree dispersal modes may affect the resilience of tropical forests and savannas against tipping. Thus, efforts to understand the impact of global change on tipping points between forest and savanna should account for the effects of seed dispersal modes.

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