Fire promotes passive directed dispersal by birds

Recent work proposes that passive directed dispersal (PDD) occurs when tracking resources leads animal vectors to sites that favor plant establishment. For example, wildland fire can attract seed-dispersing animals via the magnet effect while generating the environmental conditions that benefit common animal-dispersed plants. To test the hypothesis that frequent fire results in PDD in pine savanna, we first documented the effect of frequent fire on common bird-dispersed plants by measuring relative plant abundance and per-individual fruit production in a long-term replicated fire experiment. Focal plants occurred more frequently and produced more fruit per plant in plots burned biennially compared to plots that had been unburned for six decades. We then used a crossover Before-After Control-Impact (BACI) experiment to measure the responses of birds and bird-dispersed seed rain after fire. Despite fire increasing seed dispersal distance, the magnet effect of fire resulted in more seeds of focal plant taxa arriving in recent burns than in areas burned 1-2 years prior. Collectively, these results suggest that wildland fire promotes PDD. Given that fire is a globally pervasive process in terrestrial ecosystems, PDD may be an important mechanism shaping plant communities.