Seed dispersal drives competition between pair-growing trees: implications for forest community dynamics

Seed dispersal by animals and wind may form pair-growing trees (PGTs) and influence forest community dynamics via competition, but such impacts are hardly assessed, especially at the growth stage. In a temperate forest in Northeast China, we assessed the dependency probability, health, and growth of single-growing trees (SGTs) and PGTs of three dominant conifers: Abies nephrolepis (a highly shade-tolerant species currently dominant in secondary forests, wind-dispersed with potential animal secondary dispersal), Pinus koraiensis (the dominant climax species of primary mixed forests, animal-dispersed), and Picea jezoensis (a shade-tolerant species commonly associated with primary forests, wind-dispersed with animal secondary dispersal). We found that A. nephrolepis in PGTs had a higher proportion of unhealthy individuals than conspecific SGTs; heterospecific PGTs of all three species showed significantly lower relative growth rates than their SGTs (10–18% reduction); P. koraiensis and P. jezoensis had a competitive advantage over A. nephrolepis. These results reflect asymmetric competition driven by species differences in growth rate and shade tolerance (with A. nephrolepis being more shade‑tolerant than the other two). Our study provides the first evidence that scatter-hoarding animal- and wind-driven seed dispersal increase resource competition among PGTs during the growth stage, potentially influencing long-term community composition by favoring the performance of climax species within secondary forest matrices.