Regional tree migration outpaces local migration due to fragmentation and life history traits

Predictions of tree species range shifts have emphasized regional migration rates, while how local migration drives regional migration remains poorly understood. Landscape fragmentation is a major source of migration lag, but its interactions with species life history traits remain understudied. We aimed to clarify mechanisms underlying differences between local and regional migration rates, quantify how fragmentation and life history traits jointly shape migration, and assess temporal variation in these effects. We quantified local and regional migration rates of temperate tree species with contrasting life history traits across fragmented landscapes. LANDIS PRO incorporated key demographic processes, including seed dispersal, colonization, establishment, growth, and mortality. We assessed direct and interactive effects of fragmentation over short (0–30 years), medium (30–65 years), and long (65–100 years) timescales. Regional migration was nearly five times faster than local migration, and increasing fragmentation reduced regional migration and increased migration lags. Fragmentation more strongly constrained regional migration, whereas, among the six focal species, life history traits such as maturity age and seed production showed stronger associations with local migration. Direct effects dominated in the short term, but interactive effects became increasingly important over time, consistent with accumulating demographic delays in fragmented landscapes. Our results show that patch dynamics help explain why regional migration outpaces local migration, but reliance on regional leading-edge migration rates alone could overestimate assisted-migration distances. Comparisons among the low-, medium-, and high-fragmentation scenarios with equal habitat amount indicate that fragmentation per se can constrain regional migration independently of habitat amount. Its interaction with life history traits was consistent with demographic feedback involving seed-source reduction and delayed reproduction, which may progressively slow leading-edge dynamics and increase extinction risk. Maintaining connectivity and reproductive sources is essential to reduce demographic delays and support long-term persistence in fragmented forests.