Is fruit plasticity greater in an alien than in a native tree? A case study of the Tree of Heaven and the Narrow-leaved Ash

Abstract

Seed dispersal has been reported to influence many ecological aspects of plant biology such as community assembly, distribution patterns, population dynamics, genetic flow and invasion potential. Diaspore traits in wind dispersed plants such as weight, wing area, and pappus length should be optimized to balance the costs and benefits of dispersal. Nevertheless, selection could also favor adaptive intraspecific variation, linking dispersal traits to maternal environmental conditions. This study assessed intraspecific variation in diaspore traits of two cohabiting wind-dispersed tree species, the native Fraxinus angustifolia and the invasive Ailanthus altissima, across two contrasting habitats: road verges, characterized by disturbed, nutrient-poor soils, and riverbanks, with well-developed soils, higher water availability, and stronger competition. We hypothesized that such intraspecific variation may enhance the adaptive capabilities of A. altissima, contributing to its success as an invasive species. Our results showed that although both species exhibit variation in samara traits, only A. altissima presented habitat-dependent differences. When growing on road verges A. altissima produced heavier samaras than when growing in riverbanks, although dispersal potential of samaras remained unaffected.