Abstract
Japanese Red Maple (Acer pycnanthum) , a deciduous tree distributed in the Tokai Hill region, is ranked as VU (vulnerable) in the Red List of Japan, but is often planted as street trees. We found that American red maple A. rubrum, an exotic congener, is sometimes unintentionally introduced in these street trees. Our aim is to investigate the potential risk that the exotic species could threaten the populations of the native red maple, through various biological processes such as competition and hybridization. We first confirmed the usefulness of chloroplast genetic markers as a tool for identification of these maples, whereas Leaf Dissection Index (LDI) did not sufficiently distinguished them. Then we revealed that A. rubrum exhibited higher Pmax (maximum light-saturated photosynthetic rates) than A. pycnanthum under a dark condition, suggesting the invasiveness of the exotic maples into closed-canopy forests of A. pycnanthum. Moreover, artificial interspecific crossing between the indigenous and exotic maples yielded high seed set, suggesting successful hybridization between these maples would occur. It is urgently required to assess the state of the introduction of A. rubrum and to predict the biological impacts on indigenous plant community in more detail.
