Effects of tree cutting and mowing on plant species composition and diversity of the wetland ecosystems dominated by the endangered maple, Acer pycnanthum

Abstract

Japanese red maple, Acer pycnanthum, is an endangered species that grows only in small, discrete wetland ecosystems in central Honshu, Japan. Because of its rarity and beauty, public attention and management are typically focused only on this overstory species. For example, mowing and tree cutting of understory and ground-cover plants are practices frequently applied to develop easily accessible, park-like stands. To examine the ecological effects of these practices and discuss the role of silvicultural practices in conservation of these ecosystems, plant species composition and diversity were studied at six, unmanaged near-natural ecosystems, and they were compared with that of one managed ecosystem where tree cutting and mowing have been conducted. In addition, changes of plant species composition and diversity were investigated at one site where tree cutting was conducted. Results indicated that the near-natural ecosystems are characterized by high plant species diversity, consistent occurrence of endangered and endemic species, and virtual lack of non-native species. Plant species diversity was markedly greater in the understory and ground-cover layers than in the overstory, which was characterized by high abundance of large maple trees. In contrast, at the ecosystem where tree cutting was conducted and the ground cover annually mowed for 18 years, stem density and diversity of the understory layer were extremely low compared to those of the near-natural ecosystems. In the ground-cover layer, the species composition was markedly different from that of the near-natural ecosystems due to the presence of non-native species and species favoring open, disturbed habitats. After two years at the ecosystem where tree cutting only was conducted, a significant decrease of diversity index H′ was recorded in the ground cover. The decrease was in large part due to the spread of dwarf bamboo, which was favored by increased light irradiance. At both managed ecosystems, regeneration of Japanese red maple was lacking. Because of these dramatic changes, intensive silvicultural practices should be restricted to a few exceptional places where public interest is paramount. I recommend that silvicultural practices only be used for significant and specific conservation purposes, such as removal of invasive species. Special concern regarding the spread of dwarf bamboo is required when managers plan tree cutting at sites where the bamboo grows within or adjacent to the site.