Occurrence and landscape ecology of a rare disjunct maple species,Acer pycnanthum, and comparison withAcer rubrum

Abstract

Japanese red maple, Acer pycnanthum K. Koch, is the disjunct sister species of the red maple, Acer rubrum L. Whereas A. rubrum is one of the most widely distributed and abundant species in eastern North America, A. pycnanthum is rare in central Honshu, Japan. Although its morphological similarity to A. rubrum is well known, little is known about the sites and communities where it occurs, its natural history characteristics, sexual and asexual regeneration, and the reasons for its restricted occurrence. We located and described all known sites, totaling <18 ha, which supported populations of three or more clones. Twenty-seven of the 30 ecosystems described are remnant natural populations, which are confined to lower slopes of three river basins where wetlands have persisted and recurrently formed for millions of years due to unique geological, topographic, and soil properties. Acer pycnanthum, an obligate species of forested wetlands, occurs on diverse seepage and floodplain ecosystems that are characterized by poor drainage; acid, wet soils; high understory and ground-cover diversity, and associated rare species. The area occupied by each population is typically very small, usually <0.5 ha and often <0.2 ha. Regeneration is limited to sites with high light irradiance following disturbance. Because of the rarity of natural wetland sites, its inability to colonize upland sites occupied by dense natural vegetative cover or by planted conifers, and the encroachment of agriculture and urbanization, the occurrence of A. pycnanthum is increasingly limited. Using an ecosystem approach, conserving whole ecosystems, including their total vegetative diversity, is a high priority.Key words: biodiversity, disjunct species, landscape ecology, rare species, red maple (Acer pycnanthum, Acer rubrum), wetlands.