Successful seedling recruitment on a reclaimed hillslope provides insight into successful regeneration in the endangered Japanese red maple (Acer pycnanthum)

Abstract

The Japanese red maple, Acer pycnanthum, is an endangered tree species found in hilly regions of Tokai District, Japan. The lack of successful natural recruitment in A. pycnanthum has generated increasing concern for its population-level persistence. Recently, we found abundant A. pycnanthum saplings on a reclaimed hillslope at a housing complex in Higashiyama in Gifu Prefecture. These saplings had seeded from a single female tree in the neighbouring forest and were thriving under improved light conditions. In this study, we examined the survival, reproductive condition, diameter at breast height (DBH) and tree height of these saplings to elucidate the regeneration traits of A. pycnanthum. All saplings on the reclaimed slope were distributed within a 50-m radius of the likely parent tree. Seedlings near the forest edge grew faster than those farther away; the factors contributing to this gradient remain unknown. DBH and tree height were highly correlated. Only four seedlings, all of which had DBH > 10 cm and tree height > 8 m, had ever flowered. Based on their shoot structure, we estimated that the three male saplings had a height of 8.9 m in their first flowering year. In contrast, the height of the single female sapling was approximately 10 m when it first flowered in 2020. These data suggest that males reach maturity earlier than females. The largest sapling flowered consecutively after reaching a height of 11 m. Because only two female trees currently remain in the neighbouring forest stand, new reproductive trees of both sexes will contribute to the long-term persistence of this population.