Forest and population structure and regeneration dynamics of relict Dipentodon sinicus in southwestern China

Abstract

Dipentodon sinicus is an extant relict plant of East Asia. It is a small deciduous broad-leaved tree, the sole surviving representative of the Dipentodonaceae. We investigated forest features, population structure, and regeneration dynamics of forest stands containing this species in Caojian Forest Station of Yunnan Province and Yushe National Forest Parks of Guizhou Province, southwestern China. We identified six forest types: Carpinus kweichowensis-Liquidambar formosana-Lithocarpus glaber-Dipentodon sinicus forest (Type 1); Illicium simonsii-Salix matsudana-Schima khasiana-Dipentodon sinicus forest (Type 2); Dipentodon sinicus forest (Type 3); Dipentodon sinicus-Schima khasiana forest (Type 4); Dipentodon sinicus-Tetracentron sinense forest (Type 5); Pterocarya macroptera var. delavayi-Tetracentron sinense-Populus yunnanensis-Salix matsudana forest (Type 6). Among the six forest types, D. sinicus forest (Type 3) had the lowest values in species richness, Shannon-Wiener and Simpson's diversity indices. The maximum age of D. sinicus was 54 years, reaching 34 cm DBH, with 14 m maximum height. Its frequency distribution in DBH-and age-class displayed a sporadic pattern in various forests. Its regeneration was more active in D. sinicus forest (Type 3), Dipentodon sinicus-Tetracentron sinense forest (Type 5), and Carpinus kweichowensis-Liquidambar formosana- Lithocarpus glaber-Dipentodon sinicus forest (Type 1) than that in the other forests (Types 2, 4 and 6). D. sinicus' growth rate generally fluctuated from 1.15 to 5.62 mm/year. Its regeneration modes were seedlings and sprouts. Its seedling establishment depends on forest gaps formation by disturbances. It is clear that the population persistence of D. sinicus was maintained in habitats where natural disturbances were frequent.