Overstory functional groups indicate the legacy of land use in a secondary tropical forest in southwestern China

Anthropogenic disturbances are widespread in tropical forests and influence the species composition in the overstory. However, the impacts of historical disturbance on tropical forest overstory recovery are unclear due to a lack of disturbance data, and previous studies have focused on understory species. In this study, the purpose was to determine the influence of historical disturbance on the diversity, composition and regeneration of overstory species in present forests. In the 20-ha Xishuangbanna tropical seasonal rainforest dynamics plot in southwestern China, the historical disturbance boundaries were delineated based on panchromatic photographs from 1965. Factors that drove species clustering in the overstory layer (DBH ≥ 40 cm) were analyzed and the abundance, richness and composition of these species were compared among different tree groups based on multiple regression tree analysis. The coefficient of variation of the brightness value in historical panchromatic photographs from 1965 was the primary driver of species clustering in the overstory layer. The abundance and richness of overstory species throughout the regeneration process were similar, but species composition was always different. Although the proportion of large-seeded and vigorous-sprouting species showed no significant difference between disturbed and undisturbed forests in the treelet layer (DBH < 20 cm), the difference became significant when DBH increased. The findings highlight that historical disturbances have strong legacy effects on functional group composition in the overstory and the recovery of overstory species was multidimensional. Functional group composition can better indicate the dynamics of overstory species replacement during secondary succession.