Age structure and regeneration strategy of the dominant species in a Castanopsis carlesii-Schima superba forest

Evergreen broadleaved forests (EBLFs) is the zonal forest ecosystem of the subtropical zone in east China and have been degraded from intense recent anthropogenic disturbance. Studies of age structure of main tree species in EBLFs may provide an insight into their regeneration patterns and understand the role of disturbances in EBLFs, which are helpful to restoration of the degraded EBLFs. We constructed age structure of Schima superba, Castanopsis carlesii and Lithocarpus glaber which are the dominant species in an EBLF in Tiantong National Forest Park, Zhejiang Province, east China. All trees in two 20m ×20m plot were collected and dendroecological technique was used to measure the age of individual taller than 1. 5m, while the age of individual lower than 1. 5 was determined by counting bud scale scars. The regression relationship between DBH / H and age were established and were used to calculate the age of individuals that can not be directly measured. The value of DBH / H was used to indicate the slender degree of trunk, meanwhile the percentage of multi-stemmed individuals in all individuals (PMSI) and the sprouts number of multi-stemmed individuals (NSMS) were used to indicate the sprouting ability. The trends of DBH / H, PMSI and NSMS with increasing age were compared among 3 species. The results were shown as follows: (1) The relationship between DBH/ height and age could be well fitted by linear regression and logistic regression for three species, but these relationships collapsed with increasing age. (2) The value of DBH / H increased with age for three species and the value of PMSI and NSMS decreased with age at the young stage for Castanopsis carlesii and Lithocarpus glaber. The seedlings and saplings of Castanopsis carlesii and Lithocarpus glaber had more slender trunk and more sprouts than Schima superba, but the adults of Castanopsis carlesii had more thick truck than Schima superba and Lithocarpus glaber. It indicated that Castanopsis carlesii performed an exploiting regeneration strategy and Schima superba performed a conserved regeneration strategy in the whole life history, while Lithocarpus glaber changed the exploiting strategy in young stage into conserved strategy in mature stage. (3) The age structure of Castanopsis carlesii and Lithocarpus glaber exhibited an inverse-J type with plenitudinous recruitments, but there were a gap in the middle age class (21-40 year old) which was determined by its exploiting strategy with high exhaustion rate. The age structure of Schima superba exhibited a multimodal type with stead death rate, which was related to its conserved strategy. (4) There was a recruitment peak in the 52-60 year age class for three species, which was in accord with the time of documented selective-logging period. This intense disturbance led to secondary succession and created a high-light environment for abrupt recruitment of Schima superba. (5) All the results suggested that the age structure of each species was the synergy consequence of the regeneration strategy and historical disturbances. The age structure not only could be used to show the regeneration pattern and predict the dynamics progress as with the size distribution, but also could accurately reveal the frequency and timing of vital dynamics events.