Growth of bamboo Fargesia qinlingensis and regeneration of trees in a mixed hardwood-conifer forest in the Qinling Mountains, China

Abstract

Gap characteristics and effects of gaps on plasticity of Fargesia qinlingensis and tree regeneration were studied under canopy, and in small, medium, and large gaps in a mixed hardwood-conifer forest in the Qinling Mountains, China. Gap formation was mainly tree snapping (40%). Gapmakers were dominated by Betula albosinensis and Abies fargesii (85%). Gap area ranged from 23.8 to 594.2 m 2 and averaged 178.4 m 2. In the canopy layer, 148 adult trees and 13 species were recorded. Gaps had an obvious effect on population parameters and morphological plasticity of F. qinlingensis. Large gaps had higher densities of dead culms, lower shoot percentages, and higher dead culm percentages, suggesting that intraspecific competition for resources was stronger in large gaps. Bamboo branch angle was larger under closed canopy, indicating a lower degree of self-shading, which may facilitate light acquisition and thus enhance plant growth. Tree composition in understory was different than in canopy. Shade-tolerant species ( Malus baccata, Acer maximowiczii, and Prunus pilosiuscula) dominated the understory, while B. albosinensis, A. fargesii, and Betula utilis dominated the canopy. Tree species dominating under canopy were the same as in gaps, consisting of shade-tolerant canopy species and a few sub-canopy species. Tree seedling density and diversity were low in understory, implying an inhibitory effect (ecological filter) of dense culms on seedling establishment. Further, gap sizes occurring in the mixed hardwood zone were generally small and regeneration of shade-intolerant species was limited to the few larger gaps. Seedling density was higher in medium gaps than in large gaps and under canopy, largely due to two sub-canopy species ( M. baccata and P. pilosiuscula). Density of A. maximowiczii was similar under canopy and in various sized gaps. Age structure showed that most saplings ≥14 years old were shade-tolerant A. maximowiczii. Results suggest that current dominance of B. albosinensis, A. fargesii, and B. utilis may be replaced by shade-tolerant species such as A. maximowiczii.