Sex-specific responses of tree-ring growth to climate in the dioecious tree Populus cathayana

Aims Radial growth in response to climate has been reported in many trees,but the sex-specific responses of tree-ring growth associated with altitude in dioecious trees are still poorly known.This study aims to examine whether(i)there are sex-related responses of tree-ring growth to climate in dioecious trees;(ii)these responses could be changed with altitude elevation.Methods The tree-ring width and basal area increment(BAI)were measured over the past 30 years(1982-2011),and the sexual differences in relationship between BAI and time span and correlations between ring width and climatic factors were investigated in Populus cathayana trees at two altitude sites(1,450 m and 1,750 m a.s.l.)in Xiaowutai Mountain,Hebei,north China.Important Findings The BAI was increased over the past 30 years.Trees at high-altitude sites had significantly lower mean ring width and mean BAI than those trees at low-altitude sites(P<0.001).In addition,sexual dif-ferences in tree-ring growth and its response to climate were more pronounced by altitude elevation.Male trees had a significantly larger mean ring width and mean BAI than did females at high-alti-tude sites,whereas no significant sexual differences in these traits were detected at low-altitude sites.Female trees were sensitive to previous October-November temperatures at high altitude but to current February and April precipitation at low altitude(P<0.05),whereas male trees were sensitive to current June temperature at high altitude but to January precipitation at low altitude(P<0.05).Our results indicated that the responses of tree-ring growth to cli-mate are sex dependent and can be changed with altitude elevation.