Aims While the phenomena that environmental stresses induce growth differentiations between male and female seedlings are confirmed by many controlled experiments in recent years, the potential impacts on adult trees of dioecious plants caused by climate change have not yet attracted much attention. In order to further reveal the differential effects of climate warming on the dendrological characteristics of female and male trees, a typical dioecious plant, Populus cathayana, was selected as a test material in the study.
Methods Wood samples were taken from 40 adult trees of P. cathayana (including 20 female and 20 male individuals, respectively). We employed the dendroclimatological approach to analyze the gender-specific differences in seven tree-ring variables (i.e. maximum ring density, latewood mean density, earlywood mean density, minimum ring density, annual ring width, earlywood width, and latewood width), and their differential responses to climate factors (monthly mean, minimum and maximum air temperature and precipitation) in Xiaowutai Mountains of China.
Important findings Firstly, with an increase in the local air temperature during the past 30 years (1982-2011), the male and female P. cathayana trees exhibited the similar trend in radial growth but with apparent differences in the pattern of density growth. Compared with the males, the female trees displayed significantly (p < 0.05) higher maximum ring density and latewood mean density. Secondly, there was a similar pattern of variations in the residual chronologies between the male and female trees, but the male trees showed much higher magnitude of variations than the female trees. Thirdly, based on the residual chronologies, it was found that the response months are quite different between the two sexes. For the female trees, maximum ring density had a significant positive correlation with the maximum air temperature in current August. However, the maximum ring density was significantly and negatively correlated with the air temperature in current January and April for the male trees. Fourthly, for trees of both sexes, climate change prior to growing season limited the radial growth while maximum air temperature in current June obviously restricted the growth of earlywood. These results indicate that there are different tree-ring growth strategies between trees of different sexes in response to global warming in dioecious plants, and that the female trees invest more in density growth than the male trees.