秦岭火地塘林区油松和华山松林乔木层净生产力与气候因子的关系

以秦岭火地塘林区油松(Pinus tabulaeformis)和华山松(Pinus armandi)林为研究对象,以其生物量及树高-胸径模型为基础,运用树木年轮宽度方法推算出1973年至2011年生物量和生产力年际动态,并通过相关分析和多元逐步回归分析探讨了油松和华山松林乔木层净生产力与温度、降水之间的关系。结果显示,该林区油松林和华山松林乔木层生物量39a间增长迅速,分别从1973年的15.32 t/hm2和7.53 t/hm2增长到2011年的175.97 t/hm2和130.98 t/hm2,平均年净生产力分别为4.18 t hm-2a-1和3.20 t hm-2a-1,油松林乔木层生物量和生产力均高于华山松林;气候分析表明年净生产力与降水关系不明显,与温度关系较为密切,随气温升高呈波动上升趋势:单月气候因子中上年7月温度、当年7月温度与油松林乔木层净生产力显著正相关,上年7月温度与华山松林乔木层净生产力显著正相关;油松林乔木层净生产力动态变化主要受1—7月平均温度影响,华山松林主要受5—7月平均温度影响;油松林生产力与温度因子的相关性高于华山松林。两种林型的生物量和生产力差异是由油松和华山松生物学特性所致。

Relationship between net primary productivity of tree layer in Pinus tabulaeformis and Pinus armandi forests and climatic factors at Huoditang forest region in the Qinling Mountains

The Qinling Mountains have some of the best sites for research on impact of climate change on forest growth in China. We selected two main forest types in the mountains, Pinus tabulaeformis and Pinus armandi forests, to explore relationships between net primary productivity (NPP) of the tree layer and climatic factors in order to understand response of the growth to climate change. Nine plots of P. tabulaeformis and fifteen plots of P. armandi forests were established at the Huoditang forest region in the Qinling Mountains. More than 20 cross increment cores were extracted from different trees at each plot. After being cross dated by the skeleton diagram method, tree ring widths of increment cores were measured with WINDENDRO tree ring system. Annual diameters of sample trees were calculated using tree ring widths. Regression equations between diameter at breast height (DBH) and height of P. tabulaeformis and P. armandi forests at the Huoditang forest region were used to estimate the annual biomass and NPP from 1973 to 2011. Then correlations were analyzed between NPP and climatic factors including monthly and seasonal temperature and precipitation. Multiple stepwise regression analysis was used to select the climatic factors with the most impact on the annual NPP of the two forest types. A relatively consistent dynamic trend was found in the biomass and NPP of the two stands. The biomass of P. tabulaeformis and P. armandi forests increased dramatically in the past 39 years from 15.32 t/hm² and 7.53 t/hm² to 175.97 t/hm² and 130.98 t/hm², respectively, and the mean annual NPP were 4.18 t hm^-2 a^-1 and 3.20 t hm^-2 a^-1 respectively. Higher biomass and NPP of the tree layers were found in P. tabulaeformis compared to P. armandi forests. No significant correlation was observed between the NPP and monthly and seasonal precipitation; in contrast the NPP was closely correlated with the monthly and seasonal temperature. Among the monthly temperature factors, the temperature in July of the previous year correlated positively with NPP for P. tabulaeformis and P. armandi forests. Also the temperature in the current July correlated with NPP in the same year in P. tabulaeformis forests. Among the seasonal temperature factors, a significant coefficient was observed between the NPP of P. tabulaeformis forests and the mean temperature from January to July. A significant coefficient was observed between the NPP of P. armandi forests and the mean temperature from May to July; higher coefficients were found between the NPP of and climatic factors in P. tabulaeformis forests than that in P. armandi ones. The difference in the biomass and productivity between two kinds of forest types are due to their different biological characteristics.