Abstract:

Objective: Improving forest quality is one of the main tasks of China's forestry construction in the new period, and biomass and productivity are the two important indicators of forest quality. Poplar(Populus spp.)is the most planted broad-leaved tree species in China. Developing biomass models and analyzing impact of climate factors to productivity of planted poplar trees has an important practical significance. Method: Based on the mensuration data of above- and below-ground biomass from 450 and 147 destructive sample trees of planted poplar, respectively, collected from 15 provinces in China, one- and two-variable simultaneous biomass equations were developed using dummy variable modeling approach and error-in-variable simultaneous equation approach; and based on the paired data of diameter, height, and age of sample trees, individual tree growth models with climate factors were established. According to the individual tree diameter and height growth models and two-variable biomass equations, effects of climate factors on productivity of planted poplar trees were analyzed. In addition, based on the data of planted poplar plots of national forest inventory(NFI), the biomass and productivity of each plot were calculated, and linear regression model between productivity of planted poplar forests and climate factors was developed, which would verify the effects of climate factors on productivity of trees. Result: The coefficients of determination(R²)of one- and two-variable aboveground biomass equations for planted poplar trees developed in this study were above 0.90, and the mean prediction errors(MPEs)were within 5%; whereas the R² of belowground biomass equations were above 0.83, and MPEs were within 10%. The R² of individual tree diameter and height growth models with climate factors were above 0.70, and MPEs were within 5% and 3%, respectively. The diameter and height growth of planted poplar trees were significantly related with mean annual temperature(T). The diameter at breast height, tree height, and total biomass of a 20-years-old planted poplar tree on site for T=20℃ are 2.4, 2.4, and 9.5 times of those on site for T=0℃, respectively. The verification result using the data of NFI plots show that average productivity of poplar plantations can increase 2.5 t·hm^-2a^-1 with an increase of 10℃ for mean annual temperature, and the productivity of poplar plantation on site for T=20℃ is more than 7 times of that on site for T=0℃, which is consistent with the comparable results from developed growth models. Conclusion: The above- and below-ground biomass equations and the compatible biomass conversion factor and root-to-shoot ratio models developed for planted poplar trees in this study could meet the needs of precision requirements to relevant regulation, and could be used in application. Temperature is an important factor affecting the productivity of planted poplar trees. With the increase of mean annual temperature, the productivity of planted poplar trees increases accordingly.

Key words: biomass, productivity, dummy variable, error-in-variable, simultaneous equations