Application of the 3-PG model to predict growth of Larix olgensis plantations in northeastern China

Larch plantations play an important role in timber production and ecological benefits in China. However, our ability to quantitatively predict the growth at regional level is limited. The 3-PG model based on physiological principles is widely used to predict the stand growth of different types and to simulate the effects of forest management, climate change and site characteristics. This paper presents an assessment of the ability of the 3-PG model to simulate height, diameter at breast height (DBH), stocking, stand density and biomass partitioning in 81 plots of Changbai larch (Larix olgensis) plantations across Jilin Province, northeastern China. The results showed that 3-PG model can adequately estimate stand density, DBH, biomass partitioning, with determination coefficients (R2) between observed data and simulated data always higher than 0.93. The mean relative errors (MRE) of all indicators were below 15%. Except stocking, relative root mean square errors (RRMSE) of other indicators were below 20%. To improve the accuracy, we propose to modify the parameter values of fertility rating (FR) and age at canopy cover (fullCanAge) obtained by default so as to adjust growth rates of Larix olgensis plantations to the changeable weather condition in Jilin Province. Sensitivity analysis showed that FR and fullCanAge are the key parameters of the model. The results provided strong evidence that 3-PG can be applied over a wide geographical range using one set of parameters for Larix olgensis. The model can also be applied to estimate the impact of climate change on stands growing across a wide range of ages and stand characteristics.