Abstract
Forest stand volume is one of the key forest structural attributes in estimating and forecasting ecosystem productivity and carbon stock. However, studies on growth modeling and environmental influences on stand volume are still rare to date, especially in subtropical forests in karst areas, which are characterized by a complex species composition and are important in the global carbon budget. In this paper, we developed growth models of stand volume for all the dominant tree species (groups) (DTSG) in a subtropical karst area, the Guizhou Plateau based on an investigation of the effects of various environmental factors on stand volume. The Richards growth function, space-for-time substitution and zonal-hierarchical modeling method were applied in the model fitting, and multiple indices were used in the model evaluation. The results showed that the climatic factors of annual temperature and precipitation, as well as the site factors of stand origin, elevation, slope gradient, topsoil thickness, site quality degree, rocky desertification type and rocky desertification degree, have significant influences on stand volume, and the topsoil thickness and site quality degree have the strongest positive effect. A total of 959 growth equations of stand volume were fitted with a five-level stand classifier (DTSG–climatic zone–site quality degree–stand origin–rocky desertification type). All the growth equations were qualified, because all passed the TRE test (≤30%), and the majority of the R2 ≥ 0.50, above 70% of the RMSE were between 5.0 and 20.0, and above 80% of the P ≥ 75%. These findings provide updated knowledge about the environmental effect on the stand volume growth of subtropical forests in karst areas, and the developed stand volume growth models are convenient for forest management and planning, further contributing to the study of forest carbon storage assessments and global carbon cycling.
Highlights
Forest stand volume is one of the key forest structural attributes in estimating and forecasting timber production, fuel accumulation, ecosystem productivity and carbon stock [1,2,3]
We considered 11 potential environmental factors, which were grouped into climatic factors and site factors, to analyze the environmental effect on stand volume and further applied them in the zonal-hierarchical stand volume growth models (Table 1)
We took the six most representative DTSGs, namely, China fir, masson pine, cypress, oak, cyclobalanopsis and birch as examples, and selected their stand volume growth curves in forestland within mid-subtropical humid (MSH) and mid-subtropical subhumid (MSSH), which are denoted by degrees II, III and IV, naturally grown and planted, Rocky desertified (RD) and Nonrocky desertified (NRD), in order to compare the stand volume growth rate of different
Summary
Forest stand volume is one of the key forest structural attributes in estimating and forecasting timber production, fuel accumulation, ecosystem productivity and carbon stock [1,2,3]. [2,3,7,8], instead of on the growth models for stand volume. Such allometric equations could estimate the stand volume conveniently, they only provide an assessment for the present but not for the future, showing a weakness in representing the growth of stand volume over time, and could not fulfill the need for forest planning. The karst landscape of southwestern China, occupies approximately 3.44 million km or approximately
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