Influences of stand characteristics and environmental factors on forest biomass and root–shoot allocation in southwest China

Tree biomass and it's allocation pattern may respond to the environmental conditions and are quite important for understanding the global carbon cycling, climate change, and forest management. However, how stand characteristics (e.g. tree age, density) and environmental factor (e.g. climate, site conditions, and soil chemistry) influence the biomass and biomass allocation in southwest of China has not been well investigated. We analyzed 318 field measurements of forest biomass in this region, which 62 sites were obtained from our field measurements and the others from the national forest inventory. The results showed that the average above-ground biomass (AGB) and below-ground biomass (BGB) were 134 Mg/ha and 28 Mg/ha, respectively. The root/shoot biomass ratio (R/S) ranged between 0.06 and 0.81, with an average of 0.22. Forest stand characteristics explained 43% and 21% of the variation in AGB and BGB, respectively, while climate only explained 2–4%, reflecting the strong effect of forest features on biomass. However, only 5% of the R/S ratio was explained by climate, soil chemistry, and stand characteristics, suggesting that these factors had no significant effect on biomass allocation. In addition, the scaling exponents between AGB and BGB did not differ significantly from 1, and did not vary with mean annual temperature, mean annual precipitation, longitude, latitude, altitude, soil pH, soil total nitrogen concentration, and stand age, but did vary with soil total phosphorus concentration, stand density, and forest type. Our findings suggest that stand characteristics have a marked impact on forest biomass, and root biomass scales isometrically with above-ground biomass in southwest China.