| Popis: |
Background: Forest ecosystems play a crucial role in global carbon cycle. Identifying bio- or abio- drivers on forest biomass allocation pattern could improve our understanding in forest carbon sink, stock and cycle across various spatio-temporal scales. Through compiling a dataset (n=1931) of the root-shoot ratio from previous studies, here we implemented the Random Forest algorithm (RF) to elucidate main driven factors on the root-shoot ratio across China forest ecosystems. Results: (1) Forest age and forest density were both contributed mostly to root-shoot ratio variations regardless of forest origins (natural or planted forests). The relative important values (% increase in MSE) for forest density and forest age on the root-shoot ratio were 54.42% and 51.05% in the natural forests, and 74.61% and 117.27% in the planted forests, respectively; (2) Compared to soil variables (soil texture and nutrient status), climatic variables (temperature and precipitation) showed stronger effects on the root-shoot ratio; (3) Partial dependent analysis further demonstrated that root-shoot ratio initially decreased with forest age, but afterwards increased to a relative stable level (the turning point, e.g., ca. 150 yr for natural forests and ca.30 yr for planted forests); (4)The root-shoot ratio increased nonlinearly with an increase of forest density in both forest types. Forest density and precipitation seasonality exerted positively direct effects, while forest age together with temperature seasonality, mean temperature of wettest quarter and precipitation of warmest quarter had negatively effects on the root-shoot ratio of two forest types. Conclusions: The forest age, forest density and climate seasonality contributed mostly to variations of root-shoot ratios in China forest ecosystems. These results would improve our understanding of environmental drivers on forest biomass allocation over a large spatial scale, and to some extent provide a generally practical significance in forest management (e.g., time for timber harvest), although species-specific root-shoot ratio associated with ontogeny should be further investigated in the future. |
