3.3 Coupling effects of environmental and forest structure
attributes on the productivity and stability of planted and natural
forests
To clarify the effects of environmental and forest structure factors on
natural forest stability, we fitted a piecewise SEM. Our model
elucidated 38% of the variation in AGB stability and confirmed that the
most important determinant of stability was the direct positive
influence of stand age and the direct negative effect of precipitation
decline (Fig. 5a). Latitude played a direct significant influence on AGB
stability and an indirect influence via precipitation. Deeper soil depth
facilitates increases in tree density in natural forest. The SEM model
demonstrated that all predictor together clarified 61% of the variation
in the AGB stability of planted forest (Fig. 5b). Stand age
significantly and actively worked on the stability of planted forest.
Richness made a negative impact on the stability of planted forest.
Canopy had a direct positive impact on richness. Canopy and stand age
had a direct positive effect on tree density. More detailed information
in the SEM was presented in Table S2.
In natural forest, the predictors expounded 38% of the productivity
change. Soil depth and precipitation had direct positive effects on
productivity. Productivity decreased significantly with stand age.
Latitude affected productivity directly as well as indirectly via
precipitation (Fig. 5c). All predictors together expounded 75% of the
productivity change in planted forest. Altitude, richness, and tree
density had positive, direct effects on productivity. Stand age made a
direct negative impact on productivity and an indirect impact via tree
density (Fig. 5d). Canopy played an indirect positive role in
productivity via density and richness.