Fig. 5: Structural equation models of climate, soil pH, and AM proportion as predictors of forest productivity.
From: Higher productivity in forests with mixed mycorrhizal strategies
a Forests with low tree species richness (richness ≤ 5). b Forests with high tree species richness (richness > 5). Solid black arrows represent positive paths (p < 0.05, piecewise SEM), solid red arrows represent negative paths (p < 0.05, piecewise SEM), and solid blue arrows represent non-significant paths (p > 0.05, piecewise SEM). In addition, we included the interactive effects of T.SEAS and soil pH on AM proportion and productivity, with dashed black and red arrows representing positive and negative effects, respectively. We report the path coefficients as standardized effect sizes. Overall fit of piecewise SEM was evaluated using Shipley’s test of d-separation: Fisher’s C = 3.466 & p = 0.177 for low-richness forests; Fisher’s C = 5.206 & p = 0.074 for high-richness forests (if p > 0.05, then no paths are missing and the model is a good fit). AM proportion2, quadratic AM proportion; MAT, mean annual temperature; MAP, mean annual precipitation; T.SEAS, temperature seasonality. Note that the arrows from AM proportion to AM proportion2 reflect deterministic relations based on a calculation rather than hypothesized causal relationships.
