Environmental drivers of understory species richness (Hypothesis
1)
After model selection, three variables explained 22.6% of the total
variation: DLI explained most with 14.4%, then pH with 6.5% and then
C:N ratio with 1.7% at the subplot level. Plant species richness
generally increased with light quantity up to a maximum and then
slightly decreased (p < 0.001, r² = 0.65, Conditional R-GLMM²,
see Fig. 3), although data coverage above 40% light availability is
arguably low. Understory species richness showed a hump-shaped
relationship with soil pH, with a maximum at pH 4.8 (p < 0.001
r² = 0.45. Conditional R-GLMM²). There was a negative relationship
between soil C:N-ratio and species richness (p = 0.007, r² = 0.65,
Conditional R-GLMM²). All other variables did not correlate with species
richness.