Eight significant predictors were represented in the final biotic response model (Table 1). These included leaf area index, softwood basal area, normalized vegetation difference, slope curvature, canopy height, hardwood basal area, terrain ruggedness, and geographic distance. Just over half of the significant predictors were biotic, together explaining 41.3% of deviance. Of these, leaf area index was the strongest predictor (22.02% of deviance explained), while the most important abiotic predictor was slope curvature (5.32%). Although geographic distance was a significant predictor, it contributed little to model fit (3.02%).

In the ecosystem response model, most fitted I-spline curves increased non-linearly and some were asymptotic (Figure 3). Higher change in model transformed predictor values (y-axis, Figure 3) corresponded directly with higher predictor values (x-axis, Figure 3) for leaf area index, normalized difference vegetation index, and hardwood basal area. Spline curves for softwood basal area, canopy height, and terrain ruggedness plateaued at mid to high predictor values. Geography did not contribute significantly to model fit, suggesting variations in dissimilarity were driven by relationships with biotic and abiotic predictors that did not vary markedly across the study area. In general, steeper changes in I-spline slope (e.g., where canopy height varied between 1 and 15 meters – Figure 3B) indicated greater dissimilarity between site-pairs, while flatter curve segments indicated less change (e.g., Figure 3A – where the terrain ruggedness index exceeds 2). Spline shapes for leaf area and normalized difference vegetation indices were relatively congruent. Here they showed prominent change in dissimilarity, between site-pairs, throughout most of these predictor ranges; parallels in I-splines shape and magnitude indicated their contributions to ecosystem-level responses were quite comparable.

In our biotic response model, fitted I-spline curves for slope curvature and hardwood basal area showed direct correspondence between higher predictor values and higher ecological distance values throughout most of their range (Figure 3). In contrast, spline curves for canopy height, leaf area index, softwood basal area, and normalized difference vegetation index plateaued at mid or higher predictor values. Terrain ruggedness and geographic distance leveled off at lower values.