3.4 Watershed characteristics effects
To better understand which watershed and fire characteristics may control differences in effect sizes of nitrate and DOC, we plotted feature importance determined by Random Forests for each solute (Fig. 5). R2 values indicate that less than half of the variability in nitrate effect sizes was explained (R2 = 0.47), while most of the variability in DOC effect sizes were explained by the six watershed and fire characteristics (R2 = 0.80). For DOC, maximum elevation was the most important predictor (40%) followed by catchment area (27%), while the remaining variables were considerably less important (<15%), with climate and time-since-fire as the least important. For nitrate, maximum elevation was also the most important variable (29%). However, unlike DOC, all other predictors were at least half the feature importance of maximum elevation (15-17%). Slope was the least important predictor for nitrate (9%). We observed the DOC effects are better explained by watershed and fire characteristics compared to nitrate (Fig. 5).