Figure 2. Nutrient and consumer effects on native and exotic cover and richness.

Effect of nutrient addition and consumer exclusion on cover and richness of native and exotic plants. The Consumer by Nutrient Experiment (a and c) is a factorial combination of nutrient addition (Nut) and consumer exclusion (Fnc) replicated at 34 sites. The Multiple Nutrient Experiment (b and d) is a full factorial addition of nitrogen (N), phosphorus (P), and potassium with micronutrients (K) replicated at 37 sites. Plotted values are the estimated differences from the control of the change in cover or richness per year relative to pre-treatment sampling estimated using mixed-effects models. Interactions (for example, N*P, N*K, P*K, and N*P*K) test for additivity, with significant positive or negative values indicating super- or sub-additivity, respectively. Error bars are s.e. of the slope estimates. Slopes that are significantly different from zero are indicated as follows: ***P≤0.001, **P≤0.01 and *P≤0.05.