Modelling direct and indirect impacts of browser consumption on woody plant growth: moving beyond biomass

Models and experimental studies of the impact of mammalian browsing on plant populations typically use biomass to quantify resource pools and herbivore impacts. For many woody plant populations, however, plant height is a better measure of fitness than biomass. We describe a function that links browsing to shoot and height growth by considering both the direct impact of biomass consumption and the effect of bud‐loss. The relative importance of direct consumption and bud‐loss for height and shoot growth is tested through experimental clipping. Experimental results are used to parameterize and compare the performance of our function. We show that the impacts of bud‐loss are indeed significant for both shoot and height growth and may cause the responses of biomass and height to diverge. We also show that our function results in an improved fit to experimental results when compared with a linear function only describing the direct impact of consumption. These results suggest that the demographic impacts of browsing may diverge from the responses expected for biomass based on herbivore consumption alone. Particularly, height growth can be drastically reduced at low and intermediate levels of consumption if the impacts of bud‐loss on shoot growth are high.