Optimal anti-herbivore defence allocation in Salix polaris: doing it the arctic way?

To determine the optimal anti-herbivore defence allocation of a plant, a modelling approach is inevitable. However, models have too often been detached from field experiments and aloof of ecological knowledge. Here I present the case for combining the two approaches. Two preconditions for a simple model have to be fulfilled: 1. the investigated species should show no inducible resistance, a phenomenon often observed in temperate trees, because this requires very detailed ecological knowledge to be captured by the model, and 2. the plant species under consideration has to be flexible in its defence allocation, otherwise no optimisation can be expected under different grazing pressures. Here, I show by field experiments that these two requirements are met for Salix polaris , a high arctic dwarf shrub. This opens the way for a simple competition model to assess optimal defence allocation under different grazing intensities.