Slow Recovery of Mire Vegetation from Environmental Perturbations Caused by a Heat Wave and Experimental Fertilization

摘要

We monitored vegetation changes in an alpine mire after stopping an experiment of nutrient addition, during which the mire experienced a heat wave. We aimed at assessing the capacity of mire vegetation to recover towards the original state. Nitrogen and phosphorus were added during the growing seasons of 2002-2009. We recorded periodically the cover of all vascular plant species and moss species from 2002 to 2012, i.e., 9 years after the heat wave and 3 years after discontinuing fertilization. The principal effect of the 2003 heat wave consisted in a rapid increase in cover of vascular plants and a parallel decrease in cover of mosses. These trends slowed down after 6 years and almost totally halted 9 years after the heat wave. The heat wave was the main driver of vegetation changes but the vegetation also responded to fertilization. Species within plant functional types (PFTs) showed differing responses to the heat wave and/or fertilization. The mire vegetation showed poor capacity to recover towards the initial conditions. Changes in vegetation composition were determined by individualistic responses of species to varying ecological factors. Grouping plant species into PFTs may conceal important differences in the responses of mire vegetation to environmental changes.