Drought and grazing intensity are predicted to increase in semi-arid rangelands under global change. Although annuals often dominate semi-arid rangelands, their strategies to cope with both stressors remain nearly unexplored. Traditionally, all annuals are summarized in the category of r-species (ruderals). However, their occurrence in a wide range of habitats suggests that this view is too simplistic. Instead, annuals should differ in their key functional traits as much as other plant species groups. Based upon the fundamental trade-off between fast and slow growth, we hypothesize that annuals range along a continuum between the usually suggested fast growth-escape strategy to a slow growth-avoidance strategy, with species characterized by tolerance traits in an intermediate position. The Eastern Mediterranean Basin, with its high diversity of annuals, long history of grazing, steep aridity gradients, and extensive previous experimental and observational studies provides an ideal model system for this purpose.
Material and Methods
To test whether annuals vary in their trait attributes and whether these differences influence their performance under drought and grazing, we will investigate about 30 physiological, morphological, and life history traits in 37 Eastern Mediterranean rangeland species, and conduct a grazing and drought experiment in the greenhouse. These individual responses and trait data will be linked to in-situ abundance and distribution data (Tielbörger et al. 2014 Nat. Commun.; Bilton et al. 2016 PPEES) to determine the mechanisms for species responses under field conditions.
This project aims to overcome the uncertainties about the response of annuals to drought and grazing, with important implications for predictions of global change impacts on vegetation.