Field sites and climate change manipulations
Four field sites were chosen along a natural rainfall gradient from Northern to Southern Israel which share most abiotic characteristics except for mean and variance in rainfall conditions (details in Tielbörger et al. 2014). The sites share a Mediterranean-type climate and similar mean annual temperature (17.7–19.1°C), yet spanned a more than eight-fold difference in mean annual rainfall. They represent mesic-Mediterranean (MM, 780 mm rainfall, 33°00’N, 35°14’E), Mediterranean (M, 540 mm, 31°42’N, 35°03’E), semi-arid (SA, 300 mm, 31°23’N, 34°54’E) and arid conditions (A, 90 mm, 30°52’N, 34°46’E), respectively. The length of the rainy season increases from the driest (Dec/Jan–March) to the wettest site (Oct/Nov–May), while rainfall variability among years decreased from the driest (40% Coefficient of Variation) to the wettest site (25% CV) (Metz et al. 2018). All sites are semi-natural shrublands with mostly annual species in the inter-shrub matrix, located at south exposures on limestone bedrock with similar elevation (470–620 m a.s.l.).
Three rainfall manipulation treatments (dry, control, wet) were imposed on entire resident plant communities for ten years (2002-2012) in the two intermediate sites, M and SA. Each treatment was replicated by five randomized 10m × 25m plots per site. The two extreme sites, A and MM, contained only five control plots each and extended the range of the natural rainfall gradient. For dry manipulation, rainout shelters intercepted 30% of each rainfall event; for wet manipulation, additional sprinkler irrigation after every other rain event added in total 30% of the site’s long-term average rainfall per year; control plots received ambient rainfall (details in Tielbörger et al.2014). The magnitude of the dry manipulations approximated climate change scenarios for our study region, predicting 20% less rainfall until 2050 (Smiatek et al.2011; Samuels et al . 2013), while the wet manipulations extended the general range of scenarios.