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.