Dune crests serve as preferential habitats for perennial plants during frequent drought years

Abstract

Following frequent droughts in the last 19 years, high mortality of perennial plants was noted in the Hallamish dune field in the Negev Desert (P = 95 mm). To evaluate the vegetation change, vegetation cover and species composition were studied in 20 plots located at the semi-stable non-crusted dune crest (CR) and 20 plots located at the crusted interdune (ID) during the summer of 2012 and compared to data from 1994. In addition, periodical moisture measurements were carried out in a pair of plots, 50–100 m apart, at CR and ID between October 2009 and September 2012. The findings exhibit a substantial decrease in the living perennials (mainly consisting of shrubs), with ID exhibiting the highest reduction in living shrubs. The findings are in agreement with measurements of the available water content, AWC (i.e., above the wilting point) during 2010–2012. While being recorded at >60 cm at CR, AWC was not recorded at ID at 60–120 cm depth during the summer months. Lower evaporation rates due to higher albedo and especially subsurface flow from the adjacent highly active crest are mainly seen responsible for deeper infiltration and higher AWC at CR. It is concluded that while sufficient AWC was present at CR to sustain most of the perennial shrubs also during frequent drought years, insufficient moisture was retained at ID to sustain most perennials. Non-crusted dune crests may thus serve as preferential habitats (fertility belts) for perennial plants, providing refugia for shrubs during frequent drought years.