The effect of biocrusts on plants is ambiguous. At the Nizzana research site (Negev Desert, Israel), frequent droughts in the last 2 decades resulted in high shrub mortality, which has been explained by the negative effect of the low‐albedo crusts on soil water evaporation. Nevertheless, shallow‐rooted perennial plants, such as Stipagrostis plumosa and Cyperus sp., exhibit relatively little mortality. We hypothesized that these hemicryptophytes (HCs) grow at or adjacent to small 2‐ to 4‐m2 depressions (termed IDDEP) in the interdune (ID), which are scattered within the undulating terrain (termed IDINC) of ID, and as previously found, serve as sink for short‐distance runoff from IDINC to IDDEP. To test this, we randomly demarcated 50 5 × 5 m plots in the ID and semistable uncrusted dune crest (CR), and the cover of live HCs in the three habitats CR, IDINC, and IDDEP were monitored. In addition, the available water content (AWC) for the 0‐ to 80‐cm depth was measured during 2012–2014. Although AWC exhibited a clear pattern with IDDEP > CR > IDINC, HCs were almost absent from IDINC (above ground biomass of 0.3 kg/ha) but relatively high in IDDEP (55.3 kg/ha) and CR (113.0 kg/ha). The high biomass at CR and IDDEP is explained by higher AWC due to lower evaporation or runoff addition, respectively. The findings highlight the contrasting role played by the biocrust: Although responsible for the mortality of most perennials at IDINC due to increased evaporation, biocrusts assist the survival of relatively shallow‐rooted perennials at IDDEP through runoff generation.
Most papers on the physical condition of birds during spring migration focused on food availability preceding migratory take-off. Only a few studies examined the effect of climate conditions at the wintering grounds upon autumn arrival on bird physical condition later on. Here, we hypothesized that environmental conditions upon arrival at the wintering grounds, and not necessarily upon departure, have a crucial carry-over effect on bird spring migration. Using 29,000 observations of the lesser whitethroat,
Sylvia curruca
, and the eastern Bonelli’s warbler,
Phylloscopus orientalis
, we found temperatures upon arrival at the African wintering grounds to be the only climatic variable correlated with birds’ body state upon spring stopover in Israel, six months later. Two different mechanisms could explain these results. One possibility is that high temperatures create favorable conditions for insect activity, which allows rapid recovery from autumn migration and hence successful winter survival and maintenance. Another possible scenario is that harsh conditions, due to the heat and dry environment, cause high mortality, permitting survival of larger individuals which, then, enjoy reduced inter- and intra-specific competition. Whatever the mechanism is, our findings suggest that conditions upon autumn arrival, and not necessarily at the end of winter as traditionally thought, may have a major impact on migrating birds.
Numerous studies report shifts in bird migration phenology, presumably owing to global warming. However, most studies focus on migration patterns in the Northern Hemisphere. In this study, we investigated associations between weather conditions in African wintering grounds of the lesser whitethroat, Sylvia curruca, and spring arrival time in Eilat, Israel. Using multivariate regression models, we analysed a 30-year dataset in order to examine correlations between median springtime arrival and 46 climate variables of the wintering quarters. The model obtained exhibited a highly statistical fit, involving mean precipitation in February and March with negative effects and number of wet days during November–February. February precipitation levels were also the major factor associated with the interquartile range of arrival time. Interestingly and contrary to published results, annual or seasonal precipitation showed no correlation with spring arrival time, nor did temperature. Moreover, winter in this region falls into dry season with negligible rainfall quantities. Hence, it is unlikely that precipitation effect on habitat productivity is a driving force of migration, as suggested by other studies. Instead, we propose that precipitation in February acts as a cue for the birds, indicating the approach of spring and migration time.
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