以色列严重退化旱地长期恢复对土壤和植被的影响

Land degradation affects extensive drylands around the world.Due to long-term misuse,the Israeli Sde Zin dryland site has faced severe degradation.The study objective was to assess the feasibility of passive restoration in recovering the site.The study was conducted in four land-units along a preservation-degradation continuum:(1)an area that has not faced anthropogenic disturbances(Ecological land);(2)an area that was proclaimed as a national park in the 1970s(Rehabilitation);(3)an area that was prone,until recently,to moderate anthropogenic pressures(Triangle);and(4)a dirt road that was subjected to long-term off-road traffic(Dirtroad).Soil was sampled and analyzed for its properties.The soil physical quality followed the trend of Ecological land>Rehabilitation>Triangle>Dirtroad.Specifically,high soil salinity in the latter three land-units is attributed to long-term erosional processes that exposed the underlying salic horizons.Herbaceous and shrubby vegetation cover was also monitored.The herbaceous vegetation cover followed the trend of Ecological land(86.4%)>Rehabilitation(40.3%)>Triangle(26.2%)>Dirtroad(2.1%),while the shrubby cover was 2.8%in the Ecological land-unit,and practically zero in the other land-units.It seems that despite the effectiveness of passive restoration in recovering the soil’s physical properties,the recovery of vegetation is limited by the severe soil salinity.

枯死灌木斑块对退化旱地生态系统的调节作用

A long-term drought has led to the mass mortality of shrubs in the semi-arid Israeli Negev.The most impacted shrub species is the Noaea mucronata(Forssk.)Asch.and Schweinf.In a four-year study,we found that herbaceous vegetation growth was greater in the dead shrub patches than in the surrounding inter-patch biocrusted spaces,suggesting that the dead shrub patches encompass improved micro-habitats.However,unexpectedly,the soil moisture in the dead shrub patches was consistently lower than that of the inter-patch biocrusted spaces.At the same time,soil quality in the dead shrub patches was higher than that in the inter-patch spaces.Therefore,it seems that the overall better soil conditions in the dead patches overcome the scarcity of soil-water,supporting increased herbaceous productivity.For explaining the discrepancy between herbaceous vegetation and soil-water,we formulated a conceptual framework,which highlights the key factors that regulate soil-water dynamics in this dryland ecosystem.We demonstrate that herbaceous vegetation is facilitated in the dead shrub patches by a legacy effect that takes place long after the shrubs have died.The dead shrub patches encompass a unique form of ecosystem engineering.The study highlights the complex and unpredicted impacts of prolonged droughts on dryland ecosystems.