Shrubs enhance resilience of a semi-arid ecosystem by engineering and regrowth



Semi-arid ecosystems in the Mediterranean basin show a high degree of resilience, despite thousands of years of human disturbance. It has been suggested that this resilience is facilitated by a landscape structure that consists of woody vegetation and intershrub patches of crusted soil. We hypothesized that the woody vegetation patches have two main properties that increase the resilience of the ecosystem. The first property is the capability to accumulate water, and we hypothesized that this continues to function after anthropogenic disturbances to the shrubs. This was field-tested with a rainfall simulator by comparing the amounts of runoff and soil erosion generated by crusted intershrub patches, intact shrub patches, and disturbed shrub patches. The second property is the ability of the woody vegetation to recover after disturbances. This was tested by measuring the recovery rate of the woody vegetation, during 2 consecutive years after canopy removal. Intact and disturbed shrub patches generated similar amounts of runoff and soil erosion to one another, and much lower than crusted intershrub patches, and both kinds of shrub patches had deeper water infiltration. These results suggest that the accumulation of water under the shrub is due to surface and sub-surface soil properties, and not canopy properties. After anthropogenic removal of the woody vegetation canopy, most of the individuals regrew. These combined results suggest that the ecosystem can remain resilient to certain anthropogenic disturbances by virtue of ecosystem engineering and fast recovery by woody vegetation patches that act to conserve resources and to impede their leakage from the ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.