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Question: Ecosystem engineer patch dynamics can drive biodiversity patterns by controlling habitat heterogeneity. We studied changes to composition and diversity of shrub patch understorey plant communities to patch stage at a small scale, and to patch dynamics at larger scales. These patch dynamics were driven by widespread mortality of the facilitating engineer shrub Noaea mucronata, following a drought period.Location: Park Shaked LTER station, semi-arid northern Negev Desert, Israel.Methods: We used diversity partitioning and similarity-based metrics to relate annual plant diversity to shrub state at the scale of individual patches, and to the ecosystem engineer shrub mortality rates at larger scales. We separately tested changes to species diversity within patches and to assemblage variation among patches.Results: (1) At the patch scale, annual plant richness and diversity decreased following the loss of shrub canopy. (2) Community similarity among patches increased following shrub mortality, with a significant increase in the abundance of one dominant grass species and a decrease of most other species. (3) Taken together, these factors led to a plot-scale loss of diversity under high rates of shrub mortality. (4) Species richness and evenness metrics were significantly correlated with the shrub mortality gradient. (5) Overall, high mortality rates resulted in landscapes that were more homogeneous in both habitat structure and community composition.

Vegetation structure and patchiness are central controllers of ecohydrological function in semiarid regions. The feedback interactions between vegetation patchiness and water redistribution make semiarid ecosystems sensitive to state‐shifts, where nonlinearities appear in the structure–function correlations. Hydrological connectivity of runoff sources is functionally important for source–sink interactions over a range of spatial scales and plays a key role in ecosystem state‐shifts. Accordingly, the study of the functional responses of ecosystems to changes in connectivity is important for assessing the system's resilience in response to drivers of degradation. We used runoff data collected over 18 years in experimentally manipulated plots to study both the primary functional response to the manipulations and the changes in both structure and function over two decades. By comparing simultaneous changes in woody and herbaceous cover, biocrust cover and connectivity, and runoff yield, we examined the interactions among the different cover classes and assessed the functional consequences of these interactions. The manipulated changes in vegetation and biocrust cover caused large differences in runoff yields, with positive correlation between biocrust cover and runoff. However, changes in vegetation patterns reduced these differences, as the spread of herbaceous plant cover, at the expense of biocrust and woody cover, caused a shift in the cover–runoff relationship. The landscape was resilient to degradation due to rapid shrub growth in locations of high biocrust cover. On the other hand, a positive feedback of herbaceous plant cover replacing shrub cover caused a state‐shift, likely driven by a combination of drought recurrence and cessation of grazing.

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