The general objective addressed in this section of CASCADiS is to determine degradation reversal dynamics and thresholds as a function of plant colonization pattern and diversity. Assuming the patchy spatial structure of dryland vegetation, we have addressed this objective at two levels: at the plant patch scale and at the ecosystem scale.

Main research questions at the patch scale pursue identifying the spatial and biotic structure of plant patches that would optimize the recovery of degraded drylands. Specifically, under the framework of restoration actions applied to bare-soil dryland areas, we investigated if:

• Facilitation (individuals perform better when growing with other species) dominates in plant patches
• Diverse patches perform better than monospecific patches
• Bigger /denser patches perform better than small patches with few individuals, either from the same or different species
• Functional diversity is more relevant than species diversity for plant patch performance
• The role of patch diversity and size depends on the plant functional types considered.

At the ecosystem scale, we investigated the potential for degradation reversal and restoration of dryland ecosystems as a function of the initial plant cover and the strength of the ecohydrological feedbacks that control dryland dynamics. Specifically, we investigated if:

• For a given plant community, there is a minimum threshold for vegetation cover below which potential for recovery is negligible. From a restoration perspective, an alternative version of this question could be if, for a given plant community, there is a minimum vegetation cover value that triggers the recovery of the community.
• Higher strength of positive global ecohydrological feedbacks (decreasing vegetation cover → increasing global resource loss from the system → decreasing vegetation cover) would reduce the recovery potential of dryland ecosystems.
• Higher strength of negative local ecohydrological feedbacks (decreasing vegetation cover → increasing runon-driven inputs to plant patches → increasing vegetation growth and cover) would increase the recovery potential of dryland ecosystems.

In order to address these questions, we have followed a fully manipulative experimental approach combined with modelling. Manipulative experiments allow the isolation of the processes and factors of interest, thereby facilitating the understanding of the underlying mechanisms and providing useful information for developing general models.

Note: For full references to papers quoted in this article see

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