Integrating theory and experiments to link local mechanisms and ecosystem-level consequences of vegetation patterns in drylands

Self-organized spatial patterns of vegetation are frequent in drylands and, because pattern shape correlates with water availability, they have been suggested as important indicators of ecosystem health. However, the mechanisms underlying their emergence remain unclear. Some theories hypothesize that patterns could result from a water-mediated scale-dependent feedback (SDF), whereby interactions favoring plant growth dominate at short distances and growth-inhibitory interactions dominate in the long range. However, we know little about how the sign of net plant-to-plant interactions changes with inter-individual distance, which challenges the relevance of this SDF for vegetation pattern formation. Assuming that net plant interactions are always inhibitory and only their intensity is scale-dependent, alternative theories also recover pattern shapes observed in nature. These alternative hypotheses leading to visually indistinguishable patterns, however, predict contrasting desertification dynamics, which limits the potential use of vegetation patterns as ecosystem-state indicators. Therefore, to make reliable ecological predictions for a focal ecosystem, models must accurately capture the mechanisms at play in the system of interest. Here, we review existing theories for vegetation self-organization and their conflicting predictions about desertification dynamics. We further discuss ways to reconcile these predictions and potential empirical tests via manipulative experiments to better understand both how patterns emerge and the fate of the ecosystems where they form.