Plant spatial patterns identify alternative ecosystem multifunctionality states in global drylands

The response of dry lands to environmental gradients can be abrupt rather than gradual. These shifts largely occur unannounced and are difficult to reverse once they happen; their prompt detection is of crucial importance. The distribution of vegetation patch sizes may indicate the proximity to these shifts, but the use of this metric is hampered by a lack of large-scale studies relating these distributions to the provision of multiple ecosystem functions (multi-functionality) and comparing them to other ecosystem attributes, such as total plant cover. Here we sampled 115 dry land ecosystems across the globe and related their vegetation attributes (cover and patch size distributions) to multi-functionality. Multi-functionality followed a bimodal distribution across our sites, suggesting alternative states in the functioning of dry lands. Although plant cover was the strongest predictor of multi-functionality when linear analyses were used, only patch size distributions reflected the bimodal distribution of multi-functionality observed. Differences in the coupling between nutrient cycles and in the importance of self-organizing biotic processes characterized the two multi-functionality states observed. Our findings support the use of vegetation patterns as indicators of ecosystem functioning in dry lands and pave the way for developing effective strategies to monitor desertification processes.