Stronger fertile island patterns enhance plant facilitation in drylands, regardless of overall ecosystem fertility

Abstract Plant facilitation is a central process structuring arid ecosystems, where soil nutrients play a key role. However, it remains unclear whether the heterogeneity and availability of soil nutrients are linked to facilitation intensity at a global scale. Here, we tested two hypotheses: (i) that facilitation intensity increases with stronger fertile island patterns (higher nutrient heterogeneity at the microsite level) and (ii) that it decreases with increasing overall ecosystem soil fertility (higher nutrient availability at the ecosystem level) across drylands. To test these hypotheses, we conducted a meta‐analysis based on 94 observations from 27 studies that jointly measured plant facilitation and the fertile island effect for nitrogen and/or phosphorus in drylands. According to our first hypothesis, we found that facilitation intensity increased with stronger fertile island patterns of nitrogen and phosphorus. However, contrary to our second hypothesis, facilitation intensity did not respond to ecosystem fertility. This indicates that facilitation intensity increases as the difference in soil nutrient concentration between nurse and open microsites becomes larger, independently of overall ecosystem fertility. Synthesis . Our study provides novel insights into the role of soil nutrients in plant facilitation in dryland ecosystems. Our findings highlight that the strength of the fertile island effect is a key ecosystem feature mediating facilitation intensity, regardless of overall ecosystem fertility. These findings emphasize the need to investigate how soil degradation processes could alter fertile island patterns and facilitation processes in drylands.