The fertile island effect varies with aridity and plant patch type across an extensive continental gradient

Abstract

Perennial plants play important roles in maintaining ecosystem functions by forming fertile islands beneath their canopies. Little is known about how the fertile island effect varies among different patch types and across climatic gradients, or what drives the strength of its effect. We assessed biotic (plants, biocrusts, litter) and abiotic (soil infiltrability, labile carbon, enzymes) fertile island effects beneath three plant patch types (tree, shrub and grass patches), and collected data on biotic (canopy size, grazing intensity) and abiotic (soil texture, electrical conductivity and pH) drivers at 150 sites along an extensive aridity gradient in eastern Australia. The fertile island effect was generally apparent beneath trees, shrubs and grasses, with biotic (plants) and abiotic (soils) attributes regulated differently by plant canopy size. The fertile island effect intensified with increasing aridity, with the greatest litter and soil resources accumulated beneath trees. Our study provides evidence of the fertile island effect across the whole spectrum of the aridity gradient, with the effect depending on the target attribute and plant patch type. Forecasted increases in aridity will likely strengthen the fertile island effect beneath trees, reinforcing the importance of trees in drier environments to support critical ecosystem functions and services.