Hotspots of biogeochemical activity linked to aridity and plant traits across global drylands

Abstract

Perennial plants create productive and biodiverse hotspots, known as fertileislands, beneath their canopies. These hotspots largely determine thestructure and functioning of drylands worldwide. Despite their ubiquity, thefactors controlling fertile islands under conditions of contrasting grazingby livestock, the most prevalent land use in drylands, remain virtuallyunknown. Here we evaluated the relative importance of grazing pressureand herbivore type, climate and plant functional traits on 24 soil physicaland chemical attributes that represent proxies of key ecosystem servicesrelated to decomposition, soil fertility, and soil and water conservation. Todo this, we conducted a standardized global survey of 288 plots at 88 sites in25 countries worldwide. We show that aridity and plant traits are the majorfactors associated with the magnitude of plant effects on fertile islands ingrazed drylands worldwide. Grazing pressure had little influence on thecapacity of plants to support fertile islands. Taller and wider shrubs andgrasses supported stronger island effects. Stable and functional soils tendedto be linked to species-rich sites with taller plants. Together, our findingsdispel the notion that grazing pressure or herbivore type are linked to theformation or intensification of fertile islands in drylands. Rather, our studysuggests that changes in aridity, and processes that alter island identityand therefore plant traits, will have marked effects on how perennialplants support and maintain the functioning of drylands in a more aridand grazed world.