title: Light accelerates plant responses to warming.
abstract: Competition for light has profound effects on plant performance in virtually all terrestrial ecosystems. Nowhere is this more evident than in forests, where trees create environmental heterogeneity that shapes the dynamics of forest-floor communities(1-3). Observational evidence suggests that biotic responses to both anthropogenic global warming and nitrogen pollution may be attenuated by the shading effects of trees and shrubs(4-9). Here we show experimentally that tree shade is slowing down changes in below-canopy communities due to warming. We manipulated levels of photosynthetically active radiation, temperature and nitrogen, alone and in combination, in a temperate forest understorey over a 3-year period, and monitored the composition of the understorey community. Light addition, but not nitrogen enrichment, accelerated directional plant community responses to warming, increasing the dominance of warmth-preferring taxa over cold-tolerant plants (a process described as thermophilization(6,10-12)). Tall, competitive plants took greatest advantage of the combination of elevated temperature and light. Warming of the forest floor did not result in strong community thermophilization unless light was also increased. Our findings suggest that the maintenance of locally closed canopy conditions could reduce, at least temporarily, warming-induced changes in forest floor plant communities.
authors.affiliation: Forest &Nature Lab, Ghent University, Geraardsbergsesteenweg 267, Gontrode-Melle BE-9090, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: De Frenne
authors.affiliation: Integrative Ecology Group, Estación Biológica de Doñana (EBD-CSIC), Avda. Américo Vespucio, Sevilla E-41092, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Rodríguez-Sánchez
authors.affiliation: Forest &Nature Lab, Ghent University, Geraardsbergsesteenweg 267, Gontrode-Melle BE-9090, Belgium.
authors.forename: An
authors.initials: A
authors.lastname: De Schrijver
authors.affiliation: Forest Ecology and Conservation Group, Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK.
authors.forename: David A
authors.initials: DA
authors.lastname: Coomes
authors.affiliation: Department of Earth &Environmental Sciences, Division of Forest, Nature and Landscape, K.U. Leuven, Celestijnenlaan 200E, Leuven BE-3001, Belgium.
authors.forename: Martin
authors.initials: M
authors.lastname: Hermy
authors.affiliation: Forest &Nature Lab, Ghent University, Geraardsbergsesteenweg 267, Gontrode-Melle BE-9090, Belgium.
authors.forename: Pieter
authors.initials: P
authors.lastname: Vangansbeke
authors.affiliation: Forest &Nature Lab, Ghent University, Geraardsbergsesteenweg 267, Gontrode-Melle BE-9090, Belgium.
authors.forename: Kris
authors.initials: K
authors.lastname: Verheyen