title: Remotely sensed canopy height reveals three pantropical ecosystem states.
abstract: Although canopy height has long been a focus of interest in ecology, it has remained difficult to study at large spatial scales. Recently, satellite-borne LiDAR equipment produced the first systematic high resolution maps of vegetation height worldwide. Here we show that this new resource reveals three marked modes in tropical canopy height ~40, ~12, and ~2 m corresponding to forest, savanna, and treeless landscapes. The distribution of these modes is consistent with the often hypothesized forest-savanna bistability and suggests that both states can be stable in areas with a mean annual precipitation between ~1,500  and ~2,000 mm. Although the canopy height states correspond largely to the much discussed tree cover states, there are differences, too. For instance, there are places with savanna-like sparse tree cover that have a forest-like high canopy, suggesting that rather than true savanna, those are thinned relicts of forest. This illustrates how complementary sets of remotely sensed indicators may provide increasingly sophisticated ways to study ecological phenomena at a global scale.
authors.affiliation: School of Life Sciences, Nanjing University, 163 Xianlin Road, Nanjing, 210023, China.|Aquatic Ecology and Water Quality Management Group, Wageningen University, P.O. Box 47, NL-6700 AA, Wageningen, the Netherlands.
authors.forename: Chi
authors.initials: C
authors.lastname: Xu
authors.affiliation: Karlsruhe Institute of Technology, Institute of Meteorology and Climate Research, Atmospheric Environmental Research, 82467, Garmisch-Partenkirchen, Germany.
authors.forename: Stijn
authors.initials: S
authors.lastname: Hantson
authors.affiliation: Resource Ecology Group, Wageningen University, P.O. Box 47, NL-6700 AA, Wageningen, the Netherlands.
authors.forename: Milena
authors.initials: M
authors.lastname: Holmgren
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Wageningen University, P.O. Box 47, NL-6700 AA, Wageningen, the Netherlands.
authors.forename: Egbert H
authors.initials: EH
authors.lastname: van Nes
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Wageningen University, P.O. Box 47, NL-6700 AA, Wageningen, the Netherlands.
authors.forename: Arie
authors.initials: A
authors.lastname: Staal
authors.affiliation: Aquatic Ecology and Water Quality Management Group, Wageningen University, P.O. Box 47, NL-6700 AA, Wageningen, the Netherlands.
authors.forename: Marten
authors.initials: M
authors.lastname: Scheffer
mesh_terms: D004463:Ecology; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods*; D065928:Forests; D058998:Remote Sensing Technology; D014197:Trees
keywords: alternative stable states; climate change; desert; rainforest; remote sensing; savanna; tree cover