title: Aridity, not fire, favors nitrogen-fixing plants across tropical savanna and forest biomes.
abstract: Tropical savannas are hypothesized to be hot spots of nitrogen-fixer diversity and activity because of the high disturbance and low nitrogen characteristic of savanna landscapes. Here we compare the abundances of nitrogen-fixing and non-fixing trees in both tropical savannas and tropical forests under climatically equivalent conditions, using plant inventory studies across 566 plots in South America and Africa. A single factor, aridity, explained 19-54% of the variance in fixer abundance, and unexpectedly was more important than fire frequency, biome, and continent. Nitrogen fixers were more abundant in arid environments; as a result, African savannas, which tend to be drier, were richer in nitrogen fixers than South American savannas. Fixer abundance converged on similar levels in forests in both continents. We conclude that climate plays a greater role than fire in determining the distribution of nitrogen fixers across tropical savanna and forest biomes.
authors.affiliation: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, 08544, USA.
authors.forename: Adam F A
authors.initials: AFA
authors.lastname: Pellegrini
authors.affiliation: Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut, 06511, USA.
authors.forename: A Carla
authors.initials: AC
authors.lastname: Staver
authors.affiliation: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, 08544, USA.
authors.forename: Lars O
authors.initials: LO
authors.lastname: Hedin
authors.affiliation: Department of Biological Sciences, University of Cape Town, Cape Town, South Africa.
authors.forename: Tristan
authors.initials: T
authors.lastname: Charles-Dominique
authors.affiliation: Environmental Defense Fund, San Francisco, California, 94105, USA.
authors.forename: Amy
authors.initials: A
authors.lastname: Tourgee
mesh_terms: D000349:Africa; D017753:Ecosystem; D004784:Environmental Monitoring; D005390:Fires; D065928:Forests; D065948:Grassland; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D058458:Nitrogen Cycle; D013020:South America; D014197:Trees; D014329:Tropical Climate
chemical_list: D009584:Nitrogen
keywords: aridity; biological nitrogen fixation; fire; legumes; plant diversity; tropical forest; tropical savanna