title: CO2 and fire influence tropical ecosystem stability in response to climate change.
abstract: Interactions between climate, fire and CO2 are believed to play a crucial role in controlling the distributions of tropical woodlands and savannas, but our understanding of these processes is limited by the paucity of data from undisturbed tropical ecosystems. Here we use a 28,000-year integrated record of vegetation, climate and fire from West Africa to examine the role of these interactions on tropical ecosystem stability. We find that increased aridity between 28-15 kyr B.P. led to the widespread expansion of tropical grasslands, but that frequent fires and low CO2 played a crucial role in stabilizing these ecosystems, even as humidity changed. This resulted in an unstable ecosystem state, which transitioned abruptly from grassland to woodlands as gradual changes in CO2 and fire shifted the balance in favor of woody plants. Since then, high atmospheric CO2 has stabilized tropical forests by promoting woody plant growth, despite increased aridity. Our results indicate that the interactions between climate, CO2 and fire can make tropical ecosystems more resilient to change, but that these systems are dynamically unstable and potentially susceptible to abrupt shifts between woodland and grassland dominated states in the future.
authors.affiliation: Department of Geosciences, The University of Texas at Austin, 2305 Speedway, Stop C1160, Austin, TX 78712 USA.
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Shanahan
authors.affiliation: Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, 360 Woods Hole Rd, Woods Hole, MA 02543 USA.
authors.forename: Konrad A
authors.initials: KA
authors.lastname: Hughen
authors.affiliation: School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Box 4099, Flagstaff, AZ 86011 USA.
authors.forename: Nicholas P
authors.initials: NP
authors.lastname: McKay
authors.affiliation: Institute for the Environment, University of Arizona, ENR2 Building, 1064 E. Lowell St., Tucson, AZ 85721 USA.
authors.forename: Jonathan T
authors.initials: JT
authors.lastname: Overpeck
authors.affiliation: Department of Earth Sciences, Syracuse University, Heroy Geology Laboratory, Syracuse, NY 13244-1070 USA.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Scholz
authors.affiliation: Institute of Biodiversity &Ecosystem Dynamics, University of Amsterdam, POSTBUS 94248, 1090 GE Amsterdam, The Netherlands.
authors.forename: William D
authors.initials: WD
authors.lastname: Gosling
authors.affiliation: Department of Geosciences, University of Oslo, PO Box 1047, Blindern, Oslo 0316, Norway.
authors.forename: Charlotte S
authors.initials: CS
authors.lastname: Miller
authors.affiliation: Department of Geosciences, University of Oslo, PO Box 1047, Blindern, Oslo 0316, Norway.|Department of Geosciences, University of Akron, 126 Crouse Hall, Akron, OH 44325-4101 USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Peck
authors.affiliation: Department of Geosciences, University of Akron, 126 Crouse Hall, Akron, OH 44325-4101 USA.|Graduate School of Oceanography, University of Rhode Island, 215 South Ferry Road, Narragansett, RI 02882 USA.
authors.forename: John W
authors.initials: JW
authors.lastname: King
authors.affiliation: Department of Geosciences, University of Akron, 126 Crouse Hall, Akron, OH 44325-4101 USA.|Graduate School of Oceanography, University of Rhode Island, 215 South Ferry Road, Narragansett, RI 02882 USA.
authors.forename: Clifford W
authors.initials: CW
authors.lastname: Heil