title: Warming experiments elucidate the drivers of observed directional changes in tundra vegetation.
abstract: Few studies have clearly linked long-term monitoring with in situ experiments to clarify potential drivers of observed change at a given site. This is especially necessary when findings from a site are applied to a much broader geographic area. Here, we document vegetation change at Barrow and Atqasuk, Alaska, occurring naturally and due to experimental warming over nearly two decades. An examination of plant cover, canopy height, and community indices showed more significant differences between years than due to experimental warming. However, changes with warming were more consistent than changes between years and were cumulative in many cases. Most cases of directional change observed in the control plots over time corresponded with a directional change in response to experimental warming. These included increases in canopy height and decreases in lichen cover. Experimental warming resulted in additional increases in evergreen shrub cover and decreases in diversity and bryophyte cover. This study suggests that the directional changes occurring at the sites are primarily due to warming and indicates that further changes are likely in the next two decades if the regional warming trend continues. These findings provide an example of the utility of coupling in situ experiments with long-term monitoring to accurately document vegetation change in response to global change and to identify the underlying mechanisms driving observed changes.
authors.affiliation: Biology Department, Grand Valley State University 1 Campus Drive, Allendale, Michigan, 49401.
authors.forename: Robert D
authors.initials: RD
authors.lastname: Hollister
authors.affiliation: Biology Department, Grand Valley State University 1 Campus Drive, Allendale, Michigan, 49401 ; Department of Biological Sciences, Florida International University 11200 SW 8th Street, Miami, Florida, 33199.
authors.forename: Jeremy L
authors.initials: JL
authors.lastname: May
authors.affiliation: Biology Department, Grand Valley State University 1 Campus Drive, Allendale, Michigan, 49401 ; Department of Biological Sciences, University of Notre Dame Notre Dame, Indiana, 46556.
authors.forename: Kelseyann S
authors.initials: KS
authors.lastname: Kremers
authors.affiliation: Department of Biology, University of Texas at El Paso El Paso, Texas, 79968.
authors.forename: Craig E
authors.initials: CE
authors.lastname: Tweedie
authors.affiliation: Department of Biological Sciences, Florida International University 11200 SW 8th Street, Miami, Florida, 33199.
authors.forename: Steven F
authors.initials: SF
authors.lastname: Oberbauer
authors.affiliation: Biology Department, Grand Valley State University 1 Campus Drive, Allendale, Michigan, 49401.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Liebig
authors.affiliation: Biology Department, Grand Valley State University 1 Campus Drive, Allendale, Michigan, 49401.
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Botting
authors.affiliation: Biology Department, Grand Valley State University 1 Campus Drive, Allendale, Michigan, 49401.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Barrett
authors.affiliation: Biology Department, Grand Valley State University 1 Campus Drive, Allendale, Michigan, 49401.
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Gregory
keywords: Arctic; Cassiope tetragona; ITEX; Poa arctica; biodiversity; climate change; community change