title: Earlier snowmelt and warming lead to earlier but not necessarily more plant growth.
abstract: Climate change over the past ∼50 years has resulted in earlier occurrence of plant life-cycle events for many species. Across temperate, boreal and polar latitudes, earlier seasonal warming is considered the key mechanism leading to earlier leaf expansion and growth. Yet, in seasonally snow-covered ecosystems, the timing of spring plant growth may also be cued by snowmelt, which may occur earlier in a warmer climate. Multiple environmental cues protect plants from growing too early, but to understand how climate change will alter the timing and magnitude of plant growth, experiments need to independently manipulate temperature and snowmelt. Here, we demonstrate that altered seasonality through experimental warming and earlier snowmelt led to earlier plant growth, but the aboveground production response varied among plant functional groups. Earlier snowmelt without warming led to early leaf emergence, but often slowed the rate of leaf expansion and had limited effects on aboveground production. Experimental warming alone had small and inconsistent effects on aboveground phenology, while the effect of the combined treatment resembled that of early snowmelt alone. Experimental warming led to greater aboveground production among the graminoids, limited changes among deciduous shrubs and decreased production in one of the dominant evergreen shrubs. As a result, we predict that early onset of the growing season may favour early growing plant species, even those that do not shift the timing of leaf expansion.
authors.affiliation: Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, CO 80523, USA clivensp@rams.colostate.edu.
authors.forename: Carolyn
authors.initials: C
authors.lastname: Livensperger
authors.affiliation: Biology Department, Fort Lewis College, Durango, CO 81301, USA.
authors.forename: Heidi
authors.initials: H
authors.lastname: Steltzer
authors.affiliation: Department of Biological Sciences, University of Texas at El Paso, El Paso, TX 79968, USA.
authors.forename: Anthony
authors.initials: A
authors.lastname: Darrouzet-Nardi
authors.affiliation: Environment and Natural Resources Institute, University of Alaska Anchorage, Anchorage, AK 99508, USA.
authors.forename: Patrick F
authors.initials: PF
authors.lastname: Sullivan
authors.affiliation: Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Wallenstein
authors.affiliation: Department of Environmental Sciences, University of Toledo, Toledo, OH 43606, USA.
authors.forename: Michael N
authors.initials: MN
authors.lastname: Weintraub
keywords: Arctic tussock tundra; climate change; plant phenology; plant production; seasonality