title: Plant phenological responses to a long-term experimental extension of growing season and soil warming in the tussock tundra of Alaska.
abstract: Climate warming is strongly altering the timing of season initiation and season length in the Arctic. Phenological activities are among the most sensitive plant responses to climate change and have important effects at all levels within the ecosystem. We tested the effects of two experimental treatments, extended growing season via snow removal and extended growing season combined with soil warming, on plant phenology in tussock tundra in Alaska from 1995 through 2003. We specifically monitored the responses of eight species, representing four growth forms: (i) graminoids (Carex bigellowii and Eriophorum vaginatum); (ii) evergreen shrubs (Ledum palustre, Cassiope tetragona, and Vaccinium vitis-idaea); (iii) deciduous shrubs (Betula nana and Salix pulchra); and (iv) forbs (Polygonum bistorta). Our study answered three questions: (i) Do experimental treatments affect the timing of leaf bud break, flowering, and leaf senescence? (ii) Are responses to treatments species-specific and growth form-specific? and (iii) Which environmental factors best predict timing of phenophases? Treatment significantly affected the timing of all three phenophases, although the two experimental treatments did not differ from each other. While phenological events began earlier in the experimental plots relative to the controls, duration of phenophases did not increase. The evergreen shrub, Cassiope tetragona, did not respond to either experimental treatment. While the other species did respond to experimental treatments, the total active period for these species did not increase relative to the control. Air temperature was consistently the best predictor of phenology. Our results imply that some evergreen shrubs (i.e., C. tetragona) will not capitalize on earlier favorable growing conditions, putting them at a competitive disadvantage relative to phenotypically plastic deciduous shrubs. Our findings also suggest that an early onset of the growing season as a result of decreased snow cover will not necessarily result in greater tundra productivity.
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL, 33199, USA.
authors.forename: Roxaneh
authors.initials: R
authors.lastname: Khorsand Rosa
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL, 33199, USA.
authors.forename: Steven F
authors.initials: SF
authors.lastname: Oberbauer
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL, 33199, USA.|Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, 35487, USA.
authors.forename: Gregory
authors.initials: G
authors.lastname: Starr
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL, 33199, USA.|Rutgers University, New Brunswick, NJ, 08901, USA.
authors.forename: Inga
authors.initials: I
authors.lastname: Parker La Puma
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL, 33199, USA.|Bay Area Air Quality Management District, San Francisco, CA, 94109, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Pop
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL, 33199, USA.|Parsons Brinckerhoff, San Diego, CA, 92101, USA.
authors.forename: Lorraine
authors.initials: L
authors.lastname: Ahlquist
authors.affiliation: Department of Biological Sciences, Florida International University, Miami, FL, 33199, USA.|NEON, Inc., Boulder, CO, 80301, USA.
authors.forename: Tracey
authors.initials: T
authors.lastname: Baldwin
mesh_terms: D000413:Alaska; D057231:Climate Change; D019684:Magnoliopsida / Q000254:growth & development*; D012621:Seasons; D012914:Snow; D012987:Soil; D013045:Species Specificity; D013696:Temperature; D065929:Tundra
chemical_list: D012987:Soil
keywords: Alaska; arctic; climate change; growth form; phenology; season length; snow removal; soil warming; tundra