PARENT SESSION
Contributed Oral Session 34: Polar and Alpine Ecology: Climate Effects; Communities
Monday, August 8, 1:30 PM - 5:00 PM, Meeting Room 524 A, Level 5, Palais des congrès de Montréal
Phenology and abundance of flowering in two early-season high-altitude Brassicaceae, Thlaspi montanum and Draba aurea, are influenced by environmental variables and climate change.
Inouye, David1, 2, 1 Rocky Mountain Biological Laboratory, Crested Butte, CO, USA2 Dept. of Biology, College Park, MD, USA
ABSTRACT- I quantified long-term variation in the timing and abundance of flowering by two small early-flowering perennial species of mustards in 2x2m plots at 2,800m. I counted flowers every other day for most years since 1975 (Thlaspi; 6 plots), or 1973 (Draba; 12 plots). Mean dates of first flowering among years ranged from 11 May - 25 June for Thlaspi, and 29 May - 12 July for Draba; a significant amount of this variation (e.g, r2 = .76 - .80) is explained for both species by the total amount of snowfall during the previous winter (or the first date of bare ground). Abundance of flowering was also highly variable for both species, with peak number of flowers/year ranging from 15 - 2006 for Thlaspi and 158 - 3281 for Draba. Peak flower abundance of the two species is significantly correlated (r2 = .534, p < .001), but variables correlated with flowering are not identical for the two. Variation in flower abundance for Thlaspi is significantly correlated (r2 = .284, p = .041) with the abundance of inflorescences during the previous year, and marginally (r2 = .156, p = .069) with precipitation during July and August the previous year; for Draba significant variables include precipitation in June (the typical time of flowering; p = .047), precipitation the previous July (when fruits were ripening; p = .005), the abundance of flowers (or inflorescences) the previous year (p < .001 ), and marginally (p = .07), the length of the previous growing season. Temperature of current or previous summer does not seem to affect flower abundance, and in contrast to several other species in this habitat, abundance is not correlated with the previous winter's snowpack. A multiple linear regression model for Draba flower abundance incorporating both July precipitation and flower abundance during the previous year explains 58% of the variation in flower abundance. Since the phase change of the North Pacific Oscillation in 1998, which has resulted in a significant trend for lower winter precipitation compared to the period since the previous change in 1976, flower abundance has decreased significantly (p = .012) for Thlaspi and marginally (p = .088) for Draba. If this trend continues, Thlaspi is likely to disappear from the plots within a few years, while Draba may persist at lower abundance. Both species are visited by flies, whose abundance has declined in the past several years.
Key words: Thlaspi, Draba, phenology, climate change