PARENT SESSION
Poster Session 5: Climate Dynamics
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Reproductive responses of two forest herb species to soil warming at Harvard Forest.
Blanchard, Joseph*,1, Mohan, Jacqueline1, Hanifin, Robert2, Burrows, Elizabeth 1, Melillo, Jerry1, 1 The Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA2 Dickinson College, Carlisle, PA
ABSTRACT- Global temperatures are rising and an increase of up to 5.5 °C by the end of this century is predicted for the New England region. Increased temperatures may alter growth and reproductive patterns of forest plant species, including understory herbaceous taxa. Two such species common in northeastern forests are Trientalis borealis Raf. (starflower) and Maianthemum canadense Desf. (Canadian mayflower). At the original Harvard Forest soil warming experiment soil nitrogen availability was increased by almost 80% under warming. Previous work has demonstrated a correlation between nutrient availability and plant reproductive output. We hypothesized that these herbaceous species, which normally exhibit primarily vegetative spread, would increase sexual reproduction in response to heating. We further hypothesized that increased light availability would preferentially enhance the reproductive output of plants in the heated plot. Soil warming commenced May 2003 in a 900m2 forest tract which, by way of buried heating cables, is warmed to 5 °C above an adjacent control plot. Trientalis exhibited no overall increase in reproductive probability under heating (p=0.67) and only a modest tendency to increase flowering in response to light availability (p=0.17). Longer stems of both species were more likely to be reproductive than shorter stems (p<0.001 for both taxa), but Trientalis stems >10 cm long were less likely to be sexually reproductive in the heated plot (p<0.05). Trientalis stem density increased more in the heated treatment vs the control from 2003-2004. These data suggest an enhanced shift in reproductive effort away from sexual towards vegetative reproduction. In 2004 a smaller percentage of Maianthemum stems were sexually reproductive in the heated versus the control treatment (p=0.06); this trend was also observed in 2004 at the original experiment (p<0.001; heated for 14 years). Neither species exhibited an interaction between heating and light availability in determining reproductive probability. Overall, soil warming diminished the sexual reproduction of Maianthemum and the largest Trientalis plants. Additional sampling in subsequent years will highlight the potential long-term nature of these responses.
Key words: climate change, New England forests, Trientalis borealis, Maianthemum canadense