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Harvard Forest Symposium Abstract 2005

• Title: First-Year Reproductive Responses of Two Herbaceous Species to Experimental Soil Warming at harvard Forest
• Primary Author: Robert Hanifin (Marine Biological Laboratory)
• Additional Authors: Jerry Melillo (Marine Biological Laboratory); Jacqueline Mohan (University of Georgia)
• Abstract:

  Global temperatures are rising and an increase of up to 5.5 oC by the end of this century is predicted for the New England region. Increased air and soil 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. (star flower) and Maianthemum canadense Desf. (Canadian wildflower). We sampled both species at the Barre Woods and Prospect Hill experimental soil-warming sites in Harvard Forest to determine if a 5 oC increase in soil temperature had caused any alteration in reproductive output. Longer stems of both species were more likely to be reproductive than shorter stems, but Trientalis stems >10 cm long were less likely to be sexually reproductive in the heated plot (Figure 1). This is particularly relevant as larger plants are generally the most important individuals for the reproductive success of a population. Trientalis stem density was higher in the heated treatment in both 2003 (the onset of heating) and 2004 (1-year post-treatment), but density increased more in the heated treatment versus the control over this time period. These data suggest an enhanced shift in reproductive effort away from sexual reproduction towards vegetative spread for Trientalis. In 2004 a smaller percentage of Maianthemum stems were sexually reproductive in the heated versus the control treatment at Barre Woods (Figure 2); this trend was also observed in the original Prospect Hill site (Figure 3). An apparent decrease in Maianthemum density at Prospect Hill may further indicate lowered reproductive effort at elevated soil temperatures. 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.

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