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Publication Date


First Advisor

Jesse Bellemare

Document Type

Masters Thesis

Degree Name

Master of Science


Biological Sciences


Climatic changes, Liliaceae-Climatic factors, Liliaceae-Geographical distribution, Liliaceae-Effect of global warming on, Global warming, Biotic communities, Distribution limits, Biotic interactions, Range shifts, Clintonia borealis


Anthropogenic climate change is predicted to have major effects on the distributions of plant and animal species. Geographic ranges are expected to shift poleward and to higher elevations in many regions. To date, most research efforts have focused on documenting poleward range shifts or movement to higher elevations at the “leading edge” of species’ distributions. In contrast, range contractions and population extinctions along species’ warm-margin distribution limits have received less attention, despite the expectation that these areas may be the principal sites of biodiversity loss in coming decades.

This study investigated evidence of abiotic and biotic effects on plant performance along an elevational and climatic gradient associated with the warm-margin distribution limit of a northern forest herb, Clintonia borealis (Ait.) Raf. (Liliaceae), in southern New England. Fourteen populations of C. borealis were surveyed for plant size, leaf traits, and reproductive performance across an » 1000-meter regional elevational gradient in western Massachusetts from the Connecticut River Valley to the top of Mt. Greylock. Additionally, a supplemental pollination experiment was conducted at four sites to test for evidence of pollen limitation and inbreeding effects on seed production near the species’ warm margin distribution limit.

Across the populations surveyed, estimated population size increased significantly with an increase in elevation (R2 = 0.6813, F1,12 = 25.65, p < 0.01). Clintonia borealis populations at higher elevations also included a significantly greater proportion of flowering plants compared to low elevation populations (R2 = 0.6778, F1,12 = 25.24, p < 0.01), and C. borealis plants in higher elevation populations had a significantly greater number of flowers per plant compared to plants in low elevation populations (t = 8.00, df = 433.12, p < 0.01). Mean leaf size also tended to increase with an increase in elevation, although not significantly (R2 = 0.1489, F1,12 = 2.099, p = 0.1731). Specific leaf area was significantly higher at low elevation sites (R2 = 0.30, F1,13 = 5.65, p = 0.03), likely linked to significantly greater soil moisture (t = -7.7842, df = 131.50, p < 0.01) in low elevation population sites which were closely associated with forested wetlands, as opposed to higher elevation areas where the species extended into upland forests with lower soil moisture levels. The broader population survey suggested that low elevation populations were isolated and often limited to spatially restricted cool, mesic habitat patches in the landscape, such as mesic or wetland forest habitats; high elevation populations were often extensive and occupied a range of forest habitat settings, from uplands to wetlands, dense and widespread, with a more general distribution, highlighting the potential impact of abiotic factors.

In the pollination experiment comparing reproductive performance in two high elevation populations versus two low elevation populations, fruit set via natural open pollination was significantly higher at high elevation than low elevations (60.9% vs. 19.5%, p < 0.001). With experimental pollen supplementation, fruit set increased significantly in low elevation populations (p < 0.01), while supplemental pollination at high elevations had no effect. Elevation also had a significant effect on seed production, as high elevation populations produced more seeds per fruit compared to low elevation populations (p < 0.01), possibly linked to the smaller number of seeds produced by low elevation plants. Supplemental pollination had no significant effect on seed mass.

The results of this study indicated that reproduction in lower elevation, warm-margin distribution limit populations of C. borealis was substantially affected by both abiotic and biotic factors, likely making these populations more susceptible to decline or local extinction with climate change. Many northern forest herbs with similar ecological requirements to those of C. borealis may be at substantial risk of local extinction in coming decades. The loss of such species along their warm-margin distribution limits will decrease species diversity and has the potential to modify species interactions and influence ecosystem processes. populations (p < 0.01), but supplemental pollination had no effect on seed production as measured by mean seed count per fruit. Elevation was significantly correlated with seed mass, as low elevation populations produced heavier seeds compared to high elevation




59 pages : color illustrations. Thesis (M.S.)-Smith College, 2017. Includes bibliographical references.