Abstract Detail

Conservation Biology

Berry, Eric [1], Garrette, Ryan [2].

Impact of Shade on Seed Germination, Seedling Development, and Population Growth of the Endangered Wildflower Northern Wild Senna (Senna hebecarpa).

Northern Wild Senna (Senna hebecarpa) is an endangered native wildflower that is restricted to only 7 extant populations in New England, including our field site in Amherst, NH. The decline of the species has been attributed primarily to changes in habitat by human development, and changes in hydrology from ditching and dams that have altered the flooding regimes along stream banks and wet meadows that are the species prime habitat. Much of this habitat has undergone further change via secondary succession whereby trees and large shrubs have replaced herbaceous species as dominant vegetation. Evidence from related species indicates that S. hebecarpa may not be well adapted to such shaded conditions, raising questions about the role of succession in contributing to the species decline. Our study addressed this question by examining the impact of light intensity on seed germination, seedling growth, and seedling development. Experimental greenhouse shade experiments (ambient, light shade, heavy shade) revealed that shade-grown seeds germinated at a higher percentage, but seedlings showed signs of etiolation as measured by increased stem elongation, reduced stem diameter, and reduced leaf area. These shade-grown seedlings also exhibited traits that correspond with reduced photosynthetic capacity, including increased specific leaf area and decreased stomatal density. We incorporated these findings into matrix models parameterized using demographic field data to simulate the effect of shade on adult fecundity and the finite rate of population growth (λ). Specifically, we modeled the effect of reduced size on reproduction in hypothetical shade-grown populations experiencing 25%, 50%, and 75% reductions in adult size. Although elasticity analysis suggests that λ is relatively insensitive to changes in seed production, the magnitude of the decline in seed production produced by smaller shade-grown adults resulted in significantly lower λ’s. Our research indicates that S. hebecarpa is not well adapted to low light environments, and may therefore be vulnerable to increased shade produced from successional changes in vegetation.

Broader Impacts:

1 - Saint Anselm College, Biology, 100 Saint Anselm Drive, Manchester, NH, 03102, USA
2 - Saint Anselm College, 100 Saint Anselm Drive, Manchester, NH, 03102, USA

Keywords:
Senna hebecarpa
finite rate of growth
seedling growth and development
etiolation
secondary succession
shading effects.

Presentation Type: Oral Paper:Papers for Topics
Session: 47
Location: 551A/Convention Center
Date: Wednesday, August 4th, 2010
Time: 9:15 AM
Number: 47006
Abstract ID:204