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Emily Thompson - Plant Ecology Lab

College of William and Mary, Williamsburg, VA

Growth and reproduction of an exotic plant along a light gradient:

The case of wineberry, Rubus phoenicolasius.

In forests, plant invasions are often facilitated by an increase in light and other resources that become available after a tree-fall event or disturbance. We investigated the growth and reproduction of wineberry, Rubus phoenicolasius Maxim (Rosaceae) along a light gradient in old (>120 years succession) and young (>50 years succession) forest stands at the Smithsonian Environmental Research Center in Edgewater, MD, USA. We hypothesized that (1) non- reproductive biomass would increase as light increases and (2) reproductive biomass would increase with light after a threshold, below which fruit production would be too costly.  We measured floricanes and counted fruits per floricane in 48 15m x 15m plots ranging 0.86- 16.90% photosynthetic photon flux density (%PPFD).   We used regression equations from 15 harvested and dried plants of each floricane stem tip type (aerial, prostrate, and tip- rooted) to estimate above-ground floricane biomass for each plant within the study plots.  We calculated reproductive biomass by multiplying the mean mass of 25 dried fruits times the number of fruits per floricane.  We calculated both non-reproductive and reproductive biomass per floricane, and then averaged among floricanes within a plot.  Non- reproductive biomass was positively related to %PPFD (R²= .3379, p= 0.0114).  The relationship between light and reproductive biomass was not significant; however, floricanes of reproductive size did not produce fruits below 5% PPFD in the old forest.  No threshold existed in young forests.  These results suggest that floricane growth and reproduction were influenced by light availability, but other factors may have affected fruit production of young forest floricanes. This research has implications for the prediction of forest stands most vulnerable to invasion.

This project was presented as a poster at the winter ASLO meeting held in February 2006 in Mexico.

Funding provided by the National Science Foundation - REU