Ecological Investigation of a Population of Trillium pusillum at Redstone Arsenal, Alabama

Abstract

Trillium pusillum is a state-imperiled spring wildflower. Much information concerning its biology remains largely unknown. Four aspects of T. pusillum biology were investigated during this study. First, edge effects on life stage distribution were observed through comparative life stage counts among four belt transects. There were two edges onsite, one by a powerline and one by a road. Three transects were established at different distances parallel to the powerline edge and one transect was established parallel to the road edge. Counts of one-leaved, three-leaved, and reproductive plants were recorded three times a year for two years. Fruiting plants were counted as a subset of reproductive plants. T-tests were used to compare differences in counts between transects. Edge transects had higher percentages of reproductive plants than interior transects, which had higher percentages of one-leaved plants. Despite interior transects having smaller percentages of reproductive plants, plants in interior transects had the highest fruiting success. This study demonstrated edge effects on T. pusillum at this site. Second, deer herbivory was investigated via plant counts in ten pairs of T. pusillum clusters. Yearly plant count averages for both caged and uncaged clusters were compared via t-tests for 2016 through 2018. Plant counts did not differ significantly between caged and uncaged plots over the three years, showing no evidence of onsite deer herbivory. Third, seeds were buried in sleeves to test for a seed bank. Some seed sleeves were buried for two years while others were buried for three years. All buried seeds had germinated or rotted when they were unearthed in spring of 2018. Therefore, T. pusillum cannot retain a seed bank for more than two years. Lastly, some aspects of the pollination biology of T. pusillum were investigated, along with a survey of potential floral visitors. The pollination biology research consisted of a self-pollination study and a pollen-supplementation study. In the self-pollination study, assisted selfing flowers produced a mean of 9.3 seeds per area and spontaneous selfing flowers produced a mean of 2.3 seeds per area. For the pollen-supplementation study, supplemented flowers produced a mean of 59 seeds per area while unsupplemented seeds produced a mean of 53 seeds per area. For both studies, t-tests showed there was no significant difference between mean seed counts of the treatments, showing that T. pusillum can produce seeds through selfing and that insect pollination of flowers produces as many seeds as pollen-supplemented flowers. One last t-test compared seed means between spontaneous selfing flowers and unsupplemented flowers. It revealed a significant difference, showing that self-pollinated flowers produce many fewer seeds than insect-pollinated flowers. Thus, insects pollinating T. pusillum are highly effective at pollination. The survey of potential floral visitors consisted of a study to document potential floral visitors (through pan and fermentation traps), along with a visual floral visitor survey. Nitidulid beetles visited flowers and were the most numerous specimens captured during the visual survey. These beetles also were captured in both trap types used during the potential floral visitor study. For these reasons, members of this genus might be pollinators of T. pusillum on this site. Future research might extend these studies to examine how edge effects may influence pollination success in Trillium pusillum.