Abstract Detail

Conservation Biology

Yawn, Noah [1], Boyd, Robert [2].

7-year study reveals demographic shifts of a rare plant (Trillium pusillum) in response to herbivory.

The Least Trillium, Trillium pusillum Michx. (Trilliaceae), is a rare, herbaceous, perennial member of the Alabama (USA) flora. Alabama populations may represent a separate and distinct entity of much greater rarity, Trillium alabamicum, warranting increased conservation concerns. We examined the effects of herbivory on a population of T. pusillum at the Redstone Arsenal in Madison County, Alabama, over a period of seven years (2016–2022). Ten paired plots containing approximately equal quantities of T. pusillum individuals were randomly assigned treatment as caged or uncaged plots, thereby preventing or allowing herbivory to potentially occur. As is typical in Trillium, plants emerge from underground rhizomes in late winter and die back below ground by late spring. Plots were visited repeatedly during each growing season to count numbers of plants in each of three life history stages (e.g., single-leaf, three-leaf, flowering) as well as numbers of successful fruits produced. We also recorded and counted stems of plants eaten by herbivores during each visit. Little or no herbivory damage was observed during the first three years of the study (2016–2018). But in 2019, in open plots 45% of mean total stems/plot were eaten, and herbivory continued in open plots during 2020 and 2021, with 24% and 6% of mean total stems/plot eaten, respectively. While mean plant counts/plot did not vary significantly between open and caged plots in any year, there was a life history stage shift in open plots after herbivory. Prior to herbivory (such as in 2016), flowering stem counts were similar in open and caged plots (mean percent flowering stems were 10.4% stems/plot in caged plots and 9.2% stems/plot in open plots). In the 2021 survey year, after the herbivory damage of 2019 and 2020 and despite low herbivory in open plots that year, flowering plants were 15.5% stems/plot in caged plots but only 0.3% stems/plot in open plots. This demographic shift impacted total fruit production in 2021, when mean percent fruiting stems were 11.1% stems/plot and 0.3% stems/plot for caged and open plots, respectively. Herbivory significantly altered demographic composition and fruit production of T. pusillum in open plots implying that, over time, repeated herbivory may reduce sexual reproduction in this population. These findings support implementing management practices that reduce herbivory to conserve imperiled Trillium.

1 - Auburn University, Department of Biological Sciences, 101 Rouse Life Sciences Bldg, Auburn University, AL, 36849, USA
2 - Auburn University, Department Of Biological Sciences, 101 Rouse Life Sciences Bldg, Auburn University, AL, 36849, United States

Keywords:
Trillium
Trilliaceae
demography
herbivory
species conservation
spring ephemeral.

Presentation Type: Oral Paper
Number: CB2003
Abstract ID:228
Candidate for Awards:None