Population Status and Reproductive Biology of Clematis Morefieldii, a Federally Endangered Plant
Type of Degreethesis
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Clematis morefieldii is a federally endangered, perennial climbing vine. It inhabits limestone drains and outcrops on the Cumberland Plateau escarpments of northeast Alabama and south-central Tennessee. The NatureServe network ranks this species as imperiled in Alabama and critically imperiled in Tennessee. Given its habitat specificity, localized distribution, and rarity, it is of considerable interest to the conservation community and to the organizations obligated to manage it. Since its discovery over 30 years ago, there has been no in depth study of this species and pertinent information for management is absent. The goal of this thesis is to investigate the condition of current populations, document the species’ biology and life history, and assess impacts of herbivory. To achieve this goal, a one-year population structure and herbivory survey, a four-year reproductive attrition study, and a three-year insecticide study were conducted between 2009-2012, sponsored, in part, by the U.S. Fish and Wildlife Service. The population structure and herbivory survey estimated range-wide population numbers, described proportions of life history stages in each population sampled, and evaluated the extent of vegetative herbivory in each sampled population across the range of C. morefieldii. As of 2012, population numbers are estimated to be 8,868 in Alabama and 6,751 in Tennessee, totaling 15,619 plants across the range of the species. Non-reproductive plants made up the largest proportion of populations (~55%) and reproductive plants made up the smallest proportion (~10%). Alabama populations experienced significantly greater levels of vertebrate browse damage (3-fold) and piercing-sucking herbivore damage (2- to 3-fold) than Tennessee populations. Seedling and non-reproductive plants experienced significantly greater levels of invertebrate browse damage (1.5- to 2-fold) than reproductive plants. These descriptive data provided a snapshot of the state of populations across the species’ range. Reproductive attrition, seedling establishment, and herbivory extent were studied at The Nature Conservancy’s Keel Mountain Preserve in Madison County, Alabama. Study of reproductive attrition (2009-2012) found high levels of floral herbivory (30 to 70% loss attributed to herbivory each year) with the greatest damage occurring to flower buds in their smallest stage (15 to 50% attrition to herbivory). Post-dispersal predation of achenes (likely by rodents) was 15% after one week and slowly reached 30% by four months. Seeds failed to germinate the first year after planting, but germinated in significantly greater amounts the second year (23%) compared to the third (9%), indicating that a seed bank likely exists. To estimate the impact of invertebrate vegetative and floral herbivory on reproduction, an insecticide study (2010-2012) was designed to exclude invertebrate herbivores from some plants and compare reproductive attrition to that of control plants sprayed with water. Insecticide applications increased flower bud survival and fruit production while decreasing floral herbivory. However, reproductive output was not affected by herbivory when peak flowering/fruiting season rainfall was limiting. While recruitment is occurring in surveyed Clematis morefieldii populations, herbivore exclusion could be a viable management option for increasing plant numbers in small populations if rainfall and suitable habitat are not limiting. High levels of vegetative herbivory and low levels of florivory occurred across the species’ range in 2012. Reproductive attrition studies documented high levels of florivory, and a bottleneck in reproductive unit maturation that could limit reproductive output. Rainfall was positively associated with reproductive output, but during high rainfall years invertebrate herbivory destroys a greater percentage of reproductive units, probably due to a combination of direct (attacks on flower buds and flowers) and indirect pathways (by vegetative herbivory). Insecticide treatment could be a useful option for managers seeking to increase recruitment to small populations. Despite moderately high post-dispersal achene predation levels and only a third of seeds germinating over three years, seedling recruitment was occurring across the range of Clematis morefieldii. I conclude that despite challenges by herbivores this species is not at imminent risk of extinction due to the probable longevity of individual plants, evidence of recruitment into existing populations, and the large sizes of some populations.