Factors affecting safe-guarding of the federally endangered Schwalbea americana L. (Orobanchaceae)
Type of DegreeMaster's Thesis
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Schwalbea americana L. (American chaffseed) is a federally endangered hemi-parasitic plant (USFWS 1992). Its tendency to persist with limited recruitment and threats to its habitat make it vulnerable to extirpation. Additionally, any attempt to safe-guard a population of S. americana is made difficult by the fact that no clearly defined protocol exists for propagating and out-planting, with published studies reporting limited success. The goal of this research is to improve future conservation efforts of this rare species. The chapters in this work describe studies with the following goals. Chapter 1 describes the historic abundance, species biology and current status of S. americana. Chapter 2 uses the size class and reproductive status of plants at the one known natural site in Alabama from 2010 to 2016 to describe current trends and present short-term projections of site viability. Chapter 3 uses shade huts to examine the effect of three shade levels and the size and presence of host plants on S. americana size in an attempt to improve propagation protocols and out-planting site choice. Chapter 4 describes three preliminary studies aimed at improving future out-planting efforts. Preliminary Study 1 compares five host species by number, size and number of leaves of attached S. americana. Preliminary Study 2 examines the effect of fertilizer on S. americana size with and without a host present. Preliminary Study 3 assesses the ability of S. americana to regrow from cuttings. It also assesses the effect of smoke on regrowth of cuttings and on regrowth of the original seedlings following removal of aboveground biomass. An assessment of demographic trends of the one known S. americana site in Alabama is described in Chapter 2. If the observed trends persist there will be a minor reduction in number of active individuals of S. americana at the site in 2017 but a slight increase in number of reproductive individuals. However no definite conclusions can be drawn as to the long-term viability of the site. An apparent dormancy or extirpation of S. americana from much of the site occurred between 2008 and 2010. If S. americana has been extirpated from numerous locations at the one known Alabama site it is at increased risk of local extinction, which is of conservation concern. Long-term monitoring is needed to shed light on the viability of the known S. americana site in Alabama. The effect of shade on S. americana size was examined in Chapter 3. The first study in this chapter included a host presence/absence treatment with Pityopsis graminifolia (Michx.) Nutt. as the host and two shade levels. No effect of shade or host presence/absence was detected. When only S. americana individuals with a host present were included, P. graminifolia was correlated with increased S. americana height and leaf size. This suggests that a host’s increased ability to provide nutrients improves parasite health. The second study did not include a host treatment and examined three shade levels: no shade, 33% shade and 61% shade. The 33% shade treatment yielded S. americana with significantly greater height than those grown without shade and stems with more nodes than those grown in 61% shade. Among the three shade levels 33% shade is recommended for propagation and selection of out-planting sites over the other two. Three preliminary studies are described in Chapter 4. Study 1 examined S. americana’s response to five host species. Attached clusters of greenhouse-grown S. americana and its hosts were unearthed and measured. Eupatorium capillifolium (Lam.) Small was found to have more attached S. americana than three other host species. It was also found to have attached S. americana with significantly greater height than two other species. E. capillifolium is recommended as a potential host for growing S. americana for out-planting. Study 2 examined the effects of fertilizer on S. americana size. The first portion of the study did not include a host and included seedlings grown from seeds collected in Alabama and South Carolina, analyzed separately. South Carolina seedlings were significantly taller and had significantly larger leaves when fertilized. Alabama seedlings were significantly taller when fertilized but did not have significantly larger leaves. The second portion of the study examined S. americana grown from seeds collected in South Carolina only, with a host present. The fertilizer treatment was correlated with significantly taller S. americana but had no detectable effect on leaf size. Fertilizer is therefore recommended when growing S. americana for out-planting in order to increase seedling size. Study 3 used the seedlings from the second portion of Study 2 to determine the potential of cuttings as a method of S. americana propagation and the effects of smoke on regrowth. Half of the flats were applied with smoke then all aboveground biomass was clipped and stems were replanted. 42 out of 48 cuttings exhibited new growth following replanting. Cuttings are therefore recommended when growing S. americana for out-planting in order to increase number of stems. Smoked plants did not regrow at a greater percentage than unsmoked plants either in the original flats or as cuttings. S. americana is federally endangered and is at extreme risk of extirpation from Alabama. Its tendency to persist with limited recruitment indicates it may benefit from population augmentation. Efforts to out-plant S. americana are made difficult by a lack of clearly defined propagation and out-planting protocols. It is the goal of this research to improve future efforts through a greater understanding of the conservation concerns of S. americana in Alabama, effective propagation methods in the greenhouse and out-planting site choice for the species.