Spiranthes Parksii Correll is an endangered orchid of Texas. Populations of S. parksii are threatened by habitat loss and degradation resulting from human population growth and attendant development and resource extraction. Conservation easements have been established for the protection of the species, but little is known about the population dynamics of S. parksii and the biotic and abiotic factors which drive them. A baseline of ecological information is necessary to the creation of effective management plans for the conservation of this species. The work presented here is an experimental investigation of the affects of large herbivores on S. parksii population dynamics. We explored direct impacts of herbivore browsing as well as indirect impacts resulting from removal of neighboring vegetation on S. parksii population fluctuations and the demographic parameters underlying them. To determine direct herbivore affects on demographic characteristics and their implications for S. parksii population dynamics, we established 32, 1.5mx1.5m plots in areas of high S. parksii abundance. Each of the plots was randomly assigned one of two treatments: herbivore exclusion and control. Demographic parameters were recorded for each individual located within the plots. The data suggest that large and small herbivore browsing affects different lifecycle transitions through removal of photosynthetic and reproductive tissue. These transition alterations have the potential to affect S. parksii population growth. To investigate the indirect impacts of herbivory on S. parksii population dynamics, we established 32 5mx5m plots. Each plot was randomly assigned one of four fertilizer treatments: control, nitrogen addition, phosphorus addition, and nitrogen and phosphorus additions. One half of each plot was randomly assigned one of two biomass removal treatments: unaltered control and biomass removal during orchid dormancy. Demographic data was collected for individuals within the plots. Plots with phosphorus and nitrogen phosphorus additions generally differed regarding orchid demographic variables from nitrogen addition plots and unfertilized controls. Also, available light tended to be greater during orchid flowering in plots with biomass removed than in unclipped controls. A complete understanding of both direct and indirect herbivore impacts on S. parksii population dynamics is necessary for effective conservation of this endangered orchid.

Spiranthes parksii Correll is an endemic terrestrial orchid to the Post Oak Savannah of East Texas and is currently listed as federally endangered. The construction of Twin Oaks landfill, approximately 20 km east of College Station, TX, will destroy an estimated 379 S. parksii individuals and 44.7 ha of its habitat. Research has been funded to mitigate for this loss and includes documenting demographics, life cycle, local and landscape habitat, and on-site transplantation of S. parksii. Results found that S. parksii was highly variable between years at Twin Oaks and might be due to seasonal rainfall in rosette and early flowering growth. It was also found variable in its production of a rosette and influorescence from year to year. Individual plants were found to occur farther from drainages in higher count years, probably due to soil moisture, although further research should be conducted to confirm this hypothesis. A significant difference (p = 0.026) was found for percent canopy cover > 2 m above 1 m x 1 m quadrats with and without S. parksii, with a mean of 55 percent with S. parksii and 97 percent without S. parksii. A Non-Metric Multidimensional Scaling ordination revealed three different combinations of herbaceous species that occur with S. parksii, which were driven by the presence of three dominant bunch grasses of the Post Oak Savannah: Schizachyrium scoparium, Chasmanthium laxum var. sessiliflorum, and Andropogon ternarius. A close to significant difference (p = 0.07) was found for the leaf litter depth between quadrats with and without S. parksii, with a fewer number of stacked leaves with S. parksii. Analysis of aerial images indicated woody encroachment on Twin Oaks from 1958 to 2004 in areas that have not been mechanically cleared. Additionally, S. parksii was found to persist in an open savannah landscape and likely occurred in the same locations and more widespread in 1958 than are currently found. Transplantation of S. parksii was documented to be successful by a soil-intact method. While a bare-root method showed success with S. cernua, no conclusions can be made of its success for S. parksii due to a low sample size (n = 10).