I have been excited to make a post saying that my degree was conferred, and as of 5/26/2016, I can! You can find the full dissertation here: Dissertation
Rangeland ecosystems, and grasslands in particular, are one of the most threatened ecosystems worldwide (Hamilton et al., 2002; Heady et al., 1992; Samson and Knopf, 1994). Grasslands are primarily utilized for the production of food and fiber via livestock grazing (Huntsinger et al., 2007), and conservation of the flora and fauna found in grasslands is complicated by weed invasions, economic and social considerations, habitat destruction and fragmentation, climate change, and inherent inter- and intra-annual climatic variability (Hobbs and Huenneke, 1992; Jetz et al., 2007; Mann and Gleick, 2015; Seabloom et al. 2003). The outcomes of many restoration and management practices are not always well understood or predictable (Temperton et al., 2013). For example, many common restoration practices, like flushing the weed seed bank, have not been validated by experimental evidence. Often restoration methods that had high success in one year and setting fail to produce similar results in a different year and setting (von Gillhaussen et al., 2014; Young et al. 2013).
Chapter One focuses on a common practice in pre-restoration settings, in which water is applied to flush weeds, after which they are killed by a variety of possible methods. While this has not been fully investigated in a pre-restoration setting, the consequences of this type of weed management tactic are even less clear in a post-restoration setting. Other studies have investigated the result of very limited flushing (very few seedlings germinated) in a post-restoration setting, but only in the very short-term, stopping after the start of ambient rainfall (Wainwright et al., 2012). Thus, it was not clear whether this method for the post-restoration management of weeds – particularly in settings where use of herbicides, mowing, grazing, and burning are restricted – would effectively reduce annual grass weed pressure in the longer-term through the following growing season. We investigated the use of targeted watering in California’s long and dry summer season to flush exotic annual grasses, followed by death by desiccation, to determine if this practice could produce a substantial annual grass weed flush, provide a competitive edge to native perennial grasses, reduce the annual grass seed bank, and reduce overall exotic annual grass cover in the following growing season, and benefit native perennial grasses in the following year.
In Chapter Two we shift focus to grazing management in grasslands, and in particular, focus on the ongoing debate regarding the efficacy of rotational and continuous grazing management systems. In their pivotal paper “Rotational Grazing on Rangelands: Reconciliation of Perception and Experimental Evidence,” Briske et al. (2008) concluded that continued recommendations promoting the use of rotational grazing practices as being superior to continuous grazing practices were based primarily on anecdotal evidence, and not on the bulk of scientific evidence. However, this conclusion is limited by use of a relatively low-power vote-counting method of analysis which does not take into consideration other potentially influential factors, such as climate or scale of study, nor does it provide quantitative estimates of effects. We conducted a quantitative meta-analysis incorporating sixteen predictor variables to assess the relative performance of rotational to continuous grazing practices across the same set of studies used by Briske et al. (2008) in order to better elucidate the circumstances under which one grazing practice might be expected to produce superior results compared to the other.
Finally, in Chapter Three we shift gears to investigate the responses of wildlife to grassland restoration. While restoration is often assumed to be beneficial for wildlife, and native wildlife in particular, very few studies have investigated the responses of wildlife to restoration at large scales for a suite of species or guilds (Boyd and Svejcar, 2009), especially in the Central Valley of California (Bash and Ryan, 2002; Golet et al., 2008). We monitored rodent, snake, and diurnal raptor activity and species richness for up to four seasons in paired unrestored exotic annual grasslands and restored native perennial grasslands at four locations in the Yolo and Sacramento counties from 2014–2015. We also monitored vegetation structure and cover to investigate localized responses to vegetation parameters, such as height, bare ground, litter, and native and exotic cover. We used wildlife activity as an index of wildlife abundance, comparing relative abundance between unrestored and restored grasslands within locations. Such information will assist land managers and wildlife biologists in predicting responses of these wildlife groups to different management practices that alter vegetative composition and structure.
Bash, J.S., Ryan, C.M., 2002. Stream restoration and enhancement projects: is anyone monitoring? Environmental Management 29:877–885.
Boyd, C.S., Svejcar, T.J., 2009. Managing complex problems in rangeland ecosystems. Rangeland Ecology and Management 62:491–499.
Briske, D.D., Derner, J.D., Fuhlendorf, S.D., Teague, W.R., Havstad, K.M., Gillen, R.L., Ash, A.J., Willms, W.D., 2008. Rotational grazing on rangelands: reconciliation of perception and experimental evidence. Rangeland Ecology and Management 61:3–17.
Golet, G.H., Gardali, T., Howell, C.A., Hunt, J., Luster, R.A., Rainey, W., Roberts, M.D., Silveira, J., Swagerty, H., Williams, N., 2008. Wildlife response to riparian restoration on the Sacramento River. San Francisco Estuary and Watershed Science 6:1–26.
Hamilton, J.G., Griffin, J.R., Stromberg, M.R., 2002. Long-term population dynamics of native Nassella (Poaceae) bunchgrasses in Central California. Madroño 49:274–284.
Heady, H.F., Bartolome, J.W., Pitt, M.D., Savelle, G.D., Stroud, M.C., 1992. California prairie, in: Coupland, R.T. (Ed.), Natural Grasslands: Introduction and Western Hemisphere. Elsevier Science Publishers, New York, NY, pp. 313–335.
Hobbs, R.J., Huenneke, L.F., 1992. Disturbance, diversity, and invasion: implications for conservation. Conservation Biology 6:324–337.
Huntsinger, L., Bartolome, J., D’Antonio, C., 2007. Grazing management on California’s Mediterranean grasslands, in: Stromberg, M., Corbin, J., D’Antonio, C. (Eds.), Ecology and Management of California’s Grasslands. University of California Press, Berkeley, CA, pp. 233–253.
Jetz, W., Wilcove, D.S., Dobson, A.P., 2007. Projected impacts of climate and land-use change on the global diversity of birds. PLoS Biology 5:e157.
Mann, M.E., Gleick, P.H., 2015. Climate change and California drought in the 21st century. Proceedings of the National Academy of Sciences 112:3858–3859.
Samson, F., Knopf, F., 1994. Prairie conservation in North America. BioScience 44:418–421.
Seabloom, E.W., Harpole, W.S., Reichman, O.J., Tilman, D., 2003. Invasion, competitive dominance, and resource use by exotic and native California grassland species. Proceedings of the National Academy of Sciences 100:13384–13389.
Temperton, V.M., Hobbs, R.J., Nuttle, T., Halle, S. (Eds.), 2013. Assembly rules and restoration ecology: bridging the gap between theory and practice. Island Press, Washington DC.
von Gillhaussen, P., Rascher, U., Jablonowski, N.D., Plückers, C., Beierkuhnlein, C., Temperton, V.M., 2014. Priority effects of time of arrival of plant functional groups override sowing interval or density effects: a grassland experiment. PLoS ONE 9:e86906.
Young, T.P., Zefferman, E.P., Vaughn, K.J., Fick, S., 2015. Initial success of native grasses is contingent on multiple interactions among exotic grass competition, temporal priority, rainfall and site effects. AoB PLANTS 7:plu081.