Graduate Thesis Or Dissertation

Evaluating the Effects of Traditional Harvest and Climate on Common Camas (Camassia quamash) in Weippe Prairie, Idaho

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  • Common camas (Camassia quamash) is a culturally important wetland plant, used as a staple food source by many indigenous peoples of western North America for thousands of years. Camas populations were once widespread, but conversion of wetland prairies to agriculture has led to declines in suitable habitat. Edible camas bulbs were traditionally harvested by digging the bulbs from soil, and it has been hypothesized that this process can result in an increase in the number of camas plants growing in harvested areas. Given that camas depends on seasonally wet prairies, climate and water balance are also likely drivers of camas population density fluctuations. To better understand the influences on camas populations, I conducted an experiment at the Weippe Prairie, Idaho historical site to evaluate the strength of treatment effects of simulated traditional harvest practices, including harvest, fire, and a combination of harvest and fire on three reproductive classes of common camas plants. I considered these impacts on native and non-native prairie grasses, litter, and bare ground as well. My experiment was conducted alongside of a longer-term camas population monitoring program. I used a 10-year set of camas density and flowering rate observations to analyze responses of camas to climatic and hydrological variables including average departure from 30-year means of precipitation, and minimum and maximum temperature, as well as water balance values including minimum soil moisture, actual evapotranspiration, and water deficit. I also evaluated the effects of elevation and topographic wetness index on camas densities within the study area. Study results indicate that both harvesting practices and climactic variation can have significant impacts on camas plant productivity and reproduction, and can maintain favorable growing conditions. Common camas plant densities and flowering plant densities declined following both a simulated digging and harvesting plot treatment as well as a combination treatment of harvest and fire. Single-leaf camas plants also declined following the combination treatment of simulated harvest and fire. Flowering plant densities and multiple-leaved camas were found to increase following fire, plants also increased following fire. Disturbances caused by fire and a combination of harvest and fire resulted in lower litter cover, higher bare ground cover, and a reduction in competing plant cover. Increases in camas density were correlated with above average precipitation while decreases in camas density were correlated with above average temperatures and increased soil water deficit values. Higher camas density is correlated with lower site elevation, as well as lower values of topographic wetness index. These newfound relationships between camas productivity and the impacts resulting from camas harvesting and varying climatic conditions increase the knowledge surrounding camas growing in natural settings and may be useful for considering the physiology of other temperate geophytes, particularly those that have previously been exploited as a food source. These results will be vital when evaluating the effectiveness of restoration treatments in camas prairies.
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