Graduate Thesis Or Dissertation
 

Emergence, survival and reproduction of three species of forbs important to sage grouse nutrition in response to fire, microsite and method of establishment

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  • Since settlement of the Intermountain West, sage grouse abundance and productivity has declined and their range has decreased. The decline of sage grouse populations is primarily due to permanent loss and degradation of sagebrush-grassland habitat. Recently, several studies have shown that sage grouse productivity may be limited by the availability of certain preferred, highly nutritious forb species that have also declined within sagebrush ecosystems of the Intermountain West. During the spring and summer, forbs are extremely important in maintaining the nutritional status and productivity of pre-laying hens and growth and survival of rapidly growing chicks. Researchers studying sage grouse have suggested several methods for restoring forbs in depleted sage grouse habitat. Among the methods proposed are prescribed fires that produce small mosaics of burned and unburned patches on the landscape. For this to occur, an adequate pre-burn forb community must exist in the location of the fire. In areas without adequate pre-burn forb communites, forbs must reseed naturally or be revegetated. The purpose of this study was to determine the suitability of three species of forbs for revegetation projects where improving sage grouse habitat is a goal. Species suitability was determined by evaluating the emergence, survival and reproduction of Crepis modocensis Greene, Crepis occidentalis Nutt. and Astragalus purshii in response to method of establishment (seeding or transplanting), pre-establishment treatment (burned or unburned), and microsite (mound or interspace). Four prescription burns of sagebrush grassland were set at the United States Fish and Wildlife Service Hart Mountain National Antelope Refuge, Oregon. After burning, one experimental plot was randomly located within each burned and unburned site. Of the seeds planted in 1997, A. purshil had the lowest emergence (8%) of all three species. Both Crepis species had similar overall emergence (38%). Significantly more Crepis seedlings emerged from shrub mounds in unburned areas (50%) than in any other fire by microsite treatment (33 to 36%). Significantly more A. purshuii emerged in the burned interspace (10.9) compared to the burned mounds (3.5). Nearly twice as many emerging Crepis seedlings survived in the burned areas as opposed to unburned areas (P<0.01). This resulted in more plant establishment in burned mounds despite higher emergence in unburned mounds. Microsite also significantly affected survival of Crepis seedlings (P<0.01). Approximately 10% more Crepis seedlings survived in mounds compared to interspaces. A. purshuii seedlings also survived better in burned areas (P=0.06), but had no differential response to microsite. Fire enhanced survival of both Crepis and A. purshii transplants (P=0.08 and P=0.001), although, transplanting did not enhance plant establishment over seedings. Therefore, I conclude that revegetation of sage grouse habitat with Crepis species is a viable option given its high germinability, favorable response to fire and wide distribution.
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