Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2011
Publication Date: 12/31/2011
Citation: Williams, J.D., Hartman, H.M., Spencer, L.M., Loiland, J.O. 2011. Plant community development in a dryland CREP in Northeastern Oregon. American Journal of Plant Sciences. 2(6):744-752. Interpretive Summary: Areas adjacent to small streams in croplands have been converted to and used for crop production during the past 140 years in the Intermountain Pacific Northwest. Now many of these areas are being enrolled in federal natural resources conservation programs to provide filter strips, to improve water quality and habitat for wildlife. We sampled one such site shortly after it was seeded with a conservation mix of plants, and revisited the size six years later to determine the degree of early establishment and persistence of the vegetation. Within in year of seeding, the site had complete cover, important for protection against erosion and trapping soil washed from upland fields. One species in particular, Tall wheatgrass, dominated the site in the first two years after seeding, which grows to a height of six feet or more, providing substantial cover for birds and small to medium size mammals. After six years, the site remained substantially covered, but there was a substantial decrease in the amount of cover provided by living plant material, with the greatest decrease in living plant material coming at the expense of tall wheat grass, and a substantial increase in a number of volunteer weedy, introduced (non-native) plant species. We suggest that more active management of this site would increase its productivity and control the increase in weeds. Active management might take the form of controlled burns, grazing, or harvest by mowing or baling straw. More research is needed to determine the best management prescription to optimize the productivity of sites such as the one described here.
Technical Abstract: Riparian areas in dryland crop regions of the Intermountain Pacific Northwest have largely been converted to cropland or pasture during the last 140 years. Native riparian vegetation in flood plains was replaced by introduced species growing on abandoned floodplains intersected by narrow, incised channels. Channel migration makes these areas difficult to farm and the presence of sodic soils inhibits profitable crop production. Enrollment of these lands into conservation programs provides the opportunity to create buffer areas to capture runoff and sediment from surrounding cropland and roads before it enters streams, and create wildlife habitat. Our objective was to evaluate the vegetation development in one of the earliest sites enrolled in the Conservation Reserve Enhancement Program (CREP) in northeastern Oregon. Three stream reaches were identified by the degree of stream channel incision through the project area. Within each reach, we established permanent line transects to sample vegetation cover. Approximately equidistance, six transects were established in reach one, four in reach two, and seven in reach three. Each transect extended 50 m perpendicularly from the greenline on either side of the stream and was stratified in 5 m increments within which plant species were identified and recorded at five random points. Cover and species composition along the transects and between reaches and years were analyzed using general linear models and least-square means. Ground cover in 2000 and 2001 was complete following planting in the spring of 1999. Tall wheatgrass (Thinopyrum ponticum (Podp.) Z.-W. Liu & R.-C. Wang) dominated cover at the site in 2000 and 2001 at 77 percent and 81 percent. The next most abundant seeded species was Alkali sacaton (Sporobolus airoides (Torr.) Torr.) at eight percent cover in 2000, but it, as all other seeded species contributed less than two percent of the cover in 2001. The most abundant volunteer species in 2000 was Wild oats (Avena fatua L.), joined in 2001 by Kochia (Bassia scoparia (L.) A.J. Scott). We measured a significant, but unsubstantial three percent decrease in the total cover between the values recorded in 2000 and 2001 compared to 2007 and 2008. More importantly, this decrease was accompanied by a significant decrease in the contribution to cover by living plant material from 98 percent in 2000 and 2001 to 33 percent in 2007 and 68 percent in 2008, with the difference in cover consisting of dead plant residue and a significant decrease in cover provided by Tall wheatgrass. Increases of Canada thistle (Cirsium arvense) and Common cattail (Typha latifolia L.) were recorded between 2001 and 2007, and Basin wild rye (Leymus cinereus (Scribn. & Merr.) A. Löve) in 2008. Although native species were similarly present in 2000-01 and 2007-08, there was a minor shift in contribution from seeded to volunteer species. In terms of providing ground cover at this site, the 1999 seeding can be judged a success, especially with the establishment of Tall wheatgrass. Tall wheatgrass is well suited for sites such of this with high water tables and sodic soils, and at the end of eight years contributes a proportion of total ground cover commensurate with its ratio in the seed mix. The increased ratio of dead residue to living plant material suggests that more active management of the Tall wheatgrass stand is needed to maintain its productivity or a healthy mix of multiple species. This goal might be met by fire, grazing, or mowing, although more research is warranted to determine the optimal type, timing, frequency, and degree of disturbance needed to optimize these sites for a mix of environmental services.