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This listing directly supports DOE and contractor efforts to assess the potential impacts of Hanford Site operations on the biological environment, including impacts to rare habitats and species listed as endangered or threatened. This document includes a listing of plants currently listed as endangered, threatened, or otherwise of concern to the Washington Natural Heritage Program or the U.S. Fish and Wildlife Service, as well as those that are currently listed as noxious weeds by the state of Washington.Also provided is an overview of how plants on the Hanford Site can be used by people. This information may be useful in developing risk assessment models and as supporting information for clean-up level and remediation decisions.

Field measurements of gas exchange and growth were conducted on a C grass,Agropyron smithii, and a C grass,Bouteloua gracilis, in order to further establish the adaptive significance of the C pathway under natural conditions. Maximum rates of leaf area expansion in tillers and maximum seasonal photosynthesis rates of both species occurred during the cool, early summer month of June. The occurrence of maximum growth and photosynthesis inB. gracilis during this cool period was apparently related to its occupation of warm microenvironments next to the ground surface. As temperatures increased during the midsummer, photosynthesis rates decreased to 47% and 55% of the seasonal maximum inB. gracilis andA. smithii, respectively. Water-use efficiencies in both species were similar or slightly higher forB. gracilis during June, the period of maximum growth. By mid-July, however, leaves of the C grass,A. smithii, exhibited water-use efficiencies approximately half as high asB. gracilis. These differences in water-use efficiency were the result of differences in stomatal conductance, rather than differences in daily CO uptake rates which were similar in both species. The results demonstrate that in certain environments there are no offset periods of growth and maximum photosynthesis during the growing season in these C and C species. The greater amounts of daily water use inA. smithii during the midsummer might contribute to its much greater abundance in lowland sites in the shortgrass steppe. The C grass,B. gracilis, occurs in dry upland sites in addition to the more mesic lowland sites.

SummaryThe Hanford Site Surface Barrier Development Program was organized in 1985 to test the effectiveness of various barrier designs in minimizing the effects of water infiltration; plant, animal, and human intrusion; and wind and water erosion on buried wastes, and in minimizing the emanation of noxious gases. Plants will serve to minimize drainage and erosion, but present the potential for growing roots into wastes. Animals burrow holes into the soil, and the burrow holes could allow water to preferentially drain into the waste. They also bring soil to the surface which, if wastes are incorporated, could present a risk for the dispersion of wastes into the environment. This report reviews work done to assess the role of plants and animals in isolation barriers at Hanford. It also reviews work done to understand the potential effects from climate change on the plants and animals that may inhabit barriers in the future.Plant studies have been done on community analysis, root characteristics, water balance, and water and wind erosion. Community analyses are reviewed in the context of native plants, invasive aliens, community dynamics, and revegetation efforts. Roots are examined with respect to water balance, other root functions, and intrusion into wastes. Water balance studies have been done at various locations on site, including McGee Ranch, the 300 North grass site, the Artemisia tridentuta/ Pseudoroegneria spicata community, and at Lower Snively field. Numerous lysimeter studies have examined the role of vegetation in water balance. Work has been reviewed to quanti@ the relationship plants have on water and wind erosion.Animal studies have focused on burrowing effects on soil water balance and the transport of buried wastes to the surface. This has been done for small and large mammals on site. Studies done to determine the role of animals on waste transport to the surface are reviewed.Studies on the role of plants and animals on barriers and climate change at Hanford were reviewed. Climate change studies have focused on assessing the potential range of climate conditions barriers may be exposed to over thousands of years and the potential consequences of such exposure on the plants and animals that may inhabit a barrier, and the water balance of a barrier. Climate change studies indicate that the present interglacial may last another 10,000 years, with the continental glacial ice reaching its maximum extent (important for the Pasco Basin because of its potential for contributing to catastrophic flooding) 100,000 years or more into the future.The optimal plant community for barrier function is one composed of deep-rooted perennial shrubs and grasses. Deep-rooted perennial shrubs and grasses will minimize the risk of water drainage into the wastes and minimize erosion. The establishment of such a community in the face of the encroachment of invasive alien species is critical for proper barrier function. Investigations into the characteristics of new invasive alien species are needed. Continued research on ...

cover with 60% of the plant cover from planted species (DOE 1998). This planting met the total canopy criterion but failed the criterion of 60% relative coverage of planted species. Although the performance standard was not met, the planting is not necessarily a failure; the communities on the tower pads appear to be developing toward the desired end state. We feel that there are no reasonable mitigative actions that can be taken at this time that would significantly alter or speed up the plant community development on these sites. In fact, most options, such as overseeding, may cause damage to the currently establishing communities on those sites. No future monitoring events are scheduled for this project.