Climate Effects on Plant Range Distributions and Community Structure of Pacific Northwest Prairies
Scott Bridgham and Bart Johnson, Principal Investigators
University of Oregon
Laurel Pfeifer-Meister and Timothy Tomaszewski, Postdoctoral Associates
Lorien Reynolds, Maya Goklany, and Hannah Wilson, Graduate Students
Funded by the Office of Biological and Environmental Research,
Department of Energy (DE-FG02-09ER604719)
Pacific Northwest (PNW) prairies are an imperiled ecosystem that contain a large number of plant species with high fidelity to this habitat, many of which have northern and/or southern range limits from southwestern Oregon/northern California to Washington/southern British Columbia. The few remaining high-quality prairies harbor a number of sensitive, rare, and endangered plant species that may be lost with climate change. Thus, PNW prairies are an excellent model system to examine how climate change will affect the distribution of native plant species in grassland sites. We are experimentally manipulating temperature and precipitation in three upland prairie sites along a natural climate gradient from southwestern Oregon to central-western Washington to determine (1) how future climate change will affect the range distribution of native plant species, and (2) how viable current restoration practices are under future climate change.
Our specific objectives are to determine:
We are addressing these objectives by experimentally increasing temperature by 3 ºC with overhead infrared lamps and increasing precipitation by 25% above ambient in a full factorial design at three upland prairie sites along an approximately 600 km gradient of temperature and precipitation (Fig. 1, Table 1).
Figure 1warming, added precipitation, warming + added precipitation, and control. Each treatment is replicated five times in 7.1 m2 circular plots, for a total of 60 plots across the three sites. Construction of the experimental infrastructure and seeding of the experimental species occurred in 2009, and treatments began in 2010. Treatment effects are being examined on 14 native grass and forb species that have their northern and/or southern range limits in the PNW. The same 14 species have been seeded into each experimental plot in a grid and comprise a group of ‘indicator’ species of future climatic effects on the abundance and distribution of other range-limited native prairie species. The range-limited species have been planted in a matrix of 24 native species that are commonly used in the restoration of PNW prairies but that are not necessarily range limited, thus allowing the project to examine climate effects on dominant species and species of particular interest. The same matrix species, or close cogeners if a particular species does not occur locally, have been planted at all sites. All plots have been restored using practices typical of local conservation organizations, including the application of herbicide, mowing, and raking, before any plants were seeded. The restoration treatment reduced but did not eliminate current exotic species in the plots, and we are examining the competitive interactions and succession trajectories of the native and exotic species within each of the treatments.
We are performing an extensive demographic life cycle analysis of the range-limited species, including measurement of treatment effects on establishment, growth, survival, reproduction and phenology. Additionally, we are measuring plant community structure, above- and belowground net primary productivity, seasonal soil nutrient availability, soil organic carbon, continuous soil and air temperature, canopy temperature, and soil moisture in each plot. Other response variables, such as plant physiological responses, will be measured at one or more sites as project resources allow.
Future climate change will almost certainly impact the distributions and abundances of species, with the largest effects on rare species, species with specialized habitats, and species with relatively constrained ranges. Current modeling approaches are inadequate to provide robust predictions of how climate will impact species range distributions and abundances. The combination of a natural climatic gradient, four experimental climate treatments, and planting a common set of species within and beyond their current ranges, will provide a rich dataset to examine the effects of climate change on the distribution and abundance of plants within PNW prairies. This includes an examination of the likelihood of plant species that are near the limits of their current distribution to persist in their current habitats or to expand beyond their current range limits. We are also examining how robust current restoration techniques and plant assemblages are to future climate change. Our results will provide an important case study of how climate change will affect native biodiversity in other grassland ecosystems with high abundances of exotic species.
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This project was funded by the Office of Biological and Environmental Research, Department of Energy (DE-FG02-09ER604719)