Climate Change Impacts on the Productivity and Community Dynamics of Pacific Northwest Prairie Systems
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Preservation of Pacific Northwest prairie ecosystems depends on our understanding of how climate change will impact levels of biodiversity within these systems. In the PNW, climate change models have predicted significant increases in precipitation during the winter months and higher temperatures as well as an increase in drought incidence during the summer months. As the vegetation responds to this enhanced seasonal precipitation cycle, primary production may change alongside shifts in community dynamics in terms of functional group composition, potentially altering overall levels of biodiversity. In this study, we questioned how experimental climate change in a series of restored prairie plots in three sites across a 520 km latitudinal Mediterranean climate gradient will impact the overall productivity of species common to Pacific Northwest prairies. Our experimental treatments included ambient conditions as a control, warming by 2.5 C year-round, drought by a 40% reduction in precipitation, and finally warming with irrigation to offset the drying effect of warming. We hypothesized productivity to differ across the latitudinal gradient, with levels of primary production decreasing as we move from north to south. We also hypothesized that the effects of the treatments on productivity will vary by functional group composition (annual grasses, annual forbs, perennial grasses, perennial forbs, and nitrogen-fixing legumes). There should be higher annual plant productivity in response to warming treatments compared to their perennial counterparts, due to their ability to withstand hotter and drier climates. Lastly, we anticipated discrepancies in overall productivity depending on the treatment used. Heating and heating with added irrigation should have a positive effect on productivity, while drought will have a detrimental effect. I quantified changes in composition and productivity by clipping above-ground productivity at peak biomass, sorting by functional group, and measuring the dry weight of these functional groups. The study showed the northern site had significantly greater biomass present compared to the central and southern site, supporting the productivity gradient hypothesis. Also, annual grasses were the only functional group to show a significant positive response to the heated treatment compared to control across all three sites, lending support to the idea that heat has a favorable effect on overall productivity and annuals fare better in higher temperature conditions compared to perennials. Further studies like this that give insight on specific climate change effects within ecosystems can provide information on how to prevent biodiversity loss and protect ecosystems on a regional scale.