Effects of fire and climate on vegetation history of the Big Woods (Shuman) |
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This study examines the combined roles of of wildfire and climate variability as determinants of vegetation pattern over the past 500 years. Vegetation patterns arise in response to both climatic conditions and ecological disturbances but human activities have likely altered both these agents, thereby affecting current patterns on the landscape. In the Big Woods, changes in climate probably caused the transition from prairie to forest, but this transition also occurred on the time scale of forest responses to disturbance. This project uses information contained within lake sediments to assess past changes in both climate and fire activity. This project evaluates three key hypotheses: 1) Climate changed ~400 years ago in a manner that enabled conversion from prairie/oak savanna to closed forest; 2) Fire frequency was reduced in the Big Woods as compared to other places in Minnesota due to the presence of fire breaks; and 3) Declines in fire frequency occurred region-wide ~400 years ago. Past lake-level fluctuations are also being used as a proxy for climate variability. For more information, contact Bryan at bshuman@umn.edu. |
Vegetation and climate change of the Big Woods and oak savanna of Minnesota (Ziegler) |
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The geography of plants often is explained by climate at a global to continental scale and by disturbance at a regional to local scale. This study will investigate how climate and disturbance interact at overlapping scales to influence biogeography. Using tree rings we will reconstruct disturbance history, regeneration, and climate change in the Big Woods and oak savanna of Minnesota over the past 300 years. We hypothesize that (1) regional climate was similar in the Big Woods and oak savanna; (2) disturbance histories are different between Big Woods forests and oak savanna; (3) oak savanna historically had more disturbance by fire; and (4) pulses of tree regeneration coincide with favorable climate in the Big Woods and follow fire events in the oak savanna. Understanding vegetation response to past climate and disturbance regimes will help us predict the impact of environmental change on future vegetation patterns. Ph.D. student Julia Rauchfuss is assisting with this project. For more information, contact Susy at ziegler@umn.edu. |
Reconstructing climate from tree rings in Minnesota (Kipfmueller)
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This project is focused on reconstructing past climate variabiltiy to place 20th century climate in Minnesota in a longer-term context. Currently, there is difficulty in discerning whether temperature increases since the end of the so-called Little Ice Age are related to an anthropogenic effect or remain within the range of variability over longer time periods. In addition, it appears warm-wet conditions since about 1980 maybe novel with respect to the long term record. There is tremendous opportunity for developing reconstructions based on long calibration periods since some instrumental records extend more than 150 years in the area. This will enable testing of the stability of the tree-growth climate relationships and help better understand climate dynamics in the region. Funding is currently being sought to update several existing tree-ring chronologies as well as develop new chronologies in some areas. We are currently seeking a Master's student to assist with this project. For more information, contact Kurt at kurt@umn.edu. |
Wind speed and windpower variability in Minnesota and the upper Midwest (Klink)
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I am using wind speed observations at several 70-m monitoring sites in Minnesota to learn how wind speeds vary over space and through time. I'm interested in understanding how wind speed (and thus wind power) may be influenced by changes in hemispheric-scale circulation. Preliminary work has shown that, particularly for “significant” events like ENSO, there is a notable decrease in 70-m wind speeds at almost all of the Minnesota stations I've studied, particularly in the winter. A wind speed-ENSO relationship is dynamically plausible because the wintertime jet is farther north in ENSO years, thus moving the region of highest wind speeds away from Minnesota . I plan next to start a project to more explicitly relate near-surface wind speeds in the United States to hemispheric-scale circulation, possibly using both data and models. For more information, contact Kathy at klink@umn.edu. |
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