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MS Thesis Defense - Julie Fowler

Soil Microbial Community Dynamics in Response to Prescribed Extreme Burns of Juniperus virginiana Invasive to the Loess Canyons of Nebraska

Date: Time: 1:00 pm–2:00 pm
Contact: Tala Awada,
In Nebraska and other regions of the Great Plains, the conifer Juniperus virginiana (J. virginiana, eastern redcedar) is converting grasslands to dense woodlands. This is driven by the interacting drivers of fire suppression, altered grazing regimes, climate change and other anthropogenic factors, impacting the provisioning of ecosystem services. This vegetation regime shift modifies water resource regulation and biogeochemical cycles leading to altered edaphic properties including soil microbial community composition. To restore these grasslands and control J. virginiana spread, prescribed extreme burns are implemented as a management tool through local prescribed burn associations. We hypothesized that the alternative stable state shift to dense J. virginiana woodlands leads to a corresponding stable state shift below-ground that persists post-extreme burn and may facilitate J. virginiana re-establishment. To address this hypothesis, paired grasslands and J. virginiana woodlands in the Loess Canyons of Central Nebraska were subjected to one prescribed extreme burn between 2005 and 2019 to provide a natural burn chronosequence. We quantified J. virginiana re-establishment, soil chemistry, soil microbial biomass and microbial community composition in these paired sites across the chronosequence. Our results partially supported our hypothesis where differences in edaphic variables between J. virginiana sites and grassland sites observed post-burn were largely temporary; however, differences in soil magnesium and microbial community composition were more persistent (> 14 years post-burn). Soil magnesium values were significantly higher in the J. virginiana sites both pre-burn and post-burn across the 14 year chronosequence. Microbial communities were also distinct between J. virginiana and grassland sites pre-burn and across the burn chronosequence. Rapid recovery and/or persistence of specific edaphic factors and soil microbial communities in J. virginiana woodlands post-burn may facilitate early J. virginiana re-establishment. Management at intervals less than 14 years is needed to prevent long term changes to soil function that may facilitate J. virginiana re-establishment.

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