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Browsing by Subject "succession"

Now showing 1 - 3 of 3
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    Impacts of multiple fires and wind disturbance on forest community composition, succession and diversity in the Boundary Waters Canoe Area Wilderness.
    (2018-01) Anoszko, Elias
    Under a warming climate, the Boundary Waters Canoe Area Wilderness (BWCAW) of Northern MN is expected to see an increase in the frequency of disturbances including wildfires and severe windstorms. While boreal forests such as those of the BWCAW are generally considered disturbance adapted, it is uncertain how changing disturbance regimes will impact these forests. We used a series of recent disturbances in the BWCAW ranging from areas affected by wind or fire only, to areas affected by wind followed by fire, or multiple fires, to examine how predicted changes in boreal disturbance regimes are likely to impact these forests. We found that multiple disturbances typically had greater cumulative disturbance severity than single disturbance events and in the case of wind+fire combinations also tended to burn with greater intensity, and fire severity relative to areas affected by a single fire only. While diversity-severity relationships varied in shape, we found that diversity was generally lower at high disturbance severity relative to moderate severities. Multiple disturbances had modestly reduced diversity relative to single disturbances, but this relationship varied depending on the spatial scale of inquiry. Despite only modest impacts on diversity, multiple disturbances did have a pronounced impact on succession and composition. Regardless of pre-disturbance composition, multiple disturbances resulted in succession to aspen and paper birch, with birch being more dominant in areas burned in late season fires and aspen more dominant in areas burned by early season fires. Stands subjected to single disturbance events exhibited multiple successional pathways and mix of forest types. Our results suggest that predicted changes in boreal disturbance regimes are likely to have minor impacts on woody plant diversity, but could adversely affect disturbance adverse species, and alter the age structure and composition of forests by reducing long-lived boreal conifers and increasing the dominance of aspen and paper birch.
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    Origin and development of fungal communities in an engineered biofilter
    (2017-05-09) Oliver, Jason; Song, Zewei; Schilling, Jonathan S; schillin@umn.edu; Schilling, Jonathan
    Microbial communities underpin the performance of biofilters used for treating pollutants, but community ‘seeding’ and development is not well understood, particularly for fungi. Fungi have unique biocatalytic potential in biofilters, and identifying their inoculum sources and community succession can inform design and management strategies to improve biofilter operation. Our goal was to track fungal community development in a full-scale woodchip biofilter treating air exhaust from a swine barn facility. We sequenced fungal ITS-1 amplicons 1) from potential inoculum sources (fresh wood chip media; manure from pits below pig housing) and 2) from wood chip biofilms at the inlet and outlet of the biofilter, sampling annually over 3 years. Inlet and outlet fungal communities were distinct at the outset, but became increasingly similar by year 3. A shift from Basidiomycetes and yeasts to Ascomycetes and molds was associated with a loss of richness as the community became dominated by fungi that originated from the manure exhaust. Notably, dominant taxa were pig skin dermatophytes, likely seeded continuously from within the barn. These patterns differ from those in natural wood decomposition studies, and the results suggest that hygiene within the barn will affect the performance of biofilters located outside of the barn, an aspect of biofilter management that has not been exploited. These ‘upstream’ inoculum effects may complicate management, however, our results identify several candidate fungi and an avenue for increasing inoculum potential on a continuous basis that might be valuable for seeding biofilters, improving control, and reduce lag-times during biofilter development.
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    Pathways in old-field succession to white pine: Seed rain, shade, and climate effects
    (2005) Dovčiak, Martin; Frelich, Lee E; Reich, Peter B
    Trees slowly colonize old fields on sandy outwash in the prairie–forest ecotone of the north-central United States, and in the absence of fire, succession is expected to proceed toward oak woodland. We analyzed whether a case of unusually rapid and spatially extensive invasion by white pine (Pinus strobus) could be explained by the presence of specific temporal or spatial opportunity windows suitable for such invasion. We tested whether the invasion was temporally restricted to the period immediately after abandonment or to periods of favorable climate, and whether it was spatially restricted to areas of high seed rain or high forest-edge shade. White pine invasion into the field occurred in two waves separated from each other by a 1987–1989 drought period. The first wave (1980– 1985) occurred during a period of average climate and led to the establishment of dense sapling patches in shade near forest edges. The second wave (1991–1994) occurred during a period of high precipitation and cooler than normal temperature, and resulted in colonization of the unshaded field center. In addition to the two temporal windows, white pine invasion occurred within two spatial windows: in areas highly sheltered by forest edge and in areas receiving high white pine seed rain. Overall these windows produced three different successional pathways: (1) a slow, creeping white pine invasion into highly shaded areas with low seed rain near forest edges; (2) a rapid, discrete-step invasion in areas where seed rain was abundant enough to overcome mortality in lower shade and where early arrivals facilitate filling in by later arrivals; and (3) a deferred invasion in the field center where low seed rain and lack of shade allowed the persistence of a grassland stage until favorable climate resulted in a white pine recruitment pulse. Temporal variation in climate can accelerate or decelerate any of the three successional pathways.