Two students working at LTER site, David Peterson (Cedar Creek) and Kristin Vanderbilt (H.J. Andrews) received the Ecological Society of America’s Long-Term Studies Section travel award. The award provided funds for them to attend the August annual meeting, where they presented the following posters:
Nitrogen Losses from Experimental Watersheds in Western Oregon
Vanderbilt, Kristin, L., Kate Lajtha, and Fred Swanson, Oregon State University, Corvallis, OR 97531, USA.
Long-term precipitation and stream water chemistry data from control and logged watersheds at the Andrews Experimental Forest, Oregon were analyzed to evaluate biogeochemical differences resulting from disturbance, differing successional stages of vegetation, and varying amounts of nitrogen fixation. Nitrogen flux was closely tied to the hydrologic cycle. Nitrate export (kg/ha) in stream water was elevated in a treated watershed during exceeded that the six years following logging when diminished evapotranspiration resulted in increased stream discharge. Export of dissolved organic nitrogen from a treated watershed exceeded that from a control watershed for five years after disturbance. No difference was detected in output of total organic nitrogen between watersheds. Seasonal and annual patterns of nitrogen retention in this nitrogen-limited ecosystem, as calculated by nitrogen yield=(nitrogen output in stream water)/(input from lichen and alder nitrogen fìxation and dry and wet atmospheric deposition), differed from patterns observed in watersheds with elevated nitrogen inputs.
Vegetation structure, composition and diversity in a midwest oak savanna after 32 years of a prescribed burning experiment
Peterson, David W., and Peter B. Reich. University of Minnesota, St. Paul, MN 55108, USA.
Oak savannas were once common along the forest-prairie ecotone in eastern North America but are now rare due to land use changes and succession to forest following fire suppression. Prescribed burning is being used to restore and maintain remnant savanna areas, but little is known about the long-term effects of prescribed burning on savanna vegetation. We studied the effects of 32 years of a prescribed burning experiment on structure, composition, and species diversity in upland oak savannas and woodlands at Cedar Creek Natural History Area in Minnesota. Tree, shrub, and herbaceous vegetation were sampled on 28 large permanent plots in 20 management units that have been burned at frequencies of zero to nine times per decade. Many of these plots have been monitored since 1984 and provide data on successional trends higher frequencies significantly reduced stem densities and stand basal area of Quercus eilipsoidalis and prevented recruitment of new stems into the canopy, resulting in increased canopy openness. More frequent burning also reduced tree canopy species diversity. Understory vegetation composition and diversity varies with canopy openness, suggesting that fire might produce changes in understory composition and diversity primarily through its effects on canopy structure.