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The prairie pothole region (PPR)

The wetland complex is the functional ecological unit of the prairie pothole region (PPR) of central North America. Diverse complexes of wetlands contribute high spatial and temporal environmental heterogeneity, productivity, and biodiversity to these glaciated prairie landscapes. Climatewarming simulations using the new model WETLANDSCAPE (WLS) project major reductions in water volume, shortening of hydroperiods, and less-dynamic vegetation for prairie wetland complexes. The WLS model portrays the future PPR as a much less resilient ecosystem: The western PPR will be too dry and the eastern PPR will have too few functional wetlands and nesting habitat to support historic levels of waterfowl and other wetland-dependent species. Maintaining ecosystem goods and services at current levels in a warmer climate will be a major challenge for the conservation community.

Summary 1.Understanding the relationship between species diversity and productivity is central to linking compositional and functional aspects of terrestrial ecosystems, and little is known about such issues in boreal forests. We used structural equation modelling (SEM) to test several hypotheses about direct and indirect influences of productivity, its correlate basal area, and resources on understorey vascular plant diversity on 2025 plots in 81 southern boreal forests in Minnesota, USA. 2. We first examined the hypothesis that increasing basal area reduces plot-scale species richness due to competitive exclusion from the most limiting resource, light. As expected, light pre-emption increased with total basal area, which directly reduced understorey species richness. However, complex relations between basal area, dominant understorey species, and resource supply to the understorey can also influence understorey communities. Hence, we addressed whether plots with low light availability in the understorey were associated with low abundance of dominant understorey species and alleviation of competitive exclusion of other understorey species. SEM results showed that low light decreased total understorey cover, alleviating resource competition from this stratum and thus increasing understorey species richness. Furthermore, the cover of four dominant understorey species was positively correlated with light availability and negatively correlated with plotscale species richness. 3. Aggregating data for the 25 plots at each stand, SEM showed that stand-scale species richness was positively influenced by light heterogeneity, which in turn increased with annual above-ground productivity. 4. Species richness was positively influenced by litter %N, considered an index of nitrogen availability at the plot and stand scale. 5. Synthesis. These results suggest that understorey species richness in boreal forests is regulated by productivity, but is primarily mediated by the indirect effects of productivity of the dominant producers on resource availability and heterogeneity.

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Wetlands of the Prairie Pothole Region exist in a matrix of grassland dominated by intensive pastoral and cultivation agriculture. Recent conservation management has emphasized the conversion of cultivated farmland and degraded pastures to intact grassland to improve upland nesting habitat. The consequences of changes in land-use cover that alter watershed processes have not been evaluated relative to their effect on the water budgets and vegetation dynamics of associated wetlands. We simulated the effect of upland agricultural practices on the water budget and vegetation of a semipermanent prairie wetland by modifying a previously published mathematical model (WETSIM). Watershed cover/land-use practices were categorized as unmanaged grassland (native grass, smooth brome), managed grassland (moderately heavily grazed, prescribed burned), cultivated crops (row crop, small grain), and alfalfa hayland. Model simulations showed that differing rates of evapotranspiration and runoff associated with different upland plant-cover categories in the surrounding catchment produced differences in wetland water budgets and linked ecological dynamics. Wetland water levels were highest and vegetation the most dynamic under the managed-grassland simulations, while water levels were the lowest and vegetation the least dynamic under the unmanaged-grassland simulations. The modeling results suggest that unmanaged grassland, often planted for waterfowl nesting, may produce the least favorable wetland conditions for birds, especially in drier regions of the Prairie Pothole Region. These results stand as hypotheses that urgently need to be verified with empirical data.

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Impacts of organic matter removal and compaction on soil physical and chemical properties and forest productivity are reported from the fi rst 10 years of the Long-Term Soil Productivity Study in Great Lakes aspen ecosystems. Organic matter removal treatments included main bole, total tree harvest, and total tree harvest with forest fl oor removal. Compaction treatments included no compaction beyond normal levels from harvest, moderate compaction, and heavy compaction. Main bole harvest with no additional compaction served as the control against which other treatments were compared. Study treatments were replicated in three locations on a clay loam, silt loam, and loamy sand soil. All compaction treatments on all three soil types increased bulk density above preharvest levels. In most cases, bulk density at year 10 had decreased signifi cantly compared to year 0, but was still generally above preharvest levels. Total carbon and nitrogen showed no impact from treatment at year 10. In general, soil cations were little affected by organic matter removal. The major exceptions were lower near-surface calcium in the loamy sand soil with total tree harvest plus forest fl oor removal, and lower potassium at 10-20 cm depth in the loam soil for both total tree harvest with and without forest fl oor removal. Compaction and organic matter removal treatments impacted aboveground forest productivity, however the effects were not universal across the soil types. Aboveground biomass production declined on the loam soil with moderate and heavy compaction. Production increased with moderate compaction on the loamy sand and clay loam soils, but signifi cantly decreased with heavy compaction on the clay loam soil. Total tree harvest with forest fl oor removal reduced production on the loamy sand and loam soils, while it increased production on the clay loam soil. Results from this study suggest that heavy compaction and/or high organic matter removals (e.g., total tree harvest plus forest fl oor removal) are generally detrimental to sustaining forest productivity across soil types. Total tree harvest with limited compaction may be sustainable, at least as refl ected in 10 year results, after one harvest entry. Managers should be cautious of approaches involving whole-tree harvests, or even bole-only harvests, on short rotations (~10 years), as such approaches will limit the potential for recovery to preharvest bulk densities and may have the potential to increase compaction to levels seen with heavy compaction.