Agricultural Contribution of Nitrate-N to the Des Moines River: 1945 vs. 1980

Recently, intensive water quality monitoring has demonstrated the presence of nitrate (N03-N) in surface and groundwater throughout the Midwestern U.S. (Hallberg, 1989)

Lack of Fire Has Limited Physiological Impact on Old-Growth Ponderosa Pine in Dry Montane Forests of North-Central Idaho

Reduced frequency of fire in historically fire-adapted ecosystems may have adverse effects on ecosystem structure, function, and resilience. Lack of fire increases stand density and promotes successional replacement of seral dominant trees by late-successional, more shade-tolerant species. These changes are thought to increase competition for limited resources among trees and to increase physiological stress of dominant, fire-adapted species. However, there has been little effort to directly investigate effects of lack of fire on the physiological status of old trees, especially in unlogged, protected forests. At four remote sites in the Selway-Bitterroot region of Idaho, we tested whether the physiological status of dominant old-growth ponderosa pine trees in repeatedly burned stands (three to four 20th-century wildfires at roughly historical fire frequency) differs from trees in paired stands not burned for at least 70 years. We hypothesized that trees in relatively unburned stands would exhibit signs of physiological stress due to increased competition for resources in higher-density stands. Needle chemistry and morphological variables, fine root production, mycorrhizal infection rates, depth of soil water resources, and recent basal area growth rates were measured as indictors of competition-induced stress. Contrary to predictions, needle carbon isotopic ratio (δ13C) and fine root production, variables related to water stress, were slightly higher in repeatedly burned stands driven by site-specific responses, and there were no significant biological differences between trees in repeatedly burned stands vs. stands unburned for at least 70 years in the remaining variables. Our results raise the possibility that dominant ponderosa pine trees in uneven-aged forests may be more resilient to increased stand density associated with the lack of fire than previously thought. If so, our results have implications for the management of uneven-aged, old-growth forests

Biological-Control Herbivores May Increase Competitive Ability of the Noxious Weed Centaurea Maculosa

Biocontrol organisms are generally applied in an attempt to reduce the vigor of target species and provide native species with an competitive advantage. We tested the effectiveness of a widely used biocontrol moth, Agapeta zoegana (knapweed root moth) for two years in the field and found that it had no significant direct effect on the biomass of Centaurea maculosa (spotted knapweed), one of the most destructive invasive plants in North America. Instead of releasing a native grass from competition, the reproductive output of Festuca idahoensis planted with Centaurea was significantly lower when neighboring Centaurea had been attacked by Agapeta. In a greenhouse experiment, we found that Festuca planted in pots with Centaurea that had been attacked by Trichoplusia ni (another nonnative herbivore) had significantly smaller root systems than when they were planted with Centaurea that were protected from herbivory. Root systems of Centaurea that had been attacked by Trichoplusia exuded higher levels of total sugars, but not total phenols. We hypothesize that moderate herbivory stimulated compensatory growth, induced the production of defense chemicals that also had allelopathic effects, or stimulated root exudates that altered the relationship between Ce,Centaurea and Festuca via soil microbes. Our data suggest that herbivory may increase the negative effects of C. maculosa on neighboring plants, and that some biocontrols may have indirect negative effects on native species that are not currently recognized

Interactive Effects of Historical Logging and Fire Exclusion on Ponderosa Pine Forest Structure in the Northern Rockies

Increased forest density resulting from decades of fire exclusion is often perceived as the leading cause of historically aberrant, severe, contemporary wildfires and insect outbreaks documented in some fire-prone forests of the western United States. Based on this notion, current U. S. forest policy directs managers to reduce stand density and restore historical conditions in fire-excluded forests to help minimize high-severity disturbances. Historical logging, however, has also caused widespread change in forest vegetation conditions, but its long-term effects on vegetation structure and composition have never been adequately quantified. We document that fire-excluded ponderosa pine forests of the northern Rocky Mountains logged prior to 1960 have much higher average stand density, greater homogeneity of stand structure, more standing dead trees and increased abundance of fire-intolerant trees than paired fire-excluded, unlogged counterparts. Notably, the magnitude of the interactive effect of fire exclusion and historical logging substantially exceeds the effects of fire exclusion alone. These differences suggest that historically logged sites are more prone to severe wildfires and insect outbreaks than unlogged, fire-excluded forests and should be considered a high priority for fuels reduction treatments. Furthermore, we propose that ponderosa pine forests with these distinct management histories likely require distinct restoration approaches. We also highlight potential long-term risks of mechanical stand manipulation in unlogged forests and emphasize the need for a long-term view of fuels management

Nitrogen Spatial Heterogeneity Influences Diversity Following Restoration in a Ponderosa Pine Forest, Montana

The resource heterogeneity hypothesis (RHH) is frequently cited in the ecological literature as an important mechanism for maintaining species diversity. The RHH has rarely been evaluated in the context of restoration ecology in which a commonly cited goal is to restore diversity. In this study we focused oil the spatial heterogeneity of total inorganic nitrogen (TIN) following restoration treatments in a ponderosa pine (Pinus ponderosa)/Douglas-fir (Pseudotsuga inenziesii) forest in western Montana, USA. Our objective was to evaluate relationships between understory species richness and TIN heterogeneity following mechanical thinning (thin-only), prescribed burning (burn-only), and mechanical thinning with prescribed burning (thin/burn) to discern the ecological and management implications of these restoration approaches. We employed a randomized block design, with three 9-ha replicates of each treatment and an untreated control. Within each treatment, we randomly established a 20 X 50 in (1000 m(2)) Plot in which we measured species richness across the entire plot and in 12 I-m 2 quadrats randomly placed within each larger plot. Additionally, we measured TIN from a grid consisting of 112 soil samples (0-5 cm) in each plot and computed standard deviations as a measure of heterogeneity. We found a correlation between the net increase in species richness and the TIN standard deviations one and two years following restoration treatments, supporting RHH. Using nonmetric multidimensional scaling ordination and chi-squared analysis, we found that high and low TIN quadrats contained different understory communities in 2003 and 2004, further supporting RHH. A comparison of restoration treatments demonstrated that thin/burn and burn-only treatments created higher N heterogeneity relative to the control. We also found that within prescribed burn treatments, TIN heterogeneity was positively correlated with fine-fuel consumption, a variable reflecting burn severity. These findings may lead to more informed restoration decisions that consider treatment effects on understory diversity in ponderosa pine/Douglas-fir ecosystems