Monica L. Pokorny

Influence of Plant Functional Group Removal on Inorganic Soil Nitrogen Concentrations in Native Grasslands

Abstract High plant functional group diversity has been hypothesized to reduce resource concentrations based on the assumption that species from one functional group acquire resources similarly to one another, while species from other functional groups acquire resources dissimilarly. To determine if functional groups use soil nutrients different from one another, we investigated the impact of removing individual functional groups on soil inorganic nitrogen (NO−3 and NH+4) concentrations in the Idaho fescue (Festuca idahoensis Elmer)/bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] A. Löve) habitat type in Montana. Treatments were imposed by removing 1) all plant species (total plant removal), 2) shallow-rooted (< 15 cm) forbs, 3) deep-rooted (> 15 cm) forbs, 4) all forbs (total forb removal), 5) grasses, and 6) spikemoss, compared to intact control plots. Inorganic nitrogen was measured at 2 soil depths (0–15 cm and 16–40 cm) in the spring, summer, and fall 1 year after treatment imposition. The removal of individual functional groups generally increased soil NO−3 and NH+4 concentrations. Total plant removal increased NO−3 concentrations more than removing individual functional groups. Grass removal generally increased soil NO−3 concentrations in the 0–15-cm depth more than other functional groups removal. Whether the grass or total forb removal treatment resulted in greater soil NH+4 concentrations in the 0–15-cm depth depended on season. These results suggest that functional groups vary in their soil nutrient acquisition patterns and that increased functional diversity decreases soil nutrient concentrations. Therefore, maintaining or improving functional diversity may be a method to more fully utilize soil nutrients because functional groups can differ in their spatial and temporal acquisition of resources.

GRASSLAND INVADER RESPONSES TO REALISTIC CHANGES IN NATIVE SPECIES RICHNESS

The importance of species richness for repelling exotic plant invasions varies from ecosystem to ecosystem. Thus, in order to prioritize conservation objectives, it is critical to identify those ecosystems where decreasing richness will most greatly magnify invasion risks. Our goal was to determine if invasion risks greatly increase in response to common reductions in grassland species richness. We imposed treatments that mimic management-induced reductions in grassland species richness (i.e., removal of shallow- and/or deep-rooted forbs and/or grasses and/or cryptogam layers). Then we introduced and monitored the performance of a notorious invasive species (i.e., Centaurea maculosa). We found that, on a per-gram-of-biomass basis, each resident plant group similarly suppressed invader growth. Hence, with respect to preventing C. maculosa invasions, maintaining overall productivity is probably more important than maintaining the productivity of particular plant groups or species. But at the sites we studied, all plant groups may be needed to maintain overall productivity because removing forbs decreased overall productivity in two of three years. Alternatively, removing forbs increased productivity in another year, and this led us to posit that removing forbs may inflate the temporal productivity variance as opposed to greatly affecting time-averaged productivity. In either case, overall productivity responses to single plant group removals were inconsistent and fairly modest, and only when all plant groups were removed did C. maculosa growth increase substantially over a no-removal treatment. As such, it seems that intense disturbances (e.g., prolonged drought, overgrazing) that deplete multiple plant groups may often be a prerequisite for C. maculosa invasion.

The Effect of Five Pre-emergence Herbicides on Emergence and Establishment of Four Native Wildflowers

Careful selection of pre-emergence herbicide for control of weeds may improve establishment of native wildflowers grown for seed production. In a 28-d greenhouse herbicide injury experiment, 4 emerging wildflower species were established on soil treated with one of 6 pre-emergence herbicide treatments. No wildflower seedlings survived the atrazine treatment and few survived the sulfentrazone treatment. Of the 5 herbicides tested, DCPA applied at 1100 g active ingredient (ai) per ha (8 lb ai/ac) and trifluralin applied at 184 g ai/ha (2 pt ai/ac) caused the least reduction in wildflower seedling density, height, and shoot dry mass of all species. The densities, however, of Dalea candida Michx. ex Willd. (Fabaceae), Gaillardia aristata Pursh (Astera-ceae), and Ratibida columnifera (Nutt.) Woot. & Standl. (Astera-ceae) were each reduced in 1 of the 2 experimental runs, whereas the height of D. candida and G. aristata and the shoot dry mass of R. columnifera seedlings were reduced by trifluralin. Liatris punctata Hook. (Asteraceae) densities were reduced only by atrazine and sulfentrazone.

Can a Combination of Grazing, Herbicides, and Seeding Facilitate Succession in Old Fields?

©2013 by the Board of Regents of the University of Wisconsin System. Can a Combination of Grazing, Herbicides, and Seeding Facilitate Succession in Old Fields? Robert V. taylor (corresponding author: The nature conservancy, Enterprise, oR 97828, rtaylor@tnc.org), Monica l. Pokorny (Kc Harvey Environmental llc, Bozeman, Mt), Jane Mangold (Montana state University, Bozeman, Mt) and nathan Rudd (Bureau of Reclamation, Boulder city, nV).

Managing Spotted Knapweed (Centaurea stoebe)–Infested Rangeland after Wildfire

Abstract Invasive plants need to be managed after wildfire to suppress the invasive plant and to maintain or restore a desired plant community. Our study tested treatments that influence species availability and performance following a disturbance (wildfire). The overall objective was to determine the ability of herbicide and revegetation treatments to restore spotted knapweed–infested areas to desired plant communities after wildfire. The study consisted of a factorial combination of three herbicide application treatments (broadcast application, spot application, and no herbicide) and three seed mixture treatments (grass-only seed mix, a grass and forb seed mix, no seeding). Picloram was used for the herbicide. Both the broadcast and spot picloram application methods decreased spotted knapweed cover and density up to 80% while increasing desired grass cover and density up to 20% compared with the control. However, broadcast spraying picloram decreased species richness from 5.7 to 3.6 species 0.1 m−2 and decreased desired forb density and cover compared with spot-applied picloram treatment. Spot spraying resulted in an increase in other undesired forbs compared with broadcast spraying. Seeding with desired species had no effect on spotted knapweed cover or density. Spot spraying may help maintain desired species richness while managing spotted knapweed. Nomenclature: Picloram; spotted knapweed, Centaurea stoebe L. CEST8.

Using reinforced native grass sod for biostrips, bioswales, and sediment control.

The objective of this research was to develop and demonstrate native grass sod for sediment control from disturbed lands associated with California highways. The research evaluated native grass species for inclusion in sod and evaluated the sod at a California highway field site. Results indicated that multispecies sod has potential for use in revegetation of disturbed lands associated with highways. Native grass seed mix designs developed for the California Grassland ecoregion were field tested on a highway steep slope and swale area near Sacramento. Following an eight month propagation period, a sod composed of four native grass species was transplanted using conventional harvest and transport procedures. The sod resisted weed invasion from the underlying soil seed bank, no bare ground was present, and sediment loss was exceptionally low. Native grass sod was more expensive to implement compared with conventional hydroseeding, but their long-term maintenance and environmental costs associated are expected to be much lower.