Ecologists are searching for models, frameworks, and principles that provide a bridge between theory and the practice of restoration. Successional management has been proposed as a useful model for managing and restoring invasive-plant-dominated rangeland because it provides a framework in which ecological processes can be manipulated by managers to achieve a desired plant community. Successional management identifies three general causes of succession (site availability [disturbance], species availability [colonization], and species performance) and suggests that managers address the ecological process influencing each general cause in a coordinated fashion to direct plant community dynamics. We tested successional management using various techniques to restore invasive-weed-dominated rangeland. Our hypothesis was that successively modifying the factors influencing the causes of succession in an integrated fashion would favor the establishment and abundance of native grasses over singularly applied treatments. Thus, we anticipated that the majority of responses to multiple treatments would be explained by higher order interactions, especially in the final year of the study (2004). To test this hypothesis, we used a model system within a Festuca campestris/Pseudoroegneria spicata habitat among pothole wetlands dominated by Centaurea maculosa and Potentilla recta, two invasive species. We used three herbicide treatments (none, 2,4-D, and picloram) to influence species performance; two seeding methods (imprinting, i.e., creating a small depression and broadcasting, and no-till drilling) to influence disturbance; three seeding rates (977, 1322, and 1557 seeds/m 2 ) to influence colonization; and two cover crop treatments (with and without Triticum aestivum) to influence soil N and favor native grasses. Treatments were factorially arranged and replicated four times in a randomized complete block design in 2001 and sampled in 2002 and 2004. As predicted, plant response to treatments was dominated by two-and three-way interactions in 2004. The highest seeding rate (colonization) combined with no-till drilling (disturbance) produced the highest native grass density in 2002. These effects persisted into 2004 for P. spicata, but not for F. campestris or F. idahoensis. Combining picloram with no-till drill seeding also produced a high density of P. spicata. Drill seeding at 977 seeds/m 2 favored F. idahoensis density, while no-till drilling at 1322 seeds/m 2 favored its biomass in 2004. F. idahoensis established well after drill seeding with a cover crop and applying 2,4-D. Herbicides reduced native forb density and/or biomass, with early season forbs being more sensitive to picloram and summer forbs being more sensitive to 2,4-D. Herbicides increased exotic grasses' density and biomass but had no effect on native grasses. In most cases, integrating treatments that addressed multiple causes of succession favored a desired plant community. Thus, we accomplished our goal of using successional management to direct plant commu...

Understanding the ecological processes that foster invasion and dominance by medusahead is central to its management. The objectives of this study were (1) to quantify and compare interference between medusahead and squirreltail under different concentrations of soil nitrogen (N) and phosphorous (P) and (2) to compare growth rates of medusahead and squirreltail under field soil N and P availabilities. We grew medusahead and squirreltail in an addition series in a greenhouse and applied one of four nutrient treatments weekly: (1) low N low P (no N or P added), (2) low N high P (added 250 ml of 600 µM P solution in the form of calcium phosphate), (3) high N low P (added 250 ml of 8,400 µM N solution in the forms of calcium nitrate and potassium nitrate), and (4) high N high P (added solutions as listed above for high N and high P). After 70 d density and biomass by species were sampled. We also grew individual medusahead and squirreltail plants in control soil conditions. Biomass, leaf area, and root length were determined for each species at 14-d intervals over 72 d. Regression models for medusahead and squirreltail suggested N appeared to be playing a much larger role than P in interference between the species. The high N treatment did not increase medusahead's interference ability relative to squirreltail as we had hypothesized. Medusahead typically imposed a two-to-seven-times stronger influence on interference relationships than squirreltail. Medusahead accumulated biomass, leaf area, and root length twice as fast as squirreltail. Results from our study suggest that medusahead seedlings will likely dominate over squirreltail seedlings. To restore squirreltail to medusahead-infested rangeland, medusahead densities should be reduced with integrated weed management strategies. On medusahead-free rangeland, prevention and early detection and eradication programs are critical.

Downy brome is a problematic invasive annual grass throughout western rangeland and has been increasing its abundance, spread, and impacts across Montana during the past several years. In an effort to develop effective management recommendations for control of downy brome on Montana rangeland, we compiled data from 24 trials across the state that investigated efficacy of imazapic (Plateau®, BASF Corporation, Research Triangle Park, NC) applied at various rates and timings and with methylated seed oil (MSO) or a nonionic surfactant (NIS). We ran a mixed-model ANOVA to test for main effects and interactions across application rate (70, 105, 141, 176, and 211 g ai ha−1), application timing (preemergent [PRE], early postemergent [EPOST, one- to two-leaf growth stage], and postemergent [POST, three- to four-leaf growth stage]), and adjuvant (MSO, NIS). Application timing and rate interacted to affect downy brome control (P = 0.0033). PRE imazapic application resulted in the lowest downy brome control (5 to 19%), followed by POST application (25 to 77%) and EPOST application (70 to 95%). Downy brome control remained fairly consistent across rates within application timing. Adjuvant (MSO or NIS) did not affect downy brome control (P = 0.2789). Our data indicate that POST application at 105 to 141 g ai ha−1 provides the most-consistent, short-term control of downy brome. Furthermore, applying imazapic to downy brome seedlings shortly after emergence (one- to two-leaf growth stage) provided better control than applying it to older downy brome seedlings (three- to four-leaf growth stage).

Soil nutrients are heterogeneously distributed in natural systems. While many species respond to this heterogeneity through root system plasticity, little is known about how the magnitude of these responses may vary between native and invasive species. We quantified root morphological and physiological plasticity of co-occurring native and invasive Great Basin species in response to soil nitrogen heterogeneity and determined if trade-offs exist between these foraging responses and species relative growth rate or root system biomass. The nine study species included three perennial bunchgrasses, three perennial forbs, and three invasive perennial forbs. The plants were grown in large pots outdoors. Once a week for 4 weeks equal amounts of 15 NH 4 15 NO 3 were distributed in the soil either evenly through the soil profile, in four patches, or in two patches. All species acquired more N in patches compared to when N was applied evenly through the soil profile. None of the species increased root length density in enriched patches compared to control patches but all species increased root N uptake rate in enriched patches. There was a positive relationship between N uptake rate, relative growth rate, and root system biomass. Path analysis indicated that these positive interrelationships among traits could provide one explanation of how invasive forbs were able to capture 2 and 15-fold more N from enriched patches compared to the native grasses and forbs, respectively. Results from this pot study suggest that plant traits related to nutrient capture in heterogeneous soil environments may be positively correlated which could potentially promote size-asymmetric competition belowground and facilitate the spread of invasive species. However, field experiments with plants in different neighbor environments ultimately are needed to determine if these positive relationships among traits influence competitive ability and invader success.