Jane M. Mangold

Root plasticity of native and invasive Great Basin species in response to soil nitrogen heterogeneity

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 15NH415NO3 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.

Long-term population dynamics of seeded plants in invaded grasslands

In recent decades, dozens of studies have involved attempts to introduce native and desirable nonnative plant species into grasslands dominated by invasive weeds. The newly introduced plants have proved capable of establishing, but because they are rarely monitored for more than four years, it is unknown if they have a high likelihood of persisting and suppressing invaders for the long-term. Beyond invaded grasslands, this lack of long-term monitoring is a general problem plaguing efforts to reintroduce a range of taxa into a range of ecosystems. We introduced species from seed and then periodically measured plant abundances for nine years at one site and 15 years at a second site. To our knowledge, our 15-year data are the longest to date from a seeding experiment in invaded, never-cultivated grassland. At one site, three seeded grasses maintained high densities for three or more years, but then all or nearly all individuals died. At the second site, one grass performed similarly, but two other grasses proliferated and at least one greatly suppressed the dominant invader (Centaurea maculosa). In one study, our point estimate suggests that the seeded grass Thinopyrum intermedium reduced C. maculosa biomass by 93% 15 years after seeding. In some cases, data from three and fewer years after seeding falsely suggested that seeded species were capable of persisting within the invaded grassland. In other cases, data from as late as nine years after seeding falsely suggested seeded populations would not become large enough to suppress the invader. These results show that seeded species sometimes persist and suppress invaders for long periods, but short-term data cannot predict if, when, or where this will occur. Because short-term data are not predictive of long-term seeded species performances, additional long-term data are needed to identify effective practices, traits, and species for revegetating invaded grasslands.

Role of size and nitrogen in competition between annual and perennial grasses.

Abstract Differing life histories contribute to difficulties establishing perennial grasses on lands dominated by exotic annual grasses. In a greenhouse study, we investigated to what extent allowing the perennial grass bluebunch wheatgrass to emerge before the exotic annual grass downy brome would increase its competitive ability and whether modifying nitrogen (N) would affect competition. We conducted an addition-series factorial experiment. In three cohort treatments, the two species were seeded concurrently or bluebunch wheatgrass was at the two- or four-leaf stage when downy brome was planted. N treatments were low (ambient) or high (N added to maintain 10 mg kg−1 [0.1286 oz lb−1]). Larger bluebunch wheatgrass avoided suppression by downy brome regardless of N. Under concurrent sowing, doubling downy brome density decreased bluebunch wheatgrass biomass by 22.6% ± 2.38 SE. In contrast, when bluebunch wheatgrass had a four-leaf size advantage, the same increase in downy brome density decreased bluebunch wheatgrass biomass by 4.14% ± 2.31. Larger bluebunch wheatgrass also suppressed downy brome more effectively, but N enrichment decreased the suppressive ability of bluebunch wheatgrass. Nomenclature: Bluebunch wheatgrass, Pseudoroegneria spicata (Pursh) Á. Löve; downy brome, Bromus tectorum L. Management Implications: This study demonstrated the importance of both order of emergence and nitrogen (N) availability in the competitive relationship between bluebunch wheatgrass [Pseudoroegneria spicata (Pursh) Á. Löve] and downy brome (Bromus tectorum L.). First, we found that larger bluebunch wheatgrass seedlings avoided suppression by downy brome more effectively and that they did so regardless of N availability. However, although larger bluebunch wheatgrass also suppressed downy brome more effectively, N enrichment decreased the ability of bluebunch wheatgrass to suppress downy brome. Our results suggest that order of emergence for desired perennial vs. exotic annual grasses may be an important aspect of revegetation planning and that avoiding conditions that lead to N increases, such as soil disturbance, could allow perennial grasses to better suppress downy brome. To establish an initial size difference that favors seeded species, managers could modify the standard timing of revegetation practices to ensure that perennial species receive a sufficient head start. Another way to promote an initial size difference would be to use transplants or plugs to restore critical sites.

Revegetating Russian Knapweed (Acroptilon Repens) Infestations Using Morphologically Diverse Species and Seedbed Preparation

Abstract Highly degraded pastures and rangeland dominated by Russian knapweed (Acroptilon repens [L.] DC) are often devoid of desirable plants. Control efforts may be ephemeral because propagules of desirable species are not available to reoccupy niches made available by control procedures. Establishing desirable, competitive plants is essential for enduring management and restoration of Russian knapweed and other weed-infested plant communities. The objective of this study was to investigate the effectiveness of revegetating Russian knapweed–infested pastures with 3 nonnative, morphologically diverse species following 1 of 3 seedbed preparation treatments. In successive years, at 2 similar sites in southeastern Oregon, we sprayed Russian knapweed with glyphosate, then prepared the seedbed by burning, tilling, or leaving untreated. Following seedbed preparation, we seeded a perennial forb (alfalfa [Medicago sativa L.]), a bunchgrass (Siberian wheatgrass [Agropyron fragile {Roth} P. Candargy subsp. sibericum {Willd.} Melderis]), and a sod-forming grass (pubescent wheatgrass [Elytrigia intermedia {Host} Nevski subsp. trichophora {Link} Tvzel]) in monocultures and 2- and 3-species mixtures. We measured Russian knapweed and seeded-species density 1 and 2 years following seeding. The forb-seeding treatment decreased reinvasion of Russia knapweed by 50%–60% at 1 site, but otherwise, seeding treatment had little influence on total seeded-species density or Russian knapweed density. Tilling generally resulted in a 35%–40% reduction in Russian knapweed density compared with the control and resulted in the highest establishment of seeded species. Variability in annual precipitation appeared to influence seeded-species establishment between the sites. Our results suggest shallow tilling (10–15 cm) followed by drill-seeding desirable forbs and grasses may provide the best results when revegetating Russian knapweed infestations. Follow-up management should include strategies to enhance desirable species production while minimizing Russian knapweed reinvasion.

CONTROLLING PERFORMANCE OF BLUEBUNCH WHEATGRASS AND SPOTTED KNAPWEED USING NITROGEN AND SUCROSE AMENDMENTS

Abstract Range- and wildlands are being invaded by nonindigenous plants, resulting in an unprecedented, rapid change in plant community composition across the United States. Successional management predicts that species performance may be modified by resource availability. The objective of this study was to determine whether species performance could be altered by modifying soil nitrate (NO3–) and ammonium (NH4+) concentrations within an Idaho fescue (Festuca idahoensis)/bluebunch wheatgrass (Pseudoroegneria spicata) plant association. We planted bluebunch wheat-grass and spotted knapweed (Centaurea maculosa) in an addition series at 2 sites in southwestern Montana. Each plot in the addition series matrix was divided into thirds, and we applied nitrogen (N) to a subplot and sucrose to a 2nd subplot. The remaining subplot was not amended and considered a control. Nitrogen amendment tended to enhance the performance of spotted knapweed, while sucrose amendment had no effect. Bluebunch wheatgrass performance was not affected by either amendment. Sucrose treatments only decreased soil NO3– at the more productive site. Regression models for predicting bluebunch wheatgrass and spotted knapweed biomass accounted for only about 30% of the variation, suggesting other processes in addition to interference were responsible for explaining relative plant performance. We recommend that land managers prevent activities that increase soil N concentration while the effectiveness of carbon amendments as a means to decrease soil N concentrations and shift interference relationships is further investigated.

Downy Brome (Bromus tectorum) Control with Imazapic on Montana Grasslands

Abstract 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). Nomenclature: Imazapic; downy brome, Bromus tectorum L. BROTE. Management Implications: Management of the invasive annual grass downy brome (Bromus tectorum) remains challenging on western rangeland. Chemical control has produced inconsistent results, especially with the herbicide imazapic (Plateau®, BASF Corporation, Research Triangle Park, NC). Downy brome has been increasing during the past several years on rangeland across Montana where effective management recommendations for chemical control are needed. We compiled data from 24 independent herbicide trials across Montana, from 2000 to 2010, which investigated the efficacy of imazapic applied at various rates and timings and with methylated seed oil (MSO) or a nonionic surfactant (NIS). We tested for general trends in downy brome control across application rate (70, 105, 141, 176, 211 g ai ha−1 [1, 1.5, 2, 2.5, and 3.1 oz ai ac−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). Downy brome control was especially affected by application timing. 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 did not affect downy brome control. Our data indicated that an EPOST (downy brome at the one- to two-leaf growth stage) application at 105 to 141 g ai ha−1 provided the most-consistent control of downy brome. Most published literature on the efficacy of imazapic for controlling downy brome do not report growth stage at the time of application, but our data indicate that timing of imazapic application influences its efficacy. Therefore, land managers should be aware of the growth stage of downy brome when imazapic applications are made and interpret outcomes with this factor in mind.

Effects of Soil Texture, Watering Frequency, and a Hydrogel on the Emergence and Survival of Coated and Uncoated Crested Wheatgrass Seeds

Revegetation of degraded shrub-steppe often fails due to intense competition from weeds, highly variable environmental conditions, and limited soil moisture. The objective of this study was to test whether a commercially available seed coating and a water-retaining acrylamide copolymer hydrogel would increase seedling emergence and establishment of crested wheatgrass (Agropyron cristatum) under three watering frequencies and two soil textures. Pots were filled with one of four soil treatments: field soil, two parts field soil mixed with one part sand, field soil plus hydrogel, or field soil plus sand plus hydrogel. We seeded the pots with coated or uncoated seed and placed them in a greenhouse for 66 days. The pots were assigned one of three watering treatments: 4.5 oz (150 ml) applied one time per week, 1.5 oz (50 ml) applied three times per week, or 0.9 oz (30 ml) applied five times per week. We recorded seedling emergence at three and six weeks. At the end of 66 days, the numbers of seedlings that survived were counted and aboveground biomass was collected, dried, and weighed. We found that uncoated seed had 1.6 times greater seedling density than coated seed. Incorporation of the acrylamide copolymer hydrogel into the potting medium conferred some benefit to emergence, biomass, and survivorship of crested wheatgrass seedlings. However, it was watering frequency that produced the most consistent influence on seedling emergence, survival, and biomass. Watering three or five times per week increased emergence more than watering one time per week, but watering one time per week generally led to greater survivorship and biomass. This suggests that the use of water-retaining hydrogels may help to overcome soil moisture limitations and improve seedling establishment during revegetation of degraded shrub-steppe.

Downy Brome Control and Impacts on Perennial Grass Abundance: A Systematic Review Spanning 64 Years ☆

ABSTRACT Given the high cost of restoration and the underlying assumption that reducing annual grass abundance is a necessary precursor to rangeland restoration in the Intermountain West, United States, we sought to identify limitations and strengths of annual grass control methods and refine future management strategies. We systematically reviewed all published journal articles spanning a 64-yr period (1948–2012; n = 119) reporting data on research efforts to either directly or indirectly reduce the abundance of the most common invasive annual grass, downy brome (Bromus tectorum L.). The seven most common control methods studied were herbicide, burning, revegetation, woody removal, defoliation or grazing, soil disturbance, and soil amendment. In addition, the majority of control methods were 1) applied at scales of 10–100 m2, 2) sampled within small plots (i.e., 0.1–1.0 m2), 3) implemented only once, and 4)monitored at time scales that rarely exceeded 5 yr. We also performed summary analyses to assess how these control methods affect downy brome and perennial grass abundance (i.e., cover, density, biomass). We found conflicting evidence regarding the assumption that reducing downy brome abundance is necessary to enhance the growth and establishment of perennial grasses. All methods, with the exception of woody plant removal, significantly reduced downy brome in the short term, but downy brome abundance generally increased over time and only herbicide and revegetation remained reduced in the long term. Only burning, herbicide, and soil disturbance led to long-term increases in perennial grass abundance. We suggest that future research should prioritize a broader array of ecological processes to improve control efficacy and promote the reestablishment of desirable rangeland plant communities.

Integrating Herbicides and Re-seeding to Restore Rangeland Infested by an Invasive Forb-Annual Grass Complex

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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).