Calamagrostis Canadensis Research Articles

Comparison of four glyphosate herbicide formulations for white spruce release treatment

An operational field trial was established to compare the efficacy and white spruce (Picea glauca (Moench) Voss.) tolerance of three alternative glyphosate formulations to Vision®, Canada's originally registered forestry formulation. The trial was done at operational scale (minimum treatment unit 7 ha) using helicopter application of all products. The tested alternatives included two new generic formulations, recently registered for forestry in Canada (Glyfos-Forza® and Vantage®), and one widely used formulation in the United States (Accord®). All four formulations provided greater than 90% control of bluejoint reedgrass (Calamagrostis canadensis (Michx.) Beauv.) through 23 months post-treatment (p > 0.27). Assessed over the same period, the three Canadian formulations provided equivalent white spruce tolerance (p > 0.10), with seedlings exhibiting only minor, non-lethal herbicide injury. Accord®, not registered for use in Canada, consistently provided the best crop tolerance, but differences were only statistically significant 11 months post-treatment (p = 0.10). The results suggest that foresters may choose among the glyphosate formulations available in Canada without concern for product-related differences in efficacy and white spruce tolerance. Key words: glyphosate, white spruce, conifer tolerance, Calamagrostis canadensis, efficacy

Competition and facilitation in mixtures of aspen seedlings, alfalfa, and marsh reedgrass

Increasing demand for aspen (Populus tremuloides Michx.) and related poplar species is generating interest in their intensive cultivation. Successful establishment of aspen plantations requires minimizing the negative effects of associated plant species. Competitive and facilitative effects were isolated in field plots containing fixed-density mixtures of aspen seedlings, alfalfa (Medicago sativa L.), and marsh reedgrass (Calamagrostis canadensis (Michx.) Beauv.) in central Alberta. Although aspen survival was unaffected in mixtures, damage to aspen leaf area was lower when grown with either herbaceous species than when grown in monoculture, possibly reflecting facilitation through plant defense guilds. Over the first two growing seasons, net competition was expressed as most aspects of aspen growth were reduced. Herbaceous species reduced photosynthetically active radiation, soil moisture, and soil N available to aspen. Moreover, relative yield totals from the species mixtures examined consistently indicated either neutral effects (combined yields equaled monoculture yields) or underyielding. Despite this, evidence of facilitation was also found when aspen was grown with alfalfa, including increases of overall available soil N and transient increases in soil moisture with pulsed precipitation during drought. These results indicate that short-term facilitative aspects of aspen–legume mixtures may be exploited through an agroforestry scheme by appropriately timed harvest of the herbaceous component. Conversely, aspen establishment has limited potential for integrated production with marsh reedgrass.

Above- and below-ground effects from alfalfa and marsh reedgrass on aspen seedlings

Partitions were used to separate above- and below-ground effects of alfalfa ( Medicago sativa L.) and marsh reedgrass ( Calamagrostis canadensis (Michx.) Beauv.) on aspen ( Populus tremuloides Michx.) seedlings. Surrounding herbaceous vegetation reduced soil water, available soil nitrates and photosynthetically active radiation. Although aspen survival was not affected, net competition was expressed with competitor biomass correlated negatively with most aspects of aspen growth. Competitive differences between herbaceous species were primarily related to individual plant sizes. Herbaceous species increased soil moisture when shoots were intermixed and root barriers were in place, but did not enhance soil moisture when below-ground effects were also present. This suggests herbaceous canopies increase soil moisture by blocking evaporation, but concomitant root uptake negates this increase. Aspen made little use of the N pool outside the immediate zone around the seedling, suggesting retention of herbaceous vegetation between trees could minimize N-leakage from the system. Thus, there may be some benefit to agroforestry systems in balancing the short-term competitive effects from herbaceous species presence against longer-term negative effects on soil fertility.

Use of an Aspen Overstory to Control Understory Herbaceous Species, Bluejoint Grass (Calamagrostis canadensis), and Fireweed (Epilobium angustifolium)

Abstract To enhance white spruce [Picea glauca (Moench) Voss] regeneration and growth, the potential for using an aspen (Populus tremuloides Michx.) overstory to suppress bluejoint grass [Calamagrostis canadensis (Michx.)] and fireweed (Epilobium angustifolium L) was investigated. Response to canopy opening was assessed on 10 treatments where the canopy had been incrementally opened. At the summer solstice, measurements of attenuated light were taken at 1.3 meters (breast height). Bluejoint grass and fireweed both responded with greater ground cover as the photosynthetic photon flux density increased (R2 = 0.84, P = 0.0002; R2 = 0.90, P = 0.0001; respectively). Where aspen has developed an overstory canopy, it may be possible to control competing vegetation to create favorable environmental conditions for spruce re-establishment, growth, and release while encouraging a sustainable mixedwood stand.

Nitrogen uptake characteristics for roots of conifer seedlings and common boreal forest competitor species

Little is known about the N uptake abilities of competitor species and planted seedlings in the boreal forest. The objective of this study was to determine the Michaelis–Menten kinetic parameters of NH4+and NO3–for white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb.) seedlings, and three competitive common boreal forest early successional species: aspen (Populus tremuloides Michx.), fireweed (Epilobium angustifolium L.), and cala magrostis (Calamagrostis canadensis (Michx.) Beauv.). Uptake kinetics were measured in hydroponic cultures and expressed as maximum uptake (Imax) and ion affinity (Km). The ranking of Imaxvalues (pmol·cm-2·s–1) for NH4+uptake was calamagrostis (84.6), fireweed (58.1), white spruce (20.7), aspen (12.5), and jack pine (10.9), and for NO3–uptake was calamagrostis (17.7), fireweed (12.5), aspen (5.8), white spruce (4.5), and jack pine (2.1). The ranking of Kmvalues (µM) for NH4+uptake was calamagrostis (125.9), fireweed (163.8), aspen (205.7), white spruce (217.1), and jack pine (270.5), and for NO3–uptake was calamagrostis (229.9), fireweed (274.6), aspen (336.5), white spruce (344.5), and jack pine (350.5). Calamagrostis exhibited the greatest uptake rates and affinity for NH4+and NO3–, suggesting that silviculture practices that specifically reduce establishment of this grass should benefit the growth of planted seedlings.

Nitrogen Accumulation by Conifer Seedlings and Competitor Species From Nitrogen-labeled Controlled-Release Fertilizer

A major impediment to the establishment of outplanted conifer seedlings is competition for available soil N by early successional species. The objective of this field study was to determine the fate of controlled-release fertilizer (CRF) N in soils with outplanted white spruce (Picea glauca [Moench] Voss.) and jack pine (Pinus banksiana Lamb.) seedlings, and the effect of weed control or vegetation management (VM) on fertilizer N accumulation. Nitrogen-15 labeled CRF was placed next to the seedling root plug during planting at four boreal mixed wood sites. After one growing season in the control plots, fertilizer N recovery as a percentage of 15N added was 4% in seedlings, 3% in competing vegetation, <1% leached, and 85% residual CRF. After two growing seasons, fertilizer N recovery was 15% in seedlings, 20% in competing vegetation, <1% leached, and 58% residual CRF. Overall, VM increased seedling fertilizer N uptake by almost 300% compared with conifer seedlings in control plots. In VM plots, fertilizer bags contained more N than in control plots after two growing seasons. In both treatments, >50% of the fertilizer N remained in the fertilizer bag, presumably remaining available in subsequent seasons. Calamagrostis (Calamagrostis canadensis) was the primary competitor for fertilizer N in both growing seasons, with minor competition from fireweed (Epilobium angustifolium L.), and aspen (Populus tremuloides Michx.). The use of a point source CRF delivery method resulted in high fertilizer use efficiency (FUE), and minimized losses to competing vegetation and leaching.

Nitrogen Accumulation by Conifer Seedlings and Competitor Species From 15Nitrogen‐labeled Controlled‐Release Fertilizer

A major impediment to the establishment of outplanted conifer seedlings is competition for available soil N by early successional species. The objective of this field study was to determine the fate of controlled‐release fertilizer (CRF) N in soils with outplanted white spruce (Picea glauca [Moench] Voss.) and jack pine (Pinus banksiana Lamb.) seedlings, and the effect of weed control or vegetation management (VM) on fertilizer N accumulation. Nitrogen‐15 labeled CRF was placed next to the seedling root plug during planting at four boreal mixed wood sites. After one growing season in the control plots, fertilizer N recovery as a percentage of 15N added was 4% in seedlings, 3% in competing vegetation, &lt;1% leached, and 85% residual CRF. After two growing seasons, fertilizer N recovery was 15% in seedlings, 20% in competing vegetation, &lt;1% leached, and 58% residual CRF. Overall, VM increased seedling fertilizer N uptake by almost 300% compared with conifer seedlings in control plots. In VM plots, fertilizer bags contained more N than in control plots after two growing seasons. In both treatments, &gt;50% of the fertilizer N remained in the fertilizer bag, presumably remaining available in subsequent seasons. Calamagrostis (Calamagrostis canadensis) was the primary competitor for fertilizer N in both growing seasons, with minor competition from fireweed (Epilobium angustifolium L.), and aspen (Populus tremuloides Michx.). The use of a point source CRF delivery method resulted in high fertilizer use efficiency (FUE), and minimized losses to competing vegetation and leaching.

Revegetation of prairie pothole wetlands in the mid-continental US: twelve years post-reflooding

In the mid-1980's, thousands of wetlands in the mid-continental Unites States were restored by interrupting drainage lines; revegetation of these systems, often cropped for decades and positioned in a predominantly agricultural landscape, relied solely on natural recolonization. A study of 64 of these wetlands determined that by 1991, three years after initial reflooding, aquatic species had efficiently recolonized whereas sedge meadow and wet prairie species had not. In 2000, 41 of these restorations that had not been significantly altered or returned to cultivation were revisited and their floras characterized by cover within distinct zones. While species richness increased on every site, the rate of accumulation varied widely. Furthermore, species that had colonized since 1991, including a variety of native wet prairie and sedge meadow species, were detected only at very low abundance. In contrast, Phalaris arundinacea L., an invasive perennial, was now present on every site, often at covers approaching 75–100% in the zones in which it occurred. Other invasive perennials, including Cirsium arvense (L.) Scop. and Typha angustifolia L./glauca Godr., had expanded significantly on many sites. The overall dominance of invasive perennials has resulted in basins that are becoming more similar over time. However, present variations in species richness and composition can be attributed to flooding frequency, and, potentially, basin size and isolation from nearby natural wetlands, as shown by TWINSPAN and graphical analysis. Basins that have not been flooded at midsummer for at least seven of 12 years are among the most depauperate in the study. Yet even frequently flooded basins lack diversity if they are small (< 1.5 ha) or isolated from seed sources. Across the study, numerous species common to natural systems were notably absent or infrequently occurring, including Calamagrostis canadensis (Michx.) Beauv., Carex lacustris Willd. and Lysimachia thrysiflora L. Continuous areas of sedge-dominated meadow, a signature of prairie potholes, did not exist at any study site, nor did they appear to be forming. Given the dominance of invasive perennials and absence of many native wetland species, it appears that without significant seeding, planting and aftercare wetland restorations in fragmented landscapes have a low probability of resembling those that existed historically.

Interspecific competition for nitrogen between early successional species and planted white spruce and jack pine seedlings

Relatively little is known about belowground competition for nitrogen (N) between boreal forest species. The objective of this study was to compare the relative competitiveness of three early successional boreal forest species, trembling aspen (Populus tremuloides Michx.), fireweed (Epilobium angustifolium L.), and calamagrostis (Calamagrostis canadensis (Michx.) Beauv.), on 15N uptake and the growth response by containerized white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb.) seedlings. Three densities (0, 2, and 6 plants/pot) of each competitor species were interplanted with individual seedlings in pots with 15N-labelled fertilizer and grown for 3 months. The conifer seedlings had the greatest fertilizer 15N uptake (129.5 and 82.3 µg/m2 root for white spruce and jack pine, respectively) when grown in monoculture and the lowest uptake when interplanted with six competitor plants (9.2 and 8.6 µg/m2 root for white spruce and jack pine, respectively). Whether grown in monoculture or with conifer seedlings, calamagrostis took up the greatest amount of fertilizer 15N. Vegetation management practices that reduce the establishment of this grass species in the field should benefit N uptake and growth of outplanted white spruce and jack pine seedlings.

Effects of nitrogen on the growth of jack pine competing with Canada blue-joint grass and large-leaved aster

Biomass, leaf area, canopy photosynthesis, photosynthetic nitrogen-use efficiency (PNUE), nitrogen-partitioning ratio (NPR: ratio of nitrogen taken up by jack pine relative to two different competitor species), and nitrogen uptake (NU) of jack pine ( Pinus banksiana Lamb.) competing with large-leaved aster ( Aster macrophyllus L.) and Canada blue-joint grass ( Calamagrostis canadensis (Michx.) Beauv.) were examined at three nitrogen levels in a controlled-environment growth chamber. When grown with large-leaved aster, jack pine biomass, photosynthesis and PNUE ( p<0.001) increased as nitrogen level increased. Jack pine biomass, photosynthesis and NPR ( p<0.001) decreased as nitrogen level increased when grown with Canada blue-joint grass. At the lowest nitrogen supply level, jack pine photosynthesis decreased as competitor PNUE increased ( r 2=0.84, p<0.001). Jack pine photosynthesis decreased as NU of large-leaved aster (37.5 mg N l −1: r 2=0.75, p<0.001; 100 mg N l −1: r 2=0.86, p<0.001) and Canada blue-joint grass (37.5 mg N l −1: r 2=0.96, p<0.001; 100 mg N l −1: r 2=0.84, p<0.001) increased. NU and PNUE may play an important role in the outcome of interactions between jack pine seedlings and competing forest vegetation in newly planted stands.

Nonequilibrium dynamics of sedge meadows grazed by cattle in southern Wisconsin

Equilibrium theory predicts that after disturbance, ecosystemseventually regain the structural and functional properties characteristic oftheir predisturbance condition. This study tested this idea by examining theeffects of cattle grazing and exclusion on the long-term structuralcharacteristics of sedge meadows in southern Wisconsin. To compare structuralchanges in mean percentage cover and height, repeated measures analysis wasconducted on two sedge meadows over a twenty year period from 1977 to 1997. Onesedge meadow was recovering from cattle grazing (cattle excluded in 1973) andthe other was a reference area (nearly undisturbed). Both of these study siteschanged structurally from 1977 to 1997, supporting non-equilibrium theory.Additional observations were made in a heavily and lightly grazed sedge meadowthat were surveyed in 1977. As based on the positions of subunits in anordination graph produced using Non-Metric Multidimensional Scaling (NMS), therecovery sedge meadow became less structurally similar to the grazed and moresimilar to the reference site over the 20 year study. However, from theperspective of mean maximum height in another NMS analysis, the recovery sedgemeadow became less similar to the reference site over time likely because by1997, a shrub carr of Cornus sericea had developed in therecovery sedge meadow that had been dominated by graminoids and forbs in 1977(mean maximum height: 1977 vs. 1997; 0 vs. 47 cm). Seedlings ofCornus sericea were invading the grazed sedge meadows andin the recovery sedge meadow (cattle excluded 4 years earlier) in 1977. A shrubcarr did not develop in the reference sedge meadow. Changes in the referencesite were relatively minor over this time interval; certain species eitherincreased or decreased in dominance, e.g., Carex strictaincreased in cover (1977 vs. 1997, 20 and 28 mean percentage (%) cover,respectively). A few short-term species of the recovery sedge meadow followedthe tenets of equilibrium theory. These became less common or disappeared4–9 years after cattle exclusion including Asterlanceolatus, Calamagrostis canadensis,Poa compressa, Solidago altissima andVerbena hastata. Some of these species were eaten andlikely spread by the cattle. This study suggests that the progression of sedgemeadow to shrub carr may not be an inevitable outcome of succession but insteadcan be a consequence of past cattle grazing history. Also, because the recoveryand the reference sedge both changed structurally over time, the tenets ofnon-equilibrium theory were supported by this study.

Photosynthesis, nitrogen-use efficiency, and water-use efficiency of jack pine seedlings in competition with four boreal forest plant species

The objective of this study was to understand the mechanism underlying nitrogen (N) and water competition between jack pine (Pinus banksiana Lamb.) and four boreal forest species. Large-leaved aster (Aster macrophyllus L.), Canada blue-joint grass (Calamagrostis canadensis (Michx.) Beauv.), trembling aspen (Populus tremuloides (Michx.), and red raspberry (Rubus idaeus L.) were planted at a range of densities (0-8 plants/m2) with jack pine seedlings. Net photosynthesis (Pn), nitrogen-use efficiency (NUE), water-use efficiency (WUE) of each species were monitored over three consecutive growing seasons. Changes in available soil N and water were also measured. Jack pine Pn, NUE, and WUE decreased as competitor density increased, but these effects varied among species (p &lt; 0.001) and over time (p &lt; 0.001). The influence of density on jack pine Pn decreased over time for aster and blue-joint grass and increased over time for aspen and raspberry (p &lt; 0.001). At most sample times, jack pine Pn correlated with available soil N. In contrast, the correlation between jack pine Pn and soil water was rarely significant.

The influence of edaphic and competitive factors on productivity of marsh reed grass (Calamagrostis canadensis) in a cooperative pathosystem

Calamagrostis canadensis (Michx.) Beauv., marsh reed grass, hinders the regeneration of conifer seedlings. The influence of nutrients, autoallelopathy, and intraspecific competition on the productivity of greenhouse-grown marsh reed grass inoculated with a combined Fusarium avenaceum (Fr.:Fr.) Sacc. – Pseudomonas sp. pathosystem was studied. The productivity of uninoculated plants increased following fertilization, but these increases were not observed in inoculated plants. Leaf damage in inoculated plants was enhanced by P and K fertilization, but shoot height was not affected. Autoallelopathic straw extract interacted with intraspecific competition to nearly double pathogenic inhibition of shoot growth at high levels of competition. The straw extract also interacted with N fertilizer to reduce shoot productivity. Shoot growth was inhibited at higher levels of intraspecific competition. Responses to nutrients, autoallelopathy, and competition may be useful in developing improved biological control strategies.Key words: Fusarium avenaceum, rhizobacteria, biocontrol, bioherbicide, fertility, soil ecology.

Canadian Bluejoint Response to Heavy Grazing

A disclimax stand of Canadian bluejoint (Calamagrostis canadensis (Michx.) Beauv.) was heavily grazed by cattle and horses for 4 years to weaken the grass's competition with hardwoods important as browse and cover to wildlife. Stocking at 0.084 ha AUM(-1) resulted in uniform utilization of bluejoint and maintenance of early phenology through the growing season. Etiolated bluejoint declined about 90%, but grass production increased 10 to 15%, as fireweed (Epilobium angustifolium L.), a principal herbaceous component of the stand, decreased in response to trampling. Rhizomes of heavily grazed bluejoint had lower total nonstructural carbohydrates (TNC) (p = 0.0127), lower weight (g cm(-1) length) (p = 0.05), and reduced biomass (g cm(-3) of soil) (p = 0.05). Shoots of grazed bluejoint maintained higher nitrogen (p = 0.0001) and higher digestibility (IVDMD) (p = 0.0017) than bluejoint that was never grazed. This enabled heavily grazed bluejoint to retain good forage quality through the entire growing season, as opposed to ungrazed bluejoint, which became poor forage at the time of flowering during early July. Following one season of rest, rhizome TNC, shoot nitrogen, and IVDMD returned to levels of never grazed bluejoint. Seedhead production, seed production, seed weights, and seed viability of rested bluejoint were about the same as in ungrazed stands. On wet sites, heavy grazing does not adequately reduce the vigor of this grass. DOI:10.2458/azu_jrm_v54i3_collins

Heavy Grazing of Canadian Bluejoint to Enhance Hardwood and White Spruce Regeneration

Abstract Wet, disclimax stands of Canadian bluejoint (Calamagrostis canadensis [Michx.] Beauv.) created by logging were heavily grazed by cattle and horses years 5 through 8 after logging to weaken the grass and favor regeneration of hardwoods and white spruce (Picea glauca [Moench.] Voss). Seedling densities of hardwoods and white spruce in heavily grazed stands were not significantly different (P &lt; 0.05) from those in ungrazed stands. Heavy grazing reduced herbaceous cover and litter but was not detrimental to runoff water quality. Heavy grazing was not effective for increasing regeneration in wet disclimax stands of Canadian bluejoint where the grass had already increased following overstory removal, but earlier application and use in drier sites should be considered. North. J. Appl. For. 18(1):19–21.

Canadian bluejoint response to heavy grazing

A disclimax stand of Canadian bluejoint (Calamagrostis canadensis (Michx.) Beauv.) was heavily grazed by cattle and horses for 4 years to weaken the grass's competition with hardwoods important as browse and cover to wildlife. Stocking at 0.084 ha AUM(-1) resulted in uniform utilization of bluejoint and maintenance of early phenology through the growing season. Etiolated bluejoint declined about 90%, but grass production increased 10 to 15%, as fireweed (Epilobium angustifolium L.), a principal herbaceous component of the stand, decreased in response to trampling. Rhizomes of heavily grazed bluejoint had lower total nonstructural carbohydrates (TNC) (p = 0.0127), lower weight (g cm(-1) length) (p = 0.05), and reduced biomass (g cm(-3) of soil) (p = 0.05). Shoots of grazed bluejoint maintained higher nitrogen (p = 0.0001) and higher digestibility (IVDMD) (p = 0.0017) than bluejoint that was never grazed. This enabled heavily grazed bluejoint to retain good forage quality through the entire growing season, as opposed to ungrazed bluejoint, which became poor forage at the time of flowering during early July. Following one season of rest, rhizome TNC, shoot nitrogen, and IVDMD returned to levels of never grazed bluejoint. Seedhead production, seed production, seed weights, and seed viability of rested bluejoint were about the same as in ungrazed stands. On wet sites, heavy grazing does not adequately reduce the vigor of this grass.

The influence of edaphic and competitive factors on productivity of marsh reed grass (&lt;i&gt;Calamagrostis canadensis&lt;/i&gt;) in a cooperative pathosystem

The influence of edaphic and competitive factors on productivity of marsh reed grass (&lt;i&gt;Calamagrostis canadensis&lt;/i&gt;) in a cooperative pathosystem

Effects of controlled weed densities and soil types on soil nitrate accumulation, spruce growth, and weed growth

Soil nitrate (NO 3 −) accumulation rates were assessed among seven weed species grown in small plots during the summer of 1997, at a northern Ontario location. Objectives were (1) to quantify soil nitrate accumulation rates at varying weed densities established on three soil types (clay, loam, and sand) and (2) to assess the effects of soil nitrate levels on weed and black spruce ( Picea mariana (Mill.) B.S.P.) seedling growth and weed growth. Controlled densities (0, 0.5, 2, 8 stems per m 2) of red raspberry ( Rubus idaeus L. var. strigosus (Michx.) Maxim.), fireweed ( Epilobium angustifolium L.), and a grass species ( Calamagrostis canadensis (Michx.) Nutt.) were planted along with spruce seedlings (1 m spacing) early in the summer of 1994. Concurrently, four more deciduous weed species, trembling aspen ( Populus tremuloides Michx.), white birch ( Betula papyrifera Marsh.), green alder ( Alnus crispa (Ait.) Pursh), and willow ( Salix humilis Marsh.) were also established at four densities (0, 0.5, 2, 4 stems per m 2). In mid-summer (July) 1997, soil samples collected from the respective weed densities were placed in polyethylene bags and the bags were incubated in the respective plots for 34 days at a depth of 12 cm. Nitrate accumulation rates (μg per 100 gm of dry soil per day), weed heights, and the effective leaf area index (LAIe, in m 2 m −2, measured with a Licor LAI-2000 Plant Canopy Analyzer) of competing vegetation were consistently higher (1.4–3.0 times) for clay soil. Nitrate levels were significantly ( p < 0.05) higher in clay soils obtained from plots planted with raspberry, grass, aspen, and willow. Carbon : nitrogen (C : N) ratios were higher for loam soils than those for clay or sand soils, and these higher ratios may have resulted in more immobilization than mineralization of soil nitrogen. Nitrate levels for clays and loams correlated significantly with the LAIe of competing vegetation ( r = 0.62–0.78) and with weed growth ( r = 0.75–0.96), but non-significantly, and often negatively, with spruce stem volume. To date, soil nitrate accumulation appears to have primarily benefited cultivated weeds and not to have improved spruce growth. These findings affirm that weeds must be controlled for seedlings to benefit nutritionally.

Growth Response of Picea mariana Seedlings to Competition for Radiation

The growth response of 4-year-old black spruce seedlings (Picea mariana (Mill.) B.S.P.) to reduced radiation availability (DIFN) caused by herbaceous and woody competitors was investigated on a clay and on a loam site on a research plot in Ontario, Canada. Variability in black spruce growth was less explicable by reduced radiation availability caused by woody competitors than growth variability caused by herbaceous competitors. On the clay site, competition from fireweed (Epilobium angustifolium L.), Canada bluejoint grass (Calamagrostis canadensis (Michx.) Nutt.) and red raspberry (Rubus idaeus L. var. strigosus (Michx.) Maxim.) decreased black spruce diameter by more than 40% compared to seedlings without competition. Canada bluejoint grass and fireweed also distinctly reduced black spruce diameter performance on loam (>30%). These results are discussed in relation to the need of vegetation control.

The vegetation of wet meadows in relation to their land-use

Wetland biomonitoring approaches are needed to determine when changes in response to stressors are occurring and to predict the consequences of proposed land-use changes. These approaches require an understanding of shifts in biota that occur in response to land-use, data that are lacking for most kinds of wetlands. Changes in floristic composition corresponding to land-use differences at multiple scales (site to 2500 m radius) were characterized for 40 wet meadows associated with prairie glacial marshes in Minnesota (U.S.A.). In general, guild was more useful than species composition for indicating land-use impacts. Site impacts (stormwater, cultivation) and landscape disturbance (agriculture and urbanization, combined), coincide with a reduction in native graminoid and herbaceous perennial abundance (e.g., Carex lasiocarpa, Calamagrostis canadensis, Spartina pectinata). This vegetation is replaced with annuals (e.g, Bidens cernua, Polygonum pensylvanicum) in recently cultivated sites or introduced perennials (e.g., Phalaris arundinacea, Typha angustifolia) and floating aquatics (lemnids) in stormwater impacted wetlands. Ditches also reduce native perennial importance and increase perennials, but only when they are in highly impacted landscapes.