Native Plant Biomass Research Articles

Plant Community Biomass Shifts in Response to Mowing and Fencing in Invaded Oak Meadows with Non‐Native Grasses and Abundant Ungulates

Many herbaceous meadows are dominated by competitive non‐native grasses and subject to ungulate herbivory, ecological processes that shift the proportional biomass of plant groups in the community. Predicting the outcome of restoration is complicated because herbivory and competition can interact. We examined the relationship between herbivory by native black‐tailed deer and domestic sheep and dominance of non‐native grasses in Garry oak meadows, one of North America's most endangered habitat types. A 3‐year factorial experiment tested the effects of mowing and fencing on plant community biomass, categorized into eight groups by geographic origin (native/non‐native), growth form (annual/perennial), and plant type (forb/grass). To test if the rarity of native plant groups was related to herbivory, we estimated ungulate foraging preferences for each plant group. Mowing and fencing treatments interacted for annual and perennial non‐native grasses. Dominance was shifted from non‐native to native grasses only when both mowing and fencing were applied. Fencing increased the total biomass, whereas mowing had no overall effect; however, fencing alone did not affect any individual plant group. Mowing shifted dominance from grasses to forbs, although both native and non‐native forbs benefited from the increased light availability. We also noted that herbivore fecal pellet densities were greatest in the spring, which coincided with the peak season of their preferred plant group, native perennial forbs. Overall, applying both mowing and fencing was the most effective restoration treatment to increase native plant groups and biomass.

Litter legacy increases the competitive advantage of invasive Phragmites australis in New England wetlands

Exotic plant invaders that form monocultures and exclude native plants are often the most detrimental to native diversity and the hardest to eradicate. To generate a monoculture, the invader must garner more resources than resident natives and, once established, persist despite high densities of conspecific neighbors. Coincident with expansion and long-term persistence, successful invaders typically accumulate senesced material, but the role of this litter in mediating the invader’s ability to establish and maintain monospecific dominance has rarely been investigated. We used stands of the common reed, Phragmites australis, a prolific wetland invader in North America, to explore the impact of litter on interspecific competition with the native rush, Juncus gerardii, and intraspecific competition among live shoots. In 10 × 10 m areas positioned on Phragmites expansion fronts, we removed litter to isolate its effect from live Phragmites on light availability, aboveground biomass and community composition. Compared to adjacent, unmanipulated fronts, light availability nearly tripled and Juncus biomass increased >170% in litter removal areas after 4 months. Although the positive response of Juncus and native forbs was most pronounced on the leading edge of Phragmites stands, litter removal triggered a 271% increase in native plant biomass even in the interior of stands where Phragmites’ live stem density was highest. Litter treatment did not significantly affect Phragmites biomass, but more, shorter stems emerged in litter removals revealing Phragmites modifies stem phenotype in response to local litter and light conditions. These results suggest that litter plays a central role in Phragmites’ invasion process, from initial establishment to subsequent monospecific dominance. Thus, prescribed litter removal may be an effective strategy to enhance coexistence of native plant populations in wetlands where eradication of invasive monocultures is not an ecologically or economically feasible option.

Soil organic carbon pools and composition in a wetland complex invaded by reed canary grass

Reed canary grass (Phalaris arundinacea) invasion is prevalent in wetlands and riparian fringes, and due to differences in vegetative growth and residue quality relative to native species, P. arundinacea invasion could result in measurable effect on soil organic carbon (SOC) pools and composition. To examine these questions, plant biomass and soil samples were collected from areas invaded by P. arundinacea and areas colonized either by a native sedge Scirpus cyperinus or a mixed assemblage of 22 native species in a south-central Indiana (USA) wetland. Plant biomass composition (C, N, cellulose, lignin, and phenolics), total and water-extractable SOC pools were determined. S. cyperinus biomass contained (g kg−1 biomass) significantly (P < 0.05) more lignin (142.5 vs 72), phenolics (29.2 vs 11.2), and cellulose (260.5 vs 164.8) than P. arundinacea biomass. These constituents were also more abundant in mixed native plant material than in P. arundinacea biomass. Decomposition of plant biomass was related to residue composition with P. arundinacea shoot biomass decomposing 1.6 times faster than S. cyperinus material. SOC pools (Mg C ha−1, 0–30 cm) were larger under P. arundinacea (28.3) than under either S. cyperinus (23.9) or the mixed native species (21.8). Thus, the greater recalcitrance of native plant biomass did not translate into larger SOC pools. Furthermore, water-extractable organic C, N, and carbohydrates were significantly higher in the surface layer of soils supporting P. arundinacea than in native species. These results therefore indicate a clear effect of P. arundinacea invasion on the cycling and composition of soil organic matter at the study site.

Nutrient enrichment enhances hidden differences in phenotype to drive a cryptic plant invasion

Many mechanisms of invasive species success have been elucidated, but those driving cryptic invasions of non-native genotypes remain least understood. In one of the most successful cryptic plant invasions in North America, we investigate the mechanisms underlying the displacement of native Phragmites australis by its Eurasian counterpart. Since invasive Phragmites’ populations have been especially prolific along eutrophic shorelines, we conducted a two-year field experiment involving native and invasive genotypes that manipulated nutrient level and competitor identity (inter- and intra-genotypic competition) to assess their relative importance in driving the loss of native Phragmites. Inter-genotypic competition suppressed aboveground biomass of both native and invasive plants regardless of nutrient treatment (∼ 27%), while nutrient addition disproportionately enhanced the aboveground biomass (by 67%) and lateral expansion (by > 3 × farther) of invasive Phragmites. Excavation of experimental plots indicated that nutrient addition generates these differences in aboveground growth by differentially affecting rhizome production in invasive vs native plants; invasive rhizome biomass and rhizome length increased by 595% and 32% with nutrient addition, respectively, while natives increased by only 278% and 15%. Regardless of nutrient level, native rhizomes produced twice as many roots compared to invasives, which field surveys revealed are heavily infected with mycorrhizal symbionts. These results suggest that native Phragmites competes well under nutrient-limited conditions because its rhizomes are laden with nutrient-harvesting roots and mycorrhizae. Invasive Phragmites’ vigorous aboveground response to nutrients and scarcity of lateral roots, in contrast, may reflect its historic distribution in eutrophic Eurasian wetlands and correspond to its prevalence in New England marshes characterized by elevated nutrient availability and relaxed nutrient competition. These findings reveal that discrete differences in phenotype can interact with anthropogenic modification of environmental conditions to help explain the success of cryptic invaders.

Non-native grass invasion alters native plant composition in experimental communities

Invasions of non-native species are considered to have significant impacts on native species, but few studies have quantified the direct effects of invasions on native community structure and composition. Many studies on the effects of invasions fail to distinguish between (1) differential responses of native and non-native species to environmental conditions, and (2) direct impacts of invasions on native communities. In particular, invasions may alter community assembly following disturbance and prevent recolonization of native species. To determine if invasions directly impact native communities, we established 32 experimental plots (27.5 m2) and seeded them with 12 native species. Then, we added seed of a non-native invasive grass (Microstegium vimineum) to half of the plots and compared native plant community responses between control and invaded plots. Invasion reduced native biomass by 46, 64, and 58%, respectively, over three growing seasons. After the second year of the experiment, invaded plots had 43% lower species richness and 38% lower diversity as calculated from the Shannon index. Nonmetric multidimensional scaling ordination showed a significant divergence in composition between invaded and control plots. Further, there was a strong negative relationship between invader and native plant biomass, signifying that native plants are more strongly suppressed in densely invaded areas. Our results show that a non-native invasive plant inhibits native species establishment and growth following disturbance and that native species do not gain competitive dominance after multiple growing seasons. Thus, plant invaders can alter the structure of native plant communities and reduce the success of restoration efforts.

Invasive plant species and soil microbial response to wildfire burn severity in the Cascade Range of Oregon

Exposure of soil to severe heating during a wildfire volatilizes soil nutrients and causes mortality of microbial communities, potentially facilitating invasion by non-native plant species. In this study, we investigated the chemical and biotic factors associated with severely burned “red” soil and less severely burned “black” soil from a recently burned forest on the eastern slope of the Cascade Range in Oregon. Specifically, we examined the effects of burn severity on plant growth, AM fungal colonization and soil microbial communities as indicated by PLFA (phospholipid fatty acid) analysis. Soil nutrients, arbuscular mycorrhizal (AM) fungi, microbial abundance and plant growth were all significantly reduced in red soils. Native and non-native plants exhibited differential growth in red and black soil, with non-natives growing more rapidly. Despite this rapid growth, non-native plant biomass was significantly lower in red soil, whereas native plant biomass did not differ between red and black soils. These findings suggest that some native species may out-compete non-native species in low-resource environments, such as severely burned red soil, where organic matter, soil nutrients and soil microbes are reduced by severe soil heating.

Invasive plant removal method determines native plant community responses

Summary 1 Restoration of habitats invaded by non-native plants should include both the removal of invasive plants and re-establishment of native plant communities. To develop appropriate restoration strategies and quantify the effects of invasions, experiments that evaluate multiple removal methods and native community responses to those removal methods are needed. 2 We evaluated the response of native plant communities to removal of the invasive grass Microstegium vimineum (Japanese stiltgrass) in eastern forests in the USA. At eight field sites in southern Indiana, we applied three common removal treatments and compared native community responses among treatments and to untreated reference plots. 3 After 2 years of treatment, native community responses to Microstegium removal varied significantly among methods and plant functional groups in autumn 2006. Graminoid richness was greater when the invader was removed with hand-weeding, while graminoid biomass was lower in plots treated with post-emergent herbicide compared to reference plots. Forb richness was greater with hand-weeding and post-emergent herbicide compared to plots treated with post-emergent plus pre-emergent herbicides or untreated plots. Forb biomass was greater across all removal treatments. Overall native community diversity was 24% greater when the invasion was removed with hand-weeding and 21% greater with post-emergent herbicide compared to reference plots. No positive response in plant diversity occurred with post-emergent plus pre-emergent herbicide. 4 By spring 2007, graminoid percentage cover was greater with hand-weeding but not with herbicide treatments compared to untreated plots. However, forb cover was greater across all removal treatments compared to plots where the invader was not removed. The density of native tree seedlings was 123% greater in post-emergent herbicide treated plots than in untreated plots, indicating that the invasion was inhibiting tree recruitment. 5 Synthesis and applications. Our results demonstrate that multiple techniques can be used to control invasive plants but that the responses of native plant communities vary among removal methods. Further, greater native plant diversity and biomass following removal shows that invasions were suppressing native plant communities. Management of plant invasions should consider not only the effectiveness of removal methods but also how different methods influence native plant responses.

The role of disturbance severity and canopy closure on standing crop of understory plant species in ponderosa pine stands in northern Arizona, USA

Concerns about the long-term sustainability of overstocked dry conifer forests in western North America have provided impetus for treatments designed to enhance their productivity and native biodiversity. Dense forests are increasingly prone to large stand-replacing fires; yet, thinning and burning treatments, especially combined with other disturbances such as drought and grazing, may enhance populations of colonizing species, including a number of non-native species. Our study quantifies plant standing crop of major herbaceous species across contrasting stand structural types representing a range in disturbance severity in northern Arizona. The least disturbed unmanaged ponderosa pine stands had no non-native species, while non-native grasses constituted 7–11% of the understory plant standing crop in thinned and burned stands. Severely disturbed wildfire stands had a higher proportion of colonizing native species as well as non-native species than other structural types, and areas protected from grazing produced greater standing crop of native forbs compared to grazed unmanaged stands. Standing crop of understory plants in low basal area thinned and burned plots was similar to levels on wildfire plots, but was comprised of fewer non-native graminoids and native colonizing plants. Our results also indicate that size of canopy openings had a stronger influence on standing crop in low basal area plots, whereas tree density more strongly constrained understory plant standing crop in dense stands. These results imply that treatments resulting in clumped tree distribution and basal areas <10 m 2 ha −1 will be more successful in restoring native understory plant biomass in dense stands. Multiple types and severity of disturbances, such as thinning, burning, grazing, and drought over short periods of time can create greater abundance of colonizing species. Spreading thinning and burning treatments over time may reduce the potential for non-native species colonization compared to immediately burning thinned stands.

Aquatic Plant Communities in Waneta Lake and Lamoka Lake, New York

A point-intercept survey was implemented in August 2000 to deter- mine the distribution and richness of aquatic plant species present in Waneta Lake and Lamoka Lake, NY. Myriophyllum spicatum (Eurasian watermilfoil) was the most commonly observed species in Waneta Lake (25% of entire lake, 78% of lit- toral zone) and Lamoka Lake (43% of entire lake, 77% of littoral zone). Eurasian watermilfoil biomass (24.3 g DW/m 2 ) was also significantly greater (p ≤ 0.001) in Waneta Lake than native plant biomass. Our data suggests that Eurasian watermil- foil is invading the native plant communities of Waneta Lake and Lamoka Lake, thereby displacing native plants and limiting their growth to the shallow waters of the littoral zone.

Use of herbicides to control alligatorweed and restore native plants in managed marshes

Marsh management is used to improve the quality of wetland habitats for a variety of waterfowl and other waterbirds. However, alien plants, such as alligatorweed (Alternanthera philoxeroides (Mart.) Griseb.), may impact success of marsh management by competing with and displacing important native plants. In managed marshes, we tested effects of application rate (high, medium, and low) and timing (April and July) of two herbicides (triclopyr amine and imazapyr) on controlling alligatorweed and restoring native plants. In the year of treatment, imazapyr controlled alligatorweed better than triclopyr amine when applied in April, but the herbicides were equally effective when applied in July. High application rate of herbicides in April controlled alligatorweed better than the low application rate, but application rates of herbicides in July did not influence control. In the year of treatment, application of triclopyr amine resulted in greater native plant biomass than imazapyr. High application rate of herbicides in April resulted in greater native plant biomass in the year of treatment than low application rate, but native plant biomass did not differ among rates of herbicides applied in July. One year after treatment, the high application rate of herbicides resulted in less alligatorweed than the low application rate, and July applications of either herbicide generally controlled alligatorweed better than April applications. Application of imazapyr in July resulted in greater biomass of native plants one year after treatment than either imazapyr or triclopyr amine applied in April. This study demonstrates that single herbicide applications can be effective at controlling alligatorweed, and that these applications can have immediate and longer-term benefits for restoring native plants to managed marshes.

Reducing Euphorbia esula with a combination of sheep grazing and imazapic

Field studies were conducted in Idaho from 2002 to 2004 to determine whether summer grazing of sheep for 1 or 2 years before an autumn application of imazapic would enhance control of Euphorbia esula. E. esula, a perennial plant native to parts of Europe and Asia, has invaded the Great Plains and Rocky Mountains after its introduction into North America in the early 1880s and caused significant reductions in native plant biomass. Experiments were conducted to determine the impacts of 1 or 2 years of sheep grazing with or without a fall application of imazapic on E. esula and native plant populations. Sheep grazing was designed to remove reproductive parts from E. esula within a 10 d grazing period. Imazapic was applied at 210 g ae ha −1 with 1.25% (v/v) methylated seed oil. One year of sheep grazing did not alter measured vegetation components, but it did result in an increase of grass seed in the soil. Two years of sheep grazing increased the forb and grass cover component, increased the grass seed in the soil, and kept the E. esula seed bank from increasing. Application of imazapic reduced E. esula stem densities and cover and increased native forb cover. The combination of 1 or 2 years of sheep grazing and imazapic did not enhance the control of E. esula. However, 2 years of carefully timed sheep grazing followed with an imazapic application resulted in sustained productivity of plant biomass in the pasture. Because 2 years of sheep grazing prevented an increase in the E. esula seed bank, managers may have a better opportunity to establish desired vegetation in sagebrush steppe ecosystems after removing E. esula with imazapic.

Biosolid amendment of a calcareous, degraded soil in a semi-arid environment

Many soils in the Mediterranean region are subjected to progressive degradation as a result of water erosion. A study was carried out to examine the effects of biosolids on a degraded soil. Single doses of 40, 80 and 120 Mg haE–1 of a biosolid were applied to the surface of soil and their effects on its chemical characteristics and on the native vegetation were assessed. Soil macronutrients, micronutrients and heavy metals were tested one and five years after application. Canopy cover, biomass production and mineral composition of native vegetation were also determined. Biosolids increased the content of most nutrients in the soil, although this effect decreased over time. The soil organic matter content did not increase significantly at the beginning of the experiment, although significant differences were observed after five years. The contents of total and extractable heavy metals did not change with time after the application. The native plant biomass production and the canopy cover significantly increased with all the doses applied at the beginning of the experiment, and remained high five years after biosolids application.

A new mechanism of invader success: Exotic plant inhibits natural vegetation restoration by changing soil microbe com-munity

Since the 1950s of the last century, the exotic plant, Eupatorium adenophorum, has spread rapidly across southwest China, damaging native ecosystems and causing great economic losses. We examined the pH, N, P, K, and organic matter concentrations, and the bacterial community character (by Biolog EcoPlate™) in soils from sites heavily and lightly invaded by this exotic species. Also, soil from the lightly invaded site was treated with a water extract of E. adenophorum roots to examine the effect of the plant on soil properties. We grew three plant species, one native and two exotic, in pot experiment using soil from heavily invaded site to examine the effects of the soil on these plants growth. The soil analysis demonstrated that the pH, organic matter, total N, total P and total K in soils from the heavily invaded site were only slightly different from those of the lightly invaded site, but concentrations of NH 4 + , NO . − . and available P and K in the heavily invaded site were greater than those in the lightly invaded site. The catabolic activity of soil bacterial community in the heavily invaded site was different from that in the lightly invaded site. The catabolic activity of bacterial community in soils treated by the water extract of E. adenophorum roots changed and became similar to that in soils from the heavily invaded site. The pot experiment showed that the exotic plants growth in heavily invaded soil were not different from in lightly invaded soil; however, the native plant biomass decreased dramatically when grown in soil from the heavily invaded site as compared to soil from the lightly invaded site; and the same phenomenon was found when any potential allelopathic effects by E. adenophorum were eliminated by added activated carbon to those soils. Difference in soil nutrient availability and allelopathy could not explain this phenomenon of the native plant in the soils from the heavily and lightly invaded sites. Changes observed in the soil bacterial community were obviously related to native plant growth in those tow soils. Those results suggest that changing soil microbial community may be an important part of E. adenophorum invasion process. Since the soil microbial community serves as bridge in connection of exotic and natural plants, the exotic plant could inhibit the natural plant growth and reproduction by changing the soil microbial community in invaded site.

Phosphorus uptake, not carbon transfer, explains arbuscular mycorrhizal enhancement of Centaurea maculosa in the presence of native grassland species

Summary Previous studies have shown that arbuscular mycorrhizas (AM) enhance the growth of the invasive forb Centaurea maculosa when growing with native grass species. Using 13CO2, we tested the hypothesis that this enhancement is explained by carbon transfer from native species to C. maculosa via mycorrhizal hyphal linkages. A C. maculosa plant was paired with one of five native species – three grasses (Festuca idahoensis, Koeleria cristata and Pseudoroegneria spicata) and two forbs (Achillea millefolium and Gaillardia aristata) – in pots that separated the plants with either a mesh barrier (28 µm, excludes fine roots but not hyphae) or a membrane barrier (0·45 µm, excludes roots and hyphae). 13CO2 was added to the atmosphere of either Centaurea or the native species after 20 weeks’ growth. A 25 min pulse application was followed by 7 days’ growth and subsequent harvest. The biomass response of C. maculosa was consistent with previous experiments: C. maculosa was larger when growing in mesh barrier pots, when hyphae were able to access the opposite side of the pot; in mesh barrier pots only, biomass varied with neighbouring species. Native plant biomass did not vary between mesh‐ vs membrane‐barrier pots. There was no evidence of carbon transfer, either from the native plant to C. maculosa or in the reverse direction. Centaurea maculosa contained significantly more phosphorus in mesh‐divided pots, but this depended on the neighbouring plant. The P concentration in C. maculosa was significantly higher in mesh‐divided pots when growing with a grass and not a forb. Native species contained more P in mesh‐divided pots than membrane‐divided pots, and P concentration differed between species (higher in forbs than grasses), but did not vary between mesh‐ and membrane‐divided pots. Our study suggests that C. maculosa is able to exploit its mycorrhizal symbiosis more effectively than the native grassland species. The mechanism for this appears to be luxury consumption of P through efficient utilization of extra‐radical hyphae, but that effect is dependent on neighbouring species, and occurs when growing with a grass neighbour. Although no single study can disprove the carbon‐transfer hypothesis, our work suggests that AM‐mediated neighbour effects are the result of mycorrhizal networks that increase species’ access to P. Whether the synergistic effects of neighbours are due to complementarity of AM fungal symbionts utilized by different plant species, or have to do with the structure of AM networks that develop more extensively with multiple host plants, remains to be investigated.

Carbon Addition as a Countermeasure Against Biological Invasion by Plants

Increased nitrogen availability is known to favor invasion by non-native plants into natural grasslands. This suggests that decreasing nitrogen availability might serve as a countermeasure against invasion. One way to at least temporarily decrease nitrogen availability to plants is to increase microbial nitrogen uptake by adding carbon to the soil, and sawdust is a carbon source whose low cost could make it a practical conservation tool. To test whether adding sawdust to soil can counter the tendency of nitrogen enrichment to promote invasions by non-native plants, we hand-tilled 1.5 kg sawdust/m2 into the upper soil of the bare, nitrogen-rich patches left by dead shrubs of the nitrogen-fixing shrub Lupinus arboreus in two nearby areas with contrasting levels of invasion in a coastal grassland in northern California. After two years, in both areas, patches with sawdust had 40% less biomass of non-native plants than patches without sawdust, whereas biomass of native plants was not affected by sawdust addition. The more negative effect of sawdust on non-native species was specifically due to an effect on non-native grasses; adding sawdust increased the frequency of both native and non-native forbs. Results suggest that adding carbon as sawdust to soil can help counter invasion of grassland by non-native plants when invasion is being promoted by increased nitrogen availability, especially when the major invasive species are grasses.

Wintering Waterbird Use of Two Aquatic Plant Habitats in a Southern Reservoir

Increasing use of grass carp (Ctenopharyngodou idella) to control aquatie plants in large reservoirs has been a concern of waterbird managers because grass carp reduce biomass and diversity of native aquatic macrophytes and potentially lower habitat quality for birds. Native macrophytes were virtually climinated from Guntersville Reservoir. Alabama after the Tennessee Valley Authority (TVA) released grass carp, but Eurasian: watermilfoil (Myriophyllum spicatum) was unaffected. We revegetated 0.1-ha areas at Guntersville Reservol with native plants, and compared waterbird use and activity in native plant and miltoil habitats during October January to better evaluate effects of these habitat chauges on migrating and wintering waterbirds. We also determined the relative availability of these 2 plant types during fall and early winter. Milfoil and native plant habitats were used predominately by dabbling ducks and American coot (Fulica americana). Waterbirds were absent more often from native vegetation plots (36%) than from milfoil plots (1%) Density of waterbirds was high in native plant habitats in October, but was greater in milfoil habitats from November to January as native plant biomass declined and milfoil remained relatively abundant. Feeding was the predominant activity in most months, and time spent foraging did not differ between plant habitats in 1994-95. In 1993-94, waterfowl loraged more in native plant habitats in October and November, but foraging was greater in milfoil habitats in December and Jamiary. Submersed native plants and milfoil both were important to ducks and coot using Guntersville Reservoir Results suggest that maintaining a diverse aquatic plant community at southern reservoirs is beneficial to migrating and wintering waterbirds.

Restoring native vegetation in a Eurasian water‐milfoil dominated plant community using the herbicide triclopyr

In an effort to evaluate the selective control of the exotic weed Eurasian water milfoil (Myriophyllum spicatum L.) and to assess the recovery and restoration of the native submersed plant community, a 6-ha river and 4-ha cove plot were treated with the herbicide triclopyr at application rates of 2·5 and 1·75 mg/l, respectively, in the Pend Oreille River, WA, in August 1991. Water exchange half-lives within the plots were measured using rhodamine WT dye (river, tl/2 = 20 h; cove, t1/2 = 52 h), and triclopyr dissipation rates were also calculated (river, tl/2 = 19 h; cove, t1/2 = 53 h). Triclopyr concentrations were below the proposed potable water tolerance level (0·5 mgll) within the river treatment plot by 3 days after treatment « 0·01 to 0·41 mg/I), and 675 m downstream of that plot by I day after treatment « 0·01 to 0·47 mg/I). Following the cove treatment, triclopyr residues ranged from 0·12 to 0·29 mg/l by 7 days after treatment, and from < 0·0 I to 0·06 mg/l as close as 150 m downstream from the plot. Eurasian water milfoil biomass was reduced by 99% in the treated plots at 4 weeks post-treatment, remained low one year later (river treatment, 28% of pretreat levels; cove treatment 1 % of pre-treat levels) and was still at acceptable levels of control at two years post-treatment (river treatment, 47% of pre-treat levels; cove treatment, 24% of pre-treat levels). The four-week post-treatment efficacy results verified triclopyr concentration/exposure time relationships for controlling Eurasian water milfoil developed under laboratory conditions. Non-target native plant biomass increased 500-1000% by one year post­ treatment, and remained significantly higher in the cove plot at two years after treatment. Native species diversity doubled following herbicide treatment, and the restoration of this robust community delayed the re-establishment and dominance of Eurasian water milfoil for three growing seasons. © 1997 by John Wiley & Sons, Ltd. Regul. Rivers: Res. Mgmt, 13: 357-375 (1997)