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Invasive species have many detrimental ecological and socio-economic effects. However, invasive species can also provide novel habitat for native species. The growing rate of biological invasions world-wide presents an urgent dilemma: how can natural resource managers minimize negative effects of invasive species without depleting native taxa that have come to rely on them? Adaptive management can provide a means to address this dilemma when invasive species management plans are crafted in novel environments. We present a case study of research in support of adaptive management that considers the role of invasive water hyacinth (Eichhornia crassipes [Mart.] Solms [Pontederiaceae]) management, using herbicides, in aquatic food web functioning in the Sacramento-San Joaquin River Delta of California, USA (the "Delta"). We hypothesized that herbicide applications under current management protocols would reduce the abundance and diversity of aquatic invertebrates because they would alter both structural and biological habitat. Using a Before, After, Control, Intervention (BACI) experiment, we sampled invertebrates per gram plant biomass before and 4 weeks after glyphosate applications in treated and untreated locations. There was more plant biomass in the late-season samples because dead, dying, and living plant materials were compacted. However, there were no detectable differences between control and treated sites - or for samples before versus after the treatment date-for invertebrate abundance, species richness, or evenness. This case study demonstrates that even decaying water hyacinth serves as habitat for invertebrates that may be forage for Delta fishes. We concluded that current management practices using glyphosate do not affect invertebrate abundance during a month-long period of weed decay. These results provide valuable feedback for the "evaluate and respond" component of the adaptive management process for water hyacinth control, and demonstrate how managers globally can and should consider potential food web effects in the course of their invasive species management efforts. [ABSTRACT FROM AUTHOR]

Abstract: We used two-dimensional hydrodynamic models for the assessment of water diversion effects on benthic macroinvertebrates and associated habitat in a montane stream in Yosemite National Park, Sierra Nevada Mountains, CA, USA. We sampled the macroinvertebrate assemblage via Surber sampling, recorded detailed measurements of bed topography and flow, and coupled a two-dimensional hydrodynamic model with macroinvertebrate indicators to assess habitat across a range of low flows in 2010 and representative past years. We also made zero flow approximations to assess response of fauna to extreme conditions. The fauna of this montane reach had a higher percentage of Ephemeroptera, Plecoptera, and Trichoptera (%EPT) than might be expected given the relatively low faunal diversity of the study reach. The modeled responses of wetted area and area-weighted macroinvertebrate metrics to decreasing discharge indicated precipitous declines in metrics as flows approached zero. Changes in area-weighted metrics closely approximated patterns observed for wetted area, i.e., area-weighted invertebrate metrics contributed relatively little additional information above that yielded by wetted area alone. Loss of habitat area in this montane stream appears to be a greater threat than reductions in velocity and depth or changes in substrate, and the modeled patterns observed across years support this conclusion. Our models suggest that step function losses of wetted area may begin when discharge in the Merced falls to 0.02m3/s; proportionally reducing diversions when this threshold is reached will likely reduce impacts in low flow years. [Copyright &y& Elsevier]

The Feather River is a large flow-regulated river in the Central Valley of California. The Mediterranean climate of the area imposes a natural flow regime for the region that is characterized by predictable high flows in the winter and spring and low flows in the summer and fall. The Oroville Dam complex on the Feather River has created a permanent low-flow section of the river where a base flow is continuous year round but the natural annual variability of flow has been completely eliminated. We used this modified section of the river to examine the ecological impact that removing natural flow variability has on the macroinvertebrate assemblage and how we might measure such a change if it is present. Specifically, we examined whether biodiversity and community similarity differed between the low- and high-flow sections of the river for both benthic and drifting aquatic invertebrates. Using a modified Surber sampler we collected samples at three distinct time periods within a year (January, April, and July) for both drift and benthic fauna. Our results showed little difference between the low- and high-flow assemblages using common measures of diversity (i.e., species richness and Shannon diversity) and a measure of environmental tolerance (Hilsenhoff biotic index). Yet when we employed a multivariate measure of community similarity (i.e., non-metric multidimensional scaling) and associated statistical tests, we found significant assemblage differences between the low- and high-flow sections of the river. This study suggests that flow disturbance of this sort is likely to alter the macroinvertebrate community in ways that are not easily observed using common ecological metrics. [ABSTRACT FROM AUTHOR]

Abstract: Concerns about the effects of fire on ecologically sensitive habitats have limited the use of prescribed fire in the management of forest riparian areas. Using a beyond-BACI (Before-After-Control-Impact) experimental design, we examined the effects of a 26-ha prescribed fire that burned upland and riparian areas of a first-order watershed, and compared this to five unburned sites examined from 1 to 7 years pre-fire and 1 year post-fire. We monitored pre- and post-fire riparian vegetation, large woody debris, sediment, water chemistry, periphyton, and benthic macroinvertebrates. The prescribed fire in the riparian zone was patchy in terms of intensity, consumption, and severity; it consumed 79% of the pre-fire fuel in the riparian zone, 34% of the total surface fuel, and 90% of the total ground fuel. The prescribed fire significantly reduced percent cover of surface vegetation and plant taxa richness in comparison to unburned sites but not plant diversity (Simpson''s D). Community composition of understory riparian vegetation changed post-fire, most likely as a result of the reduction in taxa richness and cover. Riparian tree mortality (>11.5cm DBH) was only 4.4% post-fire. Similarly, there was no post-fire change in large woody debris volume and recruitment, or fine sediment in pools (V *). Post-fire, there were increases in some water chemistry parameters (SO4 −, total P, Ca2+) and a decrease in periphyton biomass; however, these changes were short-term, and recovery occurred in ≤1 year. Macroinvertebrate community composition but not density, richness, or diversity was affected 10–19 d post-fire; composition recovered within 1 year. The trends observed in this study examining multiple abiotic and biotic parameters suggest that this prescribed fire either had no or short-lasting (≤1 year) impacts on Dark Canyon Creek and its riparian zone. The limited observed impacts are at least partially a result of the small portion (<20%) of the watershed area burned, moderate topography, the low- to moderate-severity of the fire, and the relatively low precipitation (and thus, stream flow) that occurred post-fire. [Copyright &y& Elsevier]2+) and a decrease in periphyton biomass; however, these changes were short-term, and recovery occurred in ≤1 year. Macroinvertebrate community composition but not density, richness, or diversity was affected 10–19 d post-fire; composition recovered within 1 year. The trends observed in this study examining multiple abiotic and biotic parameters suggest that this prescribed fire either had no or short-lasting (≤1 year) impacts on Dark Canyon Creek and its riparian zone. The limited observed impacts are at least partially a result of the small portion (<20%) of the watershed area burned, moderate topography, the low- to moderate-severity of the fire, and the relatively low precipitation (and thus, stream flow) that occurred post-fire. [Copyright &y& Elsevier]