The Effect of Forest Type on Benthic Macroinvertebrate Structure and Ecological Function in a Pine Plantation in the North Carolina Piedmont

We examined the impact of small-scale commercial forestry on the structure and function of 6 headwater streams in the North Carolina Piedmont. During 2001–2003 terrestrial organic matter inputs, temperature, macroinvertebrate community composition and tolerance, leaf breakdown rate, and food web structure were quantified for 2 streams draining mature stands of managed loblolly pine, 2 streams draining mature hardwood forests, and 2 streams draining 3-year-old clear cuts, which had been replanted with loblolly pine. Streams in the clear-cuts and pine plantations were bordered by a 15 m hardwood buffer. Despite differences in watershed land-use, there were no significant differences in the organic matter supply or temperature between streams draining different forest types. However, algal biomass was significantly higher in clear-cut sites than forested sites, and was also higher in hardwood sites than pine sites. Streams draining the clear-cut sites contained lower macroinvertebrate richness and diversity, and fewer intolerant species, than streams draining pine and hardwood stands. Despite the differences in macroinvertebrates community composition, there was no difference among forest types in leaf-pack breakdown rates. Analysis of δ¹⁵N and δ¹³C natural abundance of functional feeding group indicated that the shredders and predators collected from streams draining clear-cuts had a δ¹⁵N value that was enriched relative to the macroinvertebrates of streams draining pine and hardwood forests. This difference in δ¹⁵N signature appears to be the result of the incorporation of riparian grass species in the clear-cuts, which have a higher δ¹⁵N, into the diet of shredders. Pine sites had similar food webs to natural hardwood sites. Our results suggest that clear-cutting changes both the trophic dynamics and macroinvertebrate composition of low-order Piedmont streams in North Carolina despite the presence of hardwood buffers. However, large differences were not found between older pine and hardwood stands, indicating rapid recovery following re-growth of forest vegetation, when hardwood buffer strips were present.     

Stream invertebrate diversity reduces with invasion of river banks by non‐native plants

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Land-use effects on structural and functional composition of benthic and leaf-associated macroinvertebrates in four Andean streams

The replacement of native forests by pastures takes place widely in the Andes. The effects of such land-use change on aquatic assemblages are poorly understood. We conducted a comparative analysis of the effects of forest conversion to pastures on the taxonomic, structural, and functional composition of macroinvertebrates (benthic and leaf-associated) in montane and upper montane streams (ecosystem type) of the south Ecuadorian Andes. Taxonomic composition of benthic and leaf-associated macroinvertebrates was different between ecosystem type and land use. Also, major differences in the structural and functional composition of benthic and leaf-associated macroinvertebrates were mainly promoted by land use in both ecosystem types. Forested streams showed higher diversity than pasture streams, sustaining more shredder, scraper, and predatory invertebrates. We also observed differences in the macroinvertebrate communities between benthic and leaf-bag samples. Leaf bags had lower diversity and more collector invertebrates than benthic samples. This study highlights the large effect of riparian forest conversion to pasture land on macroinvertebrate communities, and the importance of using appropriate sampling techniques to characterize aquatic assemblages. We also recommend the maintenance and restoration of riparian vegetation to mitigate the effects of deforestation on stream communities and ecosystem processes.     

Colonisation of experimentally immersed wood in south eastern Australia: responses of feeding groups to changes in riparian vegetation

We investigated macroinvertebrate abundance and functional feeding groups colonising experimentally-positioned woody substrates of different species in streams with three different riparian vegetation types. Native Eucalyptus forest formed a dense closed canopy over our streams; introduced (exotic, alien) pine plantation forest did not fully shade the streams, and grassland streams were completely open, although with woody riparian vegetation well upstream of our sites. Macroinvertebrate assemblages varied taxonomically and functionally with both wood species and riparian vegetation composition. Two specialist feeding groups responded clearly to riparian vegetation: wood gougers were most common in forested streams, and algal grazers in more open streams. Gougers colonised native Eucalyptus wood in preference to alien species. Other feeding groups responses showed complex interactions between vegetation and wood type. Our results indicate the importance of sampling appropriate substrates when assessing questions of this type – if seeking shifts in functional organisation, the substrates on which the feeding groups of interest occur must be sampled. The composition of the riparian strip may influence xylophilous communities as much as the structure (i.e. whether closed or open).     

Ecological values of Hamilton urban streams (North Island, New Zealand): constraints and opportunities for restoration

Urban streams globally are characterised by degraded habitat conditions and low aquatic biodiversity, but are increasingly becoming the focus of restoration activities. We investigated habitat quality, ecological function, and fish and macroinvertebrate community composition of gully streams in Hamilton City, New Zealand, and compared these with a selection of periurban sites surrounded by rural land. A similar complement of fish species was found at urban and periurban sites, including two threatened species, with only one introduced fish widespread (Gambusia affinis). Stream macroinvertebrate community metrics indicated low ecological condition at most urban and periurban sites, but highlighted the presence of one high value urban site with a fauna dominated by sensitive taxa. Light-trapping around seepages in city gullies revealed the presence of several caddisfly species normally associated with native forest, suggesting that seepage habitats can provide important refugia for some aquatic insects in urban environments. Qualitative measures of stream habitat were not significantly different between urban and periurban sites, but urban streams had significantly lower hydraulic function and higher biogeochemical function than periurban streams. These functional differences are thought to reflect, respectively, (1) the combined effects of channel modification and stormwater hydrology, and (2) the influence of riparian vegetation providing shade and enhancing habitat in streams. Significant relationships between some macroinvertebrate community metrics and riparian vegetation buffering and bank protection suggest that riparian enhancement may have beneficial ecological outcomes in some urban streams. Other actions that may contribute to urban stream restoration goals include an integrated catchment approach to resolving fish passage issues, active reintroduction of wood to streams to enhance cover and habitat heterogeneity, and seeding of depauperate streams with native migratory fish to help initiate natural recolonisation.     

Diet partitioning in sympatric Atlantic salmon and brown trout in streams with contrasting riparian vegetation

Prey intake by Atlantic salmon Salmo salar and brown trout Salmo trutta was measured across different riparian vegetation types: grassland, open canopy deciduous and closed canopy deciduous, in upland streams in County Mayo, Western Ireland. Fishes were collected by electrofishing while invertebrates were sampled from the benthos using a Surber sampler and drifting invertebrates collected in drift traps. Aquatic invertebrates dominated prey numbers in the diets of 0+ year Atlantic salmon and brown trout and 1+ year Atlantic salmon, whereas terrestrial invertebrates were of greater importance for diets of 1+ and 2+ year brown trout. Terrestrial prey biomass was generally greater than aquatic prey for 1+ and 2+ year brown trout across seasons and riparian types. Prey intake was greatest in spring and summer and least in autumn apart from 2+ year brown trout that sustained feeding into autumn. Total prey numbers captured tended to be greater for all age classes in streams with deciduous riparian canopy. Atlantic salmon consumed more aquatic prey and brown trout more terrestrial prey with an ontogenetic increase in prey species richness and diversity. Atlantic salmon and brown trout diets were most similar in summer. Terrestrial invertebrates provided an important energy subsidy particularly for brown trout. In grassland streams, each fish age class was strongly associated with aquatic, mainly benthic invertebrates. In streams with deciduous riparian canopy cover, diet composition partitioned between conspecifics with older brown trout associated with surface drifting terrestrial invertebrates and older Atlantic salmon associated with aquatic invertebrates with a high drift propensity in the water column and 0+ year fish feeding on benthic aquatic invertebrates. Deciduous riparian canopy cover may therefore facilitate vertical partitioning of feeding position within the water column between sympatric Atlantic salmon and brown trout. Implications for riparian management are discussed.     

Do non-native Platanus hybrida riparian plantations affect leaf litter decomposition in streams?

In forest headwater streams where the riparian canopy limits autochthonous primary production, leaf litter decomposition is a key process controlling nutrient and carbon cycling. Any alteration of the riparian vegetation may influence litter decomposition and detrital food webs. We evaluated the effect of non-native Platanus hybrida riparian plantations on leaf litter decomposition in Mediterranean streams. The experiment was conducted in six headwater streams; three lined by native riparian vegetation and three crossing P. hybrida plantations. We have characterized the processing rates of alder leaves and the assemblages of shredder macroinvertebrates and fungi. Litter decomposition was significantly faster in the P. hybrida than in the reference streams. Although the dissolved inorganic nitrogen concentration was higher in P. hybrida, no significant effect was observed in decomposition rates. Differences in decomposition rates reflected the macroinvertebrate and shredder colonization in alder litter, with higher abundance and richness in the P. hybrida streams. However, aquatic hyphomycete sporulation rate was higher in reference streams, suggesting that the variation in decomposition rates is a direct consequence of shredder abundance. Our findings support part of the substrate quality-matrix quality (SMI) hypothesis, which expects that high-quality litter will show increased decomposition rates in a low-quality litter matrix.     

Relationship between Riparian Vegetation and Stream Benthic Communities at Three Spatial Scales

We examined the influence of riparian vegetation on macroinvertebrate community structure in streams of the Upper Thames River watershed in southwestern Ontario. Thirty-three μ-basins (129–1458 ha) were used to identify land cover variables that influenced stream macroinvertebrates. Micro-basins represented the entire drainage area of study streams and were similar in stream order (first, second) and land cover (agricultural or forest; no urban). We described the structure and composition of riparian vegetation and benthic macroinvertebrate communities at the outflow reach. The nature of the land cover was quantified for the stream network buffer (30 m) and the whole μ-basin. The objective of this study was to measure the magnitude and nature of the relationship between the riparian vegetation and benthic macroinvertebrate community at the outflow reach, stream network buffer, and whole μ-basin scales. Taxon richness (including total number of Ephemeroptera, Plecoptera, and Trichoptera taxa) and Simpson’s diversity of the macroinvertebrate community all increased with increased tree cover in the riparian zone at the outflow reach scale. Simpson’s equitability was lower with greater agricultural land cover in the stream network buffer. No relationship between the macroinvertebrate community and land cover was found at the whole μ-basin scale. Analysis of the influence of land cover on stream communities within a spatial hierarchy is important for understanding the interactions of stream ecosystems with their adjacent landscapes.     

The effects of land use on environmental features and functional organization of macroinvertebrate communities in Patagonian low order streams

Benthic invertebrates, water quality variables, chlorophyll a and particulate organic matter (POM) were studied in 18 sites of mountain streams in Patagonia (Argentina) subjected to six different land uses: native forest, pine plantation, pasture, harvest forest, urban and reference urban. Three streams of each land use were studied in March 2006. Macroinvertebrates were sampled in three riffles and three pools (n = 108) and biomass of detrital fractions of POM were quantified. Overall benthic POM biomass was higher at native and harvest forest than pastures, whereas fine fraction (FPOM) was higher in harvest forest than in pastures. Regarding to autotrophic subsidies bryophytes were the only that changed consistently among uses. These differences in energy resources were correlated with changes in community attributes. Shredder richness was clearly higher at native and harvest forest than exotic pine plantations, collector gatherers density was consistently high at harvest sites, and total density was significantly higher at urban and harvest forest. Multidimensional scaling ordination based on macroinvertebrate density data showed a clear separation of forested (either native or exotic species) from riparian modified areas (pasture, urban and harvest sites). Environmental variables having explanation power on macroinvertebrate assemblages were mostly related with: detritus availability (wood and leaves biomass) and impairment (total phosphorous and % sand). These results confirm that macroinvertebrate assemblage structure in Patagonian low order streams can be altered by land use practices. Among guild structure measures, those indicators based on benthic community functional attributes, shredders richness and collectors density, resulted good candidates to assess land use impacts. On account of riparian corridor management may be critical to the distribution of benthic taxa, the maintenance of good conditions of vegetation adjacent to rivers will enhance water quality and the environment for highly endemic headwater communities of Patagonian streams.     

Influences of logging history and riparian forest characteristics on macroinvertebrates and brook trout (Salvelinus fontinalis) in headwater streams (New Hampshire, U.S.A.)

1. Logging can strongly affect stream macroinvertebrate communities, but the direction and magnitude of these effects and their implications for trout abundance are frequently region‐specific and difficult to predict. 2. In first‐order streams in northern New England (U.S.A.) representing a chronosequence of logging history (<2 to >80 years since logging), we measured riparian forest conditions, stream macroinvertebrate community characteristics and brook trout (Salvelinus fontinalis) abundance. Principal component analysis was used to collapse forest data into two independent variables representing variation in logging history, riparian forest structure and canopy cover. We used these data to test whether logging history and associated forest conditions were significant predictors of macroinvertebrate abundance and functional feeding group composition, and whether brook trout abundance was related to logging‐associated variation in invertebrate communities. 3. Catchments with high PC1 scores (recently logged, high‐density stands with low mean tree diameter) and low PC2 scores (low canopy cover) had significantly higher total macroinvertebrate abundance, particularly with respect to chironomid larvae (low PC2 scores) and invertebrates in the grazer functional feeding group (high PC1 scores). In contrast, proportional representation of macroinvertebrates in the shredder functional feeding group increased with time since logging and canopy cover (high PC2 scores). Brook trout density and biomass was significantly greater in young, recently logged stands (high PC1 scores) and was positively related to overall macroinvertebrate abundance. In addition, three variables – trout density, invertebrate abundance and shredder abundance – successfully discriminated between streams that were less‐impacted versus more‐impacted by forestry. 4. These results indicate that timber harvest in northern New England headwater streams may shift shredder‐dominated macroinvertebrate communities supporting low trout abundance to a grazer/chironomid‐dominated macroinvertebrate community supporting higher trout abundance. However, while local effects on brook trout abundance may be positive, these benefits may be outweighed by negative effects of brook trout on co‐occurring species, as well as impairment of habitat quality downstream. Research testing the generality of these patterns will improve understanding of how aquatic ecosystems respond to anthropogenic and natural trajectories of forest change.     

Poplar plantations along regulated rivers may resemble riparian forests after abandonment: a comparison of passive restoration approaches

Abandoning hybrid poplar plantations may be an alternative strategy for enlarging natural riparian corridors along regulated rivers where forest regeneration no longer takes place. Despite the generally high local diversity of plants in poplar plantations, their capacity to converge towards riparian forests following abandonment remains largely untested and uncertain, because maintenance‐related disturbance of plantations favors ruderal, not strictly riparian specialists. We assessed the spontaneous recolonization of vegetation in abandoned hybrid poplar plantations following two management strategies: harvesting or simple abandonment of standing trees. The floristic composition in four chronosequences of 10 active (1–15 years), 17 harvested (1–15 years), and 10 abandoned (8–20 years) hybrid poplar plantations, as well as 10 riparian sites established at gravel bars that appeared following the cessation of in‐channel gravel mining (8–25 years) along the highly regulated Garonne River (SW France) was assessed in the framework of ecological disturbance theory. Both harvested and abandoned sites still resembled active plantations more than riparian forests. When poplar resprouting was low after harvesting, sites were dominated by light‐demanding, nitrophilous herbs, sub‐shrubs, and vines showing both competitive and ruderal traits, and vegetation composition remained stable over time. Abandoned and harvested sites with high poplar resprouting developed forest communities in which competitive species that tolerate and generate shade dominated, and tree species recruitment was higher. Riparian sites hosted the highest number of indicator species, mainly wetland and exotic. Simple passive restoration strategies like abandonment of plantations can help create valuable ecosystems, although ones that diverge from riparian forests colonizing new fluvial landforms.     

Woody riparian plant distributions in western Oregon,USA: comparing landscape and local scale factors

We studied riparian forests along mountain streams in four large watersheds of western Oregon and far northern California, USA, to better understand the multiscale controls on woody riparian vegetation in a geographically complex region. In each of the four-study watersheds, we sampled woody riparian vegetation in161-ha sampling reaches that straddled the stream channel. Within each hectare, we sampled riparian vegetation and local environmental factors in 40 m² sampling plots arrayed along topographic transects. We also surveyed natural disturbance gaps in 6 ha in each watershed to explore the effects of fine scale disturbance on species distributions. We compared species composition across our study watersheds and used Nonmetric Multidimensional Scaling (NMS) and chi-squared analyses to compare the relative importance of landscape scale climate variables and local topographic and disturbance variables in explaining species distributions at sampling plot and hectare scales. We noted substantial turnover in the riparian flora across the region, with greatest numbers of unique species in watersheds at the ends of the regional gradient. In NMS ordinations at both scales, variation in woody riparian species composition showed strongest correlations with climatic variables and Rubus spectabilis cover, but the latter was only an important factor in the two northern watersheds. At the smaller scale, topographic variables were also important. Chi-squared analyses confirmed that more species showed landscape scale habitat preferences (watershed associations) than associations with topographic position (94.7% vs. 42.7% of species tested) or gap versus forest setting (94.7% vs. 24.6% of species tested). The woody riparian flora of western Oregon shows important biogeographic variation; species distributions showed strong associations with climatic variables, which were the primary correlates of compositional change between riparian sites at both scales analyzed. Additional local variation in composition was explained by measures of topography and disturbance.     

Composition of riparian litter input regulates organic matter decomposition: Implications for headwater stream functioning in a managed forest landscape

Although the importance of stream condition for leaf litter decomposition has been extensively studied, little is known about how processing rates change in response to altered riparian vegetation community composition. We investigated patterns of plant litter input and decomposition across 20 boreal headwater streams that varied in proportions of riparian deciduous and coniferous trees. We measured a suite of in‐stream physical and chemical characteristics, as well as the amount and type of litter inputs from riparian vegetation, and related these to decomposition rates of native (alder, birch, and spruce) and introduced (lodgepole pine) litter species incubated in coarse‐ and fine‐mesh bags. Total litter inputs ranged more than fivefold among sites and increased with the proportion of deciduous vegetation in the riparian zone. In line with differences in initial litter quality, mean decomposition rate was highest for alder, followed by birch, spruce, and lodgepole pine (12, 55, and 68% lower rates, respectively). Further, these rates were greater in coarse‐mesh bags that allow colonization by macroinvertebrates. Variance in decomposition rate among sites for different species was best explained by different sets of environmental conditions, but litter‐input composition (i.e., quality) was overall highly important. On average, native litter decomposed faster in sites with higher‐quality litter input and (with the exception of spruce) higher concentrations of dissolved nutrients and open canopies. By contrast, lodgepole pine decomposed more rapidly in sites receiving lower‐quality litter inputs. Birch litter decomposition rate in coarse‐mesh bags was best predicted by the same environmental variables as in fine‐mesh bags, with additional positive influences of macroinvertebrate species richness. Hence, to facilitate energy turnover in boreal headwaters, forest management with focus on conifer production should aim at increasing the presence of native deciduous trees along streams, as they promote conditions that favor higher decomposition rates of terrestrial plant litter.     

Implications of water column ammonium uptake and regeneration for the nitrogen budget in temperate, eutrophic Missisquoi Bay, Lake Champlain (Canada/USA)

Invasion by exotic trees into riparian areas has the potential to impact aquatic systems. We examined the effects of the exotic Salix fragilis (crack willow) on the structure and functioning of small streams in northern Patagonian Andes via a field survey of benthic invertebrates and leaf litter and an in situ experiment. We compared leaf decomposition of the native Ochetophila trinervis (chacay) and S. fragilis in reaches dominated by native vegetation versus reaches dominated by crack willow. We hypothesized that S. fragilis affects the quality of leaf litter entering the streams, changing the aquatic biota composition and litter decomposition. Our study showed that crack willow leaves decomposed slower than chacay, likely related to leaf properties (i.e., leaf toughness). Benthic leaf litter mass was similar between the two riparian vegetation types, though in stream reaches dominated by crack willow, leaves of this species represented 82% of the total leaf litter. Benthic invertebrate abundance and diversity were similar between reaches but species composition differed. Our study found little evidence for strong impacts of crack willow on those small streams. Further studies on other aspects of ecosystem functioning, such as primary production, would enhance our understanding of the impacts of crack willow on Patagonian streams.     

Land Use Influences Niche Size and the Assimilation of Resources by Benthic Macroinvertebrates in Tropical Headwater Streams

It is well recognized that assemblage structure of stream macroinvertebrates changes with alterations in catchment or local land use. Our objective was to understand how the trophic ecology of benthic macroinvertebrate assemblages responds to land use changes in tropical streams. We used the isotope methodology to assess how energy flow and trophic relations among macroinvertebrates were affected in environments affected by different land uses (natural cover, pasture, sugar cane plantation). Macroinvertebrates were sampled and categorized into functional feeding groups, and available trophic resources were sampled and evaluated for the isotopic composition of ¹³C and ¹⁵N along streams located in the Cerrado (neotropical savanna). Streams altered by pasture or sugar cane had wider and more overlapped trophic niches, which corresponded to more generalist feeding habits. In contrast, trophic groups in streams with native vegetation had narrower trophic niches with smaller overlaps, suggesting greater specialization. Pasture sites had greater ranges of resources exploited, indicating higher trophic diversity than sites with natural cover and sugar cane plantation. We conclude that agricultural land uses appears to alter the food base and shift macroinvertebrate assemblages towards more generalist feeding behaviors and greater overlap of the trophic niches.     

Characterization of 18S-ITS1-5.8S rDNA in eleven species in Soleidae: implications for phylogenetic analysis

Wildfire is one of the most important global agents of disturbance affecting terrestrial and riparian vegetation. Post-fire vegetation changes can alter stream resource pathways and cause channel reorganization and sediment-laden debris flows. Yet, little is known about macroinvertebrate community recovery following wildfire and debris flows and how these communities fit into the broader stream community mosaic. We examined the effects of wildfire and debris flows on relative resource availability and macroinvertebrate assemblages at 31 streams in Idaho, USA using a space-for-time study design. Wildfire and debris flows had no apparent effects on resource standing crop. However, macroinvertebrate communities among unburned, burned, and debris flow streams were quite different. Compared to unburned streams, biomass and density were higher at streams which experienced debris flows ~ 10 years post fire, but exhibited the near-complete absence of macroinvertebrates at streams with more recent debris flows. Stream macroinvertebrate communities impacted by debris flows were distinct compared to unburned and burned streams which did not experience debris flows. When found, differences in macroinvertebrate biomass, density, richness, and community structures were largely due to the incidence of debris flows. Debris flows removed the riparian vegetation, slowing its recovery, cascading to affect macroinvertebrate community structure into the long term.     

Using stable isotope analysis to assess the effects of hypolimnetic oxygenation on diet in a mixed cold- and warmwater fish community

Line-diffuser hypolimnetic oxygenation was initiated in North Twin Lake, Washington, in 2009 to mitigate reductions in Rainbow Trout (Oncorhynchus mykiss) and Brook Trout (Salvelinus fontinalis) habitat due to temperature-dissolved oxygen “habitat squeeze”. Previous studies demonstrated that trout populations rapidly expanded into increased hypolimnetic habitat within the first few years of oxygenation and previous short-term diet analyses indicated an effect on fish diet; however, the long-term effects on fish ecology have yet to be established. In this study, stable isotope analysis of fish liver tissue suggests relatively few differences in feeding ecology of principal coldwater fish species in North Twin Lake compared to unoxygenated South Twin Lake. When compared between lakes, Rainbow Trout and Brook Trout diets contained similar proportions of Daphnia, Chironomidae, and Chaoboridae. Littoral and epilimnetic-focused Golden Shiner (Notemigonus crysoleucas) diets were also similar between lakes. Observed similarities between Golden Shiner and trout diets suggest the effects of interspecific competition between salmonids and non-salmonids may be limiting trout growth and survival. Fisheries managers should therefore consider both habitat limitations and interspecific competition when managing for coldwater fish species in mesotrophic, dimictic lakes.     

Recovery of benthic macroinvertebrate and adult dragonfly assemblages in response to large scale removal of riparian invasive alien trees

Invasive alien organisms can impact adversely on indigenous biodiversity, while riparian invasive alien trees (IATs), through shading of the habitat, can be a key threat to stream invertebrates. We ask here whether stream fauna can recover when the key threat of riparian IATs is removed. Specifically, we address whether IAT invasion, and subsequent IAT removal, changes benthic macroinvertebrate and adult dragonfly assemblages, for the worse or for the better respectively. Natural riparian zones were controls. There were statistically significant differences between stream reaches with natural, IAT-infested and IAT-cleared riparian vegetation types, based on several metrics: immature macroinvertebrate taxon richness, average score per macroinvertebrate taxon (ASPT), a macroinvertebrate subset (Ephemeroptera, Plecoptera, Trichoptera and Odonata larvae; EPTO), and adult dragonfly species richness. Reaches with natural vegetation, or cleared of IATs, supported greater relative diversity of macroinvertebrates than reaches shaded by dense IATs. Greatest macroinvertebrate ASPT and EPTO were in reaches bordered by natural vegetation and those bordered by vegetation cleared of IATs, and the lowest where the riparian corridor was IATs. Highest number of adult dragonflies species was along streams cleared of dense IATs. Overall, results showed that removal of a highly invasive, dense canopy of alien trees enables recovery of aquatic biodiversity. As benthic macroinvertebrate scores and adult dragonfly species richness are correlated and additive, their combined use is recommended for river condition assessments.     

Grazing management influences the subsidy of terrestrial prey to trout in central Rocky Mountain streams (USA)

1. Research in forest and grassland ecosystems indicates that terrestrial invertebrates that fall into streams can be an important prey resource for fish, providing about 50% of their annual energy and having strong effects on growth and abundance. However, the indirect effects of land uses like cattle grazing on this important prey subsidy for stream salmonids are unclear. 2. During summer 2007, we compared the effects of three commonly used grazing systems on terrestrial invertebrate inputs to streams in northern Colorado and their use by trout. Cattle graze individual pastures for about 120 days under traditional season‐long grazing (SLG), about 35–45 days under simple rotational grazing and 10–20 days under intensive rotational grazing in this region. We also compared these effects to a fourth group of sites grazed only by wildlife (i.e. no livestock use). 3. Overall, rotational grazing management (either simple or intensive), resulted in more riparian vegetation, greater inputs of terrestrial invertebrates, greater biomass of terrestrial invertebrate prey in trout diets, a higher input compared to trout metabolic demand and more trout biomass than SLG. However, these differences were frequently not statistically significant owing to high variability, especially for trout diets and biomass. 4. Despite the inherent variability, riparian vegetation and terrestrial invertebrates entering streams and in trout diets at sites managed for rotational grazing were similar to sites managed for wildlife grazing only. 5. These results indicate that rotational grazing systems can be effective for maintaining levels of terrestrial invertebrate subsidies to streams necessary to support robust trout populations. However, factors influencing the effect of riparian grazing on stream subsidies are both spatially variable and complex, owing to differences in microclimate, invertebrate and plant populations and the efforts of ranchers to tailor grazing systems to specific riparian pastures.