APPLIED ISSUES: Effects of habitat rehabilitation on brown trout (Salmo trutta) in boreal forest streams

1. Degradation of stream habitat because of anthropogenic activities (e.g. channelisation) has had a dramatic impact on fluvial environments and their biota, and as a consequence, increasing effort has been directed towards the restoration of degraded rivers. However, a major problem is that the success (or failure) of restoration has been rarely tested using a well‐designed monitoring programme to allow reliable detection of an impact, if any exists. We used a spatially and temporally replicated, balanced Before‐After‐Control‐Impact design to assess the impact of stream habitat rehabilitation on the densities and growth of brown trout of three age‐classes in North Finnish forest streams. 2. Three separate sections in each of six streams were selected for the study. After 3 years of pre‐rehabilitation monitoring, two randomly selected sections in each stream were restored; one using large woody debris and boulders and the other using only boulders. A third section remained as an unmodified control. Monitoring of fish densities continued for 3 years after rehabilitation. 3. Rehabilitation clearly increased streambed complexity, but did not have detectable effects on brown trout stocks in either of the rehabilitation schemes (LWD or stones), except for age‐2+ and older fish which decreased in abundance compared to control reaches. A severe drought after rehabilitation in late summer 2002 reduced densities of trout to a low level in all streams, overriding any local effects of rehabilitation. Rehabilitation structures seemed to provide some safeguard against drought for age‐2 and older, but not for the younger age‐classes. 4. Our results add to the growing body of literature suggesting that large‐scale regional factors may overwhelm local management efforts. To be successful in the future, stream rehabilitation schemes must include drought refuge areas for fish and other stream biota.     

Microhabitat availability in Welsh moorland and forest streams as a determinant of macroinvertebrate distribution

SUMMARY. 1 Eighteen streams in mid-Wales were sampled for macro-invertebrates in both riffles and margins in April 1985–87. Stream macro-flora, substrata and marginal habitats were surveyed in May 1988.
2. TWINSPAN classification of the macroinvertebrate data indicated three major stream groups. One was distinguished by circumneutral pH and had a flora and fauna typical of such conditions. The other two groups consisted of acidic streams with moorland and conifer afforested catchments respectively. The forest streams were the more acidic but the two groups also differed significantly in the composition of their marginal habitats.
3 The acidic moorland streams had more vegetation ('soft' features) in the margins and supported several invertebrate taxa which were relative more abundant there than in the riffles. These taxa may be excluded from forest streams because the margins are 'hard' due to greater erosiveness and shading.
4. In view of the increasing cover by conifer afforestation in Britain, it is clearly necessary to elucidate all its effects on stream ecosystems, which include changes to the physical environment.     

The roles of grass leaf litter in streams draining tussock grassland in New Zealand: retention, food supply and substrate stabilization

1. We investigated the roles of grass litter in streams that drain upland New Zealand tussock grassland, paying particular attention to the ways in which grass leaves differed in their characteristics from much more intensively studied tree leaves. 2. The instantaneous retention rates of tussock grass leaves (Chionochloa rigida) on the bed of a second-order stream (0.157–0.515 m^?1) were significantly higher than those of the elliptical leaves of lemonwood trees (Pittosporum eugenioides; 0.068–0.180 m^?1). 3. Instantaneous retention rates of grass leaves in two third-order streams were very low. At high discharge, leaf retention rate was greater in Timber Creek (0.0040 m^?1), a braided, gravel bed stream, than in the adjacent Kye Burn (0.0010m^?1), with its well-defined channel and large, stable substrate particles. At baseflow, retention rates were similar in the two streams (0.0053–0.0064 m^?1 for Timber Creek; 0.0047–0.0058m^?1 for Kye Burn). Nevertheless, total coarse particulate organic matter (mainly derived from tussock litter) was present at lower densities in Timber Creek than Kye Bum, reflecting the instability of the bed of the former and its tendency to spread over a wide area at high discharge. 4. The results of a colonization tray experiment, in which substrate was mixed with tussock leaves, nylon ribbon or nothing, indicate that tussock leaves do not play an important role as microhabitat or food in the two third-order streams. This may reflect the poor food quality of grass litter, and/or the relatively low availability and predictability of its supply. 5. An in situ experiment revealed that tussock leaves play a role, analogous to that reported for certain seagrasses, in stabilizing substrate and reducing sediment transport, apparently by reducing bed roughness and therefore the force of friction on the bed.     

The water mites (Acari: Hydrachnidia) of streams in The Netherlands: Distribution and ecological aspects on a regional scale

The water mites of running waters in The Netherlands have been surveyed for the period 1987–1992. The aims were to investigate their present distribution, to make a comparison with historical data and to identify differences in water mite assemblages on a regional scale. The investigation covered 821 sites in eight different drainage areas. In spite of the scarcity of historical data, it may be concluded that in the course of this century about 40% of rheophilic water mites have become extinct. In canalized streams lentic species are dominant. In springs and spring streams, lotic species can survive, but the assemblages consist mainly of euryoecious water mite species.Multivariate techniques were used to show regional differences. These differences are mainly determined by stream hydraulics. The area of Zuid-Limburg can easily be demarcated by its relatively high number of rheophilic species. The man-made streams (sprengen) at the east side of the Veluwe area are characterized by a number of species which indicate undisturbed circumstances. The response of water mites to pollution of running waters is discussed.     

Leaf litter transport and retention in a tropical Rift Valley stream: an experimental approach

The impact of a drought on freshwater snail and trematode communities was investigated in a lake. Before the drought, 15 gastropod species (Valvatidae, Planorbidae, Lymnaeidae, Ancylidae, Physidae) and 10 trematode species (cercariaeum, xiphidiocercariae, echinostome, furcocercariae, notocotyle, lophocercous) were recorded. The rate of parasitism was 5.13% and there were 11 host species. The 2 major consequences of desiccation were the disappearance of snails, except Valvata piscinalis and Lymnaea peregra, and the absence of trematodes infecting the surviving snails. As soon as favourable conditions were restored, the littoral area was recolonized, first by hygrophilic and amphibious species, second by aquatic species. Nine months after the drought, the gastropod community was restored. Recolonization by the trematodes was delayed compared with that of gastropods. During the study, the overall prevalence was equal to 0.36% and only 4 trematode species and 5 host species were recorded. Because of the great variability of freshwater ecosystems, long-term studies are necessary to understand the dynamics of snail and trematode populations and determine the regulatory effect of parasitism in the field.     

Input, retention, and invertebrate colonization of allochthonous litter in streams bordered by deciduous broadleaved forest, a conifer plantation, and a clear-cut site in southwestern Japan

In headwater streams, conifer plantation forestry may affect stream communities through the quantity and quality of basal resources (allochthonous litter). We compared (1) the seasonal patterns of litter input from the riparian canopy, (2) those for the abundance of benthic and drifting litter in streams, and (3) the density of litter-associated invertebrates among streams bordered by deciduous broadleaved forest, a plantation of Japanese cedar (Cryptomeria japonica), and a clear-cut site, to extract the characteristics of conifer-plantation streams in terms of litter dynamics and benthic invertebrates. The results illustrate differences in litter input and in-stream processes between the broadleaved and plantation sites, although the total annual inputs from canopy were similar. In the broadleaved site, high litter storage was limited to winter, probably because pulsed inputs of litter in autumn were retained on the streambed but rapidly processed. In contrast, litter input was more constant at the plantation site, and litter was stored throughout the year. Although the litter-patch-specific density of total invertebrates was similar between the broadleaved and plantation sites, estimates of the reach-scale, habitat-weighted density considering differences in the coverage area of litter patches revealed considerable differences. Although the habitat-weighted density of total invertebrates was lower at the plantation site than at the broadleaved site in winter, it was noticeably higher at the plantation site in summer, owing to the seasonal stability of benthic litter abundance. Our results emphasized the importance of considering the spatiotemporal availability of benthic litter when assessing the effects of conifer plantations on stream ecosystems.     

Leaf‐litter breakdown in pasture and deciduous woodland streams: a comparison among three European regions

1. Human land‐use has altered catchments on a large scale in most parts of the world, with one of the most profound changes relevant for streams and rivers being the widespread clearance of woody riparian vegetation to make way for livestock grazing pasture. Increasingly, environmental legislation, such as the EU Water Framework Directive (EU WFD), calls for bioassessment tools that can detect such anthropogenic impacts on ecosystem functioning. 2. We conducted a large‐scale field experiment in 30 European streams to quantify leaf‐litter breakdown, a key ecosystem process, in streams whose riparian zones and catchments had been cleared for pasture compared with those in native deciduous woodland. The study encompassed a west–east gradient, from Ireland to Switzerland to Romania, with each of the three countries representing a distinct region. We used coarse‐mesh and fine‐mesh litter bags (10 and 0.5 mm, respectively) to assess total, microbial and, by difference, macroinvertebrate‐mediated breakdown. 3. Overall, total breakdown rates did not differ between land‐use categories, but in some regions macroinvertebrate‐mediated breakdown was higher in deciduous woodland streams, whereas microbial breakdown was higher in pasture streams. This result suggests that overall ecosystem functioning is maintained by compensatory increases in microbial activity in pasture streams. 4. We suggest that simple coefficients of breakdown rates on their own often might not be powerful enough as a bioassessment tool for detecting differences related to land‐use such as riparian vegetation removal. However, shifts in the relative contributions to breakdown by microbial decomposers versus invertebrate detritivores, as revealed by the ratios of their associated breakdown rate coefficients, showed clear responses to land‐use.     

Deforestation of watersheds of Panama: nutrient retention and export to streams

A series of eight watersheds on the Pacific coast of Panama where conversion of mature lowland wet forest to pastures by artisanal burning provided watershed-scale experimental units with a wide range of forest cover (23, 29, 47, 56, 66, 73, 73, 91, and 92 %). We used these watersheds as a landscape-scale experiment to assess effects of degree of deforestation on within-watershed retention and hydrological export of atmospheric inputs of nutrients. Retention was estimated by comparing rainfall nutrient concentrations (volume-weighted to allow for evapotranspiration) to concentrations in freshwater reaches of receiving streams. Retention of rain-derived nutrients in these Panama watersheds averaged 77, 85, 80, and 62 % for nitrate, ammonium, dissolved organic N, and phosphate, respectively. Retention of rain-derived inorganic nitrogen, however, depended on watershed cover: retention of nitrate and ammonium in pasture-dominated watersheds was 95 and 98 %, while fully forested watersheds retained 65 and 80 % of atmospheric nitrate and ammonium inputs. Watershed forest cover did not affect retention of dissolved organic nitrogen and phosphate. Exports from more forested watersheds yielded DIN/P near 16, while pasture-dominated watersheds exported N/P near 2. The differences in magnitude of exports and ratios suggest that deforestation in these Panamanian forests results in exports that affect growth of plants and algae in the receiving stream and estuarine ecosystems. Watershed retention of dissolved inorganic nitrogen calculated from wet plus dry atmospheric deposition varied from 90 % in pasture- to 65 % in forest-dominated watersheds, respectively. Discharges of DIN to receiving waters from the watersheds therefore rose from 10 % of atmospheric inputs for pasture-dominated watersheds, to about 35 % of atmospheric inputs for fully forested watersheds. These results from watersheds with no agriculture or urbanization, but different conversion of forest to pasture by burning, show significant, deforestation-dependent retention within tropical watersheds, but also ecologically significant, and deforestation-dependent, exports that are biologically significant because of the paucity of nutrients in receiving tropical stream and coastal waters.     

Elevated UV-B radiation has no effect on litter quality and decomposition of two dune grassland species: evidence from a long-term field experiment

From studies on living plant tissues it has been inferred that elevated UV‐B radiation could negatively affect litter quality and subsequent decomposition. However, in general, the effects of UV‐B radiation on litter chemistry and decomposition reported in the literature are variable and are often only marginally (if at all) significant. This might be due to the ecologically unrealistic conditions under which these experiments were performed. We investigated the effects of elevated UV‐B radiation on litter quality and subsequent decomposition on initial litter chemistry and long‐term (2 years) decomposition of freshly senesced Carex arenaria and Calamagrostis epigejos leaf litter under ecologically realistic conditions. This material was collected from a dune grassland that had received UV‐B radiation treatments for three growing seasons. It was then used in a 2‐year decomposition study using litter bags. We found no significant effects of elevated UV‐B radiation on any of the litter chemistry parameters in either of the two species, nor did we find significant effects on litter decomposition. However, we did find significant differences in litter decomposition between the species. These differences were related to the interspecific differences in litter chemistry, particularly the litter phenolics concentration. These results show that litter quality and decomposition in dune grasslands are, also under ecologically realistic conditions, not affected by UV‐B radiation. Instead, litter decomposition is determined by constitutive interspecific differences in litter chemistry. In conclusion, with our results added to the already existing literature, the preponderance of evidence now clearly suggests that elevated UV‐B radiation has very little, if any, impact on litter quality and subsequent decomposition in real ecosystems.     

Nitrogen retention in headwater streams: the influence of groundwater-surface water exchange

Groundwater-surface water (GW-SW) interaction lengthens hydraulic residence times, increases contact between solutes and biologically active surfaces, and often creates a gradient of redox conditions conducive to an array of biogeochemical processes. As such, the interaction of hydraulic patterns and biogeochemical activity is suspected to be an important determinant of elemental spiraling in streams. Hydrologic interactions may be particularly important in headwater streams, where the extent of the GW-SW mixing environment (i.e., hyporheic zone) is proportionately greater than in larger streams. From our current understanding of stream ecosystem function, we discuss nitrogen (N) spiraling, present a conceptual model of N retention in streams, and use both of these issues to generate specific research questions and testable hypotheses regarding N dynamics in streams.     

Crowding-induced responses in a geometrid moth revisited: a field experiment

In Lepidoptera, effects of larval crowding on life history traits may manifest themselves as changes in growth rate and duration of larval period. For the outbreaking geometrid moth, Epirrita autumnata , impacts of crowding have been shown in earlier laboratory studies, and these responses were modified by diet quality. In this study, the aim was to find out the specific nature of crowding effects of E. autumnata in the field. E. autumnata larvae were reared individually and in groups in mesh bags on mountain birch, both on good and poor quality foliage. Three field experiments were carried out with different densities in the crowded treatment (12, 21 and 45 larvae per 100 short shoots of mountain birch), simulating intermediate to severe outbreaks. The study revealed the density interval (12–21) within which impacts of crowding become evident. Significant effects were mostly found with the two highest densities in the crowded treatment combined with poor foliage quality. In those treatments, crowding resulted in 8–12% and 24–33% decrease in pupal mass and larval survival, respectively. The results of the present field experiments, however, did not corroborate the results of earlier laboratory studies: duration of larval period was not substantially affected, net effects of crowding were negative and interactions between crowding and foliage quality were contrary to those obtained in earlier laboratory studies. In many other Lepidoptera as well, the knowledge on responses to crowding may be mostly qualitative since most crowding experiments have been conducted in laboratory.     

Leaf litter processing and exoenzyme production on leaves in streams of different pH

We examined microbial colonization, exoenzyme activity, and processing of leaves of yellow poplar (Liriodendron tulipifera), red maple (Acer rubrum), and white oak (Quercus alba) in three streams on the Allegheny Plateau of West Virginia, United States. Leaf packs were placed in streams that varied in their underlying bedrock geology, and therefore in their sensitivity to the high level of acidic precipitation that occurs in this region. The mean pH of the streams was 4.3 in the South Fork of Red Run (SFR), 6.2 in Wilson Hollow Run (WHR), and 7.7 in the North Fork of Hickman Slide Run (HSR). Through time, the patterns of microbial biomass and exoenzyme activity were generally similar among leaf species, but the magnitude of microbial biomass and exoenzyme activity differed among leaf species. Pectinase activity was greatest in HSR, the most alkaline stream, whereas the activity of exocellulase and xylanase was greatest in WHR and SFR, the intermediate and acidic streams. This variation in the activity of different exoenzymes was consistent with published pH optima for these exoenzymes. Variation in processing rates, both among leaf species and among streams, seems to be related to the level of microbial exoenzyme activity on the leaf detritus.     

Spectral balance and UV-B sensitivity of soybean: a field experiment

Soybean [Glycine max (L.) Merr.] cultivar Essex was grown and tested for sensitivity to UV-B radiation (280–320 nm) under different combinations of UV-A (320–400 nm) and PFD (400–700 nm) radiation in four simultaneous field experiments. The radiation conditions were effected with combinations of filtered solar radiation and UV-B and UV-A lamps electronically modulated to track ambient radiation. Significant UV-B-caused decreases in total aboveground production and growth were seen only when PFD and UV-A were reduced to less than half their flux in sunlight. When PFD was low, UV-A appeared to be particularly effective in mitigating UV-B damage. However, when PFD was high, substantial UV-A did not appear to be required for UV-B damage mitigation. Leaf chlorophyll fluorescence did not indicate photosynthetic damage under any radiation combination. With UV-B, leaves in all experiments exhibited increased UV-absorbing pigments and decreased whole-leaf UV transmittance. Results of these field experiments indicate difficulties in extrapolating from UV-B experiments conducted in glasshouse or growth cabinet conditions to plant UV-B sensitivity in the field. Implications for UV radiation weighting functions in evaluating atmospheric ozone reduction are also raised.     

Benefits of communal breeding in burying beetles: a field experiment

1. The ultimate causes of communal breeding and joint parental care in various species of Nicrophorus burying beetles have not been resolved satisfactorily. One hypothesis suggests that females remain on the carcass for extended periods of time because joint defence affords them improved probabilities of retaining the carcass successfully in the face of intense competition from intra‐generic competitors. 2. In a field experiment designed to test this hypothesis in N. defodiens (Mannerheim), breeding associations of two females and a male were no more successful at retaining their carcass than were monogamous pairs, lending no support to the hypothesis. 3. Intra‐generic intruders that usurped already‐buried carcasses were typically much larger than the original residents. 4. The body size of original residents affected both the burial depth and the probability of a takeover. Larger beetles buried the carcass deeper and were more likely to retain possession of the carcass. Group composition also did not affect the depth at which carcasses were buried. 5. Severe and even fatal injuries incurred by some residents indicated the occurrence of violent and damaging fights between competitors over carcasses in the field.     

Offspring growth, survival and reproductive success in the bank vole: a litter size manipulation experiment

To estimate the optimality of brood size, it is essential to study the effects of brood size manipulation on offspring survival and reproductive success. Moreover, testing the generality of the hypothesis of reproductive costs requires experimental data from a diversity of organisms. Here I present data on the growth, survival and reproductive success of bank vole Clethrionomys glareolus individuals from manipulated litters. Furthermore, the survival of mothers whose litter size was manipulated was studied. At weaning, the mean weight of pups from enlarged litters was lower and from reduced litters higher compared to control litters. After winter, at the start of the breeding season, individuals from enlarged litters, especially males, were still lighter than individuals from the other two treatments. Litter enlargements did not increase the number of reproducing female offspring per mother, nor did the litter sizes of female offspring differ between treatments. There were no differences between treatments in winter survival of offspring after weaning, but among female offspring, weaning weight explained the survival probabilities over winter. A higher weight of females at winter determined the probability of starting to reproduce in spring. The survival of mothers did not seem to be influenced by litter manipulation performed the previous year. According to the results, mothers nursing enlarged or reduced litters do not gain any fitness benefits in terms of number of offspring surviving to breeding. The results are consistent with the majority of experiments conducted in birds, which have found costs of enlarged brood appearing as offspring trade-offs rather than parent trade-offs. Received: 14 December 1997 / Accepted: 1 March 1998     

Hen harriers and red grouse: economic aspects of red grouse shooting and the implications for moorland conservation

1.  Thirgood & Redpath (2008) propose ways in which red grouse : hen harrier conflicts could be resolved. It has also been suggested that grouse management could accept lower bag sizes (number of birds shot) thus reducing the need for intensive management of predators and habitats. This would allow hen harriers to co-exist more easily on grouse moors.
2.  We compare the bags, costs and incomes from these less intensive forms of grouse shooting with the more intensive driven shooting.
3.  Allowing high density grouse moors to decline to low density ones will result in greater loss of income than the corresponding saving of costs. This can result in moor owners abandoning grouse management and thus gamekeepers losing their employment.
4.  Losing gamekeepers from the uplands would jeopardize the protection of heather moorland and Special Protection Areas for birds, large areas of which are keepered and which currently support high numbers of breeding waders.
5.   Synthesis and applications . We agree with the study by Thirgood & Redpath that consideration of social and economic factors will be needed to resolve conflict but a reduction in management effort from driven to walked-up shooting is not the answer. A more satisfactory approach to the harrier : grouse conflict could be to try to reduce harrier predation by means of diversionary feeding and to address the problem of the rapid build-up in harrier numbers by exploring the use of a ceiling on harrier densities.     

Tree species richness affects litter production and decomposition rates in a tropical biodiversity experiment

We report data on leaf litter production and decomposition from a manipulative biodiversity experiment with trees in tropical Panama, which has been designed to explore the relationship between tree diversity and ecosystem functioning. A total of 24 plots (2025 m²) were established in 2001 using six native tree species, with 1‐, 3‐, and 6‐species mixtures. We estimated litter production during the dry season 2005 with litter traps; decomposition was assessed with a litter bag approach during the following wet season. Litter production during the course of the dry season was highly variable among the tree species. Tree diversity significantly affected litter production, and the majority of the intermediate diverse mixtures had higher litter yields than expected based on yields in monoculture. In contrast, high diverse mixtures did not show such overyielding in litter production. Litter decomposition rates were also highly species‐specific, and were related to various measures of litter quality (C/N, lignin/N, fibre content). We found no overall effect of litter diversity if the entire litter mixtures were analyzed, i.e. mixing species resulted in pure additive effects and observed decomposition rates were not different from expected rates. However, the individual species changed their decomposition pattern depending on the diversity of the litter mixture, i.e. there were species‐specific responses to mixing litter. The analysis of temporal C and N dynamics within litter mixtures gave only limited evidence for nutrient transfer among litters of different quality. At this early stage of our tree diversity experiment, there are no coherent and general effects of tree species richness on both litter production and decomposition. Within the scope of the biodiversity‐ecosystem functioning relationship, our results therefore highlight the process‐specific effects diversity may have. Additionally, species‐specific effects on ecosystem processes and their temporal dynamics are important, but such effects may change along the gradient of tree diversity.