Density of red alder (Alnus rubra) in headwaters influences invertebrate and detritus subsidies to downstream fish habitats in Alaska

We investigated the influence of red alder (Alnus rubra) stand density in upland, riparian forests on invertebrate and detritus transport from fishless headwater streams to downstream, salmonid habitats in southeastern Alaska. Red alder commonly regenerates after soil disturbance (such as from natural landsliding or timber harvesting), and is common along streams in varying densities, but its effect on food delivery from headwater channels to downstream salmonid habitats is not clear. Fluvial transport of invertebrates and detritus was measured at 13 sites in spring, summer and fall during two years (2000–2001). The 13 streams encompassed a riparian red alder density gradient (1–82% canopy cover or 0–53% basal area) growing amongst young-growth conifer (45-yr-old stands that regenerated after forest clearcutting). Sites with more riparian red alder exported significantly more invertebrates than did sites with little alder (mean range across 1–82% alder gradient was about 1–4 invertebrates m^?3 water, and 0.1–1 mg invertebrates m^?3 water, respectively). Three-quarters of the invertebrates were of aquatic origin; the remainder was of terrestrial origin. Aquatic taxa were positively related to the alder density gradient, while terrestrially-derived taxa were not. Streams with more riparian alder also exported significantly more detritus than streams with less alder (mean range across 1–82% alder gradient was 0.01–0.06 g detritus m^?3 water). Based on these data, we predict that headwater streams with more riparian alder will provide more invertebrates and support more downstream fish biomass than those basins with little or no riparian alder, provided these downstream food webs fully utilize this resource subsidy.     

Short-term decompositional state does not influence use of wood by macroinvertebrates in subtropical, coastal plain streams

Woody debris is an important habitat component, particularly in streams that lack other hard substrates. Research suggests a general relationship between increasing invertebrate density, diversity, and taxa richness with increasing wood decay in lotic systems, with some authors observing invertebrate taxonomic succession as decay proceeds. We designed a field experiment using colonization of known-aged woody debris in two streams to examine patterns in invertebrate colonization, density, diversity, richness, and succession. After aging woody debris 0–6 weeks in laboratory tanks and then placing the debris in the two subtropical, coastal plain streams for five additional weeks, we did not detect any statistical relationship between invertebrate density, diversity, evenness, richness, or life-history pattern with increasing woody debris decay, nor did we detect any relationships between the colonization or abundance of individual taxa and the decompositional state of the wood. In this paper, we propose two non-exclusive explanations for these trends based on opportunistic colonization and evolutionary filtering. Despite the apparent unimportance of decompositional state, woody debris still supported many taxa and remains an important habitat component. Our research further supports the importance of flooding and maintenance of intact riparian and floodplain forests to the woody debris dynamics and macroinvertebrates in coastal plain lotic systems.     

Effects of woody debris and the supply of terrestrial invertebrates on the diet and growth of brown trout (Salmo trutta) in a boreal stream

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The effects of riparian forest disturbance on stream temperature,sedimentation, and morphology

Forested headwater streams rely on their riparian areas for temperature regulation, woody debris inputs, and sediment retention. These products and services may be altered by disturbances such as timber harvest, windthrow, or development. This study investigated the effects of riparian forest disturbance by removing trees using 50 and 90% basal area harvests and by directly felling some trees into eight streams in eastern West Virginia. On summer afternoons, water temperature increased in the 50 and 90% BAH treatments at average rates of 0.18 and 0.79°C/100 m, respectively. The 90% BAH treatments had the potential to disrupt fish and invertebrate communities via increased water temperature. New roads and log landings associated with the riparian logging had no detectable effect on sedimentation or turbidity. Large woody debris (LWD) additions increased habitat complexity but no net increase in pool area was observed. Greater morphological instability was observed within the LWD addition sections as pools were both created and destroyed at significantly higher rates. Experimentally manipulating small riparian patches may be an analog for small-scale natural and anthropogenic disturbances. These common events are assumed to alter streams, but there are few experimental studies quantifying their effects.     

Spatial and Temporal Pattern of Caddisfly Distribution at a Mesohabitat Scale in two Patagonian Mountain Streams Subjected to Pastoral Use

Substrate, flow type, nutrients, aquatic vegetation, organic matter, and caddisfly community structure were studied at two low order streams (Glyn and Nant y Fall) subjected to pastoral use in the Patagonian mountains. At both sites, we examined the effect of habitat type (boulder‐pebble with and without filamentous algae, cobble‐pebble, gravel‐sand, leaf‐pack, the submerged macrophytes Myriophyllum quitense and Isoetes savatieri) and season (high and low water period) on caddisfly assemblages. Benthic particulate organic matter (BPOM) ranged between 4.6 and 472 g m^–2, all allochtonous detrital fractions were significantly higher at leaf‐packs at Glyn, whereas M. quitense habitats supported more BPOM and macrophytes biomass at Nant y Fall. As expected, boulder‐pebble sustained higher Trichoptera richness than M. quitense and gravel‐sand, moreover all habitats showed higher density than M. quitense at Nant y Fall. According to our results at least nine caddisfly species exhibited some habitat preference with boulder‐pebble and cobble‐pebble the most selected habitat. These particular habitats sustained more than 68% of the total caddisfly species. Multidimensional scaling ordination highlighted differences in composition per habitat for both sites showing a clear distinction among depositional and erosional habitats. Substrate, flow type, detritus biomass were important predictors defining assemblages. Based upon our findings, those anthropogenic actions or stressors that change hydraulic as well substrate attributes in mountain streams such as stock trampling, dredging, clearing of riparian areas, will reduce caddisfly richness. These results are relevant for outline management and conservation biomonitoring and schemes in headwater Patagonian streams as well as other similar environments worldwide (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Aquatic and riparian ecosystem recovery from debris flows in two western Washington streams,USA

An exceptionally powerful storm struck southwestern Washington in December 2007 causing large debris flows in two adjacent streams. The two affected streams had been studied prior to the storm, providing a rare opportunity to examine ecosystem recovery. We monitored the streams and their riparian zones for six years after the disturbances to determine whether recovery rates of biota, physical habitat, and water temperature differed, and if so, what factors affected resilience. Along both streams, the debris flows removed wide swaths of soil, rock, and coniferous riparian forests, widening the active channel and increasing solar exposure and summer water temperatures. Initially depauperate of vegetation, after four years red alder trees dominated the riparian plant communities. The warmer water, greater solar radiation, and unstable substrates likely contributed to variable benthic insect and tailed frog tadpole densities over time, although benthic insect communities became more similar after three years. The debris flows also decreased channel slopes and removed channel step barriers such that cutthroat trout were able to rapidly occupy habitats far upstream, but sculpins were slower to recolonize and both fish species exhibited some differences in recovery between the two streams. Crayfish were severely impacted by the debris flows; this may be due to attributes of their life history and the timing of the flows. Overall, we found that recolonizing aquatic species exhibited varying levels of resilience and recovery after the disturbances being related to the influence of physical habitat conditions, species dispersal ability, and the presence of nearby source populations.     

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.     

Benchmarks and predictors of coarse woody debris in native forests of eastern Australia

Fallen coarse woody debris (CWD) is critical to forest biodiversity and function. Few studies model factors that influence CWD availability, although such investigations are critically needed to inform sustainable forest management. We assess benchmark levels of CWD in unharvested native forests and those harvested for timber, across a range of forests in north‐east New South Wales, Australia. We found timber‐harvesting was the dominant driver of CWD, with almost double the count (pieces ha^?1) and volume (m³ ha^?1) of total CWD in selectively harvested than unharvested sites. This pattern was consistent across wet and dry forest types. Harvested sites had greater counts of hollow‐bearing logs, and greater volumes of small and medium‐sized CWD (15–50 cm diameter) than unharvested sites. There was no effect of harvesting on the volume of large CWD (>51 cm diameter). Total volumes of CWD (>15 cm diameter) varied from 114 to 166 m³ ha^?1. We found few differences in CWD counts and volumes between forest types, with grassy woodlands and forests containing less CWD than other dry and shrubby forest types, reflecting lower potential input rates. The CWD levels recorded here are similar to those recorded in dry and wet sclerophyll forests elsewhere in Australia and are typical of global estimates for ‘old growth’ forests. Using general linear models we captured up to 57% of the variation in CWD across sites, and found that timber harvesting, topography and the numbers of standing hollow‐bearing and dead trees were significant predictors of CWD. Values for unharvested forest provide a benchmark that could be used to inform retention guidelines for CWD in managed forests in this region. Further assessment of the effect of repeat timber harvesting is needed to fully understand its impact on CWD dynamics, especially if forest residues resulting from timber harvesting are removed from native forests for bioenergy production.     

Forest Age Influences In-stream Ecosystem Processes in Northeastern US

A disturbance or natural event in forested streams that alter available light can have potential consequences for nutrient dynamics and primary producers in streams. In this study, we address how functional processes (primary production and nutrient uptake) in stream ecosystems respond to changes in forest canopy structure. We focus on differences in incoming irradiance, nutrient uptake (NO₃, NH₄, and PO₄) and open-channel metabolism seasonally in 13 forested streams that drain forests with different canopy structures (10 to >300 years old) in the northeastern United States. Light irradiance was related to forest age in a U-shaped pattern, with light being the greatest in both young open forests (<50 years old) and older growth forests (>245 years old), whereas the darkest conditions were found in the secondary growth middle-aged forests (80–158 years old). Streams that had adjacent open or old-growth riparian forest had similar conditions with greater standing stock biofilm biomass (chl a), and elevated ER in October compared to streams with middle-aged riparian forests. Compared to all sites, streams with old-growth riparian forest had the greatest in-stream primary production rates (GPP) and elevated background nutrient concentrations, and to a lesser degree, increased nutrient retention and uptake (V _f). Streams draining older forests tended to be more productive and retentive than middle-aged forests, likely due to increased light availability and the age and structure of surrounding forest canopies. Middle-aged forests had the least variation in response variables compared to streams in young and old-growth riparian forests, likely a result of uniform canopy conditions. As the structure of widespread middle-aged forests in NE US is altered by loss of specific tree species, climate change, and/or human activity, it will impact in-stream production and nutrient dynamics and may ultimately alter nutrient loading in downstream catchments.     

What predicts the use by brook trout (Salvelinus fontinalis) of terrestrial invertebrate subsidies in headwater streams?

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Effects of forest fire on headwater stream macroinvertebrate communities in eastern Washington,U.S.A.

1. Recent increases in fire frequency in North America have focused interest on potential effects on adjacent ecosystems, including streams. Headwaters could be particularly affected because of their high connectivity to riparian and downstream aquatic ecosystems through aquatic invertebrate drift and emergence. 2. Headwater streams from replicated burned and control catchments were sampled in 2 years following an intense forest fire in northeastern Washington (U.S.A.). We compared differences in benthic, drift and emergent macroinvertebrate density, biomass and community composition between five burned and five unburned catchments (14–135 ha). 3. There were significantly higher macroinvertebrate densities in burned than control sites for all sample types. Macroinvertebrate biomass was greater at burned sites only from emergence samples; in benthic and drift samples there was no significant difference between burn and control sites. 4. For all sample types, diversity was lower in the burned catchments, and the macroinvertebrate community was dominated by chironomid midges. 5. Compared to the effects of fire in less disturbed ecosystems, this study illustrated that forest fire in a managed forest may have greater effects on headwater macroinvertebrate communities, influencing prey flow to adjacent terrestrial and downstream aquatic habitats for at least the first 2 years post‐fire.     

Bryophyte species richness and composition in young forests regenerated after clear-cut logging versus after wildfire and spruce budworm outbreak

The disturbance regime in mixed-wood forests of eastern Canada is characterized by both natural disturbances including wildfires and insect outbreaks as well as forestry. The understanding of how understorey plant assemblages respond to different disturbances is mostly limited to short-term wildfire-logging comparisons of vascular plants. Here, we compare patterns of species richness and composition of four bryophyte guilds in young forests (approx. 40 years old) regenerating after clear-cut logging, wildfire, and spruce budworm outbreak. In addition, young forests were compared with mature spruce-fir dominated stands (approx. 90 years old). Although similar in overall species richness at the scale of 1,000 m² all young forest types were compositionally distinct with fewer species than mature forests. Stands developed after spruce budworm outbreaks had the highest canopy cover values and the highest surface area of coarse woody debris. These stands had similar numbers of woody debris species as mature forests and were closest to mature forests in species composition. Wildfire-disturbed sites were dominated by deciduous trees and a high number of treebase species. Finally, young managed forest had the highest number of forest floor bryophytes at the scale of 100 m² among the three young forest types, but was compositionally far from mature forests in their woody debris flora. In conclusion, young forests regenerating after natural disturbances are distinctly different from young forests regenerated after clear-cutting and if natural disturbances are eliminated certain species (e.g., epixylic and treebase species) might become more restricted to older stands in the landscape.     

Influence of fishes on macroinvertebrate communities and insect emergence production in intermittent stream refuges

1. Drying intermittent stream networks often have permanent water refuges that are important for recolonisation. These habitats may be hotspots for interactions between fishes and invertebrates as they become isolated, but densities and diversity of fishes in these refuges can be highly variable across time and space.
2. Insect emergence from streams provides energy and nutrient subsidies to riparian habitats. The magnitude of such subsidies may be influenced by in-stream predators such as fishes.
3. We examined whether benthic macroinvertebrate communities, emerging adult insects, and algal biomass in permanent grassland stream pools differed among sites with naturally varying densities of fishes. We also manipulated fish densities in a mesocosm experiment to address how fishes might affect colonisation during recovery from hydrologic disturbance.
4. Fish biomass had a negative impact on invertebrate abundance, but not biomass or taxa richness, in natural pools. Total fish biomass was not correlated with total insect emergence in natural pools, but orangethroat darter (Etheostoma spectabile) biomass was inversely correlated with emerging Chironomidae biomass and individual midge body size. The interaction in our models between predatory fish biomass and date suggested that fishes may also delay insect emergence from natural pools, altering the timing of aquatic–terrestrial subsidies.
5. There was an increase over time in algal biomass (chlorophyll-a) in mesocosms, but this did not differ among fish density treatments. Regardless, fish presence in mesocosms reduced the abundance of colonising insects and total invertebrate biomass. Mesocosm invertebrate communities in treatments without fishes were characterised by more Chironomidae, Culicidae, and Corduliidae.
6. Results suggest that fishes influence invertebrates in habitats that represent important refuges during hydrologic disturbance, hot spots for subsidy exports to riparian food webs, and source areas for colonists during recovery from hydrologic disturbance. Fish effects in these systems include decreasing invertebrate abundance, shifting community structure, and altering patterns of invertebrate emergence and colonisation.

     

Structural characteristics and aboveground biomass of old‐growth spruce–fir stands in the eastern Carpathian mountains,Ukraine

Abstract

Temperate old‐growth forests are known to have ecological characteristics distinct from younger forests, but these have been poorly described for the remaining old‐growth Picea abies–Abies alba forests in the eastern Carpathian mountains. In addition, recent studies suggest that old‐growth forests may be more significant carbon sinks than previously recognized. This has stimulated interest in quantifying aboveground carbon stocks in primary forest systems. We investigated the structural attributes and aboveground biomass in two remnant old‐growth spruce–fir stands and compared these against a primary (never logged) mature reference stand. Our sites were located in the Gorgany Nature Reserve in western Ukraine. Overstory data were collected using variable radius plots; coarse woody debris was sampled along line intercept transects. Differences among sites were assessed using non‐parametric statistical analyses. Goodness‐of‐fit tests were used to evaluate the form of diameter distributions. The results strongly supported the hypothesis that old‐growth temperate spruce–fir forests have greater structural complexity compared to mature forests, including higher densities of large trees, more complex horizontal structure, and elevated aboveground biomass. The late‐successional sites we sampled exhibited rotated sigmoid diameter distributions; these may reflect natural disturbance dynamics. Old‐growth Carpathian spruce–fir forests store on average approximately 155–165 Mg ha^?1 of carbon in aboveground tree parts alone. This is approximately 50% higher than mature stands. Given the scarcity of primary spruce–fir forests in the Carpathian region, remaining stands have high conservation value, both as habitat for late‐successional species and as carbon storage reservoirs.     

Effect of Downed Woody Debris on Small Mammal Anti‐Predator Behavior

Anti‐predator behavior can affect prey growth, reproduction, survival, and generate emergent effects in food webs. Small mammals often lower the cost of predation by altering their behavior in response to shrubs, but the importance of other microhabitat features, such as downed woody debris, for anti‐predator behavior is unknown. We used giving‐up densities to quantify the degree to which downed woody debris alters perceived predation risk by small mammals in southeastern pine forests. We placed 14 foraging trays next to large downed woody debris, shrubs, and in open areas for 12 consecutive nights. Moon illumination, a common indicator of predation risk, led to a similar reduction in small mammal foraging in all three microhabitats (open, downed woody debris, and shrub). Small mammals perceived open microhabitats as riskier than shrub microhabitats, with downed woody debris habitats perceived as being of intermediate risk between shrub and open microhabitats. Despite the presumed benefits of the protective cover of downed woody debris, small mammals may perceive downed woody debris as a relatively risky foraging site in southeastern pine forests where the high diversity and abundance of rodent‐eating snakes may provide a primary predatory threat.     

Effect of a leaf-shredding invertebrate on organic matter dynamics and phosphorus spiralling in heterotrophic laboratory streams

Summary The effect of invertebrate shredders on organic matter dynamics and phosphorus spiralling was studied over a 30-week period in laboratory streams. The streams were fed by groundwater, layered with cobble and gravel from a natural stream, covered with opaque material to eliminate algal growth, and initially contained 195 g/m² of autumn-shed leaves. Four weeks after leaf addition, leaf-shredding snails (Goniobasis clavaeformis) were added to each of three streams in densities of 75, 220, and 800/m². A fourth stream contained no snails and served as a control.Presence of snails increased the loss rates of coarse particulate organic matter (CPOM) and total organic matter (TOM), primarily by increasing leaf fragmentation and seston export. Although snail feeding increased specific metabolism of microbes associated with CPOM and cobble surfaces, it was not enough to compensate for reduction in bacterial cell numbers per unit surface area and in stream TOM. Consequently mineralization of detritus and whole stream phosphorus utilization rate were maximum in the stream with no snails and decreased with increasing snail density. From previous simulations of a stream model based on the nutrient spiralling concept, we predicted that there should be an intermediate shredder density which would minimize phosphorus spiralling length (maximize phosphorus utilization) in a natural stream nearby. Our current results conflict with the model-based predictions primarily because the increase in microbial metabolism was less important than reduction in bacterial cell numbers and total benthic organic matter resulting from snail feeding. Although our results indicate macroinvertebrate shredders reduce phosphorus utilization in headwater streams, shreders may increase nutrient utilization downstream where riparian inputs are lower, thus linking low- and high-order streams.Research supported by the National Science Foundation's Ecosystem Studies Program under Interagency Agreement No. BSR-8103181, A02 with the U.S. Department of Energy, under Contract No. DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.Publication No. 2394, Environmental Sciences Division, ORNL     

Combined effects of an anthropogenic (forest harvesting) and natural (extreme rainfall event) disturbance on headwater streams in New Zealand

1. Although extreme hydrological events are a natural component of river ecosystem disturbance regimes, their frequency is predicted to increase with climate change. Anthropogenic activities have the potential to exacerbate the impact of such disturbances but there are few studies on the combined effects of both anthropogenic and extreme hydrological disturbances on stream ecosystems.
2. We investigated the recovery of stream ecosystems over a 5-year period following the impact of an anthropogenic (forest clear-cut harvesting) and an extreme rainfall disturbance (estimated one-in-100 year average return interval) that generated debris flows in three headwater streams in New Zealand.
3. Initially, most of the riparian vegetation was eliminated and showed little recovery 1 year later. Subsequent riparian recovery was led by wind-borne, light-demanding, pioneering exotic weed species, lengthening and altering the long-term successional and recovery trajectories to a pre-disturbance composition of indigenous shrubs.
4. Stream shade, water temperature, and habitat had largely recovered after 5 years. However, the contribution of large wood to channel morphology and in-stream habitat was compromised due to diminished wood supplies in the stream channel and a hiatus in up-slope wood inputs until the riparian vegetation re-establishes and the next crop of trees matures.
5. After an initial decline, most indigenous fish taxa thrived in the post-disturbance conditions, with significant increases in densities and biomass. The more sensitive fish taxa were scarce or absent, particularly those taxa that prefer pools with overhead and in-stream cover provided by riparian vegetation and wood. Recovery of these taxa was outside the time frame of this study. Riffle dwelling fish communities were more resilient than pool dwelling fish communities.
6. Invertebrate densities showed a similar response to fish. Post-event invertebrate community composition differed from that typically found in post-harvest headwater streams, comprising comparatively lower proportions of Chironomidae, Oligochaetes, and Mollusca taxa, and higher proportions of Trichoptera taxa. Progression toward pre-event community composition was evident 5 years after the event.
7. The compounding effect of forest removal from harvesting, along with riparian vegetation and wood removal by debris flows, lengthened the recovery of riparian vegetation and wood supplies with cascading effects on in-stream habitat and biological communities.

     

Changes in habitat structure, benthic invertebrate diversity, trout populations and ecosystem processes in restored forest streams: a boreal perspective

1. Most Finnish streams were channelised during the 19th and 20th century to facilitate timber floating. By the late 1970s, extensive programmes were initiated to restore these degraded streams. The responses of fish populations to restoration have been little studied, however, and monitoring of other stream biota has been negligible. In this paper, we review results from a set of studies on the effects of stream restoration on habitat structure, brown trout populations, benthic macroinvertebrates and leaf retention. 2. In general, restoration greatly increased stream bed heterogeneity. The cover of mosses in channelised streams was close to that of unmodified reference sites, but after restoration moss cover declined to one‐tenth of the pre‐restoration value. 3. In one stream, densities of age‐0 trout were slightly lower after restoration, but the difference to an unmodified reference stream was non‐significant, indicating no effect of restoration. In another stream, trout density increased after restoration, indicating a weakly positive response. The overall weak response of trout to habitat manipulations probably relates to the fact that restoration did not increase the amount of pools, a key winter habitat for salmonids. 4. Benthic invertebrate community composition was more variable in streams restored 4–6 years before sampling than in unmodified reference streams or streams restored 8 years before sampling. Channelised streams supported a distinctive set of indicator species, most of which were filter‐feeders or scrapers, while most of the indicators in streams restored 8 years before sampling were shredders. 5. Leaf retentiveness in reference streams was high, with 60–70% of experimentally released leaves being retained within 50 m. Channelised streams were poorly retentive (c. 10% of leaves retained), and the increase in retention following restoration was modest (+14% on average). Aquatic mosses were a key retentive feature in both channelised and natural streams, but their cover was drastically reduced through restoration. 6. Mitigation of the detrimental impacts of forestry (e.g. removal of mature riparian forests) is a major challenge to the management of boreal streams. This goal cannot be achieved by focusing efforts only on restoration of physical structures in stream channels, but also requires conservation and ecologically sound management of riparian forests.     

Ecosystem Linkages between Southern Appalachian Headwater Streams and Their Banks: Leaf Litter Breakdown and Invertebrate Assemblages

We examined red maple (Acer rubrum L.) leaf litter breakdown in streams and riparian zones at two sites in the southern Appalachian Mountains to understand how differences in abiotic and biotic factors influence leaf breakdown rates. Litterbags were placed in three riparian habitats differing in litter layer moisture: stream > bank > upland. Invertebrates colonizing litterbags at one site were also examined to determine how variations in community and functional structure affect breakdown rates. Leaves broke down fastest in streams and slowest in upland habitats, whereas bank habitats were intermediate and characterized by high variability. Faster leaf breakdown rates in streams appeared to be a function of greater moisture availability, a more stable thermal regime, and a higher biomass of leaf-shredding invertebrates, especially the stonefly Tallaperla. In addition, patterns of leaf breakdown and invertebrate community structure provided evidence for a stronger than expected ecological connection between the stream and the bank. Overall, detritus processing within this narrow riparian ecosystem varied considerably depending on the availability of moisture. Results from this study show that stream channel–floodplain interactions in riparian ecosystems of steep forested mountains are analogous to ones in larger downstream or low-gradient systems. Riparian zones throughout a river network display a remarkable heterogeneity in their ability to process organic matter, which is ultimately driven by changes in hydrological conditions. Received 6 March 2001; accepted 3 July 2001.     

Increased growth rates of stream salamanders following forest harvesting

Timber harvesting can influence headwater streams by altering stream productivity, with cascading effects on the food web and predators within, including stream salamanders. Although studies have examined shifts in salamander occupancy or abundance following timber harvest, few examine sublethal effects such as changes in growth and demography. To examine the effect of upland harvesting on growth of the stream‐associated Ouachita dusky salamander (Desmognathus brimleyorum), we used capture–mark–recapture over three years at three headwater streams embedded in intensely managed pine forests in west‐central Arkansas. The pine stands surrounding two of the streams were harvested, with retention of a 14‐ and 21‐m‐wide forested stream buffer on each side of the stream, whereas the third stream was an unharvested control. At the two treatment sites, measurements of newly metamorphosed salamanders were on average 4.0 and 5.7 mm larger post‐harvest compared with pre‐harvest. We next assessed the influence of timber harvest on growth of post‐metamorphic salamanders with a hierarchical von Bertalanffy growth model that included an effect of harvest on growth rate. Using measurements from 839 individual D. brimleyorum recaptured between 1 and 6 times (total captures, n = 1229), we found growth rates to be 40% higher post‐harvest. Our study is among the first to examine responses of individual stream salamanders to timber harvesting, and we discuss mechanisms that may be responsible for observed shifts in growth. Our results suggest timber harvest that includes retention of a riparian buffer (i.e., streamside management zone) may have short‐term positive effects on juvenile stream salamander growth, potentially offsetting negative sublethal effects associated with harvest.