Summary1. Temperate forests managed to maximize sustainable yield of wood products can reduce the availability of dead wood on the forest floor and in adjacent streams, which in turn can impair ecological processes such as retention and transformation of organic matter. Lack of tools to link ecological processes with their effects on human well-being leads forest managers to ignore the cost on other services from terrestrial and aquatic ecosystems. 2. We examine how adding dead wood to restore stream channel complexity affects the provision and value of selected ecosystem services, mainly related to the retention and transformation of matter and cycling of nutrients, as well as to the effects on aquatic biota. Specifically, we evaluated the cost-effectiveness of stream restoration through a comparative analysis of four reach-scale projects in streams flowing through temperate forest and into a drinking water reservoir and two scenarios of active and passive restoration at the basin scale. 3. Results indicate that the lack of dead wood in streams has an important economic cost because of the effects on fish provisioning, opportunities for recreation and tourism, water purification and erosion control. Active reach-scale restoration resulted in a 10-to 100-fold increase in the monetary benefits provided by streams, accounting as much as 1Á8 € per metre of restored river length each year. Results of the reach-scale cost-benefit analyses estimated that the time required to recover the active restoration investment ranged from 15 to 20 years in low-to middle-order streams. 4. Synthesis and applications. Our study showed that restoration of natural wood loading in streams greatly increases the ecosystem services they provide. The benefits in terms of the analysed services surpass the costs of active restoration over realistic timeframes, whereas this was not the case for passive restoration. Inclusion of other ecosystem services such as conservation of biodiversity might make restoration more economically profitable. Overall, our study provides a decision framework for managing temperate riparian forests in the context of ecological services.

1. Channel complexity affects the physical structure, biotic communities and functioning of stream ecosystems. Large wood (LW) is a key element in the creation and maintenance of physically complex stream channels in forested areas. 2. In an attempt to enhance stream habitat quality and ecosystem functioning and to reduce inputs of organic matter to a downstream reservoir, LW was experimentally introduced into four mountain streams in the Basque Country (northern Spain), ranging in channel width from 3 to 13 m. Following a before-after/control-impact (BACI) design, streams were monitored during 1 year prior to wood addition and during 2 years after addition in one control and one experimental reach per stream. 3. Areal cover of benthic organic matter in the entire channel was measured from regular transects and the mass of stored organic matter from random Surber samples. Breakdown of organic matter was assessed in litter bag experiments performed with black alder leaves. When 50% of the initial mass in the bags remained, invertebrates associated with leaf bags were collected. 4. Wood placement produced a 2-to 70-fold increase in the storage of organic matter, especially in thick deposits upstream from wood jams, with values in excess of 2 kg AFDM per m 2 in the small streams. The accumulation of organic matter produced by wood introduction decreased with increasing stream size. 5. Despite the large increase in the availability of organic matter, litter breakdown rates were unaffected by the experimental reaches, suggesting large increases in the total amount of organic matter consumed at the reach scale. 6. Numbers of invertebrates and shredders per gram of leaf litter did not respond to wood addition. Average body mass of invertebrates associated with leaf litter showed a nonsignificant decreasing trend, which might reflect increased recruitment. 7. Although the effects of wood addition can depend on wood stability and stream size, adding LW to restore channel complexity can improve environmental conditions for invertebrate communities and affect stream ecosystem functioning, enhancing the efficiency to use organic matter inputs on a reach scale.

No abstract

No abstract

Summary Organic matter inputs to streams can be retained in contrasting sites, from small leaf packs on top of cobbles to thick organic deposits trapped by wood jams. Differences in environmental conditions and in stability among sites can affect the biological communities, the quality of organic matter and its use by consumers. We measured the accumulation and composition of coarse organic matter and the breakdown of alder leaves on the surface of the streambed, inside gravel bars and in thick litter deposits trapped by log jams. We also monitored fungal sporulation rates and macroinvertebrate diversity and density in these retention sites. The amount of organic matter in these locations differed significantly among sites and ranged from 118 g m−2 in gravel to 11 562 g m−2 in jams. The biomass of shredders also differed significantly among retention sites, being highest in jams (1440 mg m−2) and lowest in gravel (86 mg m−2). Breakdown of alder leaves in fine‐mesh bags did not differ among retention sites. In coarse‐mesh bags, leaf breakdown rate was significantly lower in gravel bars than in surface sites or jams. Despite large differences in amount and quality of organic matter between surface sites and jams, alder leaves broke down at the same rate. Density of invertebrates in bags and fungal sporulation rates tended to be highest in surface sites and lowest in gravel bars. The contribution of microbes to breakdown was 67% in gravel, 52% in surface and only 28% in jams. Overall, the differences among sites in leaf breakdown were correlated with invertebrate density. Our results showed large differences in the amount and quality of organic matter accumulated, in biological communities and in the use of organic matter among retention sites of a single stream reach. This spatial variability should be taken into account in studies of ecosystem functioning related to organic matter.