The productivity or availability of juvenile habitats have theoretically been shown to determine size distributions of adult individuals and population abundance. Brown trout (Salmo trutta) is a species where adults may inhabit lakes and use connected streams for spawning and as nursery habitats for juveniles. This project aimed to estimate what factors determine the density and growth of juvenile brown trout in mountain streams. This was done by sampling 21 mountain streams for juvenile brown trout densities and growth, habitat availability and stream size, productivity, and resource availability. Additional data were obtained from other mountain streams from the Swedish Electrofishing Register. My results showed that measures of stream productivity and estimated benthic resource availability did not affect the densities and biomass of older juvenile brown trout. Instead, higher densities of older juvenile brown trout were related to increasing stream size (stream width x water depth). This is likely due to interference competition for space, where territory size influences the growth and densities of brown trout in streams but also that larger streams can provide refuges for larger individuals during periods of drying and thermal stress. This indicates that my estimate of stream size is an important factor determining densities of older juvenile brown trout in low-productive mountain streams. Stream size can be suggested to be a used as proxy for density and production of larger juvenile brown trout and therefore it may also be used to predict adult lake-living brown trout population size structure and abundance.

What drives species diversity across landscapes is one of the most fundamental questions in ecology. Further, understanding the mechanisms underlying species diversity patterns is important not only for forming and challenging ecological theories but also essential for appropriate landscape management and effective nature conservation. This thesis focuses on patterns of vascular plant, moss and liverwort species richness and composition in relation to water flow in boreal-forest catchments, focusing mostly on riparian zones (RZs), that is terrestrial areas bordering streams and rivers. I addressed some of the most essential questions related to the ecology of riparian vegetation including the role of stream network position, groundwater (GW) flow paths, substrate availability, upland perturbations, and stream restoration. I also investigated how riparian soil processes and habitat properties relate to these factors in order to provide a holistic understanding of riparian dynamics. The results showed that the species richness and composition of riparian vascular plants, mosses and liverworts are strongly influenced by position along the stream network, GW discharge, presence of variable substrates in RZs, and by stream restoration. Generally, more species were found downstream in the network, at sites with inputs of upland GW, sites with high diversity of substrates (e.g., open mineral soil, rocks, stones, wood and bark), and along streams restored after channelization. This thesis also describes how riparian habitat properties responded to position in the landscape and human impacts, thus providing mechanistic links between plant species diversity and riparian processes across spatial scales. These ecological insights are further implemented into numerous recommendations for freshwater and upland management in boreal Sweden. Given that streams and rivers connect landscape elements both longitudinally and laterally I argue that management plans should be designed for entire catchments instead of individual river segments. Ignoring the connectivity of streams as well as the high connectivity of riparian areas to uplands via GW flows may result in failure of restoration, mitigation and/or protection actions. Further, during forestry operations more emphasis should be placed on GW discharge areas along streams and rivers, because they represent important ecological and biogeochemical hotspots in the landscape. The riparian buffers left along streams in boreal catchments affected by forestry are presently insufficiently wide and often uniform in width. This threatens the assemblages of species in GW discharge hotspots and the ecosystem services they provide. Overall, this thesis describes a holistic picture of riparian diversity patterns and riparian processes in boreal landscapes, acknowledges and elaborates on current ecological theories, presenting new patterns in biodiversity, and offers management guidelines.