Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5.
Channel morphology and habitat characteristics of stream segments draining unharvested old-growth forests were compared with those from streams within intensively and moderately logged basins. Sites covered a broad geographic range in western Washington State and were stratified by basin area and channel gradient. Although the number of pieces of large woody debris (LWD) within stream channels was unaffected by timber harvest, there was a clear reduction in LWD size in harvested basins. Timber harvest also resulted in a shift in location of LWD towards the channel margins, outside the low-flow wetted width of the channel. Intensive harvest simplified channel habitat by increasing riffle area and reducing pool area and depth, although the commonly used index of pool-to-riffle ratio appears inadequate to document these changes. Given the natural variation from stream to stream, we conclude that simple counts of instream LWD and channel units (habitat types) are not useful as management objectives. Instead, these attributes should be used collectively as indicators of the complexity and stability of in-stream habitat with respect to the specific channel and valley geomorphology.
Habitat unit classification can be a useful descriptive tool in hierarchical stream classification. However, a critical evaluation reveals that it is applied inappropriately when used to quantify aquatic habitat or channel morphology in an attempt to monitor the response of individual streams to human activities. First, due to the subjectivity of the measure, observer bias seriously compromises repeatability, precision, and transferability of the method. Second, important geomorphic and ecological changes in stream habitats are not always manifested as changes in habitat‐unit frequency or characteristics. Third, classification data are nominal, which can intrinsically limit their amenability to statistical analysis. Finally, using the frequency of specific habitat unit types (e.g., pool/riffle ratio or percent pool) as a response variable for stream monitoring commonly leads to the establishment of management thresholds or targets for habitat‐unit types. This, in turn, encourages managers to focus on direct manipulation or replacement of habitat structures while neglecting long‐term maintenance or re‐establishment of habitat‐forming biophysical processes. Stream habitat managers and scientists should only use habitat unit classification to descriptively stratify in‐stream conditions. They should not use habitat unit classification as a means of quantifying and monitoring aquatic habitat and channel morphology. Monitoring must instead focus on direct, repeatable, cost‐efficient, and quantitative measures of selected physical, chemical, and biological components and processes spanning several scales of resolution.
We measured large woody debris (LWD) in 20 known bull trout (Salvelinus confluentus) spawning stream reaches from logged and wilderness watersheds in northwestern Montana. Mean bankfull width of stream reaches was 14.1 m ranging from 3.9 to 36.7 m. Streams were large enough to move LWD and form aggregates. We determined the characteristics of individual pieces of LWD that were interactive with the stream channel. Large, short pieces of LWD attached to the stream bank were the most likely to be positioned perpendicular to stream flow, while large, long pieces either tended to be parallel to the flow or, when attached, were most apt to extend across the channel thalweg. Observations indicated that the majority of pools were formed as scour pools by either very large LWD pieces that were perpendicular to the stream or multipiece LWD aggregates. Among reaches in wilderness watersheds, ratios of large to small LWD, attached to unattached LWD, and with and without rootwads were relatively consistent. However, among reaches with logging in the watershed, these ratios varied substantially. These results suggest that logging can alter the complex balance of delivery, storage, and transport of LWD in northern Rocky Mountain streams, and therefore, the likely substantive change in stream habitats.Résumé : Nous avons mesuré les gros débris ligneux (GDL) dans 20 tronçons de cours d'eau servant de frayères à l'omble à tête plate dans des bassins exploités par l'industrie forestière et des bassins sauvages du nord-ouest du Montana. La largeur moyenne des tronçons à pleins bords était de 14,1 m, avec une fourchette de 3,9 m à 36,7 m. Les cours d'eau étaient assez larges pour que les GDL se déplacent et forment des agrégats. Nous avons déterminé les caractéristiques des morceaux de GDL qui interagissaient avec le chenal. Les morceaux gros et courts attachés à la berge étaient les plus susceptibles de se positionner perpendiculairement au courant, tandis que les morceaux gros et longs se plaçaient parallèlement au courant ou, s'ils étaient attachés, étaient les plus susceptibles de se placer en travers du thalweg du chenal. Les observations ont montré que la majorité des fosses sont le résultat de l'affouillement causé soit par de très gros morceaux de GDL perpendiculaires au courant, soit par des agrégats composés de plusieurs morceaux de GDL. Parmi les tronçons des bassins sauvages, les rapports des gros aux petits GDL, des GDL attachés aux GDL non attachés, des GDL avec et sans attaches racinaires, étaient relativement constants, alors qu'ils variaient considérablement parmi les tronçons des bassins soumis à l'exploitation forestière. Ces résultats permettent de penser que l'exploitation forestière peut altérer l'équilibre complexe de l'apport, de l'installation et du transport des GDL dans les cours d'eau du nord des Montagnes Rocheuses, et donc occasionner des modifications potentiellement importantes des habitats lotiques.[Traduit par la Rédaction] Hauer et al. 924
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.