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This study is a broad and critical review of the transdisciplinary literature on the construction of culverts and their impacts on stream hydrology and geomorphology as well as on stream habitats and biota. For engineers, a culvert is a structure, usually of the tunnel type, that transfers a stream or open drain under a road, railway line, or other obstacle from one side to the other. In fact, culverts are complex hydraulic structures whose impacts on stream ecosystems must be evaluated and understood before they are designed. The objective of this paper is to analyse and discuss recent knowledge about culvert functioning in terms of their negative effects on the passage of freshwater biota, particularly fish, and on entire stream ecosystems. We present the results of many studies showing that improperly designed culverts are barriers for migrating animals and usually have serious ecological consequences (mainly disturbances to fish life history). We also pay attention to different culvert modification methods that increase their passability for organisms and mitigate the impacts of culverts on the surrounding environment. The other purpose of this review is therefore to emphasize that the integration of the knowledge and professional experience of biologists and ecologists with those of river managers, river engineers, hydraulic engineers, hydrologists, and geomorphologists is necessary to design culverts that preserve the natural properties of streams. [ABSTRACT FROM AUTHOR]

The circumpolar boreal zone is one of the world’s major biogeoclimatic zones, covering much of North America and Eurasia with forests, woodlands, wetlands, and lakes. It regulates climate, acts as a reservoir for biological and genetic diversity, plays a key role in biogeochemical cycles, and provides renewable resources, habitat, and recreational opportunities. Poor agreement exists amongst scientists regarding this zone’s delimitation and the areal extent of boreal forests, even though the zone has been well-studied. This paper reviews the literature on the phytogeography of the zone and makes use of a geographic information system (GIS) and published maps to delineate a current map of the North American boreal zone and the hemiboreal subzone, which is a transitional area lying immediately to the south of the boreal zone that is usually included in the boreal zone by Europeans but excluded by North Americans. On the basis of the map described here, the boreal zone covers about 627 million ha, or 29% of the North American continent north of Mexico. If the hemiboreal subzone, at 116 million ha, is included, then 34% of the same area is covered. Forests and other wooded land (362 million ha) cover 58% of the North American boreal zone on the basis of current forest inventory data. With forests and other wooded land of the hemiboreal subzone (68 million ha) factored in, this percentage remains basically unchanged. Values reported in this paper are compared with other published statistics. Important sources of error contributing to differences in areal statistics are discussed. [ABSTRACT FROM AUTHOR]

The downstream ecological effects of large impoundments have previously been reviewed; however, little is known about the downstream ecological effects of small man-made impoundments. In this review, we examine 94 papers focusing on the effects of small impoundments on stream habitat conditions and macroinvertebrates. Most studies (89.3%) address the effects of small impoundments on physical and chemical habitat conditions, while fewer studies (48.9%) address the effects on macroinvertebrates. In general, most studies report no significant downstream effects of small impoundments on physico-chemical variables, whereas macroinvertebrates richness and abundance increased or decreased. Mean effect sizes (as Cohen's d) for physico-chemical variables range from −0.82 to 0.68 (small weir: −0.21 to 0.35; run-of-river dam: −0.82 to 0.64; low head dam: −0.49 to 0.68), and from −0.03 to 0.63 for macroinvertebrates abundance and richness. Our assessment of the published literature demonstrates the advantage of combining qualitative and quantitative analyses, and that, while small impoundments may have minimal significant effects on most physico-chemical variables, macroinvertebrates' richness and density may be affected. This review is relevant for management and scientific communities to identify potential alterations of stream habitats and biota by small impoundments. [ABSTRACT FROM AUTHOR]

A review of road-ecology literature suggests that impacts of forest roads on species and ecosystems begin during the road construction phase, but persist and accumulate well after a road is no longer in use. Over this time, impacts stemming originally from construction, but then also from the continued physical presence and human use of the road, follow complex multiple pathways ending in diminished species persistence. Yet in practice, road-impact considerations rarely extend beyond short-term issues related to road construction or beyond the spatial extent of the road corridor. Even when the range of potential impacts is recognized, managers rarely have a framework for assessing those impacts. This can be problematic, as informed decisions regarding the long-term, wide-ranging ecological consequences of road placement, design, and use can lessen the degree to which a road modifies the composition, structure, and function of forest ecosystems. This paper presents a conceptual framework for organizing, synthesizing, and applying our growing understanding of how roads affect forest ecosystems. The framework includes two parts: (1) a series of impact-hypothesis diagrams wherein ecological impacts are organized relevant to three phases of road existence: construction, presence and use; and (2) a five-step approach whereby ecological impact and road importance can be evaluated and a decision matrix used to determine appropriate mitigation strategies. Highlights of a case study conducted in southwestern Nova Scotia are presented to illustrate the applicability of the framework. [ABSTRACT FROM AUTHOR]

Changing the taxonomic scale of a biotic-assemblage dataset influences our ability to detect ecological patterns. In bioassessments, a test-site’s biological community is compared against a benchmark to indicate ecosystem condition, but the taxonomic resolution needed to judge impairment reliably is the subject of much scientific debate. This paper reviews taxonomic sufficiency for freshwater benthic-macroinvertebrate bioassessments. Three main issues are discussed: (1) the ecological significance of different taxonomic aggregations; (2) trade-offs involving taxonomic detail and information content versus money, time, expertise, and data quality; and (3) sampling- and analytical-method-specific factors affecting taxonomic sufficiency. Although Species should be the default taxonomic level for bioassessments, taxonomic sufficiency is chiefly determined by a study’s purpose, and pragmatism often dictates reduced detail. When a taxonomic-minimalism approach is necessary, a quantitative criterion for taxonomic sufficiency should be specified; this criterion should be based on an optimization of cost-benefit trade-offs associated with different taxonomic scales. Mixed-level aggregations, as well as morpho-species and ecological-trait classifications should be considered in this optimization process. Looking to the future, closer ties between taxonomists and bioassessment researchers would benefit both of their disciplines. Such coordination would provide the autoecological information and better diagnostic tools (such as keys and molecular methods) needed for biomonitoring, and better (and more widespread) biomonitoring would fuel taxonomy’s resurgence. [ABSTRACT FROM AUTHOR]

A comprehensive review of Holocene paleoenvironmental data has been prepared, providing the basis for evaluating natural variability in climate and ecosystem dynamics in the northern Columbia River basin. The paleoenvironmental record reveals four major climatic shifts and a number of less well-defined climatic changes throughout the Holocene. The major climate changes are (1) a cool or cold, late-glacial climate at the end of the last glaciation (>11 500 cal. year BP), (2) an interval of drought and maximum summer warmth during the early Holocene (ca. 10500 to 8000 cal. year BP), (3) a mid-Holocene trend towards a cooler, more moist climate (ca. 8000 to ca. 4000 cal. year BP), and (4) a relatively stable climate persisting from ca. 4000 cal. year BP until the arrival of European settlers. Air temperatures have warmed by about 1 °C over the past century. Minor climate events that are emerging as global in nature include Little Ice Age (1200–150 BP) conditions, and a late Holocene cool wet period (3500–2500 BP). These are observed in some study sites examined in this paper and may be related to large-scale cycles of 2800–2000 and 1500 years. A discussion of changing atmospheric circulation patterns, and the causes of long-term climatic change are included, together with a discussion of the implications of the paleoenvironmental record for understanding future climate, and the likely response of communities and ecosystems. [ABSTRACT FROM AUTHOR]