1.A Overview of Structure and Scale • What are the structural components of a stream corridor? • Why are stream corridors of special significance, and why should they be the focus of 1 restoration efforts? • What is the relationship between stream corridors and other landscape units at broader and more local scales? • What scales should be considered for a stream corridor restoration? 1.B Stream Corridor Functions and Dynamic Equilibrium • How is a stream corridor structured from side to side? • How do these elements contribute to stream corridor functions? • What role do these elements play in the life of the stream? • What do we need to know about the lateral elements of a stream corridor to adequately characterize a stream corridor for restoration? • How are the lateral elements of a stream corridor used to define flow patterns of a stream? 1.C A Longitudinal View Along the Stream Corridor • What are the longitudinal structural elements of a stream corridor? • How are these elements used to characterize a stream corridor? • What are some of the basic ecological concepts that can be applied to streams to understand their function and characteristics on a longitudinal scale? • What do we need to know about the longitudinal elements that are important to stream corridor restoration? 1.A Physical Structure and Time at Multiple Scales 1.B A Lateral View Across the Stream 1 Corridor 1.C A Longitudinal View Along the Stream Corridor stream corridor is an ecosystem that (Figure 1.1). Water and other materials, usually consists of three major ele- energy, and organisms meet and interact ments: within the stream corridor over space and time. This movement provides critical func- Stream channel tions essential for maintaining life such as Floodplain cycling nutrients, filtering contaminants Transitional upland fringe from runoff, absorbing and gradually re- leasing floodwaters, maintaining fish and Together they function as dynamic and wildlife habitats, recharging ground water, valued crossroads in the landscape. and maintaining stream flows. The purpose of this chapter is to define the components of the stream corridor and intro- duce the concepts of scale and structure. The chapter is divided into three subsections. Figure 1.1: Stream corridors func- tion as dynamic crossroads in the landscape. Water and other materi- als, energy, and organisms meet and interact within the corridor. Section 1.A: Physical Structure and stream corridors. The focus here is Time at Multiple Scales on the lateral dimension of struc- An important initial task is to iden- ture, which affects the movement tify the spatial and time scales most of water, materials, energy, and or- appropriate for planning and de- ganisms from upland areas into the signing restoration. This subsection stream channel. introduces elements of structure Section 1.C: A Longitudinal View used in landscape ecology and re- Along the Stream Corridor lates them to a hierarchy of spacial scales ranging from broad to local. This section takes a longitudinal The importance of integrating time view of structure, specifically as a scales into the restoration process is stream travels down the valley from also discussed. headwaters to mouth. It includes discussions of channel form, sedi- Section 1.B: A Lateral View Across ment transport and deposition, and the Stream Corridor how biological communities have The purpose of this and the follow- adapted to different stages of the ing subsection is to introduce the river continuum. types of structure found within 1–2 Chapter 1: Overview of Stream Corridors 1.A Physical Structure and Time at Multiple Scales FAST FORWARD A hierarchy of five spatial scales, which Physical Structure range from broad to local, is displayed Landscape ecologists use four basic in Figure 1.2. Each element within the terms to define spatial structure at a scales can be viewed as an ecosystem particular scale (Figure 1.4): with links to other ecosystems. These Preview Chap- linkages are what make an ecosystem’s I Matrix, the land cover that is domi- ter 2, Section E external environment as important to nant and interconnected over the for a discussion proper functioning as its internal envi- majority of the land surface. Often of the six criti- cal functions ronment (Odum 1989). the matrix is forest or agriculture, but theoretically it can be any land performed by Landscapes and stream corridors are stream corridor cover type. ecosystems that occur at different spa- ecosystems. tial scales. Examining them as ecosys- I Patch, a nonlinear area (polygon) tems is useful in explaining the basics that is less abundant than, and differ- of how landscapes, watersheds, stream ent from, the matrix. corridors, and streams function. Many I Corridor, a special type of patch that common ecosystem functions involve links other patches in the matrix. movement of materials (e.g., sediment Typically, a corridor is linear or elon- and storm water runoff), energy (e.g., gated in shape, such as a stream heating and cooling of stream waters), corridor. and organisms (e.g., movement of mammals, fish schooling, and insect I Mosaic, a collection of patches, none swarming) between the internal and ex- of which are dominant enough to be ternal environments (Figure 1.3). interconnected throughout the land- scape. The internal/external movement model becomes more complex when one con- These simple structural element con- siders that the external environment of cepts are repeated at different spatial a given ecosystem is a larger ecosystem. scales. The size of the area and the spa- A stream ecosystem, for example, has an tial resolution of one’s observations de- termine what structural elements one is input/output relationship with the next Landscapes, observing. For example, at the landscape higher scale, the stream corridor. This watersheds, scale one might see a matrix of mature scale, in turn, interacts with the land- stream corri- scape scale, and so on up the hierarchy. forest with patches of cropland, pasture, dors, and clear-cuts, lakes, and wetlands. Looking streams are Similarly, because each larger-scale more closely at a smaller area, one ecosystems ecosystem contains the one beneath it, might consider an open woodland to be that occur at the structure and functions of the a series of tree crowns (the patches) different spa- smaller ecosystem are at least part of the against a matrix of grassy ground cover. tial scales. structure and functions of the larger. Furthermore, what is not part of the On a reach scale, a trout might perceive smaller ecosystem might be related to pools and well-sheltered, cool, pockets it through input or output relationships of water as preferred patches in a matrix with neighboring ecosystems. Investigat- of less desirable shallows and riffles, and ing relationships between structure and the corridor along an undercut stream- scale is a key first step for planning and bank might be its only way to travel designing stream corridor restoration. safely among these habitat patches. Physical Structure and Time at Multiple Scales 1–3 Region Scale Chesapeake Bay Watershed Landscape Scale Patuxent River Watershed mixed landscape • suburban • agricultural Valley and Ridge • forest cover Region Washington, DC Stream Corridor Scale Patuxent Reservoir Patuxent Stream Watershed Corridor Damascus Brighton Montgomery Co. Stream Scale DC P a t u x e n t R reach i v e r S tate Park Reach Scale Figure 1.2: Ecosystems at multiple scales. Stream corridor restoration can occur at any scale, from regional to reach. 1–4 Chapter 1: Overview of Stream Corridors input environment output environment Figure 1.3: A simple ecosystem model. ecosystem Materials, energy, and organisms move from an external input environment, through N the ecosystem, and into an external out- put environment. At the other extreme, the coarsest of the Structure at Scales Broader Than imaging satellites that monitor the earth’s the Stream Corridor Scale surface might detect only patches or cor- ridors of tens of square miles in area, The landscape scale encompasses the and matrices that seem to dominate a stream corridor scale. In turn, the land- whole region. At all levels, the matrix- scape scale is encompassed by the larger patch-corridor-mosaic model provides a regional scale. Each scale within the hier- useful common denominator for de- archy has its own characteristic structure. Landscape scribing structure in the environment. The “watershed scale” is another form of ecologists use Figure 1.5 displays examples of the ma- spatial scale that can also encompass the four basic trices, patches, and corridors at broad stream corridor. Although watersheds terms to define and local scales. Practitioners should occur at all scales, the term “watershed spatial struc- always consider multiple scales when scale” is commonly used by many practi- ture at a par- planning and designing restoration. tioners because many functions of the ticular scale— stream corridor are closely tied to drain- matrix, patch, age patterns. For this reason, the “water- corridor, and shed scale” is included in this discussion. mosaic. mosaic patch matrix matrix patch Figure 1.4: Spatial patch structure. Landscapes can be described in terms of matrix, patch, corridor, and matrix mosaic at various scales. corridor Physical Structure and Time at Multiple Scales 1–5 BALTIMORE POOL URBAN MATRIX CHESAPEAKE BAY RIFFLE WASHINGTON, DC POOL (a) (b) Figure 1.5: Spatial structure at (a) broad and (b) local scales. Patches, corridors, and matrices are visible at the broad regional scale and the local reach scale. Regional Scale I Major forested areas (e.g., redwood A region is a broad geographical area forests in the Pacific Northwest). with a common macroclimate and I Major metropolitan zones (e.g., the sphere of human activities and interests Baltimore-Washington, DC, metro- (Forman 1995). The spatial elements politan area). found at the regional scale are called I Major land use areas such as agricul- landscapes.