Riparian Zone

by

Futoshi Nakamura

• LAST REVIEWED: 15 January 2020
• LAST MODIFIED: 15 January 2020
• DOI: 10.1093/obo/9780199363445-0007

Introduction

The word “riparian” is derived from the Latin word “riparius,” meaning of or belonging to the bank of a river. “Riparian zone” refers to a broader zone spanning from the riverbank to the floodplains; it occasionally includes hill slopes that may influence the stream ecosystem. The term can also be used to describe wetlands and lakeshores. In this article, however, the discussion is confined to areas associated with stream/river courses, although some principles are applicable to other riparian ecosystems and their management. A riparian zone extends from headwater streams to lowland rivers (longitudinally), from surface waters to groundwater (vertically), and from stream banks to hillside slopes (transversely). A riparian zone consists of diverse, dynamic, and complex biophysical landscape elements that provide essential habitats for various terrestrial and aquatic organisms in all or specific stages of their life cycles. Thus, biodiversity in a riparian zone is generally higher than in upland ecosystems, and riparian habitat specialists increase the entire regional biodiversity (gamma diversity) at the watershed scale. Ecological functions (or ecosystem services) of the riparian zone have been studied since the early 1970s. Appropriate riparian buffer width has also been discussed with respect to creating guidelines for stream conservation. Currently, a riparian zone is defined as an aquatic and terrestrial interface or ecotone, emphasizing its ecological functions. Productive riparian forests have been harvested for timber production in headwater basins and deforested by farmland development and cattle grazing in alluvial floodplains. Additionally, riparian forests have been removed for channelization and road construction, which decreases buffering and shading effects. As a result, sediment, fertilizers, pesticides, and other contaminants pollute streams and rivers, which also experience increases in water temperature. These abiotic changes collectively exert detrimental effects on fish and other aquatic organisms. Today, the riparian zone is recognized as a key ecotone for watershed management; therefore, the conservation and restoration of these zones are discussed in the context of ecosystem management at the landscape level.

Papers

Riparian zones can be defined in various ways, which sometimes causes confusion for scientists and the general public. The simple definition is “areas associated with water courses,” but our current understanding of riparian zones is much more complex. Fluvial geomorphologists and hydrologists may define riparian zones as areas inundated by floods or simply as bars, banks, and floodplains. Plant and animal ecologists may focus on the structure and composition of riparian flora and fauna and the habitat dynamics maintaining their life cycles. Swanson, et al. 1982 is the first work to define the riparian zone from the perspective of ecological functions, describing it as an area in which biological, physical, and chemical interactions between aquatic and terrestrial ecosystems occur. Thus, it forms three-dimensional zones of direct interactions that extend outward to the limits of flooding, upward into the canopy of streamside vegetation, and down into the groundwater system (see Ecological Functions). Gregory, et al. 1991 extends the concept of Swanson, et al. 1982 by including the spatial and temporal patterns of hydrologic and geomorphic processes, terrestrial plant succession, and aquatic ecosystems. The authors of Naiman and Decamps 1997 further developed their concept of a riparian zone as an interface or ecotone that controls energy and material exchange between terrestrial and aquatic ecosystems and that maintains dynamic environments critical for various organisms. Thus, the current definition of a riparian zone and a basic knowledge of its structure and function are founded on the efforts described above in the 1980s and 1990s. In publications since 2000, Benda, et al. 2004 discusses the riparian zone in the contexts of stream networks and disturbance regimes at the watershed scale, and Amoros and Bornette 2002 discusses the connectivity of diverse wetlands and waterbodies that maintain biodiversity and ecosystem services.

• Amoros, C., and G. Bornette. 2002. Connectivity and biocomplexity in waterbodies of riverine floodplains. Freshwater Biology 47:761–776.

  DOI: 10.1046/j.1365-2427.2002.00905.x

  A good review for understanding connectivity in river-floodplain landscapes. The lateral (river and floodplain) and vertical (surface and groundwater) hydrological connectivities and their effects on diversity of stream biota are discussed.

• Benda, L. E., N. L. Poff, D. Miller, et al. 2004. The network dynamics hypothesis: How channel networks structure riverine habitats. BioScience 54:413–427.

  DOI: 10.1641/0006-3568(2004)054[0413:TNDHHC]2.0.CO;2

  Hypotheses raised in this paper address how basin size, basin shape, drainage density, and network geometry influence the diversity of riparian and stream habitats. Roles of channel confluences in a stream network are emphasized in a fluvial geomorphic context.

• Gregory, S. V., F. J. Swanson, W. A. McKee, and K. W. Cummins. 1991. An ecosystem perspective of riparian zones. BioScience 41:540–551.

  DOI: 10.2307/1311607

  A highly cited review paper that first synthesized a diverse array of ecosystem functions of riparian zones. A well-organized, geomorphic template of riparian zone and ecological processes is provided.

• Naiman, R. J., and H. Decamps. 1997. The ecology of interfaces: Riparian zones. Annual Review of Ecology and Systematics 28:621–658.

  DOI: 10.1146/annurev.ecolsys.28.1.621

  Another highly cited review paper on riparian zones. It encompasses life-history strategies of riparian plants, ecological functions, and the provision of diverse habitats for various animals.

• Swanson, F. J., S. V. Gregory, J. R. Sedell, and A. G. Campbell. 1982. Land-water interactions: The riparian zone. In Analysis of coniferous forest ecosystems in the western United States. Edited by Robert L. Edmonds, 267–291. US/IBP Synthesis Series 14. Stroudsburg, PA: Hutchinson Ross.

  The first review providing a functional definition of a riparian zone. Most currently acknowledged functions are discussed in this review; a riparian zone in coniferous forests of the Pacific Northwest, United States, is the focal ecosystem.