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Ecosystem functioning in small streams and their riparian areas in response to partial harvest riparian management
Marczak, Laurie B.
Forest and stream food webs are widely viewed as energetically coupled, particularly with respect to the contributions of riparian forests to stream ecosystems. Increasingly, researchers are recognizing the reciprocal nature of connections between streams and forest, with streams providing critical inputs to riparian forests [1]. Stream food webs receive important subsidies of energy from terrestrial invertebrate and detrital inputs, downstream transport from small headwaters and spawning migrations. Inputs of particulate organic matter from riparian forests represent an important energy source for stream production [2] while accidental inputs of terrestrial invertebrates are a major prey category directly available for stream consumers such as fish [3]. Conversely, stream ecosystems subsidize forest food webs through emerging aquatic invertebrates that are prey for a variety of terrestrial consumers [4, 5] and as conduits for marine nutrients in the form of salmon carcasses [6-8]. The intent of the proposed research is to clarify the effects of forest harvesting in either disrupting or enhancing the magnitude of subsidies to stream environments and the reciprocal feedback to terrestrial habitats. In recent years, concurrent with an increased awareness of the importance of dynamic functioning of ecosystems, there has been an upsurge of interest in the dynamic consequences of resources subsidies for maintaining ecosystem function and patterns of biodiversity [6, 8-10]. Landuse changes such as forestry can fundamentally alter the flux of materials between terrestrial settings and aquatic systems. It has been clearly shown in a range of habitats that these changes in subsidy quantity or pattern have important effects on patterns of biodiversity [11]. Forest harvesting frequently converts coniferous stands to deciduous forest ? at least in the short term. These forests exhibit considerable variation in their contribution of both falling terrestrial invertebrates and organic matter to streams [12]. At the same time, reforestation efforts that focus on softwoods may result in a decrease in deciduous inputs to streams [13]. Stream canopies may shift towards greater deciduous cover with harvesting and back towards coniferous cover through either natural succession of due to direct reforestation efforts. Although the consequences of timber harvesting for both streams and forest ecosystems have been extensively investigated over the past several decades, less is understood about the consequences of post-harvest forest succession on the connections between stream and riparian ecosystems. Regenerating forests in the coastal region are frequently dominated by red alder (Alnus rubra) and vine maple (Acer circinatum) in addition to quick growing shrubs such as salmonberry (Rubus spectabilis). Although these deciduous trees and shrubs are not considered valuable from the perspective of either timber production or as a source of wood for fish habitat, red alder in particular has the potential to alter both terrestrial productivity [14] and diversity [15] as well as stream productivity and diversity [13, 16]. Wipfli [10] and Allan [12] found that red alder may provide greater inputs of terrestrial invertebrates to drift-feeding fishes than systems with little alder. Alder leaf litter to streams is more nutritious and more quickly broken down than similar coniferous material [14] and streams flowing through areas with a deciduous canopy tend to export greater absolute quantities of aquatic invertebrates during emergence than similar streams under deciduous canopies [Richardson unpublished data, 17]. Current provincial guidelines for timber harvest recognize the need for protection along fish-bearing or drinking water streams. Streams without fish or streams less than 1.5m wide at bankfull currently receive no mandatory riparian reserves during harvesting [18]. Not only do these streams typically drain into lower salmon-bearing reaches, they ...
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Executive Summary
Canopy Conversion Effects (Poster)

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