Riparian areas in the Canadian boreal forest and linkages with water quality in streams

Abstract

Riparian areas in the Canadian boreal forest represent the transition zone between terrestrial and aquatic ecosystems. We review factors that influence riparian vegetation communities and the associated interactions with boreal streams. Regional and local drivers (e.g., climate, edaphic factors, and natural disturbances) that affect upland boreal vegetation also operate in riparian areas. However, the proximity of riparian areas to the stream channel not only modifies some of these drivers, but it means that the stream itself becomes a driver of riparian vegetation dynamics. For example, hydrological disturbances like flooding and ice scour affect soil texture and alter successional pathways, sometimes completely denuding streambanks of vegetation. Even in riparian areas unaffected by such catastrophic disturbances, saturated soil conditions can influence riparian forest composition and nutrient cycling. Saturated soils support lower mineralization rates, therefore organic layers store relatively more carbon and nitrogen than adjoining upland soils, and primary productivity is generally lower. Saturated soils also have implications for the ability of the riparian area to “buffer” streams from inputs of water and nutrients. For example, reducing conditions in riparian soils could be the sites for nitrate removal from groundwater by denitrification. Spatial variation in weather, soils, vegetation cover, slope, accumulation of organic matter, geographic location, and relief undoubtedly add to the complexity of understanding the role of riparian systems in Canada’s vast boreal forest. However, the opportunity to identify patterns relating to riparian areas will assist in our understanding and management of these multifaceted systems.