Riparian vegetation patterns and links with surface waters in the boreal forest

Riparian areas in the Canadian boreal forest represent the transition zone between terrestrial and aquatic ecosystems. Factors that influence riparian vegetation communities and the associated interactions with boreal streams were reviewed. Regional and local drivers (e.g., climate and site hydrology) 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 surface and subsurface 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, 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 understanding and management of these multifaceted systems.;Among forested settings, riparian areas have been identified as having the most diverse vegetation, yet riparian communities seem to be among the least studied. The Forest Watershed and Riparian Disturbance project, a small watershed project initiated on the Boreal Plain, provided an opportunity to examine riparian diversity. The study design consisted of pre-harvest/reference, one year post-harvest, and six year post-fire data collection and included: two mature stand types (deciduous: Populus tremuloides and Populus balsamifera and coniferous: Pinus contorta and Picea mariana), three vegetation communities (riparian, transition, and interior forest) inventoried for four layers (ground vegetation (<1 m), shrubs (1 to 3 m and >3 m), and trees), and four treatments ('cut-toshore', 30 m buffer, fire, and pre-harvest/reference sites). Three transects with plots for all vegetation layers were established for 22 sites. Species inventory was used to calculate species richness (number of individual species) which was then subject to analysis. Overall, deciduous stands were more species rich when compared to coniferous stands. Pre-harvest/reference species richness for the: (1) deciduous stands for all vegetation layers remained relatively constant for the three communities, (2) coniferous stands for ground vegetation and shrub layers decreased from riparian to interior forest communities, (3) deciduous tree layers remained relatively similar for the three communities sampled, and (4) coniferous tree layers increased from riparian to interior forest communities. Post-treatment species richness for the: (1) tree layer of both stands in transition and interior forest communities decreased one year post-harvest under cut-to-shore conditions, (2) deciduous shrub > 3 m and 1 to 3 m layers decreased one year post-harvest under cut-to-shore conditions in interior forest, and riparian and transition communities respectively, (3) tree layer of both stands under buffer conditions is maintained in interior forest communities and in transition communities of coniferous stands when compared to cut-to-shore conditions, (4) ground vegetation layer of both stands under buffer conditions is maintained in interior forest communities when compared to cut-to-shore conditions, (5) coniferous stands appear to have re-established in all layers of as well as in shrub layers of deciduous stands six years post-fire, (6) tree, tall shrub, and ground vegetation layers of coniferous communities were generally less than that found in deciduous communities six years post-fire, and (7) ground vegetation layer for both stands appeared to be uniformly well established six years post-fire.;Keywords: Boreal forest; Buffers; Disturbance; Riparian area; Specie richness, Streams; Vegetation dynamics...