Ministry of Environment Sensitive Ecosystems Inventories

Riparian Ecosystems of Eastern Vancouver Island and the Gulf Islands

Riparian ecosystems occur on floodplains adjacent to lakes, streams and rivers where high soil moisture and light conditions support distinct soils and plant communities. They vary in width from less than one metre along stream banks to more than 100 metres near large rivers.

The Sensitive Ecosystems Inventory classifies Riparian ecosystems into riparian gullies (RI:g) and seven structural stages of floodplain vegetation based on age and structure of dominant vegetation. The seven structural stages include: sparsely vegetated areas and gravel bars (RI:1); herb dominated areas (RI:2); shrub/herb dominated areas (RI:3); deciduous pole/sapling stands (RI:4); young deciduous forest (RI:5); mature coniferous-deciduous forest (RI:6); and older forest (RI:7). Riparian units often occur as a complex of more than one stage.

Riparian ecosystems comprise 1.6% of the entire SEI study area and 20.6% of the total area. They are more commonly found in the Nanaimo and Comox-Strathcona Regional Districts.

Values and Ecological Attributes of Riparian Ecosystems

Riparian ecosystems support a disproportionately high number of vascular plant, moss, amphibian and small mammal species for the area they occupy. Structurally diverse forest features, such as snags, downed logs and a multi-layered/uneven-aged canopy, offer a concentration of varied habitat niches. In addition, their association to rivers and streams, and surrounding coniferous forests create specific microclimates and habitats preferred by certain species. Although fragmented, riparian ecosystems may still function as important wildlife corridors due to their linear nature.

Riparian ecosystems play important roles in aquatic habitat protection. The variety of dense vegetation provides shade, bank stability, and increased channel habitat to streams and rivers. Floodplains act as storage sites for surface water, protect river channels and reduce erosion by regulating rainfall run-off. Soil microorganisms and vegetation in riparian ecosystems filter out harmful sediment and nutrient from agricultural fields.

Conservation Concerns of Riparian Ecosystems

Direct impacts such as logging, land development, river engineering and floodplain filling are responsible for the damage to or removal of riparian vegetation.

Deforestation activities and increased impervious surfacing are indirect impacts which can cause significant increases in the size, duration and frequency of flood events. Such changes in hydrologic regime accelerate bank erosion and influence the replacement of coniferous trees with flood tolerant species.

Climate change is potentially the most devastating cumulative impact affecting Riparian ecosystems on the east coast of Vancouver Island.