Classification of vegetative lagg types and hydrogeomorphic lagg forms in bogs of coastal British Columbia, Canada

Key Messages A classification scheme was developed for laggs (marginal transition zones) of bogs. Regional differences in vegetative lagg types were observed. Half of the studied laggs differed from the classic notion of a lagg as being topographically confined. A “lagg” is usually defined as the confined transition zone along the outside margin of a raised bog, characterized by a fen or swamp plant community. It is an important landscape element for biodiversity and helps to maintain a high water table within the peat mass of a bog, but has received little research attention. Greater knowledge of the variability in laggs will improve designation of appropriate conservation sites and restoration of damaged bogs. We therefore examined the hydrological, hydrochemical, vegetative, and peat characteristics of laggs of bogs in coastal British Columbia, Canada. The 17 studied lagg transects were classified into four vegetative lagg types: Spiraea Thicket, Carex Fen, Peaty Forest, and Direct Transition. These vegetative lagg types fell within two hydrogeomorphic lagg forms: confined or unconfined. The Spiraea Thicket and Carex Fen laggs were topographically confined at the bog margin and characterized by a higher water table and a smaller tree basal area compared to the unconfined Peaty Forest and Direct Transition laggs. Half of the studied laggs were unconfined, highlighting the importance of considering both confined and unconfined laggs in the delineation, conservation, and restoration of raised bog ecosystems. La classification des types végétatifs de marécage bordier et des formes hydrogéomorphiques de marécage bordier dans les tourbières de la côte de la Colombie‐Britannique, Canada Un « marécage bordier » est compris de manière générale comme la zone de transition confinée le long de la berge extérieure d'une tourbière ombrotrophe qui se distingue par un marais ou une communauté composée de plantes marécageuses. Cette composante primordiale du paysage contribue à la biodiversité et au maintien d'une nappe phréatique élevée dans l'étendue de tourbe d'une tourbière. Pourtant, elle a suscité peu d'intérêt auprès des chercheurs. L'approfondissement des connaissances de la variabilité des marécages bordiers apportera un éclairage sur les modes de sélection des sites de conservation appropriés et de restauration des tourbières endommagées. La présente étude a donc porté sur les divers aspects liés à l'hydrologie, l'hydrochimie, aux végétaux et à la tourbe des m