The evolution and maintenance of white spruce woodlands on the Mackenzie Delta, N.W.T., Canada

Abstract

White spruce forests on the most elevated surfaces of the Mackenzie Delta are dying out and are being replaced by open spruce/lichen‐heath or spruce/bog woodlands. Soil profiles indicate that these woodlands have not received flood‐deposited sediments for many years. The active layer is only 20 to 50 cm deep by mid‐summer, and the organic soils are colder and more acidic than soils under white spruce forests flooded during spring ice breakup in 1961, 1972, and 1982. Spruce regeneration is limited to those stands that are flooded periodically, have moderately‐closed canopies, and have a ground cover of herbs rather than feathermosses and lichens. It is proposed that a decrease in flood frequency is primarily responsible for the poor regeneration of white spruce on the most elevated delta surfaces. Spruce woodlands on the delta could succeed to tundra vegetation if present fluvial regimes continue.

Treeline (Pinus sylvestris) landscape evolution in the Swedish Scandes – a 40-year demographic effort viewed in a broader temporal context

“…Pearce et al 1988;Ågren & Zackrisson 1990). In the present case study, it appears that the net population curve (Fig.…”

Climatic Signals in δ13C and δ18O of Tree-rings from White Spruce in the Mackenzie Delta Region, Northern Canada

“…Old-growth spruce forests develop on delta surfaces that have been cryostatically uplifted above the level of regular flooding (Kokelj and Burn, 2005). Fire has an important ecological role in boreal forests (Black and Bliss, 1978), but wildfire in the Mackenzie Delta is rare resulting in the development of old-growth forests and preservation of standing deadwood (Pearce et al, 1988;Kokelj and Burn, 2004).…”

Cessation of ice-wedge development during the 20th century in spruce forests of eastern Mackenzie Delta, Northwest Territories, Canada

“…Ecological succession on the alluvial surfaces of the Mackenzie Delta is related to flooding frequency and sedimentation, which decline with increasing terrain elevation (Gill 1972;Pearce et al 1988). In turn, soil microclimate, permafrost temperatures, and near-surface ice contents vary among ecological communities (Smith 1975;Kokelj and Burn 2005 of forest succession has been described by Pearce et al (1988).…”

“…In turn, soil microclimate, permafrost temperatures, and near-surface ice contents vary among ecological communities (Smith 1975;Kokelj and Burn 2005 of forest succession has been described by Pearce et al (1988). The first stage of forest succession is the spruce-alder and bearberry (SAB) (Picea-Alnus-Arctostaphylos) association that establishes on alluvial surfaces above the level of annual flooding (Pearce et al 1988). The terrain is characterized by the presence of a thick active layer and warm permafrost due to absence of an insulative surface organic horizon and to a deep snow cover in winter (Table 1).…”

“…While alluvial surfaces aggrade, SAB associations are replaced by spruce-feathermoss (SF) (Picea-Hylocomium) communities as flooding frequency decreases, surface organic matter accumulates, and the active layer thins (Table 1) (Gill 1973;Smith 1975;Pearce et al 1988). Infrequent flooding and low sedimentation rates (<1 cm a -1 ) enable a thick moss cover to establish.…”