The Alaska Vegetation Classification - Alaska Geobotany Center ...

LA. 1.1. Closed Black Spruce-White Spruce ForestDescription-These stands have tree coverof more than 60 percent that is almost entirelycontributed by black spruce and white spruce(fig. 9). These are slow-growing stands, andthe trees rarely exceed 25 centimeters (10 in)d.b.h. and 24 meters (75 11) tall, even at 100to 200 years of age. White spruce is oftenolder and larger than the black spruce inthese stands. A few paper birch trees may bepresent, but they do not provide significantcover. Reproduction is usually abundantand primarily black spruce, but occasionallynumerous white spruce seedlings occur. Onsome sites, reproduction may be nonexistentor consist of only a few birch seedlings.The shrub layer generally is weakly developed.Alnus crispa and willows severalmeters tall usually are present. Other understoryshrubs growing less than 1.5 metersFigure 9-Closed needleleal forest of mixedblack and white spruce with Equiserurnarvense, E. prafense, and the mossesHylocornium splendens and Rhylidiadelphuslriquelrus in the herb and moss layers.(5 ft) tall include Rosa acicularis, Viburnum edule, Ledumgroenlandicurn, Vacciniurnuliginosum, V. vitis-idaea, Ribes spp., and sometimes Empetrum nigrum. Equisetumsylvaficum frequently dominates the ground layer of flood-plain stands. Cornuscanadensis and Linnaea borealis are common herbs. A thick layer of feathermossesusually is present, generally dominated by Rhytidiadelphus triquetrus and Hylocorniurnsplendens. Sphagnum spp. may be important locally.Phases-At high elevations, Betula nana and Arctostaphylos rubra may be importantshrubs. Aulacomniumspp. and fruticose lichens dominate the moss and lichen layer.Distribution and site characteristics-Closed black spruce-white spruce forestsare common near the northern and western limits of trees, on flood-plain terraces ininterior Alaska, and at the bases of south-facing slopes. Soils generally are poorlydrained silts with a surface horizon about 10 centimeters (4 in) thick that is overlainby a decimeter or two of organic remains and the living moss mat. Soil pH is usuallyslightly acid (6.5) to neutral. Permafrost is often present at depths of 50 to 60 centimeters(20 to 24 in). These communities occasionally are found on moderatelywell-drained soil, but permafrost is almost always present.Successional status-On flood-plain terraces, these communities generally aretransitional between closed white spruce stands on well-drained soils of the youngerterraces and open black spruce stands on poorly drained soils of older terraces. Soilorganic matter, depth to permafrost, and drainage are intermediate between thewhite spruce and black spruce communities.Closely related types-Closed black spruce-white spruce stands can resembleboth open and closed stands of both white spruce forest and black spruce forest,depending on the proportion of the two species and the density of the tree cover.Photographs-Viereck 1970a, figure 5; figure 9, this publication.Primaty references-Viereck 1970a, Viereck and others 1983, Yarie 1983.67