Balsam poplar [Populus balsamifera). — 

 This species forms essentially pure stands on re- 

 cently deposited alluvium. (Northern black Cot- 

 tonwood is considered a part of this general 

 type.) Following fires, balsam poplar may in- 

 vade upland areas beside large streams. It may 

 occupy flood plains indefinitely if they frequently 

 receive new deposits of silt. However, on stable 

 sites white spruce gradually gains dominance. 

 As small trees the poplars are subject to fire 

 damage, but above 30 feet in height they be- 

 come well pruned and are progressively less 

 susceptible to fire damage; as a bottomland type 

 it does not comprise a true fire hazard. 



Willow-alder [Salix spp. -Alnus spp.). — 

 Such a complex is not necessarily related to the 

 early stages of succession, but it is included with 

 the other hardwood stands. Willow is found 

 along banks of rivers and intermittent streams 

 and extends to the treeless plains of the Arctic. 

 Alder is found along rivers and at brush lines on 

 mountain slopes. These two species do not tend 

 to carry fire unless extremely dry weather prevails 

 and high winds are blowing. When they do 

 burn, they burn hot and thus increase the resis- 

 tance to control. 



SECONDARY STAGES IN FOREST SUCCESSION 



White spruce-paper birch (Picea glauca- 

 Betula papyrijera.). — This type is more ad- 

 vanced than either the paper birch or quaking 

 aspen types. It may develop immediately after 

 fires or it may result from gradual entry of white 

 spruce into an originally paper birch stand. Bar- 

 ring disturbance, a pure relatively open spruce 

 stand will result. Fire tends to perpetuate the 

 birch but reduce the spruce. The horizontal and 

 vertical continuity of fuel, accompanied by the 

 flammable birch bark, causes this type to be 

 very susceptible to high rates of fire advance, 

 both along the ground and into and through 

 the tree crowns. 



White spruce-quaking aspen. — Develop- 

 ment of this type is analogous to that of the 

 white spruce-paper birch type except that aspen 

 dies out rapidly at about 60 years, while birch 

 will remain for 100 to 130 years. The aspen is 

 reestablished easily after a fire, chiefly because 

 of its capacity to produce root suckers. 



CLIMAX FORESTS 



White spruce [Picea glauca). — White spruce 

 becomes climax on well-drained land. Young 

 stands are usually even-aged, but may become 

 uneven-aged with maturity. White spruce fol- 

 lowing immediately after a fire tends to be 

 dense, but if it develops as a replacement of 

 aspen, birch, or poplar it is likely to be relatively 

 open. It is probably longer lived than other trees 

 in Interior Alaska; ages up to 300 years are not 

 uncommon. An occasional tree may attain a 28- 

 inch diameter and a height of 90 feet. However, 

 an average-sized tree would be more nearly 14 

 inches in diameter and 70 to 80 feet in height. 



Single, light surface fires do not destroy the 

 stand but create openings for the invasion of 

 hardwood species. Repeated severe fires may 

 cause an area to become essentially treeless, 

 supporting only herbaceous or shrub communi- 

 ties, sometimes developing into an aspen or 

 birch stand. Revegetation following fire is 

 rapid; bare areas are rarely seen. The out- 

 standing effects of fires are that (1) most 

 amounts of existing timber are destroyed and 

 (2) the subclimax types (principally quaking as- 

 pen and paper birch) are, at least temporarily, 

 greatly increased at the expense of the white 

 spruce type. 



In a white spruce stand the trees have 

 heavy, narrow crowns extending to the ground, 

 except trees in mature stands may often have 

 the lower limbs pruned. On dry slopes and in 

 the higher benchlands, white spruce tends to be- 

 come an open woodland type of growth, where 

 shorter height, broader crowns, and branches 

 extending to the ground tend to persist through 

 maturity. In open stands grass, dwarf birch, 

 Laborador tea, and sedges are typical, as is a 

 heavy continuous ground cover of moss. In dense 

 stands, moss may be heavy along with needles, 

 branchwood, and species of Vaccinium. 



Black spruce [Picea mariana). — Black spruce 

 can be termed a physiographic climax. It grows 

 on poorly drained areas in relatively flat valley 

 bottoms, on flat to gently rolling land, and on 

 cold slopes having a northern exposure. It forms 

 pure stands of usually small, slow-growing trees. 

 Permafrost is often found at depths of only 12 



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