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spatial arrangement of plants, or forest structure (Franklin and Dyrness, 1973; Figure 61). Typically, the initial grass/forb stage lasts about 5 years. By this time the shrubs stand tall enough to overtop and overshadow the Forests herbs, which soon wither and die in the darkness. The shrubs live 20–25 Figure 61. Structural Trends during Forest Succession 1 Logs and snags remain from previous stand. 2 Young trees recruit with several shrub species. 3 The next generation of trees dominates after about 20 years. 4 Mortality of canopy trees allows the development of understory trees and shrubs. 5 A multi-layered canopy and many age classes of logs and snags are hallmarks of old growth.(Kellerman)

Figure 61. Structural Trends during Forest Succession 1 Logs and snags remain from previous stand. 2 Young trees recruit with several shrub species. 3 The weight, next generation of trees after 20 years. 4 Mortality of the first herbs to appear are typically those present in the gain and thereby raisedominates the biomass ofabout the site. Nutrient areas, canopyfrom treesthe allows the development ofto understory trees and shrubs. 5 A forest, because seeds blow in from nearby sites. By the uptake soil must be initially high support the increase original multi-layered canopy and many age classes of logs and snags are hallmarks of inold biomass. Since photosynthesis occurs only in the leaves and second year, the site will have welcomed a cloud of windborne growth.(Kellerman) green stems, the slow rise in foliage biomass mirrors a slow rise seeds from distant weedy plants, which soon dominate. In the in gross primary production. These both peak at about 50 years hemlock zone, these include woodland groundsel (Senecio (in the young forest stage), and then level off. Meanwhile, wood sylvaticus), fireweed (Epilobium angustifolium), bull thistle biomass continues to rise with the growing branches, trunks, (Cirsium vulgare), and bracken fern (Pteridium aquilinum) (Franklin and roots, and levels off only after 400-600 years. So though and Dyrness, 1973). Some of the shrubs that dominate after gross production stays constant, net production actually drops the fifth year are residual, such as vine maple (Acer circinatum), because the trees burn more and more sugars simply to keep trailing blackberry (Rubus ursinus), and Oregon grape (Berberis the enlarging trunks and branches alive (Franklin, et al., 1981). nervosa), while others are invaders (willows and snowbrush). Net production reaches a minimum when the wood biomass Moisture conditions often control this sequence. In dry areas levels off. [. . .] in the hemlock forest, the commonest seral (= transient Structure successional) shrubs are salal, Douglas fir, and sometimes These functional trends underly some simple adjustments in the bigleaf maple (Franklin and Dyrness, 1973). Medium-wet seral spatial arrangement of plants, or forest structure (Franklin and communities are shrubbier, with dense tangles of huckleberry Dyrness, 1973; Figure 61). Typically, the initial grass/forb stage (red and evergreen), salmonberry, and salal. Moist to wet areas lasts about 5 years. By this time the shrubs stand tall enough almost always grow red alder, salmonberry, and sword fern in to overtop and overshadow the herbs, which soon wither and seral communities, and often vine maple and thick-leaved lotus. die in the darkness. The shrubs live 20-25 years, until a legion Sometimes western hemlock and western redcedar appear of equal-aged, evenly spaced trees overtops them. From this from the very beginning and remain through to the climax stage; time on, the dense canopy blocks the sun and nearly eliminates other times the hemlock does not appear until after 50 to 100 the understory. The canopy dominates until the forest becomes years but eventually takes command because it reproduces old growth. At this time, an occasional old, decadent tree blows better under shade than nearly all other Northwest forest trees. down, opening the canopy and inviting sunlight to stream to the Western redcedar tolerates slightly less shade than western forest floor. A community of herbs and shrubs springs up in this hemlock, and remains through the climax stage only in wet- to pool of light, and eventually a quiltwork of patchy understory very wet sites. [. . .] emerges in the mosaic of sunlight wrought by randomly windblown trees.

Forest Function, Structure, and Habitat

Composition The kinds and numbers of herbs and shrubs that first appear after a disturbance in any forest zone depend on the type of disturbance, environmental conditions (especially moisture), and the kinds of seed available and hence nearby plants. On clearcut

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The inhabitants of a forest live sheltered lives. The blanketing canopy shields them from the sun and wind, traps heat, raises humidity, conserves moisture in and above the soil, and hastens the buildup of nurturing carbon dioxide. Old growth is especially comfortable because its age grants it not just one but several

Profile for University of Puget Sound

Bookends Reader  

Welcome new students! This reader is a collection of readings from and about Puget Sound and that will be at the heart of the Bookends orien...

Bookends Reader  

Welcome new students! This reader is a collection of readings from and about Puget Sound and that will be at the heart of the Bookends orien...