A stand of Quercus garryana (30% canopy cover) above The Dalles Oregon on the Co

Question

A stand of Quercus garryana (30% canopy cover) above The Dalles Oregon on the Columbia River with an understory of Pseudoroegneria spicata ssp. spicata (35% canopy cover), and Bromus tectorum (70% canopy cover). Similar stands can be found across the Columbia River in south-central Washington. a. What is the PNV classification hierarchy (continental formation to plant association) for the stand? b. What is the NVCS classification hierarchy (class to plant association) for the stand? c. Stands of this ecosystem type occasionally have a few individuals of Pinus ponderosa, but this species never occurs as an abundant species in the community. What does this suggest about the character of the effective environment of sites dominated by this plant association?

Explanation / Answer

Tree canopy is the layer of leaves, branches, and stems of trees that cover the ground when viewed from above. Quercus garryana, or the Garry oak/ Oregon white oak is a tree species that grows from sea level to 210 meters (690 ft) altitude in the northern part of its range, and at 300 to 1,800 meters (980 to 5,910 ft) in the south of the range in California. Here on the Dalles Oregon on the Columbia River it occupies 30 % canopy cover. Pseudoroegneria spicata is a species of grass that occupies 35 % canopy cover. Bromus tectorum is an winter annual grass native to Eurasia usually germinating in autumn, overwintering as a seedling, then flowering in the spring or early summer.

The National Vegetation Classification is a hierarchical system designed to classify existing vegetation (i.e. plant cover, floristic composition, and vegetation structure occurring in a specific place at a specific time) on the basis of both physiognomic and floristic criteria. The upper levels of the classification adepend on growth form, structure, and cover, while the lower levels are floristic, based primarily on species composition and abundance. The middle-tiered levels are based on a combination of physiognomic and floristic characteristics.

Here Quercus garryana forms the upper level, Bromus tectorum forms the middle level and Pseudoroegneria spicata ssp. spicata forms the lower level.

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