Morphology

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Description

More info for the terms: mesic, shrub, tree

This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available [60,63,64,67,91,98].

Pacific dogwood is a native, deciduous, multi-branched tree, sometimes considered a shrub. Average mature-height estimates range from 20 to 75 feet (6.1-22.9 m) and canopy spread is often 20 feet (6.1 m) [60,64,76,83,85,104]. Young bark is thin and smooth, but ridges develop later making the trunk appear scale like [23,98]. The maximum trunk diameter reported for Pacific dogwood was 24 inches (61cm) [67]. The root system, commonly a taproot, penetrates deeply [67].

The growth form of Pacific dogwood may change with site conditions. When grown under a canopy of vegetation, the trunk is normally tapered and the crown is slender and short. When developed under a sparse canopy or in the open, the trunk is typically shorter, and the rounded crown can be as wide as it is tall [67]. Pacific dogwood branches have fine hairs and bear simple, opposite leaves that measure between 2 and 5 inches (5.1-12.7 cm) long by 1.5 to 2.8 inches (3.8-7.1cm) wide [11,60,64,67,91,98]. Leaves are hairier on the underside but have stiff appressed hairs above [60,91]. Pacific dogwood bears 2-seeded drupe fruits that are 1 to 1.5 cm long [63,64,91,98]. Commonly each drupe is comprised of 20-40 drupelets that are slightly flattened from being held in a tight cluster; contained seeds are smooth [67,91].

As a subcanopy species, Pacific dogwood has several shade growing adaptations. At 1/3 full sunlight, Pacific dogwood maintains maximum photosynthetic potential [11]. Branches are self-shading; leaf petioles orient downward allowing leaves to rest on and shade the branches. Although the trunk of Pacific dogwood can be damaged by direct sunlight [84,104], established plants may initiate shoot growth from the crown to shade and protect the exposed trunk [104].

Although typically considered a mesic species, Pacific dogwood is quite drought tolerant. The osmotic potential at zero turgor is -2.2 MPa; leaves begin to lose turgor pressure at 16-18% relative water deficit [108].

Botanical characteristics are altered when plants are infected with dogwood anthracnose, a nonnative fungal disease caused by Discula spp., common in Pacific dogwood [22,24,30,31,32]. Fungal activity is usually greatest from May through early July. However, the fungus can be active any time conditions are moist and plants are growing [24]. Infected leaves develop blotches and often drop early. Defoliation can be extreme. Twigs with this fungal disease are depressed in spots and allow the fungus to progress into leaf buds, killing them and setting back spring emergence [32]. Seed production diminishes with anthracnose infection [38]. This fungal disease is considered threatening to native Pacific dogwood populations because of its rapid spread and severe effects [25]. Control measures have been described by many [24,30,31,32].

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