The ecology of Atlantic white cedar wetlands - USGS National ...

stands, the mature cedar has a long, clear, almostcyiindrical bole which rapidly tapers within a shortcrown. The crown in dense stands is typically shorl,narrow, and conical, usually covering the upper 30%of the trunk. Open-grown trees are more tapered,with longer crowns and more limbs than those growingin a dense stand (Korstian and Brush 1931).The root system of C. thyoides is shallowand spreading, penetrating only the upper 0.3 to 0.6rn of peat when the substrate is permanentlysaturated. Roots extend deeper when the watertable is not as near the surface.The mature leaves are flat, small, overlappingscales with a prominent resin gland andnumerous ring structures. The microscopic structureof cones, leaves, seeds, and pollen is describedby Belling (1 987).Atlantic white cedar is monoecious, but thestaminate (male) and pistillate (female) flowers areproduced on separate shoots. t lower buds areformed in spring in the Virginia-North Carolina area(Korstian and Brush 1931) and in summer in southernNew Jersey (Little 1941). When mature, the foursided,oblong, brown staminate flowers are about 3mm long. The pale green 3 mm-wide pistillateflowers are borne on short lateral branchlets of terminalshoots (Korstian and Brush 1931)(Figure 19).Pollen. Pollen grains are spheres 21 to 24pm in diameter with an outer sculptured wall. As thepollens of C. thyoides, arbor-vitae (l'huja occidentalis),and red cedar (Juniperusvirginiana) are superficiallyindistinguishable in form (Belling 1977, 1987),the three species have been recorded by palynologistsas "cedar" (Cupressaceae) despite their significantdifferences in habitat.The light-green angular six-sided cones maturein early autumn and become dark red-brown thefollowing year.Seeds. The 3 mm-long, flat, rounded seedsare encircled by a darker winged membranous margin.There are ca. 1,014,000 seedslkg; the averageweight per thousand is 0.96 g.3.2 SILVICAL HABITS3.2.1 Seed Pr-. .-. The onset of seed productionvaries greatly with environmental conditions: theclimate, water level, substrate, and competition withother cedars and other species. Little (1950) observedthat the onset of cone-bearing in New Jerseycedars in natural stands ranged from 7 years on 0.24m trees through 22 years on 1.28 m trees. Nurserygrownfield transplants produce seed as early as 3years after germination.Little (1950) noted that trees growing in theopen tend to produce more cones than those inclumps, although dominant trees in clumps may beas prolific as open-grown trees of the same size. Theamount of seed produced varies from year to year;abundant crops occur at about 2- or 3-year intervals(Cottrell 1929; Little 1 950).-. Seed dispersal is influencedby weather (temperature, relative humidity, rainfall,wind direction, and velocity), the height and diameterof the parent tree, and the density and height of surroundingvegetation. Seed dispersal starts in earlyautumn; most of the seed is released before the endof winter. In New Jersey, the peak of seedfall occursin a 2-week period in late October and early November(Little 1941).In seed-trapping experiments, Little (1950)confirmed that density and height of the surroundingvegetation can almost completely prevent thedispersalof seeds beyond the edge of a stand. Seedfall perunit area decreases greatly as distance from the treeincreases. Heavy rainfall causes complete closing ofthe cones; lighter rain reduces the rate of seedfall dueto the partial closure of cones (Little 1940). Highwinds increase the quantity of seeds falling; winddirection also greatly affects seed movement (Little1 940).-. Seed viability is highly variable.The most important factors appear to be theage, genetics, general health, and nutrition of theparent tree; climate; and weather. The first seedcrops of a tree have a lower average germination ratethan later production.m.. .Under natural conditions,much white cedar seed does not germinate until thestart of the 2nd or 3rd growing season after seed fall(G. Emerson 1846; Moore 1939; Little 1950). Overwinterstorage in a cool, moist medium, such as themoss and peat of a swamp floor, apparentlypromotes germination.