Monday, Week 15 Populus : the poplars -Divided into two major groups:

Transcription

1 Monday, Week 15 Populus: the poplars The genus comprises approximately 35 species that are wide-spread throughout the Northern Hemisphere, including North Africa, Eurasia and North America. Approximately 10 species native to N. America. Several hybrids and cultivars have been developed that grow very rapidly; 30' tall and 5.5" diameter in ten years. Used to reforest degraded sites, for pulp and lumber production and as ornamentals. Many insect pests and pathogens, short-lived, roots invade sewers & drains and sprouts are prolific. Contain salicin...used medicinally. -Divided into two major groups: 1) balsam poplars and cottonwoods, P. trichocarpa and (P. balsamifera), P. deltoides swamps, creeks, riverbanks northern spp. are fire adapted (balsam poplars), southern spp. are strictly riparian and can withstand prolonged flooding. Thick walled capsules 3) aspens, P. tremuloides and P. alba. Northern spp. adapted to cold climates, fire adapted and readily sprout from roots when burned flws. / 6-12 stamens, thin-walled capsules, non-resinous buds 94

2 Balsam poplars Populus trichocarpa: black cottonwood Occupies moist sites, especially gravelly & sandy alluvial soils of the Pacific slope, Northern Rockies and locally in the intermountain west. Establishes pure stands on gravelly & sandy river bottoms, but is also found serally on more mesic sites where it is replaced by more shade tolerant species including, grand fir, western red-cedar and western hemlock. It is shade intolerant. It is the largest native species of Populus in N. America and may reach ' tall and 4-5' diameter at maturity. Leaves are 3-6" long and are variable in shape from lanceolate on vigorous young growth to ovate with an acute to acuminate apex and a rounded to cordate base and crenate to serrate margin on mature growth. Green above and pale whitish to yellow below with conspicuous fragrant resin. Round petiole and fine toothed in comparison to P. deltoides. Bark is smooth and grayish on younger trees, but becoming gray-brown and furrowed on older trees. Reproductive Features: Dioecious, male and female flowers in catkins. Fruit is ca. 1/4" long pubescent capsule with many comose seeds. Seeds are wind/water dispersed. Due to rapid growth, has become an important source of pulp and soft lumber used in making boxes, crates and pallets. Hybrids have been developed with very rapid growth to establish plantations for pulp and lumber production. (Populus balsamifera: balsam poplar) Occupies riparian areas and lower slopes of the boreal and northern deciduous regions and locally in the Rockies. Not in Idaho! Occurs in pure stands and in association with white spruce, paper birch, quaking aspen and balsam fir. It is very shade intolerant, seral. May reach 60-85' tall and 1-2' diameter at maturity. Ranges farther north than any tree in N. America, to the Arctic slope! Populus deltoides: eastern cottonwood Occupies riparian areas from the Great Plains to the east coast in pure stands and in association with other hardwoods. Achieves best growth on alluvial soils and may reach ' tall and 3-4' diameter at maturity. Capable of very rapid growth, particularly for the first years. Some may reach 100' tall in ten years! Leaves are 3-7" long, deltoid to ovate-deltoid shaped with a coarsely serrate margin (in comparison to P. trichocarpa), acute to acuminate apex and a truncate to cordate base. Lustrous green above and pale below with a laterally flattened petiole. Shallow wide-spreading root system. Bark is smooth and yellowish on young trees, but becoming gray and furrowed on older trees. 95

3 Reproductive Features: Dioecious, male and female flowers in catkins. Fruit is a glabrous 3/8" capsule with many comose seeds. Aspens Populus tremuloides: quaking aspen Occupies variable soils from sea level in riparian areas to mountain slopes. Has the largest range of any tree native to N. America, including the Cascades, Sierras and Rockies as well as the northern deciduous and boreal regions. Like all species with such broad distributions, geographic patterns of variation exist. It is a very aggressive pioneer species that is well adapted to fire. Seeds germinate well in inorganic soils and roots send up prolific new sprouts. It is relatively short-lived above ground, shade intolerant and is eventually replaced by more tolerant species. May reach 50-60' tall and 1-2' diameter at maturity. Scattered dominants may survive succession. Life history of producing sprouts from wide-spreading roots of parental trees results in groves of clones. Clones may live over a million years and may represent the largest orgainsm or super-organism on earth Leaves are variable in shape from suborbicular to broadly ovate with a crenate to serrate margin, acute to acuminate apex and a rounded base. Petioles are laterally flattened which causes leaves to "quake" in even a slight breeze. Bark is smooth from greenish white to cream colored, becoming darker and furrowed on lower portions of older trees. Wide spreading root system. Reproductive Features: Dioecious, male and female flowers borne in catkins. Fruit is a capsule approximately 1/4" long. Seeds germinate best in mineral soils. -Wide-spreading roots send up abundant sprouts to establish clonal groves. Populus alba: white poplar Aspen native to Eurasia, but widely planted as an ornamental in N. America. Has naturalized locally in southern Canada and US. Tolerates urban conditions and drought. Many cultivars have been developed. Very common ornamental. Roots clog drains and sewers. Invades open sites due to prolific root sprouting. Leaves are 2 1/2-4" long, dark green above with dense white pubescence below and variably 3-5 lobed with blunt lobes and variously toothed margins. Vigorous growth is more prominently lobed. Has a flattened petiole. Bark is white and smooth on younger trees, but becoming dark and furrowed on the lower trunk on older trees. 96

4 Reproductive Features: Dioecious, male and female flowers borne in aments and are densely pubescent. Fruit is an egg-shaped capsule with many comose seeds. Like all aspens, sends up sprouts from wide-spreading roots. Aggressively establishes itself on open sites. 97

5 Week 15 Wednesday Salix: the willows The genus comprises approximately 300 species that are wide-spread throughout the cooler regions of the Northern Hemisphere. Approximately 100 species native to N. America 40 in ID. Taxonomically very challenging group Require abundant moisture so generally found in wetlands and riparian zones important in soil stabilization to prevent streambank erosion. Also important wildlife browse moose, beavers wetc. Yellowstone Lamar valley story Contain salicin...used medicinally. Salix alba cv. tristis - weeping willow Not the only weeping species [and not all S. alba are weeping (e.g., var. vitellina golden willow)], but the most apparent in the temperate regions Cultivar developed from the wide-ranging Eurasian species since all cultivated from single clone, all male individuals Leaves 3-6 long, 3/8 to 1/2 wide, alternate, simple, very narrowly lance-shaped, finely serrated margin, yellow-green above, milky green below. Slender, smooth, bright yellow twig, hanging or drooping for long distances, almost ropelike; buds are small, appressed and covered by a single, cap-like scale. Terminal buds lacking. Salix exigua coyote willow, sandbar willow Widespread in N. Am. from Sierra Nevada to Appalachains. In the west from the Rocky Mountains to central Sierras. Other closely related spp. in Cascades and northern Sierra Nevada. Distributed in moist places, especially along riverbanks on gravel bars and sandbars. Mostly in lower elevations. A thicket forming shrub with numerous small diameter stems, spreads by underground root suckering, may reach up to 25 feet tall. Leaves lanceolate to linear, 2 to 5 long and very narrow, entire or with a few scattered teeth, green to gray-green above, paler and may be hairy below generally with a silvery pubescence on both sides. Twig slender, pale green to tan, may be reddish in winter, fuzzy or not, buds covered by a single cap-like scale. Bark silvery gray to gray-green, becoming shallowly fissured with time. Reproductive Features: Dioecious; infl. 1 to 2 1/2 inches long, fuzzy catkins on a slender 1 inch stem, yellowish white, appearing in spring with the leaves. Fruit 1/4, long-pointed capsules in long, narrow clusters; each capsule contains numerous comose seeds. 98

6 Salix scouleriana Scouler willow Widespread Boreal and western North American spp. (northern Rockies and Cascades). Most common willow in forest understory or disturbed forest sites. Often upland spp. major component of brushfields at higher elevations to subalpine, but is also found as a riparian spp. at lower elevations. Typically a tall shrub to small tree 25 Vegetative features: Leaves distinctly obovate, 3 to 5 long, margins usually entire but may have a few wavy teeth or edges rolled under, often arranged in a fan-like fashion at the ends of twigs, dark green above, paler and maybe reddish hairy below. Twig slender, yellowish brown to red, may have some tomentum; red buds are large and pointed, with a single cap-like scale. Bark gray to gray-brown, smooth with diamond shaped lenticels when young, later becoming shallowly fissured and scaly. Reproductive features: Dioecious; infl. 1-2 long catkins, appearing in spring with the leaves. Fruit ¼ long-pointed, hairy capsules in oblong clusters; each capsule contains numerous small comose seeds. 99

7 Fagales: This large group includes a great amount of variety, including two prominent families of north-temperate wind-pollinated trees. Betulaceae - The birch family Comprsies 6 genera and approximately 170 species of trees and shrubs that are primarily distributed throughout cool temperate regions of the Northern Hemisphere. 5 genera/33 species are native to North America. Leaves are simple, alternate and deciduous doubly-serrate margins All are monoecious with male and female flowers borne in wind pollinated catkins on same tree! Fruits are samaras (winged nutlets - Alnus and Betula) or nuts (Corylus, Carpinus and Ostrya). -Samara single seeded, dry, indehiscent winged fruit -Nut hard, dry, indehiscent fruit, usually with 1 seed. Bracts that subtend flowers are very important characters for species ID. Genus Fruits Infructescence/bracts Misc impt. ID chars Betula Small samaras Deciduous, 3-lobed bracts, persistent axis Bark large evident lenticels, papery catkins Alnus Small samaras Persistent, woody bracts Carpinus Samll nut Large 3-lobed bracts in loose clusters Ostrya Small nut Bladder-like bracts in loose clusters enclose nut Corylus Medium nut Bracts surround nut form beak Persistent female catkins, stalked buds, triangular pith Musceled, smooth bark Shreddy bark, hoplike infructescence Broad, pubescent leaves no female catkin paired fruits 100

8 Week 15 Friday Guest Lecture Dr. Bill Rember Geology and Paleobotany of Miocene Lake Clarkia Geologic and paleobotanical history of the Miocene flora of the northern Rockies. 101