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SPECIES: Salix exigua | Sandbar Willow
GENERAL BOTANICAL CHARACTERISTICS : Sandbar willow is a short-lived deciduous shrub or small tree up to about 26 feet (8 m) tall, with soft weak wood, and thin gray-green to brown bark [7,54,62]. Staminate and pistillate flowers occur on separate plants as catkins. The fruit is a narrowly ovoid capsule. The three subspecies as a whole are characterized as (1) having numerous slender stems, (2) forming thickets through the underground spread of root suckers, and (3) having long and narrow mature leaves (5 to 20 times as long as wide) which are equally green on both surfaces [7,10,23]. The three subspecies intergrade, making identification difficult; general botanical characteristics of the subspecies include [7,10,16,54,62]: ssp. exigua ssp. interior ssp. melanopsis Mature Height 6-12 f (2-4 m) 20 feet (6 m) 12 feet (4 m) Mature Leaves lanceolate linear-lanceolate linear or oblong entire/few toothed remotely dentate toothed/subentire up to 13 cm long up to 12 cm long up to 12 cm long Male Catkins 1-4.5 cm long 3-4 cm long 1.5-3.5 cm long Female Catkins 1.5-6 cm long 2.5-3 cm long 2-4 cm long Capsule 4-7 mm long 6-7.3 mm long 3-5 mm long sessile pedicellate/glab. sessile/glabrous Twigs of Season thin-dense sparse-moderate pubescence,with pubescence,with strait appressed loosely appressed hairs wavy/curly hairs RAUNKIAER LIFE FORM : Undisturbed State: Phanerophyte (nanophanerophyte) Undisturbed State: Phanerophyte (microphanerophyte) Burned State: Hemicryptophyte REGENERATION PROCESSES : Sandbar willow is able to reproduce vegetatively by sprouting from underground shoot buds which occur on lateral roots and produce male or female clones. This method of vegetative reproduction (suckering) is uncommon in willows and occurs only in section Longifoliae [1]. Suckering allows this plant to spread and form colonies or thickets that may be several meters in diameter [1,10]. On a sandbar in Wisconsin estimated to be approximately 45 to 50 years old, more than 97 percent of sandbar willow (ssp. interior) stems sampled were clones 1 to 3 years old [3]. Regeneration may also occur through broken pieces of stems and roots which are transported and deposited by floodwaters and later sprout. This is a common method of vegetative reproduction in willows and may be important in initial colonization of some disturbed sites, although seeding seems to be more important [65]. Reproduction occurs sexually through the production of numerous seeds. Flowers are pollinated by insects, commonly by bees [41]. After fertilization, a capsule develops which eventually splits open, dispersing the numerous tiny seeds which are covered with a cottony down which aids in their dispersal by wind and water [2,41]. The nondormant seeds have a thin seed coat and germinate soon after being dispersed. On adequate substrates most germinate within 24 hours [12]. Ware and Penfound [59] found that seeds older than 1 week rarely germinated; thus seeds must land on suitable sites quickly if they are to germinate. Seeds kept at 32 to 41 degrees F (0-5 deg C) can be stored 4 to 6 weeks [8]. Seeds require light for germination [8]. Fresh alluvium deposited along rivers provides an ideal substrate for establishment. These sites have constant soil moisture and generally have no overstory trees to shade out this light-sensitive species [23]. SITE CHARACTERISTICS : Sandbar willow is found almost exclusively in riparian habitats, occupying banks of major rivers and smaller streams, lakes and ponds, marshy areas, alluvial terraces, and ditches [16,23,54,64]. It characteristically forms zones immediately adjacent to the water's edge. These areas are subjected to periodic flooding which often deposits sand and cobble below the high water mark. With severe annual flooding it may be the only shrub to survive in this zone [10]. Although often found below the high water mark, it must have a portion of its crown out of the water during part of the summer to survive [52]. Sandbar willow may also occur on moist, well-drained benches and bottomlands [10]. It normally does not exist in the understory due to its shade intolerance, and is generally replaced by cottonwoods. Soils: Sandbar willow occurs on a wide range of soil textures, but usually occurs on soils derived from alluvial or fluvial parent material of mixed geologic origin [60]. In western Montana it is typically found on coarse-textured substrates of sand or gravel, but in eastern Montana it may occur on fine-textured silts [23]. It also occurs on a wide range of soil types in eastern Idaho and western Wyoming. Sandbar willow communities there occupied soils from fine-loamy or finer textures, to coarse-textured soils with up to 35 percent rock fragments [64]. Associates: Adjacent drier areas may be dominated by cottonwoods, green ash (Fraxinus pennsylvanica), water birch (Betula occidentalis), thinleaf alder (Alnus incana ssp. tenuifolia), and other willows [23,64]. Elevation: Sites in the Intermountain West are typically at low to mid-elevations. Stands in Montana, Wyoming, and Idaho are adjacent to uplands commonly dominated by conifers, and big sagebrush (Artemisia tridentata) and Idaho fescue (Festuca idahoensis) [10,24,43,64]. Elevational ranges for several western states are presented below [10,14,24,25,42,42,48,62]: 2,700-8,500 feet (825-2,590 m) in UT 5,000-9,000 feet (1,524-2,743 m) in CO 8,000 feet (2,438 m) in s CA 3,200-6,700 feet (975-2,042 m) in MT 3,400-8,600 feet (1,036-2,621 m) in WY ssp. exigua: below 6,000 feet (1,830 m) in east-central ID ssp. melanopsis: 6,000-7,000 feet (1,830-2,130 m) in ec ID ssp. exigua: 3,500 to 3,900 feet (1,067-1,181 m) Trans Pecos TX ssp. interior: 1,800 to 3,600 feet (549-1,097 m) Trans Pecos TX SUCCESSIONAL STATUS : Sandbar willow is a pioneer species that colonizes new sand and gravel bars. After initial colonization, it helps stabilize the sand and gravel deposits, which allows other species to follow [49]. It may dominate these disturbed areas for only a few years before being replaced by cottonwoods. Repeated flooding may allow sandbar willow to persist [24], but once cottonwoods become established it cannot regenerate and establish itself. In Kansas, it occurs only as a pioneer; stands there maintain themselves for about 10 years before cottonwood becomes established and shades them out [4]. SEASONAL DEVELOPMENT : Catkins of sandbar willow develop over a several weeks, with the first expanding with the leaves and then continuing to develop as the leaves mature [10]. Flowering times for several states follow [14]: State Flowering Begins Flowering Ends CO May July MT May July UT April July WY May July Noble [67] reported that in Minnesota seeds were shed from early June to late July, which is commonly the time the rivers are dropping in elevation and exposing moist substrates favorable for germination. Seed dispersal probably coincides with local flooding patterns. In Oklahoma Ware and Penfound [59] reported that plants produce leaves by March 28, fruits by May 5, and seedlings by May 15.

Related categories for Species: Salix exigua | Sandbar Willow

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Information Courtesy: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Fire Effects Information System

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