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trees and share a common ancestor. However they do not share a common root system, as connections <br />Planting aspen in a non-irrigated location in a Colorado study was not successful (Shepperd and Mata <br />2005). Transplanting greenhouse or nursery-grown aspen seedlings into the field has similar problems to <br />those of natural seedlings, indicating that the small root mass of transplanted seedlings is insufficient to <br />absorb enough moisture to maintain the seedlings during periods of summer drought in the wild. Re- <br />break down from generation to generation as new trees grow new roots. <br />Most aspen stands are composed of one to several clones that may persist along a continuum of <br />succession stages, from sparsely growing individuals to apparently stable pure or near-pure groves. <br />Although clones are often separate and distinct from one another, studies have demonstrated spatial <br />intermingling where multiple clones are co-located (DeByle 1964; Milton and Grant 1980; Wyman and <br />others 2003; Hipkins and Kitzmiller 2004). <br />Compared to conifers, aspen ramets -individual stems, or suckers, of the same genotype from a <br />parent root system -are relatively short lived. This is due to succession (replacement of aspen by more <br />shade tolerant species) and/or a typical onslaught of mortality related to stem decays and diseases from <br />ages 80 to 100 years (Baker 1925; Hinds 1985; Potter 1998; Rogers 2002). Aspen thrive where somewhat <br />regular and frequent disturbance promotes regeneration (DeByle and Winokur 1985). Occasionally aspen <br />stands appear to perpetuate themselves with regular low-level regeneration in multi-layer stable stands <br />(Mueggler 1988; Cryer and Murray 1992). Aspen in the western U.S. are longer lived than elsewhere. <br />Healthy aspen trees can live over 300 years (Personal Comm., John Shaw, Forester, USDA Forest <br />Service, Rocky Mountain Research Station) and can attain diameters up to 96.5 cm (38 inches) diameter <br />at breast height (dbh), however most aspen are typically much younger and smaller. Many mature stands <br />in Colorado are currently over 120 years of age (Shepperd 1990). Tree form varies from shrubby at upper <br />and lower forest margins to over 30.5 in (100 ft) in height in prime locations with average heights of 15 to <br />18 in (50 to 60 ft) (Baker 1925). <br />In any case, the initiation of bud growth must also be accompanied by sufficient sunlight and warmer <br />soil temperatures to allow the new suckers to thrive (Navratil 1991, .Doucet 1989). Full sunlight to the <br />forest floor best meets these requirements. However, young aspen suckers are susceptible to competition <br />from other understory plants and herbivory from browsing ungulates (primarily elk and deer) even if <br />abundant suckers are present. <br />Having access to a well developed parental root system gives aspen sprouts a great advantage over <br />other plants. The parent roots supply carbohydrates and access water deep in the soil profile allowing <br />sprouts to grow rapidly, out-compete other vegetation, and withstand frequent droughty conditions in the <br />West.