It is a very shade intolerant species and requires full sun in order to become established. Aspen are primarily dioecious, producing good seed crops every 4-5 years. Although 10 year old trees can produce seeds, the optimum age is between 40 and 70 years. Flower catkins appear in June and are wind pollinated. These suckers are clone trees, which are genetically identical to the parent tree.
Many aspen stands consist of one clone.
Each lateral root may contain thousands of budding sites, up to 600 per 18 inch section of root. Although the individual stems may only live to be 200, the clone may be thousands of years old. Aspen is winter deciduous, although photosynthesis may continue during sunny winter days, as the bark tissues have a high chlorophyll content. The trunks of aspen often look greenish in color. In autumn the vibrant red, gold, orange and yellow colors of aspen leaves provides a striking display in California's mountains.