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Broadleaved Trees of Yosemite National Park (1947) by C. Frank Brockman


BIGLEAF MAPLE

Acer mocrophyllum Pursh. — Maple Family (Aceraceae)

This common tree can be readily recognized by even the most casual observer by its large, characteristic leaves. Although it may be found as high as 5,500 feet in elevation in Yosemite National Park, it is most common between 3,000 and 4,500 feet where it grows in moist, gravelly soils upon hillsides, in protected locations at the base of cliffs, or in the rich alluvial soils bordering streams. Its natural range includes an area along the Pacific Coast from south-eastern Alaska to southern California.

Although it is not exceptionally large as a rule, it is a handsome tree. Mature specimens may attain a maximum of 80 feet in height and two to two and one-half feet in diameter. When growing in the open the large, heavy branches produce a broad, spreading, round-topped crown densely covered with foliage. In less favorable situations it is characterized by a more ragged, less pleasing appearance. New twigs are smooth and green, while larger branches have a pale grey or reddish-brown color. Gray to reddish-brown bark with hard, scaly ridges characterize the trunks of larger trees. Although it grows rapidly at first its rate of growth decreases with age. It reaches maturity in about 200 to 300 years.

The foliage is unmistakable. Borne on stems four to six inches long, the

Foliage and seeds of bigleaf maple (Inch squares on background)
[click to enlarge]
Photo by Brockman

Foliage and seeds of bigleaf maple (Inch squares on background)
large leaves, which may occasionally be more than twelve inches across, are especially noteworthy. They are borne opposite on the branches, are smooth and shiny green above, pale green below, and palmately divided into five broad lobes.

Although the foliage of some of the eastern maples assume vivid hues before dropping from the tree in the fall, such is not the case with this western species. In autumn the color of its foliage is not particularly attractive, being generally characterized by dull brownish to yellow shades. However, this maple has other interesting features, not the least of which are the large, pendent clusters (racemes) of fragrant yellow flowers which enliven the appearance of the tree during the early spring when the leaves are unfolding. These clusters, which include both staminate (male) and pistillate (female) flowers, are from four to six inches long. Insects, which are attracted in great numbers to these flowers, serve to pollinate the blossoms. The characteristic fruit a pair of nut-like seeds, each attached to a large blade-like wing—is fully developed by July. At that time they are about one to two inches long. Their green color, typical of midsummer, changes to a light brown in the early fall.

The bigleaf maple can be recognized in winter by the stout twigs with their opposite leaf scars. The leaf scars are rather large, V-shaped or U-shaped in outline, upon which are from five to nine vascular bundle scars.



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