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


Cover, Broadleaved Trees of Yosemite National Park
[click to enlarge]
Quaking Aspen

Yosemite Nature Notes

THE MONTHLY PUBLICATION OF
THE YOSEMITE NATURALIST DEPARTMENT
AND THE YOSEMITE NATURAL HISTORY ASSOCIATION


VOL. XXVIJANUARY, 1947NO. 1

Broadleaved Trees of Yosemite National Park

By C. FRANK BROCKMAN

INTRODUCTION

This booklet, designed as a companion to “Cone-bearing Trees of Yosemite,” will aid Park visitors in the completion of a study of the trees of this area. Although the forests of Yosemite National Park are primarily coniferous (1), one will find a number of broadleaved species which embody specific interest due to the character of their spring floral display, their form, the odor of their foliage, the color of their foliage in the fall, the nature or color of seeds and the manner of seed dispersal, their habitat, and similar factors. These things render them conspicuous, thus serving to highlight the otherwise sombre nature of our coniferous forests. Furthermore, it will be obvious even to a casual observer that there is a considerable concentration of broadleaved trees in Yosemite Valley which, although but a small part of Yosemite National Park, is the section most frequented by the majority of visitors. Thus, to a large number of people, the broadleaved trees attract attention out of proportion to their relative abundance in Yosemite forests.

[ (1) Thirty-five species of trees grow naturally in Yosemite National Park. Eighteen, the greater part of this number, are broadleaved. However, while this group is in the majority insofar as number of species is concerned, Yosemite forests are essentially coniferous in type, being dominated by the sixteen species of cone-bearing trees which are found here in much greater abundance. In addition the California torreya (Torreya californica), which possesses needle-like, evergreen foliage but which is not a cone-bearing tree, is native to Yosemite National Park. Because of the similarity of its foliage to that of many conifers a description of that species will be found in the booklet on cone-bearing trees.

Attention should also be called to those trees which are not native to the Park but which were introduced into the area during the pioneer period. Included in this category are the American elm, black locust, sugar maple, and a number of varieties of fruit trees—largely apple. The latter are found principally in three orchards on the Valley floor which were planted during the 60’s by James C. Lamon and James M. Hutchings, early settlers in this area, (See page 30).]

The California black oak, which occurs in abundance in the Valley, is of significant importance in this regard, particularly in the fall when the acorns are conspicuous features, and when its foliage assumes the rich golds and browns characteristic of the season. Likewise the Pacific dogwood is distinctive, not only in the spring when it is festooned with numerous large white blossoms, but also in the fall when it bears clusters of bright red seeds, and when the foliage takes on a characteristic autumnal red. Other species possess outstanding characters of a similar nature which attract their share of visitor interest. The foliage of the California laurel gives off a penetrating, pungent odor when bruised; the holly-like leaves of the canyon live oak rarely fail to attract attention; and the quivering of the long-stemmed leaves of the aspen is a familiar sight in the “high country.”

Leaf Fall and Autumnal Color of Foliage

With few exceptions the broadleaved trees of Yosemite National Park lose their leaves in the fall. This, and its related phenomena, is the result of the tree’s preparation for winter for as the season approaches, deciduous trees must necessarily be ready to withstand its rigors. These preparations are largely to prevent excessive transpiration, since abnormal loss of water may result in the death of the tree. They are responsible for the vivid fall colors characteristic of the foliage of many deciduous trees, the annual loss of foliage, and the development of many features useful in winter identification.

During the summer the leaves serve as places of food manufacture. As autumn approaches, practically everything of nutritive value to the tree is gradually transferred to other parts and the leaves soon become mere skeletons, their cells containing only pigments which are of no further use. These pigments are responsible for the fall colors.

Leaf fall, most obvious of the deciduous tree’s preparation for winter, is anticipated weeks before the occurrence of this event. By midsummer a layer of loose cells begins to form across the base of the leaf stem. When complete it extends entirely across the stem at the point where it joins the twig, except for the vascular bundles which must necessarily remain open to facilitate the transportation of food and moisture. Subsequently an additional layer of corky cells form under the one previously developed. With the advent of fall, with its rains and frosty nights, small crystals of ice develop between the two cell layers. These exert a prying action which snaps the leaf from the twig. The leaf scar, which would otherwise have remained as an open wound, is protected by the corky cell layer.

However, this is but one episode in the tree’s preparation for winter. By midsummer the buds, conspicuous on the naked twigs in winter, are formed. These contain the rudimentary foliage or flower parts destined for development in the following summer which are protected by scales, waxes, gums, or hairs. In addition growth is retarded and finally ceases, the recently formed tissues are “hardened,” and the bark of the twigs and branches is increased in thickness through the addition of corky tissue.

Identification of Decidious Trees In Winter

Such preparations are responsible for the development of a variety of features by means of which one may readily identify deciduous trees in winter primarily by an examination of the naked twigs. Varying with the species, in a manner similar to the more familiar foliage, flowers, or fruits, one finds buds of distinctive form and protective devices placed in typical positions on the twigs, leaf scars of distinctive size and shape with their vascular bundle scars (from one to many) arranged in specific patterns upon the surface, and stipule scars which are present on the twigs of certain species. In addition one may note the color, taste and odor of the twig, the nature and number of the lenticels in the bark, the color and character of the pith found in the central portion of the twig, and the bark itself. The form of the tree is also of assistance in winter identification. This has many variations, from an upright pattern (as in the case of the Pacific dogwood) wherein the trunk or central

willows, black cottonwood, white alder
[click to enlarge]
From drawing by C. Frank Brockman

1. WILLOWS. Twigs slender, round in cross section. Leaf scars alternate, U-shaped and narrow, with three bundle scars. Buds sessile (not stalked), small, oblong and with but one exposed bud scale. Pith round in cross section and small.

2. BLACK COTTONWOOD. Twigs moderately stout, slightly angular in cross section. Leaf scars large, alternate, broadly crescent shaped to triangular, with three bundle scars. Buds sessile, elongated, conical, gummy and fragrant, with 6-7 overlapping scales. Pith rather small, somewhat 5-angled in cross section.

3. WHITE ALDER. Twigs slender, somewhat 3-sided in cross section. Leaf scars alternate; half round, raised, with three bundle scars. Buds large and stalked, with 2-3 reddish-brown valuate (not overlapping) scales.


axis of the tree is continued through the crown, to a wide-spreading type (as in the California black oak) in which case the trunk divides into several large limbs.

Beauty of Deciduous Trees In Winter

The beauty of our deciduous trees in winter should not be overlooked. Even though devoid of foliage at that time the rigors of that season lend a distinctive charm to these trees. This is of particular importance in areas such as Yosemite Valley. Here, after a snow storm, the naked branches of the California black oak are often sheathed with a coating of snow which presents a glistening pattern against the background of a blue Sierra sky. On such occasions these trees contribute, in no small measure, to the development of a veritable fairyland of exquisite beauty.

Plan and Organization of This Publication

The descriptions of the broadleaved trees found in Yosemite National Park, as noted on the following pages, are presented in a style designed primarily for the layman. In addition to the descriptive text, with accompanying illustrations, a simple field key (see page 37) is also included to serve as an aid in quick identification. For those who wish to pursue this subject to greater lengths the list of selected references (see page 40) will be of particular value.

California black oak, bigleaf maple, pacific dogwood
[click to enlarge]
From drawing by C. Frank Brockman

4. CALIFORNIA BLACK OAK. Twigs moderate to slender, often fluted. Leaf scars alternate, moderate to small in size, half round and somewhat raised, with numerous bundle scars. Clusters of several buds at tip of twig; lateral buds solitary. Buds sessile (not stalked) with overlapping scales arranged in fire ranks. Pith small and somewhat star-shaped in cross section.

5. BIGLEAF MAPLE. Twigs stout. Leaf scars opposite, U-shaped, and with 5-9 bundle scars. Buds sessile, stout, blunt, with 3-4 pairs of overlapping scales. Several buds clustered at tip of twig; lateral buds solitary.

6. PACIFIC DOGWOOD. Twigs slender. Leaf scars opposite, narrow, crescent or U-shaped with three bundle scars. Leaf scars encircle twig, are commonly raised during first winter on petiole bases—later sluff off at level of twig. Buds solitary, stalked, oblong, with pair of valuate scales.


Yosemite Valley oaks in winter
[click to enlarge]
Photo by Ansel Adams

Yosemite Valley oaks in winter


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