In the Yosemite National Park we have nine species of trees, representing six genera, belonging to the broad-leaved type: White Alder, California Black Oak, Canyon Live Oak, Yellow Willow, Black Cottonwood, Quaking Aspen, Nuttall Dogwood, Big-Leaf Maple, and California Laurel.

Almost everyone knows a few of these trees; the Black Oak, the Willow, and the Maple are familiar in a vague way, at least, whereas the tendency is to call all the others evergreens and let it go at that.

The broad-leaved trees have certain characteristics which set them apart. They have two seed-leaves, and are therefore known as dicotyledonous. The leaves, as the division name implies, are broad instead of linear; moreover, they usually have a network of veins. The tree tends to divide into branches not far above the ground instead of sending up a main trunk as the axis; this characteristic is typical and not constant, however. The growth of the wood in the stems is by annual concentric layers beneath the bark, in which these trees resemble our first group, but they differ in lacking the resinous pockets which are more or less common among the Gymnosperms, and particularly

Leaves of the Broad-Leaved Trees

noteworthy in the firs. Many of the broad-leaved trees reproduce or regenerate by crown-sprouting from the roots, which is rare among the conifers, although it is a characteristic of the Coast Redwood.

All the broad-leaved trees of our region happen to be deciduous except the Canyon Live Oak and the California Laurel. The White Alder loses its leaves in September or October, while they are still green. The others of this group give the Yosemite Valley and the higher mountainsides their gorgeous autumn coloring, along with such shrubs as the Azalea, the Creek Dogwood, and, in the upper Canadian or lower Hudsonian zones, the Mountain Ash.

These trees are all to be found in the Transition Zone, and of them all only the Quaking Aspen goes much beyond the border of the Canadian Zone; it ventures even into the Hudsonian belt at times. There are Black Cottonwoods and Black Oaks through the Little Yosemite, and occasionally one sees them even higher, where sun and exposure are unusually favorable. The Huckleberry Oak, a shrub rather than a full-grown tree, in appearance very similar to the Canyon Live Oak, is common in the Canadian Zone around the rim of the Yosemite Valley and in similar places on the Tuolumne watershed. For the most part, however, it is only through the Transition Zone that we need compare the broad-leaved trees.

Most of this type are water lovers. The alder is nearly always found overhanging the banks of a limpid stream. The cottonwood likes the meadows and the quiet stretches of the river; the aspen, too, likes water, but it may often be found on talus slopes beneath a granite cliff, where water trickles beneath the rocks or drains through porous soil. So, too, with the maple; its favorite haunts are near the foot of some waterfall, or at such places as the old spring near Happy Isles and along the talus slopes on the shaded south side of the Valley. The California Black Oak is another denizen of the meadows, but it will take root among the rocks when it finds a pocket of good soil. The Canyon Live Oak likes the sunny slopes of the northern wall; laurel grows with it there, but develops more notably in moist, cool places.

Among these trees the shapes of the leaves are so distinctive that there is little difficulty in classifying them, once an opportunity for close examination is given. The margin of the leaf may be entire, or may be toothed, or deeply notched or lobed. Some trees have their leaves definitely opposite or alternate on the branch; the maple and the dogwood belong in the first category, the trees of the laurel, willow, birch, and oak families in the second. When the flowers are available, the type of bloom helps identify the tree—the flowers in catkins, like the alder, or in a head, like the dogwood. Then there are the fruits—the flyaway, cottonheld seeds of the cottonwood, the winged samaras of the maple, the familiar acorn of the oak, the olive-like fruit of the laurel.

CHART FOUR
Broad-Leaved Trees*

TREE	LEAVES	ARRANGEMENT OF FLOWERS	FRUIT
1. White Alder	Toothed; alternate	In catkins; both kinds on same tree	Small, woody cone
2. California Black Oak (Kellogg Oak)	Deeply parted lobes, with bristle-tipped points; alternate	Similar to Canyon Live Oak	Acorn in tawny cup
3. Canyon Live Oak	Entire or toothed; alternate	Pollen-bearing in catkins; fruiting minute, scaly bodies; both on same tree	Acorn in cup covered with golden fuzz
4. Yellow Willow	Entire; other willows often toothed; alternate	In catkins; staminate and pistillate on different trees; fertilized by insects	Fruit a pod; seeds with tuft of hair for wind distribution
5. Black Cottonwood	Finely toothed; alternate	Similar to willow	Similar to willow; seed pods in cottony spray
6. Quaking Aspen	Faintly toothed; alternate	Similar to willow	Similar to willow; tiny brown seeds
7. Nuttall Dogwood	Entire; wavy margins; opposite	Flowers perfect; clustered in head, surrounded by large white bracts	Head of bright red drupes
8. Big-Leaf Maple	Palmately lobed; opposite	In pendent clusters; perfect and imperfect flowers often mixed	Seeds in winged samaras
9. California Laurel	Entire; aromatic; alternate	In umbel, or loose cluster	Olive-like drupe

* These all occur in the Transition Zone, but Quaking Aspen is found more commonly in the Canadian Zone, and often in the Hudsonian. California Black Oak and Black Cottonwood may nut well up into the Canadian Zone.

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