Читать книгу The Trees of San Francisco - Michael Sullivan - Страница 13

Don’t Do This!

INDULGE me as I rant about two of my gripes concerning trees in San Francisco. The city has its share of beautiful trees, but there are times when I walk down a street and cringe. If I could change only two things about what happens to trees in this city, these would be the two:

  LAVENDER IN THE TREE BASIN. Most street trees in San Francisco are planted as young trees in 2-foot-square cuts in the sidewalk, and people have a natural desire to plant flowers or other plants in the basins. Anything planted there will compete with the young tree just getting established, but plants with woody stems—such as lavender, rosemary, and ivy—are especially bad. Mature trees are not affected much, but the aggressive roots of these plants can choke a young tree by competing for water and nutrients.

  AGGRESSIVE PRUNING. Why are so many San Franciscans afraid to let their trees grow? Trees are topped, or aggressively pruned, for many reasons, chiefly to keep upper branches out of overhead wires and to protect views. But I suspect many tree owners think they are helping the tree by lopping off the ends of branches to reduce the tree’s height or size, or to make the tree bushier or denser. Some plants react well to being cut back hard in this way, but most trees are not among them. Take my advice: let your tree grow, and help create a mature canopy your neighbors will appreciate.

Melaleuca quinquenervia

CAJEPUT

Of the 200-plus varieties of Melaleuca in Australia, the cajeput is the one most commonly cultivated, so much so that Australian sources refer to it as the “quintessential” melaleuca. Called broad-leafed paperbark Down Under, this tree has gray-green, leathery, 2- to 4-inch oval leaves and grows quickly to 20–30 feet. The tree’s spongy white bark can easily be peeled off in sheets and is used as a lining for hanging baskets. The yellowish-white flowers bloom in clusters from June to August, but they are not as showy as those of the flaxleaf paperbark (Melaleuca linariifolia ), a close relative that is also popular in San Francisco. The cup-shaped 3/16 -inch seed capsules form in clusters 2–3 inches long, and they can persist on branches for a year or longer. Cajeputs are well adapted to San Francisco’s conditions, tolerating poor and even salty soil and strong winds.

LOCATION: North side of 16th St. at Wisconsin St. on Potrero Hill; also Bryant St. (east side) between 18th and Mariposa Sts. in the Mission

The tree was introduced into southern Florida in the early 1900s for swamp drying. Having no natural enemies, it spread aggressively, crowding out the native vegetation that is essential for supporting animal life. Now, the cajeput poses a serious environmental threat to the Everglades and other expanses of southern Florida, where it is growing explosively, turning the natural grassy wetlands into dense melaleuca thickets. Biological control is now offering hope, however. The U.S. Department of Agriculture is releasing several species of Australian snout beetles, which are specific to melaleuca and feed on its shoots, reducing the plant’s ability to reproduce.

Aesculus californica

CALIFORNIA BUCKEYE

LOCATION: 2694 McAllister St./Willard St. N. near the University of San Francisco campus; also at 124 Lower Terrace/Levant St. in the Upper Market neighborhood

This is one of the few trees in this book that is a true San Francisco native, existing within the current city limits before the arrival of Europeans. The California buckeye also is one of the state’s most beautiful native trees, growing to 20 feet in height on wind-protected sites in the dry slopes and canyons of the coastal range and Sierra foothills. The tree produces showy, long-lasting clusters of white flowers in May and June. One or two pear-shaped fruits form on each flower cluster, and inside each fruit’s leathery jacket is a seed with a shiny brown coat. The tree’s light green leaves are divided into five to seven leaflets, which drop in July (an adaptation to long, dry summers) unless summer water is provided.

American Indians crushed this tree’s poisonous seeds and added them to dammed-up streams to stupefy fish, making them easy to catch. (Today you may find California buckeyes near old Indian campgrounds.)

Perhaps because of its spreading form, the California buckeye is rarely planted as a street tree in San Francisco, due to narrow urban setbacks. You can view a large and spectacular specimen in a yard at 2694 McAllister Street, near the University of San Francisco campus. The tree was scheduled for removal in 1999 in connection with new construction on the lot, but after a neighborhood outcry, plans for the house were changed to build around, and preserve, the tree. As part of the settlement, the property owner signed a tree easement with Friends of the Urban Forest, protecting the tree from future removal—and making this the only tree in the city protected by a contract.

Schinus molle

CALIFORNIA PEPPER TREE

A mature California pepper arching over a backyard patio is a cliché of Sunset magazine’s California lifestyle. Cliché or not, the California pepper is one of the most beautiful trees available to San Francisco tree lovers. Mature peppers have wonderfully gnarled trunks, supporting rounded crowns of graceful, arching branches. The fernlike foliage is finely textured, with bright green leaves composed of many leaflets. California peppers have either male or female flowers; female flowers develop into drooping clusters of showy rose-colored peppercorn berries in the fall and winter. The seeds are sometimes sold as pink peppercorns, although in large quantities they can be toxic. (To avoid messy fruit drop, many city dwellers plant trees with male flowers only.) Like its relative the Brazilian pepper, this tree is related botanically to mangos, pistachios, and cashews, as well as to poison ivy and poison oak; contact with its leaves can cause dermatitis or allergic reactions in some individuals. Despite its common name, this tree is native not to California but to the Andes Mountains in Peru (in fact, many sources now use Peruvian pepper tree as the common name). It has, however, become naturalized in chaparral areas of Southern California.

LOCATION: 4019 26th St./Sanchez St. in Noe Valley

Pyrus calleryana

CALLERY PEAR

Two cultivars of callery pear are common on San Francisco streets. ‘Aristocrat’ is most common and has a rounded form. ‘Chanticleer’ has a more upright form. Each variety has dark green, glossy leaves that, in hotter climates, turn showy reds and scarlets in the fall. But with few exceptions we get only greens and yellows in cool, foggy San Francisco (I’ll admit that I chose one of the exceptions for the photo at right). The tree is bare November–March, although individual trees can differ significantly in this aspect. Flowers appear in March, but in San Francisco this tree is not planted for its flowers, because it does not bloom well in the city’s mild climate. (Hmm … no flowers, disappointing fall color … I will reveal some personal prejudice and say I am not a fan of this tree in San Francisco.) Flowers are often followed by a few inconspicuous clusters of round, pea-sized, green or brown pears hidden amid the foliage. This fast-growing tree (particularly the ‘Aristocrat’ cultivar) reaches heights of 25–35 feet. Callery pear is native to China and Vietnam.

LOCATION: 239 Connecticut St./18th St. on Potrero Hill; also 436 Cole St./Fell St. in the Haight-Ashbury

Phoenix canariensis

CANARY ISLAND DATE PALM

Years ago, I didn’t associate palm trees and San Francisco. Los Angeles, sure, but San Francisco? Since the early 1990s, however, Canary Island date palms have been used extensively in high-profile street-landscaping projects in San Francisco. In 1993, the tree was used to line the entire length of upper Market Street, to spectacular effect. In the late 1990s, Canary Island date palms were planted at the city’s waterfront along the Embarcadero, from AT&T Park all the way to Fisherman’s Wharf, replacing the elevated freeway that formerly cut off the city from its bay views. Plenty of San Franciscans complained at the time, concerned that the palms were “Los Angelizing” the city. Fortunately, they lost that aesthetic battle, and the stately Canary Island date palm is now very much part of the San Francisco fabric.

The Canary Island date palm supposedly was introduced to California by Spanish mission priests during the 18th century. The tree has a massive trunk, 4–5 feet in diameter, which in its natural state is roughened by the woody remnants of old palm fronds. In cultivation, the trunk is usually trimmed to a smooth cylinder. The gracefully arching leaves are 15–20 feet long, with 2-inch-wide leaflets measuring 12–16 inches long. Cream-colored flowers appear in clusters, with male and female flowers on different trees; the female trees produce (inedible) clusters of datelike ¾ -inch seeds in the fall. The tree is native to Spain’s Canary Islands, in the Atlantic off the southwest coast of Morocco.

LOCATION: Corner of Dolores St. and 20th St. in the Mission; many other specimens in the Dolores St. median intermixed with other palm species

Ceratonia siliqua

CAROB

This tree has biblical roots. It is said that the foot-long, brown, leathery fruit pods of the carob tree were the “locusts” that St. John the Baptist survived on in the wilderness in the Gospel of Mark. The pods are also thought to be the “husks” that tempted the prodigal son in the New Testament parable.

Rich in sugar and protein, the carob’s pods can be milled to a fine powder for use as a chocolate substitute. Within the pods, the carob seeds are of remarkably uniform weight, and ancient Mediterranean civilizations used them as a unit of measure to weigh gems and other precious substances (the Arabic word for the carob seed was quirat , from which our word carat originates). You will rarely see the pods or seeds of the carob in San Francisco, because only female trees produce them (11 months after pollination), and the females are seldom planted on city streets.

LOCATION: Northeast corner of 22nd and Dolores Sts. (on Dolores) in the Mission; also at 850 Florida St./20th St. in the Mission and at 957 Cole St./Parnassus Ave. in Cole Valley

Female seedpod

The carob is a native of the eastern Mediterranean. It grows to 30 feet, with a dense, rounded crown. This is a tree to plant for its foliage. The glossy, dark green leaves are beautiful and distinctive, with each compound leaf divided into 4–10 round leaflets. Small, inconspicuous red flowers form in spring. Not surprisingly, given its desert origin, the carob is very drought tolerant. A drawback: Carobs have extremely invasive roots, and mature trees will cause significant sidewalk damage.