Alien plants growing without cultivation in California

Abstract

This is a total of 29,747,588 acres of land disturbed by man for the purpose of growing introduced and useful species or utilized for graz- ing.This acreage does not include the forest or grazing lands publicly owned.The establishment of these alien crop plants greatly modified, and in certain areas almost completely destroyed, the original plant covering.Further, with the development of the livestock industry, there followed major changes in the vegetation of the extensive areas grazed by domestic animals.Most of the useful agricultural crop plants introduced by man have stayed within the limits prescribed.A few, escaping, have become what we choose to call weeds-notably Johnson grass, 4 certain species of Medicago, artichoke thistle, and common hemp.By various well-known agencies the majority of the alien plants of California have been introduced unwittingly ; and many have become highly undesirable, constituting our worst weeds.There are approximately 526 species of them growing uncultivated within our borders.Of these, some 125 species have become weeds of agricultural significance.Many aliens, however, although introduced long ago, have not proved capable of establishing themselves here over any considerable extent of territory; numerous species of "weeds," so-called, have but little economic significance.Others, especially certain grasses and the erodiums, have proved valuable as forage plants.Some immigrants, however, have spread with alarming rapidity and become of primary importance as weeds, notably Johnson grass, Klamath weed, hoary cress, 5 puncture vine, Napa thistle, yellow star thistle, Russian knapweed, Russian thistle, mustards (Brassica spp.), Bermuda grass, camel thorn, and wild morn- ing-glory.The invasion of California by alien plants has usually been regarded as starting with the first missions.In the words of Parish (1920) :It will be safe, then, to assume a very definite date for the beginning of that for- eign invasion which since has so greatly modified the plant population of the state. Bul. 637]Alien Plants Growing without Cultivation 5 was stretched northward along the coast, until, in 1823, the last was founded, in honor of San Francisco de Solano, near the site of the present town of Sonoma.Everywhere, one of the first proceedings was the planting of gardens, and the sowing of fields; and the neophytes, as they gathered in, were taught to be farmers and herdsmen, so that each mission speedily became a hive of industry, based on its wide acres and countless herds.Eventually a considerable secular immigration came from Mexico by way of Lower California and of Sonora; the last passing through the present Arizona and the Colorado Desert ; and a scanty commerce, licit and illicit, visited the ports.Since Parish wrote these words, Hendry (1931) and Hendry and Bellue (1925, 1936) have made admirable studies of the seeds found in adobe bricks from the walls of old buildings, including missions, whose construction dates are known.The seeds in most instances are fairly well preserved and capable of positive identification.According to these studies red-stem filaree, curly dock, and prickly sow thistle had a wide distribution before the establishment of the first missions-that is, before 1769.During the Spanish or Mission Period (1769-1824), there is evidence of the introduction into Alta California of such important aliens as common foxtail, lamb's-quarters, black mustard, bur clover, Napa thistle, Italian ryegrass, annual bluegrass, wild oat, nettle-leaf goosefoot, rough pigweed, creeping buttercup, annual yellow sweet- clover, cheese-weed, wild carrot, and Chilean tarweed.These are now widespread in the state, though not all have become troublesome as weeds.Famous early botanists, visiting California, make scant reference to alien plants.In 1831-32 David Douglas traveled extensively on the Pacific Coast, and in 1836 Thomas Nuttall journeyed along our south coast ; they made extensive collections, but included no mention of aliens.During 1843-44 John C. Fremont coursed the state from one end to the other, but records only one such plant, red-stem filaree.Howell (1937c) was privileged to examine a collection of California plants made by the Russian-American Company in 1840-41, chiefly in Sonoma County.Among the 346 specimens, representing 214 species and varieties, were several aliens-definite evidence that certain species had occurred even at that early date.The following are included : red-stem filaree, white-stem filaree, annual bluegrass, windmill pink, wild radish, red pimpernel, tomatillo, yellow oxalis, black nightshade, selfheal, and a Malva species (seedling) .University of California -Experiment Station oat and red-stem filaree "took possession of the country."These immi- grants increased until the native species diminished in quantity to the point where animals began grazing the introduced species.These, in turn, began to disappear and to be replaced by Mediterranean barley, rat's-tail fescue, and upright chess, the three chief range grasses in 1902.Davy described, in 1902, a third immigration : white-stem filaree, ripgut grass, common foxtail, Napa thistle, smooth cat's-ear, bur clover, and other weeds were "establishing themselves along the roadsides and around ranch houses."Bauer (1930), studying the vegetation of the Tehachapi Mountains, finds that on the floor of the San Joaquin Valley, at the base of the Te- hachapis on the north, prominent grasses are red brome, ripgut grass, common foxtail, beardless wild-rye, and alkali sacaton.He recognizes five distinct types of vegetation: (1) desert;(2) woodland-blue oak and valley oak;(3) conifer forestyellow pine, and the like; (4) grass- land; and (5) chaparral.Characteristic of the grassland are red brome, Australian chess, ripgut grass, soft chess, common foxtail, wild oat, scratchgrass, and needle-and-thread.Bauer states