77 



SHADE TREES FOR CALIFORNIA 



W. W. WAGENER 



Climate is the key to the trees that 

 can be grown in a region. On the Pa- 

 cific coast, the key to the climate is the 

 Pacific Ocean, which imparts its rela- 

 tively mild temperatures and its char- 

 acteristic summer droughty period. 

 The region embraces more than 16 of 

 latitude and extends inland about 120 

 miles to the high barrier formed by the 

 Sierra and Cascade Mountain chains. 

 East of the barrier, the climate is arid 

 or semiarid and has a much greater 

 yearly range in temperatures. Eastern 

 Washington, eastern Oregon, and a 

 part of eastern California share this in- 

 terior type of climate. This article dis- 

 cusses shade trees in California; the 

 next article is about trees in the north- 

 ern Pacific area the western parts of 

 Washington and Oregon. 



No part of the United States presents 

 a greater diversity in climate, topog- 

 raphy, and soils than California. Rela- 

 tively mild winter temperatures and a 

 long summer dry season are common 

 to all parts of the State except the 

 higher mountains, but in other respects 

 even a few miles may bring wide dif- 

 ferences in the conditions that govern 

 tree growth. 



Few trees, consequently, have suffi- 

 cient adaptability to be satisfactory in 

 all parts of the region, and the planter 

 must make his choice on the basis of 

 the conditions prevailing in his own 

 neighborhood. An important consider- 

 ation in inland districts is whether the 

 tree is to receive supplemental irriga- 

 tion, directly or indirectly, or whether 

 it must depend on moisture provided 

 by the winter rains. Another is whether 

 the ground contains appreciable quan- 

 tities of soluble salts, commonly known 

 as alkali. If so, the choice should be 

 species known to be alkali-tolerant. 



From the thousands of trees that 

 will grow successfully in California, or 

 parts of it, I shall discuss here a limited 

 number that are generally suitable for 



shade and ornament or have specific 

 qualities that fit them for use under 

 conditions that are unfavorable for 

 most species. In general, I omit trees 

 used primarily for accent or specimen 

 planting, the palms, nearly all of the 

 eucalypts, and a few species of other 

 types that once were popular but are 

 not recommended now because of in- 

 sects, diseases, or undesirable qualities. 

 Among the last are the elms, Monterey 

 cypress, and the black acacia. 



Besides the trees here described, the 

 owner who is considering planting 

 around the home should not overlook 

 the ornamental and shade value of our 

 fruit and nut trees. The apricot, avo- 

 cado, cherry, orange, kaki persimmon, 

 mission fig, Persian walnut, and many 

 another often serve a double utility. 



THE CALIFORNIA LIVE OAK is a 

 rather evenly rounded tree when it is 

 young; it spreads broadly with age. 

 It grows up to 30 to 75 feet rather 

 slowly at first but faster when it is well 

 established and supplied with mod- 

 erate amounts of water in summer. Its 

 leaves are small and oval, dark green 

 and glossy above, paler below, and 

 rather dense. It casts a fairly dense 

 shade unless the crown is thinned by 

 pruning. For yards, streets, and road- 

 ways it is satisfactory in the coastal dis- 

 tricts, where it is native, and also in 

 the less hot and dry parts of the in- 

 terior. In some districts it is subject to 

 defoliation by the larvae of the Cali- 

 fornia oak moth which never kill the 

 tree and are readily controlled by 

 sprays. Some trees suffer from mildew 

 in the coastal districts that have sum- 

 mer fogs. Because heavy pruning and 

 heavy summer watering favor the de- 

 velopment of mildew, the tree should 

 not be planted on lawns or other areas 

 that are constantly irrigated. Despite 

 these disadvantages, the merits of the 

 tree make it good for many districts. 



