Silvical Characteristics of Monterey Pine (Pinus radiata D. Don) Douglass F. Roy U. S. FOREST SERVICE RESEARCH PAPER PSW- 31 Pacific Southwest Forest and Range Experiment Station Berkeley, California 1966 Forest Service - U. S. Department of Agriculture Contents Introduction ---------------------------------------------------------------------------------- 1 Habitat Conditions --------------------------------------------------------------------------- 1 Climatic ---------------------------------------------------------------------------------- 1 Edaphic ---------------------------------------------------------------------------------- 2 Physiographic --------------------------------------------------------------------------- 2 Biotic ------------------------------------------------------------------------------------- 3 Life History ---------------------------------------------------------------------------------- 6 Seeding Habits -------------------------------------------------------------------------- 6 Vegetative Reproduction -------------------------------------------------------------- 7 Seedling Development ----------------------------------------------------------------- 8 Seasonal Growth ------------------------------------------------------------------------ 9 Sapling Stage to Maturity ------------------------------------------------------------- 10 Special Features ------------------------------------------------------------------------------ 15 Races and Hybrids --------------------------------------------------------------------------- 15 Literature Cited ------------------------------------------------------------------------------ 16 The Author DOUGLASS F. ROY is responsible for the Station's silvicultural studies of pines, mixed conifers, and true fir types. Native of San Francisco, he earned B.S. (1946) and M.S. (1962) degrees in for- estry at the University of California. Upon joining the U.S. Forest Service in 1946 he was assigned to the Station's research staff at Berkeley. Since 1963, he has been headquartered at Redding, California. Figure 1.―The natural range of Monterey pine. onterey pine (Pinus radiata D. Don) is coast (fig. 1). The largest stand is 8,000 to 12,000 1 paradoxical. This tree, which now has acres on and adjacent to the Monterey Peninsula. The second largest is about 2,500 acres surround- little economic importance in its native M ing the town of Cambria, which lies about 85 miles stands, has been planted more abundantly through- southeast of Monterey. Another isolated stand of out the world than any other American tree. Its about 500 acres is at Pico Creek, about 6 miles introduction as a forest tree into the Southern north of the main Cambria forest. The northern- Hemisphere has been particularly successful. Ex- most grove probably is less than 1,000 acres,2 and tensive stands of Monterey pine now grow in New only a part of this area is clothed by pure stands Zealand, Australia, Chile, and South Africa. Plant- of pine. It is in the Swanton area, 40 miles north- ings also have been successful in Spain, Argentina, west of Monterey and about 14 miles from Santa and Uruguay. Cruz. The natural range of Monterey pine is extremely Another natural stand is found on Guadalupe limited. On the United States mainland it is con- Island situated about 200 miles off the coast of fined to three localities on the central California Lower California (fig. 1).3 Habitat Conditions Climatic Forests on the Monterey Peninsula are shrouded by clouds or fogs at least one-third of the time. Monterey pine grows in a humid climate. The Consequently summer fogs contribute significant annual precipitation is seasonal, however, and amounts of available moisture. As much as 0.57 varies from 15 to 35 inches. The minimum rainfall inch of fog-drip per week was measured at higher in one year has varied from 5.68 inches at Del elevations of the peninsula.5 Monte to 12.37 inches at Santa Cruz. And maxi- Average mean daily temperatures range from mum annual rainfall has ranged from 28.98 inches 48° F. to 52° F. during January and 60° F. to at Monterey to 50.41 inches at Santa Cruz. About 64° F. in July. Winters are relatively mild although 70 to 75 percent of this moderate amount falls in frosts occur occasionally. The last killing frosts the rainy season that extends from December in the spring generally come between February 5 through March. Three-fourths of the 50 to 55 and February 28; the first killing frosts in the fall rainy days in each year occur during these four are expected between November 30 and December months. Each of the other eight months have, on 10. The days free of killing frosts each year num- the average, less than 2 inches of rain. In fact, ber 300 or more. The greatest seasonal range of rainy days in July and August are rare (Lindsay temperature recorded near Monterey pine stands [1932]; Martin and Kincer 1934). is 24° F. to 98° F. (Sprague 1941). Although Monterey pine grows in a humid climate throughout the year, humidity is higher 1 McDonald, John Bruce. An ecological study of Mon- in summer and winter than in spring and autumn. terey pine in Monterey County, California. 1959. (M.S. For example, the average minimum relative hu- thesis on file at Univ. Calif., Berkeley.) 2 Forde, Margot Bernice. Variation in the natural popu- midity at Monterey for July is between 60 and 70 lations of Monterey pine (Pinus radiata [D.] Don) in percent (Lindsay [1932]). This high humidity California. 1962. (Ph.D. thesis on file at Univ. Calif., is maintained by summer fogs. The characteristic Berkeley.) 3 Howell 1941; Jepson 1910, 1923, 1925; Newcomb patterns of fog movement inland seem to explain 1959; Sargent 1922. the distribution of the Monterey pine forest where 4 Forde, M. B. Op. cit. See footnote 2. other factors are not limiting.4 5 McDonald, J. B. Op. cit. See footnote 1. 1 Edaphic Santa Lucia clay loam, which is high in organic matter, acid in reaction, permeable, well drained, Monterey pine grows on a variety of soils devel- and easily eroded. Colma loam also is represented. oped from different parent materials. The soil series represented characteristically are coarse- This soil, formed from weakly consolidated marine textured sandy loams, strongly to very strongly sediments, is slightly acid and well drained. Small acid in reaction, and extremely to moderately areas of Tierra loam, Lockwood loam, and Wat- permeable. Sometimes they are leached in an A-2 sonville loam also are within the forest. horizon. The best sites have soils that are sandy Humus development generally is good on sites barns to fine sandy loams in texture, well drained where mature pines reach heights of 80 feet or and moderately deep. McDonald6 reported that he more. Here pole stands, 50 to 60 feet tall, and could not find trees growing on soils less than 9 stands of larger trees have litter 3 to 6 inches inches deep. Near rock outcroppings, Monterey deep with active disintegration on the bottom to pine generally does not grow taller than 70 feet, form a definite humus layer. Beneath this layer, and soils at least 3 to 4 feet deep appear necessary considerable organic matter darkens the soil for trees to reach 100 to 120 feet (Lindsay several inches deep. On poor sites humus does [1932]). not develop (Lindsay [1932]). Most of the Monterey Peninsula is formed by granitic rocks, but basalts, sandstones, shales, and Physiographic schists also occur. The soils, however, are derived mainly from an overlying shallow marine deposit. In general, Monterey pine is found on gentle The most extensive soil series is the shallow phase to moderate slopes, from sea level to a maximum of Elkorn, which sustains a uniform forest with elevation near 1,000 feet, and from the sea to trees occasionally more than 100 feet tall and 36 about 6 miles inland. At Swanton, where rainfall inches in diameter. Most of this soil is 3 to 4 feet is more abundant, this species grows on all aspects. deep. It is a calcareous sandy loam that is well But at both Monterey and Cambria, which are drained and often is high in organic matter.7 The significantly drier, the hot and dry south aspects shallow phase of McClusky sandy loam also sup- are not favorable sites. All areas where Monterey ports a large forested area, but is less productive. pine is established naturally are well drained. This soil is 20 inches to 5 feet deep, averaging Swanton, at latitude 37° north, is the most 40 inches. Bedrock outcrops in a few places. The northerly area of natural Monterey pine stands. relatively heavy subsoil causes imperfect drainage. Here patches of Monterey pine are scattered on Other poorer soils in the Monterey area are Santa the narrow coastal stretch of rolling terrain be- Lucia clay loam derived from slow weathering of tween the sea and the steep slopes of Ben Lomond silicious shales, and Chamise sandy loam. Mon- Mountain. Most of the pines grow at elevations terey pine also grows on these soils and on coastal between sea level and about 500 feet, but a few dune sand, which is fine, high in silica content, are found on the steep slopes up to 800 feet. The and poor at retaining moisture (Carpenter and best sites are on the hilly country a few hundred Cosby 1929). yards to a mile and a half from the coast (Lindsay The rocks in the Cambria area are early Jurassic [1932]). slates, cherts, sandstones, and limestones, but the The main pine stand in the Monterey area is Monterey pine forest grows almost entirely on located on the Monterey Peninsula, latitude 36½ ° Arnold sandy