WHITE PINES OF WESTERN NORTH AMERICA 223 



Jackson, 1967) . Additional hybrids with P. flexilis and P. stvobus 

 have been reported by Wright (1959) . There is some question about the 

 identity of the P. ayacahuite trees used in making the last two hybrids 

 listed above. It is possible that these trees may themselves be hybrids, 

 i.e., P. x holfovdiana (J. W. Andresen, personal communication). 



Mexican white pine would appear to have very good potential for 

 planting as a timber tree in areas where the climate is moderately warm 

 and moist. The P. ayacahuite x griffithii hybrid also appears to have 

 considerable potential for slightly cooler areas. The relative blister 

 rust resistance of P. ayacahuite is largely unknown (Bingham 2 ). 



Sugar Pine (P. lambertia na) 



Sugar pine is the largest of the white pines, reaching heights to 

 250 feet and diameters of 10 feet (Fowells, 1965). It is native to the 

 mountain ranges of west-central and southwestern Oregon, California, 

 extreme west-central Nevada, and a small area in northern Baja California 

 in Mexico (Critchfield and Little, 1966; Map 7) . Best growth is obtained 

 on deep, well -drained soils in areas where the annual precipitation is 

 40 to 50 inches per year. The species most often occurs over an elevation 

 range of 3,000 to 5,000 feet; however, the extreme lower limit is about 

 1,000 feet in western Oregon and the extreme upper limit is about 10,500 

 feet in southern California and Baja California (Fowells, 1965). 



Sugar pine usually occurs in mixed stands with a wide variety of 

 other species including: Pinus ponderosa Laws., Pinus jeffreyi Grev . § 

 Balf . , Abies magnifica A. Murr., Abies concolor (Gord. and Glend.) Lindl., 

 Abies pvoceva Rehd., and Pseudotsuga menziesii (Mirb.) Franco. Single, 

 large, old trees may contain 25,000 board feet of lumber or more but the 

 average yield per acre would probably not be much over 50,000 board feet 

 of sugar pine (Fig. 7). In well-managed young stands on the best sites, 

 yields of 85,000 board feet per acre are expected at 100 years (Fowells, 

 1965) (Fig. 8). On medium sites, dominant young trees reach 100 feet in 

 height and 21 inches in diameter at 100 years. On high-quality sites they 

 are slightly taller and about the same diameter at 60 years (Fowells, 1965) 



Sugar pine is planted on a commercial scale in Oregon and California 

 and also has been tried in several countries around the world. New Zealand 

 has some 180 acres of plantations with growth ranging from moderate to 

 good, i.e., 90 feet tall and 25 inches in diameter at 48 years (Streets, 

 1962) . However, it appears that few, if any, of the countries that have 

 experimented with sugar pine plan any large scale plantings because of 

 establishment difficulties and restrictive site requirements for good 

 growth. 



Attempts to cross sugar pine with other species have been successful 

 only with Pinus avmandii Franch. and Pinus koraiensis Sieb. $ Zucc. 

 (Righter and Duffield, 1951). Practical interest in the hybrids has been 

 related to the possibility of introducting blister rust resistance. The 

 significance of these crosses from a taxonomic and evolutionary point of 

 view is also of prime interest. 



Although sugar pine is an important and productive tree in its 

 natural habitat it has not found too much favor in trials elsewhere. This 

 is perhaps due to its site requirements for good growth; also, the species 

 is highly susceptible to the white pine blister rust disease (see Bingham 2 ) , 



