Growth and Yield
Growth of pinyon, though maintained with little loss of vigor throughout the life of the tree, is extremely slow. Height growth of saplings, for example, is only about 10 to 15 cm (4 to 6 in) yearly, and mature trees grow even more slowly, averaging 5 to 10 cm (2 to 4 in) per year. Diameter growth also is slow, especially on poor sites, where 80 to 100 years can elapse before diameters at breast height reach even 10 to 15 cm (4 to 6 in). On better soils, however, 150-year-old trees may grow to a diameter of 30 cm (12 in). Mean annual diameter growth of pinyon culminates at about 1.8 cm (0.7 in) per decade, when trees are approximately 50 years old. The gross annual increment on sample plots in northern New Mexico woodlands also reflects the slow growth rate, averaging about 0.42 m³/ha (6 ft³/acre) for pinyon alone, and 0.66 m³/ha (9.5 ft³/acre) for all species. Gross cordwood increment for all species was 0.88 m³/ha (0.14 cord/acre) (38,66,67).
Pinyon is a long-lived tree, maturing in 75 to 200 years. Dominant trees in a stand are often 400 years old, and pinyons 800 to 1,000 years old have been found. Depending on the site, mature trees range between 3.0 and 15.5 m (10 to 51 ft) in height and 15 to over 76 cm (6 to 30 in) in d.b.h. Although large trees are common, especially in northern New Mexico, pinyons generally are small trees, usually less than 10.7 m (35 ft) tall and 46 cm (18 in) in diameter (66,67). The largest living pinyon recorded grows in New Mexico and measures 172 cm (68 in) in d.b.h., 21.0 m (69 ft) in height, and has a crown spread of 15.8 m (52 ft) (2).
Because of the growth habit of woodland species, tree volumes are not only difficult to measure but can vary more than 300 percent for trees of the same diameter. There is less variation in well-formed trees, however, and the gross volume of a representative pinyon with a basal diameter of 30 cm (12 in) and 7.6 m (25 ft) tall is 0.22 m³ (7.7 ft³), measured to a 10-cm (4-in) top. Woodland volumes vary considerably, depending on species composition and density. In northern New Mexico and Arizona, mixed stands may contain cordwood volumes ranging from about 5.0 to 157.4 m³/ha (0.8 to 25 cords/acre), with average volumes of about 69.3 m³/ha (11 cords/acre). Cordwood volumes of nearly pure pinyon stands average about 75.6 m³/ha (12 cords/acre). Low volumes are a reflection of the small trees generally associated with woodlands. The average size tree in many New Mexico stands is only 15 cm (6 in) in diameter at ground line and about 2.7 m (9 ft) tall (16,67).
The density of pinyon in woodlands varies considerably, ranging from few or none to several hundred stems per hectare. Nevertheless, the density in a typical northeastern Arizona stand averages about 235/ha (95/acre) in stems less than 7.6 cm (3 in) in d.b.h.; 200/ha (81/acre) from 7.6 to 15 cm (3 to 6 in) in d.b.h.; and 89/ha (36/acre) more than 15 cm (6 in) in d.b.h. (67). Mixed woodlands are denser and more productive than pure stands of either pinyon or juniper, and can approach or exceed 3,459 stems/ha (1,400/acre) (9,57). The higher values have been attributed to differences in rooting habit and drought tolerance of the two species. The shallower penetrating roots of pinyons limit interspecific root competition for soil moisture in mixed stands. This, combined with the lower photosynthetic rate of pinyons compared to that of junipers at higher water stresses, allows more complete site utilization in mixed stands (10,25,57). The average number of pinyons suitable for Christmas trees varies from a few trees per acre to a fairly large number.
- Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp. http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm
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