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Trends in Growing-Stock Growth

The effects of reforestation and the resulting volume increases had a dramatic effect on growing-stock growth. As growing-stock volume increased during the first three survey periods after World War II, so did the average annual growth of growing stock (fig. 16.21). From 1953 to 1982, total growing-stock growth increased from 6,683 million cubic feet per year to 11,323 million cubic feet per year. During this period, softwood growing-stock growth increased by 73 percent, while that of hardwoods increased 65 percent (table 16.19). After 1982, growth of both softwoods and hardwoods decreased slightly. From 1982 to 1999, average annual growth of softwoods declined 5 percent and hardwood growth decreased 2 percent. These data indicate that average annual growth of growing stock peaked in the 1970s and has since leveled off. After a decline in 1982, the subsequent survey showed a slight increase, 11 percent, in average annual growth. This increase corresponds to the time when gains in forest land in the South began to outpace losses (see Total change in forest land: additions and diversions). Changes in timberland area often lead to changes in growing-stock growth. Therefore, this increase in area produced an increase in average annual growth of growing stock.

It is important to realize that while the rate of growth has slowed since the mid-1970s, growth is still occurring. In 1999, southern forests produced 10,862 million cubic feet of wood per year.

Dividing average annual growth by growing-stock volume creates a ratio that reveals the relationship between growth and standing volume. Historically, average annual softwood growth represented between 4.90 and 6.25 percent of the total softwood growing-stock volume (fig. 16.22). Hardwood growth rates fluctuated between 3.1 and 4.1 percent. The dip in average annual growth that occurred due to changes in timberland during the 1970s is clearly visible in the figure.

Growth trends by ownership

Because NIPF landowners control the majority of the timberland, growth on NIPF land mimics the trend of all landowners (fig. 16.23). Average annual growth of growing stock is the average increase in volume of growing-stock trees. It includes any volume from new trees or timberlands. Average annual growth of growing stock on NIPF land was 4,586 million cubic feet per year in 1953 and increased to 7,962 million cubic feet per year by 1982 (table 16.20). The growth rate dropped to 6,705 million cubic feet per year in 1989 before reaching the latest level of 7,271 million cubic feet per year.

Growth rates on forest industry land and national forests differ from the NIPF trend and from each other. Growth on national forests rose from 432 million cubic feet per year in 1953 to a peak of 667 million cubic feet per year in 1982. However, by 1999, the average annual growth on national forests was back to 511 million cubic feet per year. Conversely, growing-stock growth on forest industry land reached its highest point 2,618 million cubic feet per year in 1999.

The reason for the differing patterns of growth rates lies in the motives and management practices of the two different ownerships. Forest industry tries to maximize profit and therefore the volume cut in its operations. This approach leads to management practices that focus on smaller, younger trees that grow more vigorously. Thus, forest industries growth rates benefited in the 1950s, 1960s, and 1970s from early reforestation efforts and during the 1980s and 1990s from its focus on smaller, faster growing trees.

National forests are not managed to maximize timber production; they are managed to meet the needs of a diverse group of users. Many national forest management plans require long rotations. As these stands age, growth rates in them decline. Nevertheless, these stands produce fiber and wood products along with the other benefits for society.

Growth rates on other public timberland reached all-time highs in 1999. In fact, with the exception of the 1989 estimate, the average annual growth of growing stock for this land has increased steadily. A large part of the reason for this increased growth is land acquisition. From 1953 to 1999, 3.3 million acres of public land were acquired (table 16.2).

Average annual growth by forest type

Annual growth of growing stock in various forest types has always been of keen interest. The average annual growth of growing stock in loblolly pine plantations more than doubled between 1989 and 1999 (fig. 16.24 and table 16.21), going from 879 million cubic feet per year to 1,768 million cubic feet per year. Meanwhile, the growth of natural pine stands dropped from 2,646 million cubic feet per year to 2,412 million cubic feet per year. In 1999, planted stands accounted for 10 percent of the South’s total growing-stock volume, but produced 23 percent of the average annual growth of growing stock.

Total growing-stock growth for the 12 Southern States rose from 9,391 million cubic feet per year to 10,478 million cubic feet per year. Forest types other than planted pine that gained growth were oak-pine with a 10-percent increase, oak-hickory with a 9-percent gain, and oak-gum-cypress with a 4.6 percent gain. The elm-ash-cottonwood, maple-beech-birch, and natural pine forest types all experienced decreases in average annual growth.

Average annual growth for latest surveys

Alabama’s 2000 survey revealed net annual growth of softwood growing stock averaged 884 million cubic feet per year, an increase of 34 percent since the previous survey period. Softwood growth increased 91 percent on public lands, 36 percent on NIPF lands, and 25 percent on forest industry land. Planted stands accounted for half of the softwood growth. Net annual growth of hardwood growing stock averaged 596 million cubic feet, an increase of 5 percent since the previous survey period. Hardwood growth increased 25 percent on public lands and increased 12 percent on NIPF lands, but decreased 35 percent on forest industry lands.

South Carolina’s net annual growth of softwood growing stock almost doubled since the State’s last survey, going from 343 million cubic feet to 661 million cubic feet per year. Softwood growth was up on all ownerships, reflecting the recovery from Hurricane Hugo. Net growth of softwoods on forest industry timberland increased 61 percent and averaged 205 million cubic feet per year. Net annual growth of softwoods on NIPF land rose from an annual rate of 207 million cubic feet to 415 million cubic feet. Net annual growth of South Carolina’s hardwood increased 61 percent to 292 million cubic feet. As with softwoods, hardwood net growth increased on all ownerships, including a 57-percent increase to 243 million cubic feet per year on NIPF land.