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Shifts in acreage of planted and natural stands: reclassifying forest management types

Natural succession and disturbance, artificial regeneration, and timber harvesting alter species distributions and stocking levels. A change in forest management type often results. For example, when oak or other hardwoods become established in a natural pine stand, the management type classifications can change from natural pine to oak-pine and eventually to upland hardwoods. Or a planted pine stand, after a final harvest or following some intermediate treatment, can become stocked with enough hardwood stems to change its management type to planted oak-pine. Moreover, even if no harvesting or management activity occurs, a planted stand may, through natural succession, become indistinguishable from a natural stand and would be classified as natural pine, oak-pine, or hardwood.

Table 16.9 displays the changes in forest management types that occurred between 1989 and 1999. The columns of the table give the most recent (1999) estimate of acres in each management type. The extreme left column lists the previous management type that identifies how these acres were classified in the previous (1989) inventory. Data for Kentucky were not available.

Using the management type totals for 12 of the region’s 13 States, planted pine and planted oak-pine combined totaled 34 million acres in 1999. Most of that acreage—about 22 million acres—was classified as planted pine/oak-pine in the previous survey. Planted pine/oak-pine acreage increased 12 million acres between surveys. What was the source for the increase in acres of planted stands? More than 3 million of the additional acres classified as planted pine/oak-pine in 1999 were natural pine stands in 1989. Another 1 million acres of natural oak-pine were reclassified as planted stands, as were nearly 5 million acres of upland and lowland hardwoods combined. The change in management type classification for these acres likely occurred as the result of harvesting followed by artificial regeneration.

Acres previously classified as nonforest were sources for "new" planted stands. Between 1989 and 1999, over 3 million acres of nonforest land were regenerated and reclassified as planted pine/oak-pine stands. It is these acres that account for much of the increase in timberland area since 1989. The greatest loss of timberland to nonforest occurred in upland hardwood forest types, which lost over 2 million acres since 1989.

Many timberland acres with a planted forest management type also were reclassified. In all, about 3 million acres identified as planted pine/oak-pine in 1989 were reclassified as natural stands by 1999. This change in type included 1 million acres reclassified as upland hardwoods, 970,000 acres reclassified as natural pine, and 408,000 acres reclassified as natural oak-pine.

Stand-age structure: young pine plantations and older natural stands

The importance of stand age has increased as planted stands have accounted for an increasing percentage of the South's timberland area. Part of the argument against pine plantations is that the intensively managed, comparatively young planted pine stands lack the biological diversity of natural stands. This shortcoming makes plantations less desirable for wildlife habitat, recreation, and other forest-derived amenities.

As a general rule, management of pine plantations dictates that few stands ever reach 50 years of age. Of the 34 million acres of planted pine/oak-pine stands in 1999, over half were less than 13 years old, and 81 percent were less than 23 years old (fig. 16.14 and table 16.10). Planted stands reaching 50 years or older are often being managed for sawtimber, or are possibly no longer being managed at all, and were left to return to a natural condition.

Natural stands tend to encompass a wider range of stand ages, but few 100 year-old natural stands still exist in the South. In 1999, only 3 million acres of southern timberland supported stands older than 93 years, and 88 percent of those stands were hardwoods (table 16.10).

The age distribution for hardwoods showed that most stands were between 33 and 62 years old (fig. 16.14). Thirty-four percent of hardwood stands were younger than 33 years, and less than one-quarter were older than 62 years. Natural pine/oak-pine acres were skewed toward comparatively young age classes—53 percent of the stands were less than 33 years old.