Net annual growth is the total volume of wood to live growing stock added through new growth in one year minus all losses from growing stock due to insects, decay, fire, and removals (i.e. timber harvesting and land clearing). When net annual growth is divided by removals (or harvest), the resulting value provides an indication of whether growing stock volume is rising or falling. A net annual growth to removals value of one or greater indicates that growing stock volume is rising; a value of less than one indicates that volume is declining.

 

In the United States, net growth has exceeded removals for both hardwoods and softwoods for at least 50 years consecutively; for hardwoods this has been true for at least the past 70 years (Figure 13, Table 6). The most recent (2002) growth to removals ratio for U.S. hardwoods is 1.74.

Figure 13
Net Growth/Removals Ratios on Timberland
U.S., 1952-2001

 

Source: USDA - Forest Service RPA Assessment, 2000; Smith et al., 2004.

Table 6
Net Forest Growth/Removals Ratios on Timberland - U.S., 1952-2001

 

Source: USDA-Forest Service, RPA Assessment 2000; Smith et al. 2004.

Although the net annual growth to removals ratio applies only to forestland that has not been formally placed in a reserved status, not all such land is, in fact, available for periodic timber harvesting. Lands managed by the U.S. Forest Service provide an example of such lands; though technically available for harvest, in reality little to no harvesting activity occurs today on lands that comprise the National Forests.

Because of tightening restrictions on timber harvesting on government-controlled forestland, privately held forests provide an inordinately large share of the nation's timber supply. For instance, privately owned forestlands of the United States comprise about 57 percent of all forestland, but 71 percent of all timberland, and 92 percent of removals from growing stock. Moreover, the percentage of removals coming from privately owned land has increased in recent decades as removals from government lands have declined. As a result of these changes, the difference between growth and harvest on privately owned forestland has narrowed in recent decades, interrupted only by the recession marking the beginning of the new millennium (Figure 14). The growth to removals ratio is expected to continue to shrink through at least 2020.

 

Figure 14
National Trends in Growth and Harvest in U.S.
Privately Owned Forests, 1953 - 2020

Billions of cubic feet/ year

 

 

Source: USDA - Forest Service, 2000.

 

Forests of the East are overwhelmingly privately owned and dominated by hardwoods. Annual growth substantially exceeds annual removals for both northern and southern hardwoods (Figures 15 and 16), although the gap between growth and removals is narrowing in the South. In both regions the hardwood growth/removals ratios are declining, but remain well above 1.0 (Figure 17).

Page url: http://www.fsclumber.us?trendsintimbergrowthandre.htm