A third factor causing the decline in net 
annual softwood growth is a rise in 
mortality—it roughly doubled in a 10-year 
period. Much of the increase in mortality 
is attributable to losses from pine bark 
beetles. Suppression is the second-leading 
cause of loss, followed closely by disease. 
before it turns back up. On forest industry land, softwood 
growth continues to rise throughout the projection period 
and climbs to 1.6 billion cubic feet a year, more than 75 
percent above current levels. Currently, forest industry land 
produces about 32 percent of the softwood growth. This 
proportion is projected to climb to about 47 percent in 
2020. 
By management type, pine plantations are projected to 
provide an increasing share of the softwood growth. In 
1984, net annual growth of softwood on pine plantations 
totaled 0.9 billion cubic feet, about 30 percent of total 
softwood growth. Softwood growth on pine plantations is 
projected to increase to 2.5 billion cubic feet and eventually 
accounts for 72 percent of the total. Even by 2000, pine 
plantations will provide 64 percent of the softwood growth. 
Trends in the South Central Region 
The most recent inventories in the South Central region have 
also shown declines in softwood net annual growth (app. 
tables 3.22 and 3.36). Net annual softwood growth rose 
steadily between 1952 and 1976 but appears to have 
peaked around 1980, according to the most recent data 
available. Increases prior to 1976 reflect strong ingrowth 
of softwood trees to merchantable size on large acreages of 
new pine forests naturally regenerated or planted on cutover 
timberland and idle cropland and pasture prior to 1962. 
[52 
Almost all of the recent decline in softwood growth has 
occurred on other private timberland. Forest industry 
owners have steadily increased planting and the conversion 
of natural to planted pine, and this is reflected in increases 
in softwood growth. Softwood growth on public lands has 
fallen slightly, primarily because of withdrawals of timber- 
land for wilderness or other uses that restrict timber 
harvesting. 
These changes are reflected in the trends in softwood growth 
by management type. Softwood net annual growth on pine 
plantations increased by 26 percent between 1976 and 1984. 
In contrast, softwood net annual growth in natural pine and 
mixed pine—-hardwood stands declined by 14 percent. 
The drop in net annual softwood growth on other private 
timberland is caused by a number of factors. First, the area 
in pine has declined steadily since 1962. This is the result 
of timberland clearing for other uses, lack of pine regen- 
eration after final harvest, and selective cutting that produces 
a net acreage shift to hardwood types. 
Prior to 1962, the cropland area declined, and much of the 
idle land regenerated naturally or was planted to pine. As 
these young stands reached merchantable size, high rates 
of ingrowth contributed to increases in net annual growth. 
The fourth factor causing the decline in 
net annual softwood growth is a reduction— 
20 to 30 percent over large areas in the 
South—in the annual rates of tree diameter 
growth. The causes of this reduction have 
not been determined. Changes in stand 
density and age, drought or other weather 
factors, the loss of residual fertilizer in 
old fields that came back to pine, and 
atmospheric deposition are all possible 
contributing factors. 
