MORE TREES

The first figure gives total growing hardwood and softwood timber in the United States according to Forest Statistics of the United States, U.S. Forest Service (1987) &ndash U.S. Dept. of Agriculture, 319 S.W. Pine Street, P.O. Box 3890, Portland, OR 97208, compiled by K.L. Wad-dell, D.D. Oswald, & D.S. Powell. The values are 610243, 659343, 693976, 725054, and 755996 million cubic feet for the years 1952, 1962, 1970, 1977, and 1987 respectively. I have drawn the figure and least squares line which gives a 1958 to 1993 increase of 23%.

Long-lived pine trees are especially useful indicators, since they provide long baselines with which to compare recent tree growth. Therefore, Donald A. Graybill and Sherwood B. Idso, Global Bio-geochemical Cycles , Vol. 7, No. 1, pp 81-95 (1993) have measured tree-ring growth in long-lived pine trees at 14 locations in California, Nevada, Colorado, and Arizona. From 15 to 30 trees at each location were cored with 4.5 mm diameter bores about 4 feet from the ground. Widths of tree-rings in these cores were measured to 0.01 mm. Standard corrections and population normalization were applied to these measurements. The second figure shows smoothed 20-year averages of these normalized widths beginning in 150 AD; the third shows normalized measurements of Bristlecone Pine beginning in 1680.

The greatly increased growth rates of these pine trees which exactly parallel the industrial production of carbon dioxide during the past century is obvious. Moreover, it is known that animal populations increase in direct proportion to plant populations.