All Live Trees

80

The basic data for all live trees (crop and noncrop) during the third period for each treatment by year are given in table 2. At the end of the third treatment period, the total number of trees per acre varied from 83 to 938 and the average d.b.h. from 7.1 to 13.2 inches. Basal area per acre varied from 77.0 to 261.0 square feet and total volume per acre from 2,192 to 7,508 cubic feet. Treatment 1 has less basal area and cubic-foot volume at the end of the third treatment period than at the end of the second period because of the continued heavy thinnings called for in the study plan.

The spread in average diameter between treatments and the control continued to widen. Total volume in cubic feet varied according to stand density in either number of trees or basal area-the higher the density, the greater the volume.

The gross PAI and cumulative volume yield (see appendix 2 for calculation procedures) for all trees is given in table 4. The diameter PAI varied from 0.33 to 0.56 inch on treatment plots compared with 0.11 inch for the control plots. The basal area and cubicfoot volume increment among the eight treatments were largest for treatment 7 and smallest for treatment 1. Treatments 5, 6, 7, and 8 had a larger gross basal area PAI than the control plots (table 4). The gross basal area PAI per acre for treatment 7 for the third treatment period was 10.0 square feet compared with 8.8 for the control plots; yet the total basal area of the live trees was 150.0 and 256.3 square feet at the beginning of the 1974 growing season for treatment 7 and the control plots, respectively.

The gross PAI per acre for the third treatment period varied from 223 cubic feet for treatment 1 to 437 for treatment 7 compared with 440 cubic feet for the control plots.

Figure 5 gives the cumulative cubicfoot volume by treatments for 1975 for trees larger than 11.5, 9.5, 7.5, 5.5, and 3.5-inch d.b.h. Trees 12 inches and larger in the treatment plots had significantly more volume than trees

CUNITS PER ACRE

1 2 3 4 5 6 7 8 CONTROL TREATMENT

200

CUBIC METERS PER HECTARE

Figure 5.--Cumulative 1975 cubic-foot volumes for trees larger than 11.6-,

9.6-, 7.6-, 5.6-, and 3.6-inch d.b.h. by treatments; a cunit is 100 cubic feet.

in the control plots. Trees in all treatments except 1 and 2 had more cubic-foot volume in trees 10 inches and larger than did trees in the control plots. Volume of trees 8 inches and larger in treatment 7, however, was approximately equal to that of the control plots, but trees in all other treatments had less volume. Although the control plots have much more total cubic-foot volume, this additional volume is contained in the 639 trees (68 percent of the total) that are less than 7.6-inch d.b.h. (table 14). Most of the mortality will probably occur in these size classes over the next few years. Also, trees in the thinned plots are growing at a much faster rate than the trees in control plots. This could mean that the volumes in at least some of the thinned plots in the next treatment periods will equal or surpass those of the control plots.

Figure 6 shows the cumulative 1975 Scribner board-foot volumes for trees larger than 11.5-, 9.5-, and 7.5-inch d.b.h., all to a 6-inch top diameter. Only in treatments 7 and 8 did trees 7.6-inch d.b.h. and larger have more total board-foot volume than trees in the control plots. Trees 9.6-inch d.b.h. and larger, however, in all treatments except treatment 1 have more volume; and trees 11.6-inch d.b.h. and larger in all treatments have a larger board-foot volume than trees in the controls.

This further emphasizes the greater volume in the larger tree sizes in the treatment trees over those in the control plots. Trees in treatments 7 and 8 have more board-foot volume than trees in the controls, but the difference in volume between treatments 4, 5, and

Of

6 and the controls is not great. special interest is treatment 4 which now has more board-foot volume in trees 11.6 inches and larger than the control plots have in trees 9.6 inches and larger. As the growing stock in treatment 4 increases with time, the board-foot volumes could exceed those of the control and possibly of treatment 7.

In figure 7 the Scribner board-foot volume thinned in 1966, 1970, and 1973 are added to the 1975 volumes in figure 6. With these additional volumes, only treatments 1 and 2 have less total board-foot volume than the control plots.

18

THOUSAND BOARD FEET PER ACRE

2 3 4 5 6 7 8 CONTROL TREATMENT

Figure 6.--Cumulative 1975 Scribner board-foot volumes for trees larger than 11.5-, 9.5-, and 7.5-inch d.b.h. to a 6-inch-top diameter by treatments.

1 2 3 4 5 6 7 8 CONTROL TREATMENT

Figure 7.--Scribner board-foot volumes in 1975 and total volumes thinned in 1966, 1970, and 1973 by treatments for trees 7.6-inch d.b.h. and larger to a 6-inch-top diameter, based on 16-foot logs.

Crop Trees

The stand data by treatment for the crop trees are given in table 3. At the end of the third treatment period, the cubic-foot volume of the crop trees in the treatment plots was 1.7 to 2.1 times that of the trees in the control plots. The gross PAI data for crop trees are shown in table 5. The basal area PAI of the crop trees for the third treatment period for the thinned plots was 2.7 to 4.6 times greater than the basal area PAI of the crop trees on the control plots. The basic data for the crop trees by treatment and plot for the third treatment are found in table 8. The gross cubic-foot PAI for the crop trees in the thinned plots are from 2.2 to 3.6 times that of crop trees in the control plots. These data show that the growth rates of the crop trees in the thinned plots are increasing with time relative to those of the crop. trees in the control plots (see discussion under "Crop Trees" for the second treatment period).

Discussion, All Treatment Periods, 1963-75

Data for All Live Trees

Natural suppression mortality reduced the number of trees on the control plots by 46 percent (1,727 to 938 per acre). Mortality on the thinned plots was minimal (table 6). After the calibration thinning in 1963, the number of trees per acre in the thinned plots varied from 328 to 365. As a result of three treatment thinnings, the number of trees per acre in 1975 varied from 83 to 260 (table 2). The average d.b.h. for all trees on the thinned plots at the end of the 1963 growing season was just over 5.0 inches. By the end of the 1975 growing season, the average d.b.h. of trees on the thinned plots varied from 10.9 to 13.2 inches. In contrast, the average d.b.h. of trees on the control plots was 3.8 inches in 1963 and 7.1 inches in 1975.

Basal area per acre for the thinned plots varied only from 49.0 to 50.4 square feet at the beginning of the calibration period (1963). By the end of the 1975 growing season, the basal area per acre for the thinned plots ranged from 77.0 to 169.8 square feet because of treatment differences. The basal area per acre of the control plots increased from 138.1 square feet in 1963 to 261.0 square feet in 1975. The cubic-foot volume per acre for the thinned plots varied from 720 to 768 in 1963 and from 2,192 to 4,959 in 1975. The control plots contained 1,982 cubic feet per acre in 1963 and 7,508 in 1975 (table 2).

Table 12 presents net PAI per acre for the average diameter, basal area, and cubic volumes for all trees. The basal area PAI for the thinned plots during the calibration period varied from 11.8 to 12.7 square feet; for the control plots, it was 15.5 square feet. For the first treatment period, the basal area PAI varied from 11.1 to 13.6 square feet, and the control plots averaged 11.0 square feet. For the second treatment period, the basal area PAI varied from 8.2 to 12.4 square feet for the thinned plots and averaged 9.2 square feet for the control plots. For the third treatment period, the basal area PAI of the thinned plots varied from 6.3 to 9.9 square feet, and that of the control plots averaged 2.3 square feet. From 1963 through 1975, treatments 5, 6, 7, and 8 each had a larger basal area increment than the control plot (table 12). Table 4 shows that the basal area PAI for all plots was considerably lower for the 1972 growing season which accounts for some of the difference between the PAI for the first treatment period and the second treatment period for treatment 7.

A comparison of the change in cubicfoot PAI for the treatments and for the control plots shows that the change in cubic-foot PAI for treaments 3 through 8 was greater than that for the control plots for both the first and second treatment periods. For example, PAI for treatment 7 was 275, 428, and 496 for the calibration, first treatment, and second treatment periods, respectively; the corresponding PAI for the

control plots was 460, 512, and 515 (table 12). Thus, treatment 7 PAI increased 153 cubic feet between the calibration period and the first treatment period and 68 cubic feet between the first treatment period and the second treatment period, compared with 52 and 3 cubic feet for the control plots.

For the third treatment period, the cubic-foot PAI for treatments 1 and 2 was less than the cubic-foot PAI for treatments 1 and 2 for all previous periods (table 12). The cubic-foot PAI for all treatments for the third treatment period was below that for the second treatment period. Only treatment 1, the lowest level of growing stock, had a lower PAI than the control plots. The large reduction in the PAI for the control plots is attributed to the mortality that occured in 1974. A comparison of the PAI between treatments 1 and 2 and between treatments 3 and 4 for the second and third treatment periods shows that the increased level of growing stock in treatments 2 and 4 has produced an increased PAI. A comparison of the PAI between treatments 5 and 6 and between treatments 7 and 8 for the second and third treatment periods shows that the decreased level of growing stock in treatments 6 and 8 has produced a decreased PAI.

There was no ingrowth in any of the plots from 1964 through 1975.

Data for All Live and Dead (Mortality) Trees

The cumulative gross basal area yield for all trees by treatment and thinning period is shown in figure 8. The amount of material removed by the calibration thinning was derived from the control plot data since records were not kept of the actual amount removed during the calibration thinning.

Figure 9 shows the gross cubic-foot yield by treatment and thinning period. Note the uniformity of initial volume even though the initial level of growing stock was determined by basal area. There were only minor fluctuations in cubic-foot volume increment during the calibration period. Growth during the

SQUARE FEET PER ACRE

80

1 2 3 4 5 6 7 8 CONTROL TREATMENT

20

Figure 8.--Cumulative gross basal area yield by treatment and thinning period.

first and second treatment periods is directly correlated with the level of growing stock in each treatment period (tables 2 and 4). In the third treatment period, however, treatment 7 with a beginning volume of 4,092 cubic feet had a cubic-foot PAI of 437 compared with a beginning volume of 6,955 cubic feet and a cubic-foot PAI of 440 for the control plots. Treatment 7 had the greatest total cubic-foot yield of any treatment. Figures 10 and 11 show the gross periodic annual increment by treatment and thinning period. 10 illustrates the relationship of the gross PAI by period within each treatment. Treatments 5, 6, 7, and 8 each had a greater difference in gross cubicfoot PAI between the calibration period and the first treatment period than did the control plots. This was also true between the first treatment period and the second treatment period. For example, the gross PAI for treatment 7 was 275 cubic feet for the calibration period and 428 cubic feet for the first treat

Figure