No. 92 

1959 

HARDWOODS ON POORLY DRAINED SITES 

DO NOT RESPOND TO LOW THINNING 

Little is known about the effects of thinning upon 

hardwoods in southern New Jersey. To supply some of this 

needed information, State foresters have established several 

thinning studies. This research note reports the results 

of two of these studies, both located in stands of the pin 

oak-sweetgum type. One study was in Salem County, the other 

in Cumberland County. 

The Studv 

In 1946, when these studies were started, the two 

stands had some common characteristics. They were composed 

primarily of several oak species, sweetgum, and red maple; 

but most of the dominant trees were oaks. The Cumberland 

County stand was 45 years old, the Salem County stand 47 

years old. 

Two $-acre plots were established in each stand. Both 

of the Salem plots were located on Elkton loams and had a 

site index of 65. The thinned Cumberland plot had chiefly a 

Showell loam soil and a site index of 55; the control plot 

had chiefly a Fallsington loam soil and a site index of 50.l 

Prior to thinning, plots in the Salem stand were similar. However, those in the Cumberland stand differed appreciably, as shown by the following per-acre values: 

Average Basal Merchant able 

- Plot - Stems - diameter 'area - vo 1 ume 

Salem: (No.) (Inches) (Sq.ft.1 (Cu.ft.1 

Thinned 672 5.3 103 2,288 

Unthinned 548 5.4 87 1,850 

Cumber1 and : 

Thinned . 820 4.9 107 1,781 

Unthinned 1,204 3.8 9 7 1,137 

l~chnur, G.L. Yield, stand, and volume tables for even-aged upland oak forests. U.S. Dept. Agr. Tech. Bul. 560. 88 pp. 1937. 
In 1946 one of the paired plots in each stand received 

a low thinning. This removed 62 percent of the stems and 30 

percent of the basal area in the Salem stand, and 42 percent 

of the stems and 28 percent of the basal area in the Cumberland stand. In both areas, red oaks, white oaks, and sweetgum were favored, thus increasing the proportions of these 

species in the thinned plots. 

Results 

During the 10 years that followed, the thinnings had 

relatively little consistent effect upon stand growth, either in diameter, basal area, or cubic-foot volume (table 1). 

Although the thinned Cumberland plot showed greater volume 

growth than the control, its increment formed a smaller percentage of the 1946 post-thinning volume than that of the 

unthinned plot. The growth percent on the thinned Salem 

plot was also less than that of the control. 

Since hardwood buyers in New Jersey are, at present, 

interested chiefly in sawtimber, the effect of thinning on 

future sawtimber trees was considered. The 25 largest deTable 1.--Ten-year growth of all trees and of crop trees 

following thinning 

Increment in: 

I I I I Average diameter 

Inches Inches scl.ft. u. Cu.ft. Cu.ft. 

Salem 

Thinned 0.9 1.3 14 14 570 499 

Unthinned 0.8 1,6 22 19 - 875 -1 693 

I I 

Cumberland 

Thinned 0.6 1.6 2 6 16 691 479 1 Unthinned 0.9 1.4 13 13 628 371 

Basal area per acre 

'TO a top diameter of 4 inches d.0.b. 

Merchantable volume 

per acre1 

Crop trees 

sirable trees per plot were selected as crop trees and their 

growth was computed (table 1). These computations indicated 

that low thinning did not consistently stimulate the 10-year 

diameter, basal area, or volume growth of the crop trees. 

In fact, in both stands, the growth percent of crop trees in 

the thinned plot was less than that in the unthinned plot. 

All trees 

While some thinnings generally have little influence 

on total stand growth, they do have a highly important effect in redistributing growth, in reducing the volume in 

low-value species, and in increasing the volume of desirAll trees Crop trees All trees Crop trees 
able species. In these studies no such changes occurred, 

probably because desirable species dominated the stands before treatment. Then too, differences between plots of each 

pair in site, stocking, and diameter distribution could have 

masked, in part, real differences in response to thinning. 

Since a low thinning was employed, it is also doubtful 

whether the quality of crop trees on the thinned plots was 

greatly improved. 

Conclusions 

Low thinnings made in 45- and 47-year-old hardwoods on 

moderately productive, poorly drained sites in southern New 

Jersey did not increase the 10-year growth of either the entire stand or of selected crop trees. Where desirable stems 

were already dominant, low thinnings did not improve stand 

composition. 

--H. B. TEPPER 

Northeastern Forest Experiment Station 

Forest Service, U.S. Dept. Agriculture 

and G. T. BAMFORD 

Forest Management Section, N.' J. 

Dept. of Conservation and Economic Development 

AGRICULTURE-FOREST SERVICE-UPPER DARBY