No. 103 

1960 

EFF'ECT OF COMPETITION ON HEIGHT GROWTH 

AND SURVIVAL OF PLANTED JAPANESE LARCH 

On the Dilldown Unit of the Delaware-Lehigh Experimental Forest in Pennsylvania, several planting studies have 

been made with the aim of finding the most economical and 

practical methods of converting scrub oak areas to productive high-forest types. These studies have already shown 

the need for site preparation prior to planting. Seedlings 

planted on prepared areas grew significantly faster than 

those in the untreated areas.' 

One of several methods of site preparation tried in 

these studies was by means of a rototiller--a machine that 

operates on the principle of a rapidly revolving cylinder 

armed with tines or knives. The tiller usea in this study 

was a large, heavy model; it worked a strip 6 feet wide and 

was capable of chopping up the brush and mixing it into the 

surface 6 inches or so of soil. However, because of many 

stones in the soil of the experimental area, the machine 

could not be run at normal speed. Consequently, some of the 

heavier root crowns were not cut off and, in general, the 

roots were not as thoroughly macerated as would have been 

possible in stone-free soil. 

In one phase of the rototiller tests, intensity of 

site preparation was varied by working the strips one, two, 

or three times. Subsequent observations of Japanese larch 

planted on these strips showed that survival and growth 

varied with intensity of treatment. The extent of the differences and their probable cause are discussed below. 

1 

McNamara, E F. and Reigner, I. C Root competition slows growth of 

plantings on unprepared sites in scrub oak. Northeast. Forest Expt. Sta. Forest Res. Note 54. 3 pp. 1955. 
Methods 

Three plots, each about 800 feet long and comprising 

five strips, were prepared and planted in the spring of 1951. 

In one plot each of the five strips was tilled once; in a 

second plot they were tilled twice; and in a third plot, 

three times. One row of Japanese larch seedlings was planted in each strip. The seedlings were good-quality 2-0 stock 

ranging from 0.8 to 2.0 feet tall, and averaging about 1 

foot. 

Survival was checked annually, and after the third 

year heights were measured each year on an approximately 10- 

percent sample through the 1956 growing season. There are 

no data after 1956--the sixth year--because the planting was 

destroyed by a wildfire in May 1957. 

Results 

Rather unexpectedly, the site treatments affected 

seedling survival: the more intensive the treatment, the 

better the survival (table 1). The difference between the 

single and triple treatments was significant statistically, 

by conventional t-test, at the 1-percent level (after arcsin transformation of the percentage data). Differences between the single and double, and between the double and 

triple treatments, were significant at the 5-percent level. 

Height growth also increased with intensity of treatment, as the following tabulation shows: 

Rototiller 1953 height 1956 height 

treatment (feet) - (feet) 

Single 

Doub 1 e 

Triple 

For both of the years shc;vn, differences between the single 

and triple treatments were significant at the 1-percent 

level, and those between the single and double treatments 

were significant at the Spercent level. The double-treatment vs. triple-treatment differences were not significant. 

Growth during the first 3-year period was faster than 

in the second 3 years of all treatments. Assuming a mean 

height of 1 foot at the time of planting, the 3-year growth 

figures are: 

Rototiller 1951-53 growth 1954-56 growth 

treatment (feet) - ( - feet) 

Single 

Double 

Triple 
Table 1.--Survival of planted Japanese larch seedlings 

as affected bv Rototiller treatments 

Survival at the end of-- 

Rototiller 

treatment 2nd 4th 6th 

growing growing growing 

season season season 

Percent Percent Percent 

Sing1 e 7 4 72 7 0 

Double 81 80 78 

Triple 89 86 85 

, 

Discussion 

These are not good growth rates for Japanese larch, 

and the decline during the second 3 years is not a normal 

growth pattern. On the contrary, if the factors governing 

growth remain the same, growth rates normally increase after 

the second or third year. This is demonstrated by another 

planting of the same species at Dilldown, even though our 

data on it are not strictly comparable to those given above. 

In this planting, strips were cleared with a root-rake and 

have remained essentially free of competing vegetation. The 

seedlings averaged about 1.5 feet at planting, and 2.5 feet 

after 2 years. But during the next 3 years they put on more 

than 3 feet, reaching a mean height of 5.75 feet in the 

fifth year. 

The cause of the comparatively poor growth in the 

rototiller planting is believed to have been the increasing 

competition--largely root competition, since very few trees 

were overtopped. The rototiller did not remove the vegetation as does a root rake or bulldozer--it merely set back 

this vegetation. Root crowns of many of the scrub or bear 

oak clumps remained wholly or partly in place, and resprouted vigorously. Of greater importance, probably, was the recovery by stoloniferous and root-suckering species such as 

blueberry, sheep laurel, chokeberry, bracken fern, and sassafras, which can regenerate from separate pieces of stolon 

or root. The less intensive the treatment, the quicker 

these species recovered, but by the end of the third year 

they had practically regained their former density, even on 

the triple-tilled strips. 

Japanese larch is noted for its inability to withstand competition, In view of this species characteristic, 

the generally poor growth of the trees in this planting over 

the 6-year period, the somewhat better growth under the more 
intensive site treatments, and particularly the decline in 

growth as the native vegetation recovered, all support the 

theory that competition was the chief inhibiting factor. If 

the planting had not burned out, it is possible that the 

trees, after slowly gaining some additional root and crown 

development, would have overcome the depressive effects of 

the competition and grown at a satisfactory rate. In this 

particular case we shall never know. However, on the basis 

of the evidence at hand, it does not seem advisable to plant 

Japanese larch in scrub oak areas without some sort of site 

preparation that completely removes all vegetation in the 

vicinity of each seedling. For this purpose, clearing strips 

by means of a bulldozer or root-rake is recommended. 

--E. F. McNAMARA and IRVIN C. REIGNER 

E. F. McNAMARA is District Forester for the Delaware District of the 

Pennsylvania Department of Forests and Waters; he is stationed at Stroudsburg, 

Pa. IRVIN C REICNER is a Research Forester at the New Lisbon (N. J. ) Research 

Center of the Northeastern Forest Eperirnent Station, U.S. Forest Service.