No. 101 

1960 

NEMATODES INHABIT SOILS 

OF FOREST AND CLEAR-CUT AREAS 

Nematodes are present in all forest soils, but their 

effects on forest trees are not known. The known destructive nature of these worms on other woody crops suggests 

that they may also be involved in causing some of the unexplainable losses in vigor and mortality of forest trees. 

Nematodes are unsegmented roundworms. They comprise 

99 percent of the animal forms larger than protozoa in the 

soil. Many nematodes are not plant parasites; but approximately 150 species do feed on higher green plants. Some 

species are capable of destroying large fields of different 

crops. All known plant-parasitic nematodes have a stylet 

in their anterior end, which is used for puncturing plant 

cells and sucking out the cellular contents. Most of these 

parasites have a large host range. Nematode diseases of 

woody ornamentals, fruit trees, and forest tree seedlings in 

the nurseries are known. Many plant diseases are incited by 

a fungus-nematode complexes. ' 

Soil conditions and species of green plants growing 

in any area affect nematode populations. The clear-cutting 

of a small area in an established forest causes changes in 

soil conditions, and species of green plants not common in 

the forest abound in these cleared areas. 

A study was made on the Bartlett Experimental Forest 

in New Hampshire to determine whether there was a difference 

between the types and numbers of nematodes inhabiting the 

soils in small clear-cut areas and the adjacent forest. 

 or a detailed account of nematodes, see Christie, J. R. Plant nematodes, 

their bionomics and control. 256 pp. Drew Co., Jacksonville, Fla. 1959. 
Materials And Methods 

Ten soil samples were collected from four selected 

clear-cut areas, each approximately 2/3 acre. *A similar 

number of samples were collected from the forest. The 

samples (5 pounds each) were collected at random from the 

upper 8 inches of soil, in plastic bags. Each bag was 

securely tied, assuring an air-tight seal. All collections 

were made on November 10, 1959. 

The soil from each sample was passed through an 8- 

mesh screen, and five subsamples were selected from each 

sample, each containing 25 ml. of loose soil. Each subsample 

was poured into a nematode-trapping apparatus. 

The nematode traps (fig. 1) were made of common 

waxed-paper drinking containers .2 Three types of containers 

were used. An inverted 5-inch cup with the bottom cut out 

(A) served as a support. A cone cup (B) was placed on this, 

and was filled with water to within 4 inch of the top. The 

top unit (C) was made of two bottomless &pint cups, with 

wet-strength paper tissue held taut between them to form a 

tissue bottom. 

The soil sample was poured into this top unit, which 

was then placed gently into the water-filled cone. The 

active nematodes were washed from the soil; and after maneuvering through the tissue they fell to the bottom of the 

water-filled cone. After 24 hours the bottom 24 ml. was 

pipetted from each cone and poured into Syracuse glasses 

divided into nine sections on the outside bottom surface 

with a marking pencil. The nematodes were counted under 

low power (9X) of a dissecting microscope. 

After being counted, the nematodes from the clearcutting and forest samples were placed in separate containers. The bottom 5 ml. of each container was pipetted into 

a Syracuse glass. Twenty-six water mounts were examined 

from each collection. The number of nematodes on each slide 

was recorded, and all stylet-possessing forms were recorded 

and identified by genus. 

Results 

There were great differences among the total numbers 

of nematodes contained in all soil samples, but the subsamples from each sample were always fairly consistent in 

their nematode numbers. More nematodes were contained in 

the 50 subsamples (24,933) from the clear-cutting than in 

the 50 forest subsamples (15,525) . 

+he nematode-trapping apparatus described was perfected by members of the 

Plant Pathology apartment at West Virginia University. 
Figure 1. --The nematode trapping apparatus made of waxedpaper containers. A, the support; B, cone, filled with 

water; and C, top unit, consisting of two cups holding a 

diaphragm of wet-strength paper tissue. The nematodes, 

washed out of soi 1 samples, work their way through the 

tissue diaphragm a.nd are collected in the bottom of th.e 

cone. 

The amount of organic matter and the moisture content 

in the clear-cutting samples were lower than in the forest 

samples. 

The 52 water mounts made from the 100 subsamples contained mostly freeliving forms. Samples from the clearcuttings contained more of these forms than those from the 

forest. Species of Rhabditus were most common. Seven other 

genera of freeliving forms were observed. 

A total of 1,500 nematodes were counted in the water 

mounts from the forest samples and 37 percent were styletpossessing forms. The stylet-possessing forms made up 27 

percent of the 1,687 nematodes counted in the water mounts 

from the clear-cutting samples. 

The majority of the stylet-possessing forms responsible for the high count from the forest samples were tentatively identified as Aphelenchoides sp. Many of these nematodes were not mature. A total of 404 Aphelenchoides sp. 

were counted in the water mounts from the forest samples, 

and 233 from the clear-cutting samples. 

A species of Dorylaimus was common in all the water 
mounts; 129 were counted from the clear-cutting samples and 

114 from the forest samples. 

A greater variety and number of other stylet-possessing nematodes were observed in the water mounts from the 

clear-cutting samples (96) than from the forest samples (39). 

Among the genera observed were Pratylenchus, Rotylenchus, 

Ditylenchus, Criconemoides, Tylenchorhynchus, Tylenchus, and 

Helicotylenchus. 

Discussion 

Although a very small sampling was used in this in- 

-vestigation, it is of interest to conjecture that 37 percent 

of the 15,525 nematodes counted from the 50 forest subsamples and 27 percent of the 24,933 nematodes counted from 

the 50 clear-cutting subsamples were possible plant parasites. The number of possible plant parasites from the 

clear-cutt ing subsamples (6,732) would then be greater than 

the number from the forest subsamples (5,744). Since each 

subsample contained 25 ml. of soil, 50 subsamples would 

contain 1,250 ml., or la liters of soil. So the possibility 

exists that several thousand possibly plant-parisitic nematodes are present in every quart of soil in the forest areas 

sampled. 

It should be pointed out that a nematode with a stylet does not necessarily indicate that, it is a parasite on 

higher plants. Many nematodes possessing a stylet feed on 

fungi, algae, and other nematodes. Since some species of 

Aphelenchoides and Dorylaimus are not plant parasites, care 

was taken in this note not to insinuate that all species 

possessing a stylet are plant parasites. Conversely, some 

freeliving forms, especially Rhabditus spp., have been 

associated with damping-off because they have been found inside seedling roots soon after disease symptoms were observed. 

The results suggest that there are differences in 

numbers and types of nematodes between the two areas. Soil 

conditions and species of green plants in the clear-cuttings 

differed from those in the forest. The large numbers of 

nematodes in the clear-cuttings may have been the result of 

these differences. 

Because of the possible effect of nematodes on forest 

trees, it seems that further research on nematodes in forest 

soils would be worth while. 

--ALEX L. SHIGO and GEORGE YELENOSKY 

Laconia Research Center 

Northeastern Forest Experiment Stat ion 

Forest Service, U.S. Dept. Agriculture 

Laconia, N.H.