No. 113 

1961 

HUMUS DEPTHS UNDER CUT AND 

UNCUT NORTHERN HARDWOOD FORESTS 

Harvesting timber on lands devoted primarily to 

watershed management may alter, for better or worse, many 

features of a forested watershed. One such feature is forest humus. The beneficial role of forest humus in watershed 

management is widely recognized. A protective mantle of 

humus serves to cushion the impact of rain, to impede surface runoff, to restrict soil freezing, to favor infiltration, and to store certain amounts of rainfall. 

In general, the effects of timber harvesting upon 

humus depths are extremely variable, depending in part upon 

timber type, climate, and degree of cutting. Theoretically, 

humus should be shallower under heavily-cut stands than 

under uncut stands, at least for the first several years. 

Opening the canopy would reduce the leaf supply; and exposing the humus to direct solar radiation would speed decomposition. 

Sartz and Huttinger (4) found less humus under stands 

with fair stocking than under stands with good stocking. 

Curves developed by Morey (3) of humus depth over stand age 

in temporary hardwoods and long-lived hardwood forest types 

in the Connecticut River Valley show that humus depth reaches a minimum 20 to 30 years after clearcutting. Then humus 

begins to build up, and reaches its original depth 70 to 80 

Years after clearcutting. Carmean (1) reported that 4 

years after clearcutting the weight of humus on the clearcut 

and uncut plots was not significantly different; this was a 

study on poor oak sites with thin mor humus in Ohio. 
Study Area And Method 

There were two reasons for making this study: (1) To 

obtain some information on humus depths in northern hardwood 

stands in the White Mountain region of New Hampshire. Such 

information is virtually non-existent. (2) To compare humus 

depths under uncut stands with humus under stands that were 

partially cut and clearcut 20 to 25 years ago. 

Humus measurements were made on six plots at the U.S. 

Forest Service's Bartlett Experimental Forest at Bartlett, 

New Hampshire. The plots were situated on two areas about 4 

mile apart. Site quality of the level lower area was greater than that of the steeper upper area. 

The upper area had been partially logged about 1875. 

An uneven-aged stand of beech, sugar maple, and yellow birch 

(about 75, 10, and 5 percent, respectively) occupied this 

area in 1934 when the experimental cuttings were made. The 

soil is Hermon very stony sandy loam, a well-drained podzol. 

The lower area, which is more accessible, had been 

clearcut about 1875, and an even-aged second-growth stand 

developed. In 1937 this area had a 60-year stand of red 

maple, paper birch, and white ash (30, 15, and 15 percent, 

respectively). The soil is Waumbek stony fine sandy loam, a 

moderately well-drained podzol. 

A clearcut plot, an individual-tree-selection plot, 

and an uncut control plot were established in the upper and 

lower areas during the period 1934 to 1939. Cutting practices employed are described in table 1. Each plot was 10 

acres in size. 

To determine the effects of these treatments on humus 

depth, humus was measured in 1959 on a sampling grid covering 1 acre in the center of each plot. In each acre-grid a 

cut of humus down to the mineral soil was extracted at 60 

points, a sufficient number of observations to render a difference in humus depth between cutting practices of 0.5 inch 

significant at the 5 percent level. This cut was examined 

and the L, F, H, and A1 layers, if present were measured to 

the nearest 1/10 inch. The humus type was classified according to Hoover and Lunt (2). 

Results 

Mor-type humus predominated on the plots. Only a few 

mulls and duff mulls were found, and they did not appear to 

have been influenced in their development by the churning 

action of soil organisms commonly associated with mull formation. More likely, the presence of mull-like humus was 

due to mixing by windthrow or past logging operations. The 

scarcity of mull types and the uncertainty as to whether 

they were true mulls led to excluding them from this report. 
Table 1 .--Average humus de~ths on clearcut. ~artiallv cut. 

and uncut plots at the Bartlett Experimental Forest, 

-I 

Bartlett, New Hampshire, 1959 

Plot character layer F layer H 

LOWER AREA 

This area clearcut about 1875. Soil type is 

Waumbek, a moderately well-drained stony fine 

sandy loam. Slope 3-8 percent. 

Inches Inches 

1. Clearcut in 1939. 0.50 *2.35 

2. Thinning cut in 1937, removing 

40 percent of volume. .44 .95] 

3. Uncut. .41 3.37 

UPPER AREA 

This area partly cut about 1875. Soil type 

is Hermon, a well-drained very stony sandy 

loam. Slope 25-35 percent. 

4. Clearcut in 1935. *0.51 2.05 

5. Cut in 1934 by individual-treeselection method. 30 percent 

of volume removed. 

81 2.27 

6. Uncut. .72 2.33 

* 

Plots that have significant differences in F or H layers 

are joined by lines. These differences are significant at the 1- 

percent level. 

Average depths of the F- and H-layers of the mors are 

given in table 1. Clearcutting reduced the depths of the Hlayers in the lower plots. The H-layer in Plot 1, which was 

clearcut in 1939, averaged 2.35 inches, while on the uncut 

Plot 3 it was 3.37 inches. The 1.02-inch difference was 

significant at the 1-percent level. A similar comparison 

between the clearcut and uncut plots (4 and 6) of the upper 

area gave a difference of 0.28 inches, which was not significant. 

Partly cut plots had intermediate depths, and differences between them and the more heavily cut and uncut 

plots were not significant. On both sites an orderly trend 

of a decreasing H-layer with increasingly heavy cuts is apparent. 
The wide range of depths of the F-layers between 

plots of the upper area proved to be highly significant. The 

greater depth of this layer in the partly cut plot may be 

attributable to the more vigorous crowns and dense understory of the forest cover. Thinner F-layers on the lower 

set of plots may be due to conditions more favorable to 

rapid decomposition. 

Literature Cited 

1. Carmean, W. H. 

1959. Litter weight not reduced following clearcutting of poor-site oak stands. Jour. Forestry 

57: 208-209. 

2. Hoover, M. D., and Lunt, H. A. 

1952. A key for the classification of forest humus 

types. Soil Sci. Soc. Amer. Proc. 16: 368-370. 

3. Morey, H. F. 

1942. The application of our knowledge of the organic 

layers of the soil profiles to flood control. 

Pa. State Coll. Hydrology Conf. Proc. 1941: 

143-148. 

4. Sartz, R. S., and Huttinger, W. D. 

1950. Some factors affecting humus development in the 

Northeast. Jour. Forestry 48: 341-344. 

--GEORGE HART 

Research Forester 

Northeastern Forest Experiment Station 

Forest Service, U.S. Dept. Agriculture 

Laconia, N. H. 

AGRICULTURE-FOREST SERVICE-UPPER DARBY