[f=$ United States &. i Department of Agriculture 

Forest Service 

Northeastern Forest 

Experiment Station 

The Northern Hardwood Forest 

Ecosystem: Ten Years of 

Recovery from Clearcutting 

J. W. Hornbeck 

C. W. Martin 

R. S. Pierce 

F. H. Bormann 

G. E. Likens 

J. S. Eaton 
Abstract 

Two even-age management systems, progressive strip cutting and block clearcutting, have been studied since 1970 on small watersheds at the Hubbard Brook 

Experimental Forest, New Hampshire. In the strip cutting, all merchantable trees 

were harvested in a series of three strips over 4 years (1970-74). In the block 

clearcutting, all trees were harvested in a single operation in 1970. This paper 

contrasts progressive strip cutting and block clearcutting for the 10-year period 

after initiation of harvest in terms of hydrologic response, erosion losses, stream 

water ions, nutrient leaching, nutrient removals in harvested products, and natural regeneration of vegetation. 

The Authors 

J. W. HORNBECK, C. W. MARTIN, and R. S. PIERCE are with the Northeastern 

Forest Experiment Station, Durham, New Hampshire. F. H. BORMANN is with 

Yale University's School of Forestry and Environmental Studies, New Haven, 

Connecticut. G. E. LIKENS and J. S. EATON are with the Institute of Ecosystem 

Studies, The New York Botanical Garden, The Mary Flagler Cary Arboretum, 

Millbrook, New York. 

Manuscript received for publication 25 March 1986 

Northeastern Forest Experiment Station 

370 Reed Road, Broomall, PA 19008 

February 1987 

COVER-Harvested watersheds at the Hubbard Brook Experimental Forest in 

New Hampshire. 
Contents 

The Study Area ...................................... 2 I Design and Methods .................................. 3 

Watershed Harvests ................................. 3 

Hydrology Studies .................................. 4 

Erosion Losses in Streamflow ........................ 5 

Weir Basin Data .................................. 5 

Turbidity Data ................................... 5 

Stream Water Ions and Nutrient Budgets .............. 5 I Biomass and Nutrients in Harvested Products .......... 6 

Regeneration ....................................... 6 

Results .............................................. 6 

Hydrologic Response ................................ 6 

Strip Cutting ..................................... 6 

Block Clearcutting ................................ 8 

Erosion Losses ..................................... 8 

Stream Water Ions .................................. 9 

Calcium ......................................... 9 

Potassium ........................................ 9 

Magnesium ....................................... 10 

Sodium .......................................... 10 I 

...................................... I Ammonium 10 

I Hydrogen ........................................ 10 

Nitrate .......................................... 10 

Sulfate .......................................... 11 

......................................... 1 Chloride 11 

Cation-Anion Summary ........................... 12 

Nutrient Budgets .................................... 12 

Calcium ......................................... 13 

Potassium ........................................ 13 

Nitrate ........................................... 13 

Sulfate .......................................... 13 

Biomass and Nutrients Removed by Harvest ........... 15 

Regeneration ....................................... 15 

Discussion ........................................... 16 

Changes in Water Yield ............................. 16 

Erosion Losses in Streamflow ........................ 18 

Concentrations of Stream Water Ions ................. 20 

Mechanisms Affecting Concentrations ............... 20 

Sulfate .......................................... 21 

Hydrogen ........................................ 21 

Management Implications .......................... 22 

Evaluation of Nutrient Removals and Leaching Losses . . 22 

Calcium ......................................... 24 

Potassium ........................................ 24 

Magnesium ....................................... 25 

Nitrogen ......................................... 25 

Sulfur ........................................... 25 

Phosphorus ...................................... 25 

Management Implications .............................. 25 

Regeneration ....................................... 26 

Conclusion ........................................... 27 

Acknowledgment ...................................... 27 

Literature Cited ...................................... 28 
Introduction 

Northern hardwood forests in the Northeastern United 

States provide highly valued goods and services, including 

timber, recreation, esthetics, wildlife, and watershed protection. Because these products cannot always be obtained 

simultaneously, controversy sometimes arises over how 

best to use the resources of the northern hardwood forest. 

The best known example is the conflict over the use of 

clearcutting for harvesting northern hardwoods (Horwitz 

1974). Clearcutting is defined as the harvesting in one cut 

of all trees on an area for the purpose of creating a new, 

even-aged stand (USDA 1973). For forest managers, 

clearcutting is an attractive silvicultural method because it 

is economical and amenable to the increasing mechanization accompanying harvests, and it favors new stands with 

high proportions of commercially valuable species of Betula 

and Acer. On the other hand, since the late 1960's there 

has been an increased awareness of possible adverse 

effects of clearcutting on soil nutrients, water quality, wildlife, esthetics, and stand regeneration. 

Some of the concerns about clearcutting have eased. 

Forest managers addressed the problem of esthetics by 

making clearcuts smaller, cleaning up debris to improve 

the appearance of the harvest site, and locating boundaries 

of cut areas to fit the landscape. But other concerns, such 

as those regarding soil nutrients, hydrology, and stand 

regeneration, could not be addressed adequately, and 

stimulated new research. This paper is an example, reporting research begun in 1970 at the height of the concerns 

over clearcutting. The study involves two types of clearcutting in northern hardwoods, block and progressive strip, and 

how each affects nutrient and hydrological cycling and 

stand regeneration. The results span 10 years, or from 

harvest well into the establishment of new stands. 

Progressive strip cutting evolved from block clearcutting as 

an attempt to further favor regeneration of birches by more 

closely controlling variables such as distance to seed 

sources, light, moisture, and scarification of the seedbed. 

The method of strip cutting applied in our study is recommended by Marquis (1066) and Safford (1983) and entails 

cutting strips about 25 m wide oriented along the contour 

with 50-m-wide uncut strips between them. After a 2-year 

period for establishment of regeneration, a second series of 

25-m strips are cut on the southernmost or westernmost 

side of the original cut. The remaining strips are then cut 

after a second establishment period of 2 years. As in block 

clearcutting, all merchantable stems are removed and 

scarification is encouraged during logging, with appropriate 

measures to avoid erosion (Marquis 1969; Filip 1969). 

After the first strip is cut, it receives shade from the trees 

on its south or west border. This provides favorable conditions for germination and early survival. When the second 

strip is cut, it receives shade for initial establishment but 

also allows the first strip to receive direct sunight. Thus, 

both the first and second strips receive shade for seedling 

establishment, and then direct sunlight for best growth. 

During these harvests, seed sources are close by in the 

uncut strips. When the third strip is cut, it receives only 

minimal shade, and seed sources are more distant. However, Betula and Acer seedlings that survive the first year 

or two of direct sunlight then have optimal growing conditions in terms of light and moisture. 

By stretching over 4 years, strip cutting would seem to 

lessen some of the environmental concerns surrounding 

block clearcutting. The strips of varying ages of living 

vegetation minimize erosion and leaching of nutrients to 

streamflow. However, testing is needed to determine if 

advantages of strip cutting in terms of stand regeneration 

and protection of site and stream water outweigh the convenience and economics of block clearcutting. Our study 

addresses some of these questions. 

The Study Area 

Our study was conducted on the 3,000-ha Hubbard Brook 

Experimental Forest in West Thornton, New Hampshire. 

Hubbard Brook is operated by the USDA Forest Service's 

Northeastern Forest Experiment Station. Four small watersheds were used: watershed 6, an untreated control for the 

nutrient cycling studies, is 13 ha; watershed 3, an 

untreated control for the hydrologic studies, is 42 ha; watershed 4, which was strip cut, is 36 ha; and watershed 101, 

which was clearcut as a block, is 12 ha (Fig. 1). The watersheds extend from 450 to 800 m above sea level and have 

southerly aspects and herage slopes of 20 to 30 percent. 

Descriptions of the study sites have been given in previous 

publications of the Hubbard Brook Ecosystem Studies. 

Vegetation has been described by Bormann et al. (1970) 

and Siccama et al. (1970). The biogeochemistry is 

described in Likens et al. (1977), and the hydrology and 

climate in Hornbeck et al. (1970). Soils on the study watersheds are derived from coarse-textured, glacial till material 

that has been subjected to frost action, erosion, and deposition since glacial retreat about 14,000 years ago. Till 

depths range from 0 to 5 m. The surficial layers have 

weathered to form fine sandy loams classed as Lithic and 

Typic Haplorthods. Soil profiles often are mixed due to 

treethrow, but usual development includes 0, E, Bhs, Bs, 

and C horizons that differ markedly in physical and chemical properties. Soil depths average 0.5 m on top of a dense 

basal till nearly impermeable to roots and water. The more 

common soil series include Marlow, Lyman, Peru, Hermon, 

and Monadnock. 
HUBBARD BROOK 

EXPERIMENTAL FOREST 

West Thornton, New Hampshire 

Figure 1.-The Hubbard Brook Experimental Forest and location of study watersheds 

3, 4, 6, and 101. 

Design and Methods 

Watershed Harvests 

In preparation for harvest, watershed 4 was surveyed into 

49 strips, each 25 m wide. The strips were oriented from 

east to west roughly parallel to watershed contours. Harvests were done in the autumn months, generally a favorable time for minimizing logging disturbance. The first 

series of strips was harvested from September 28 to October 29, 1970, the second series from September 7 to October 1, 1972, and the third series from October 1 to November 1, 1974 (Fig. 2). A variable-width buffer strip of uncut 

trees, from 15 to 25 m wide, was left on both sides of the 

major stream channel to minimize solar heating and sedimentation of streams. 

The block clearcut on Watershed 101 (Fig. 3) was carried 

out from October 30 to ~ovember 28, 1970, or immediately 

after harvest of the first series of strips. No streamside 

buffer strip was left during the block clearcutting. 

On both the strip cut and block clearcut, all trees and 

snags more than 2.5 cm in d.b.h. were felled. Merchantable tree boles as determined by the operator were transported by rubber-tired skidders to landing areas adjacent to 

the base of the harvested watersheds. Tops and branches 

were left on site, but were moved if they fell in stream 

channels. Main skidder trails were laid out generally along 

ridges, well away from streams in accordance with USDA 

Forest Service specifications. Culverts were used at stream 

crossings and water bars were placed on skid trails immediately after completion of logging. Skidder operators were 

encouraged to vary their routes to provide scarified conditions necessary for successful germination and growth of 

birch seed. In general, every effort was made to perform an 

ecologically sound logging operation that would encourage 

regeneration yet minimize damage to forest soils and 

streams. 
Figure 2.-East to west views across strip-cut watershed showing: (A) first strip cut; 

(B) first and second strips cut; (C) all strips cut; (D) regeneration at 10 years after 

initial harvest. Cleared area in foreground is an earlier deforestation experiment on 

Hubbard Brook watershed 2 (see Pierce et al. 1970). 

Hydrology Studies 

Volume of precipitation is sampled by a network of standard and recording gages that have a density of one gage 

per 15 ha of watershed area. Streamflow from watershed 3, 

the control for the hydrology studies, and from watershed 

4, the strip-cut watershed, is measured continuously with 

120° V-notch weirs (Reinhart and Pierce 1964). Streamflow 

from watershed 6, the control for the nutrient cycling studies, is measured with a tandem 60-cm-wide flume and a 

90° V-notch weir. A water year of June 1 through May 31 is 

used for summarizing and analyzing hydrologic data at 

Hubbard Brook (Likens et al. 1977). 

Effects of the strip cutting on water yield have been determined using the control watershed concept. For 9 years 

before treatment, streamflow values from watershed 4 and 

control watershed 3 were used to develop linear regression 

equations between the two watersheds. Separate regressions were prepared for various streamflow values, including monthly, seasonal, and annual totals. After strip cutting, 

streamflow values from watershed 3 (the control) were used 

in the equations to determine what the streamflow values 

would have been for watershed 4 had it not been strip cut. 

As an example, the water year equation is: 
Estimated flow 

from watershed 4 = 1.54 + 1.03 (flow from control) 

A difference in streamflow between the actual watershed 4 

measurement and the estimated flow for the same watershed was considered statistically significant and was attributed to strip cutting if the deviation exceeded the 95 percent confidence interval about the regression line. 

Watershed 101, the site of the block clearcutting, does not 

have a stream gage. Instead, daily streamflow was simulated using BROOK, a hydrologic model developed and 

tested on forested watersheds at Hubbard Brook and also 

tested at other locations (Federer and Lash 1978a,b). The 

decision to use simulation rather than a gaged watershed 

was based on three factors: (1) remaining gaged watersheds at Hubbard Brook were needed for future studies, (2) 

earlier studies have successfully demonstrated the use of 

hydrologic simulation (Sollins et al. 1980; Leaf and 

Alexander 1975), and (3) hydrologic models have become 

sophisticated and tests show that they are capable of 

highly accurate estimates of measured streamflow (Singh 

1982). Regarding the last point, we tested BROOK by 

simulating several years of pre- and post-harvest 

streamflow from the strip-cut watershed. Monthly sums of 

simulated daily flows were within + 3 percent of measured 

flow except for a few summer months which had total flows 

of less than 0.5 cm. Thus the capability of the BROOK 

model to simulate streamflow usually is within the 3- to 

5-percent error range associated with stream gaging 

(Hornbeck 1965). 

Inputs required to run BROOK, including daily air temperature and precipitation, were collected at watershed 6 about 

1.5 km to the east. Various parameters used in the model, 

such as leaf area index, stem area index, and depth of the 

rooting zone, were adjusted to simulate flow during the 

postharvest period. Streamflow was simulated for the same 

period using parameters for an undisturbed forest. Differences in streamflow for the two simulations were attributed 

to harvest. 

Erosion Losses in Streamflow 

Erosion and resulting losses of organic and inorganic particulate matter in streamflow are extremely difficult to quantify for forests. Fortunately, erosion usually is not serious in 

undisturbed northern hardwood forests; with proper precautions, it can be controlled during and after harvests (Patric 

1976; Patric et al. 1984). In our study, care was taken to 

minimize erosion. However, to ensure that a large increase 

of eroded material and associated nutrients did not go 

undetected, we per~odically measured material trapped in 

the weir basins, and also sampled stream turbidity, a commonly used index of suspended material. 

Weir basin data. Eroded material can leave the watershed 

in particulate form, either as suspended load transported 

by turbulent water or as bedload moving along the bottom 

of the stream channel. As streams leave the watershed, 

velocity is slowed by the weir basins, and heavier particulate matter settles out. The weir basins for the control and 

strip-cut watersheds have been cleaned, and oven-dry 

weights of the material removed have been obtained on an 

annual basis since 1965. 

Turbidity data. Suspended particulate matter that normally 

would not settle in the weir basin was sampled by turbidity 

measurements. Grab samples were obtained periodically 

during nonstorm periods and during most storm events. 

Sampling was continued for 6 years after initiation of the 

strip cutting and for 3 years after block clearcutting. The 

longer interval for the strip cutting was needed to span the 

three separate harvests. 

Samples were analyzed with an electronic turbidimeter and 

results expressed as Jackson Turbidimeter Units (JTU). A 

value of less than 1 JTU represents clear water while a 

value of several hundred JTU represents a large amount of 

suspended material. Turbidity cannot be used to quantitatively express erosion losses, but turbidity values do indicate whether sizeable amounts of eroded materials are 

reaching the stream channel and leaving the watershed. 

Stream Water Ions and Nutrient Budgets 

Details of methods used in collecting and analyzing stream 

samples are given in Likens et al. (1977). Briefly, weekly 

grab samples were collected just above the weirs on watersheds 4 and 6 since 1963, and at the lower boundary of 

Figure 3.-Block clearcut is in foreground. Strip cut and 

an earlier deforestation experiment are at upper right. 
watershed 101 since 1969. The samples were returned to 

the laboratory and analyzed for pH, specific conductance, 

and chemical ions, including Ca2+, Mg2+, K+ , Na+, NH4+, 

S042-, NOa, and CI-. THe pH was determined potentiometrically, the anions and NH4+ by automated colorimetric 

analysis, and the cations by atomic absorption; PO4" was 

measured during part of the study, but usually was below 

the detection level of 0.003 mg L-'. Effects of harvest on 

stream water ions usually were obvious, and were easily 

demonstrated with graphs. We plotted mean monthly concentrations obtained by weighting individual weekly values 

for volume of streamflow, and then averaging over the 

month. 

Nutrient budgets were determined by converting the ionic 

concentrations of precipitation and streamflow to inputs 

and outputs as mass per unit area. Daily inputs and outputs are calculated as the product of the ionic concentration (mg L-l) in the weekly sample times volume (L) of 

water for each day represented by the sample. The same 

regression technique described for water yield studies was 

used to determine effects of harvest on nutrient outputs. 

Biomass and Nutrients in Harvested Products 

During harvest, pulpwood and sawlogs were scaled at 

landings located at the base of the strip-cut and blockclearcut watersheds. The scale data were converted to 

solid cubic volume by a formula for truncated cones. Constants developed at Hubbard Brook by Whittaker et al, 

(1974) were applied to convert the volumes to oven-dry 

weight of biomass in bark, heartwood, and sapwood. Nutrient contents of these three components are available from 

chemical analyses of plant tissues made at Hubbard Brook 

(Likens and Bormann 1970). The estimate of nutrient 

removal in kg ha-' was obtained by multiplying biomass by 

percent nutrient content for elements of interest. 

Regeneration 

Regeneration on the block-clearcut and strip-cut watersheds has been surveyed on permanent plots at intervals 

of 1 to 3 years since harvest. Detailed results will be 

reported in a separate paper, but a summary of regeneration at years 2 and 10 after harvest is included in this 

paper. The summary is based on surveys of fifty-seven 25 

by 25-m plots on the strip cut, and forty-eight 25 by 25-m 

plots on the block clearcut. Plots on the strip cut were 

chosen randomly after stratification by elevation and year 

cut. Plots on the block clearcut were chosen at random 

with no stratification since the harvest was completed in a 

single operation and the elevation range of the entire harvest area was about the same as for the mid-elevation plots 

on the strip cut. 

A nested design was used for sampling each plot. The 

entire 25 by 25-m plot was used to sample trees more than 

10 cm in d.b.h. Trees between 2 and 10 cm d.b.h. were 

tallied on a 1 by 25-m strip-running the length of either the 

east or west side (decision by coin toss) of each plot. 

Lesser vegetation was surveyed on four I-m2 subplots 

spaced evenly along the 1 by 25-m strip plot. Within each 

of these subplots, stem counts were made by species for 

trees, shrubs, and herbs less than 0.5 m tall and for those 

more than 0.5 m tall. Visual estimates of percent of plot 

covered were used in place of stem counts for grasses, 

sedges, rushes, and mosses. Data from the subplots were 

averaged to give stems per m2 for each 1 by 25-m strip. 

Estimates of aboveground biomass of regeneration were 

obtained by establishing 46 additional plots on the strip-cut 

watershed, stratified by elevation and year cut. On these 

plots, individual species were clipped, grouped according 

to height or d.b.h. class, and.oven dried at 105OC. Stem 

counts for individual species from the regeneration survey 

were multiplied by corresponding oven-dry weights to 

obtain biomass estimates on a kg ha-' basis. 

Results 

Hydrologic Response 

Strip cutting. Removal of the forest by strip cutting caused 

streamflow to increase in the 4 water years spanning harvest and for 3 additional years (Table 1). The annual 

increases ranged from 22 to 114 mm. The minimum value 

occurred the first year after the first set of strips was harvested, and coincided with below-average precipitation 

(Table 1). The maximum value occurred with two-thirds of 

the watershed harvested and coincided with an annual 

precipitation that exceeded the long-term average by 40 

percent. Above-average precipitation is recognized as 

necessary for optimum increases in streamflow from deforested areas (Douglass and Swank 1972). Increases or 

decreases in water yield were statistically significant in 9 of 

the 10 years after harvest, and totaled 397 mm or 4 percent more than would have occurred if the watershed had 

not been harvested. Over three-fourths of this increase 

occurred in the first 5 years, or while the watershed was in 

the process of being harvested. 

Most of the annual increase occurred during the growing 

season (Table 1). Thus, streamflow increases resulted 

primarily from a reduction in transpiration and canopy 

interception rather than from increased snow accumulation 

within the strips. As further evidence, changes in 

streamflow for the dormant season (October through May) 

and the period of major snowmelt runoff (March 1 through 

May 15) usually were small and not statistically significant 

(Table 1). 
Table 1.-Streamflow and precipitation for strip-cut and block-clearcut watersheds, in millimeters 

(cutting on both watersheds began in 1970) 

Streamflow, strip-cut watershed Streamflow, block-clearcut watershed Precipitation 

Year after Estimate Change due Simulated Simulated Change due Departure from 

cutting if uncut Actual to cutting for uncut for cut to cutting Actual 23-year mean 

1 a 

2a 

3b 

4b 

5c 

6' 

7C 

8' 

gc 

1 OC 

Total 

1 a 

2a 

3b 

4b 

5c 

6' 

7C 

8' 

gc 

1 OC 

WATER YEAR (JUNE-MAY) 

+ 22* 769 1 046 + 278 

+ 46* 1007 1163 + 155 

+114* 1363 1455 + 92 

+ 67* 777 81 6 + 39 

+ 55* 1221 1260 + 41 

+81* 876 896 + 20 

+ 69* 1031 1046 + 15 

- 14 888 893 +8 

- 30* 743 744 + 1 

- 27* 844 840 +4 

41 1 951 9 653 

GROWING SEASON (JUNE-SEPT) 

+ 28' 46 208 + 237 

+ 36* 114 254 + 140 

+91* 324 409 + 85 

+ 38* 98 143 + 45 

+81* 196 232 + 36 

+ 38* 77 99 + 22 

+ 27* 108 118 + 10 

+2 84 90 +6 

+6 58 63 +5 

-0 30 35 +5 

Total 

1 a 

2a 

3b 

4b 

5c 

6' 

7C 

8' 

gc 

1 OC 

347 592 

DORMANT SEASON (OCT-MAY) 

-4 748 756 +8 

-5 725 766 + 41 

+ 14 894 909 + 15 

+ 33 1039 1046 +7 

+ 33 680 674 -6 

- 22 1024 1029 +5 

+ 34 876 896 + 20 

+ 42* 1031 1046 + 15 

- 15 888 893 +5 

- 35 743 744 + 1 

Total 77 110 

Continued 
Table 1 .-Continued 

Streamflow, strip-cut watershed Streamflow, block-clearcut watershed Precipitation 

Year after Estimate Change due Simulated Simulated Change due Departure from 

cutting if uncut Actual to cutting for uncut for cut to cutting Actual 23-year mean 

SNOWMELT (MARCH 1-MAY 15) 

1 a 472 473 + 1 503 502 - 1 d 

2a 51 5 51 0 -5 478 470 -8 d 

3b 461 489 + 28 471 450 - 21 d 

4b 454 459 +5 594 576 - 18 d 

5C 402 421 + 19 31 8 31 2 -6 d 

6' 496 49 1 -5 521 496 - 25 d 

7C 463 485 + 22 473 476 +3 d 

8' 336 347 +11 470 469 - 1 d 

9' 595 572 - 23 571 554 - 17 d 

1 Oc 340 325 - 15 301 296 -4 d 

* Significant at 0.05 level of probability. Entire strip-cut watershed harvested. 

a One-third of strip-cut watershed harvested. Precipitation for this period not related to streamflow. 

Two-thirds of strip-cut watershed harvested. 

Although strip cutting did not change the volume of and 36.7i28.7 kg ha-' for the strip cutting. Thus, strip 

snowmelt runoff, it did affect timing. With reduced shade cutting did not result in any important changes in amounts 

after harvest, snow melted more quickly and snowmelt of material leaving the watershed as bedload or heavy 

runoff was advanced. In monthly analyses (Fig. 4), this particulate matter. 

effect shows as an increase in streamflow for March or 

April, the first month of major snowmelt. Decreases in 

streamflow then occur in 1 or 2 following months, while in 

undisturbed watersheds, snowmelt progresses at the usual 

speed. The increases and decreases during snowmelt 

months balance closely. 

Block clearcutting. On the basis of streamflow simulation, 

block clearcutting caused streamflow to increase by 278 

mm, or 36 percent in the first year after harvest (Table 1). 

The increases tapered off rapidly with revegetation, and 

annual streamflow was nearly like the control watershed by 

the sixth year of regrowth. Total increase in streamflow for 

the 10-year period of study was 653 mm, or 7 percent more 

than if the watershed had not been harvested. As with the 

strip cutting, most of the annual increase occurred in the 

growing season (Table 1). Snowmelt runoff was advanced 

slightly more than on the strip cut due to the absence of 

uncut strips. 

Erosion Losses 

For the 6 years before harvest, erosion losses measured as JJASONDJFMAM JJASONDJFMAM 

material trapped in the weir basins averaged 33.6 k 17.2 kg water Year 2 Water Year 5 

(first strip cut) 1011 strlps cul) ha-' for the control watershed and 40.4k25.1 kg ha-' for 

the strip cutting. Averages for the 10-year postharvest Figure 4.-Change in streamflow, by month, for 2 

period were 37.7k 10.8 kg ha-' for the control watershed selected years after strip cutting. 
The conclusion is the same for suspended materials as 

determined by turbidity measurements. During and after 

harvest, 325 samples were collected for turbidity analysis 

from both the control and strip cut, and 160 samples were 

collected from the block clearcut. A summary of these 

samples by turbidity class is shown in Table 2. About onehalf of the samples were collected during storm events and 

should represent maximum effects of harvest. 

The 11 samples falling in the 11-40 JTU class probably are 

the result of logging disturbances, especially since no 

corresponding values occurred for the control watershed. A 

more important point is that turbidity values remained quite 

low and exceeded 1 JTU on few occasions. 

Stream Water Ions 

Calcium. Before harvest, concentrations of Ca2+ averaged 

about 2 mg L-' on the strip-cut watershed and just over 1 

mg L-' on the control and block-cut watersheds (Fig. 5). 

The concentrations were fairly stable throughout the year, 

and there were no obvious seasonal patterns. 

Strip cutting caused Ca2+ to increase slightly, mostly during the dormant seasons (Fig. 5). The best example was in 

the dormant season 1 year after harvest of the first strip 

when Ca2+ was increased by an average of 0.8 mg L-'. 

The increases were smaller in subsequent dormant seasons, even with cutting of the second and third sets of 

strips. 

-CONTROL 

3.0 --.--STRIP CUT 

YEAR BEFORE HARVEST YEAR AFTER HARVEST 

4 5 6 7 8 9 10 

YEAR AFTER HARVEST 

Jackson Turbidimeter Units 

Item (1 1-5 6-10 11-40 

Total 301 11 4 9 

Block clearcut 

Nonstorm periods 52 5 1 1 

Storm events 88 10 2 1 

Total 140 15 3 2 

Figure 5.-Weighted, mean monthly Ca2+ in stream 

water, by calendar year. Table 2.-Number of samples collected for postharvest turbidity analysis 

Control 

Nonstorm periods 175 3 0 0 

Storm events 143 4 0 0 

Total 31 8 7 0 0 

Strip cut 

Nonstorm periods 171 2 2 3 

Storm events 130 9 2 6 

The block cut caused a similar pattern. Effects were greatest in the dormant season 1 year after harvest; Ca2+ concentrations from the block cut exceeded values for the 

control watershed by about 3 mg L-' (Fig. 5). The effects 

of block cutting then declined gradually and were minimal 

by the end of the third year after harvest. 

Potassium. Preharvest levels of K+ averaged 0.2 mg L-' 

for the study watersheds (Fig. 6). A seasonal pattern of low 

values in summer and a rise to higher concentrations in 

winter is correlated with vegetation activity (Johnson et al. 

1969). Potassium concentrations for the strip-cut watershed 

increased immediately after cutting and on average were 

about 0.1 mg L-' higher than on the control during the 2 

years after the first strip cut; 0.2 to 0.3 mg L-' higher after 

the second sets of strips was cut; and 0.3 to 0.6 mg L-' 

higher after the third set was cut. As with Ca2+, the treatment effect was greatest in the dormant season. Unlike 

Ca2+, the increases have persisted and the maximum 
-CONTROL 3 STRIP WT 2 C ,9 

... ... BLOCK CUT - . -2 

. :1 9 

4 1.0 /..... : !,A ,. .. . .. ; .. . . ... . .. .. . . .. , . .. . . . 

YEAR BEFORE HARVEST YEAR AFTER HARVEST 

YEAR AFTER HARVEST 

Figure 6.-Weighted, mean monthly K+ in stream water, 

by calendar year. 

increase of 0.6 mg L-' occurred in April of the 10th year 

after harvest. 

Potassium concentrations also responded immediately to 

block clearcutting. By the end of the second dormant season they were 5 times higher from the block clearcutting 

than from the control watershed (Fig. 6). Concentrations 

have declined since then, but the effects of cutting remain 

evident through the 10th year of regrowth. 

Magnesium,, Magnesium in stream water averaged about 

0.4 mg L-' before harvest and did not fluctuate with season or discharge. Effects of harvest occurred at the end of 

the first summer after cutting; there was an increase of 0.2 

mg L-' on the strip cut and 0.5 mg L-' on the block cut. 

The increases persisted at declining levels for 1 112 years 

on the block cut. There were increases of less than 0.1 mg 

L-' on the strip cut until 1 year after the final set of strips 

was harvested. 

Sodium. Before harvest, Na+ concentrations were fairly 

stable at about 1 mg L-', though peaks of up to 2 mg L-' 

sometimes appeared in late summer. In the first 5 years 

after the start of strip cutting, many of the monthly values 

showed statistically significant increases, but the average 

increase for the period was less than 0.2 mg L-'. Block 

cutting caused Na+ concentrations to increase by a maximum of 0.2 to 0.3 mg L-', but the increases did not last 

beyond the second year after harvest. 

Ammonium. Ammonium in streams from an undisturbed 

forest seldom exceeds 0.1 mg L-' and usually is less than 

0.02 mg L-'. Strip cutting and block clearcutting had no 

detectable effect on NH4+ in stream water. 

Hydrogen. Results are illustrated by a plot of weighted, 

monthly means of H+ expressed as both mg L-' and pH 

(Fig. 7). Streams from the three study watersheds had 

small but consistent differences in H+ during the preharvest period. These differences of 0.002 to 0.020 mg L-', 

spanning a pH of 4.7 to 5.7, are typical of natural variation 

between watersheds at Hubbard Brook (Johnson 1979). 

Strip cutting caused H+ in streamflow to be more variable 

and slightly elevated in the second and third years of harvest (Fig. 7). During these 2 years, H + averaged 

0.005 & 0.003 mg L- l, representing an average increase in 

H+ of 0.002 to 0.003 mg L-', or a decrease in pH from 5.7 

to 5.3. 

For the block clearcutting, increases in H+ appeared in the 

first spring after harvest, and elevated levels of 0.010 to 

0.025 mg L-' occurred through the second summer after 

harvest (Fig. 7). On the basis of the pretreatment relationship with the control watershed, these values represent an 

average increase of about 0.004 mg L-', or a decline in 

pH from 5.0 before harvest to 4.8 for the first 2 years after 

harvest. After the second summer, H+ in stream water 

declined gradually to 0.002 to 0.004 mg L-' (pH 5.4 to 

5.7), or below the average of 0.010 mg L-' (pH 5.0) that 

occurred for the watershed during preharvest. 

Nitrate. During the calibration period, streams from the 

study watersheds showed cyclic NO3- concentrations 

related to seasonal growth patterns of vegetation. Minimum 

concentrations of 0.05 mg L-' occurred in summer and 

autumn. The concentration rose in late autumn as vegetation became dormant, reaching maxima of up to 5 mg L-' 

in March or April, then decreasing to low levels in May and 

June (~ig. 8). 
STRIP CUT . 

Y 

.03 1 .. ..... BLOCK CUT A 

YEAR BEFORE HARVEST YEAR AFTER HARVEST 

.s i 

YEAR AFTER HARVEST 

Figure 7.-Weighted, mean monthly H+ and pH in stream water, by calendar year. 

Nitrate increased immediately after strip cutting and 

remained higher than on the control watershed for 4 years. 

Average mean monthly concentrations were 2 mg L-' 

higher than on the control for the first year after cutting, 

and 4 mg L-' higher for the second year. After the second 

set of strips was cut, NO3- remained higher, but differences between watersheds were smaller. In year 6, NO3- 

for the strip cut dropped below the control and remained 

there through the 10th year (Fig. 8). 

Nitrate did not respond to block cutting for 7 months, then 

rose over the next 11 months to a maximum of 26 mg L-' 

(Fig. 8). This is an estimated increase of 23 mg L-' compared with the control watershed. The NO3- concentrations then fall off rapidty arrd hae been less than those on 

the control watershed since the middle of the third year 

after harvest. 

Sulfate. Sulfate is the dominant anion in streams from the 

study watersheds. Seasonal patterns of SO4 in streams 

from undisturbed forests usually show a gradual rise 

thmugh the growing season to peaks of around 7 mg L-' 

in late autumn and early winter, then a decline through the 

winter, reaching minimum concentrations of about 5.5 mg 

L-' in late spring (Fig. 9). 

Sulfate decreased after strip cutting. The decrease was 

most pronounced during late autumn and early winter of 

the first year after the first set of strips was cut. During this 

period, concentrations from the strip-cut watershed were 

about 1.5 mg L-' below control watershed values (Fig. 9). 

Cutting the second and third sets of strips had less impact 

on SO4'-, and the control and strip-cut watersheds seldom 

differed by more than 0.5 mg L-'. 

The impact of block cutting on SO4'- is more difficult to 

discern. During the short time when determinations were 

made before cutting, SO4'- from the watershed to be 

block cut was below SO4'- from the forested control 

(Fig. 9). This difference continued after cutting, with'maximum differences of more than 2 mg L-' in the last half of 

the first and most of the second year after harvest. During 

the third and fourth years, SO4'- from the block cut began 

to approach values for the control, indicating that the differences in the 2 previous years were due to cutting. 

Chloride. Chloride concentrations during preharvest averaged 0.5 mg L-' for all study watersheds, and there were 

no seasonal patterns. In the summer after cutting of the 

first set of strips there was a mean increase of about 0.1 

mg L-'. The increase disappeared by winter and there 
- CONTROL . . 

---.STRIP CUT . . . . BLOCK CUT . . ......... .: 

. . . . :. . 

YEAR BEFORE HARVEST MAR AFTER HARVEST 

YEAR AFTER HARVEST 

Figure 8.-Weighted, mean monthly NO$ in stream 

water, by calendar year. Note expansion of scale for 

years 4 through 10 after harvest. 

were no further changes due to strip cutting. Block cutting 

caused CI- to increase by a maximum of 0.4 mg L-' in 

the first summer after harvest. This increase also was short 

lived and was absent by the second summer after harvest. 

Cation-anion summary. A comparison of the ionic strength 

of stream water is a convenient way of summarizing effects 

due to harvest. Table 3 shows mean annual ion concentrations for year 1 before harvest and for year 2 and year 5 of 

the harvest period. For year 2 after harvest, when harvest 

effects were at a maximum, the sum of measured ions for 

the strip-cut and block-cut watersheds was 16 and 104 

percent greater, respectively, than in year 1 before harvest. 

The same comparison for the control watershed shows a 

decrease of 7 percent in measured ions. By year 5 of the 

harvest period, the sum of measured ions had returned to 

levels found before harvest. 

.... '' e -CONTROL 5 

STRIP WT P 

-....BLOCK CUT 9 t 2 * I 

YEAR BEFOAE HARVEST YEAR AFTER HARVEST 

4 5 6 7 8 9 10 

YEAR AFTERHARVEST 

Figure 9.-Weighted, mean monthly SO4'- in stream 

water, by calendar year. 

In terms of ion balance, SO4'-, the dominant anion 

showed a slight decline in year 2 after both strip and block 

cutting. However, large increases in No3- resulted in net 

increases in the sum of anions. The increases in anions 

were countered by large increases in Ca2+ and Mg2+ on 

the strip cut and Ca2+, Mg2+, and K+ on the block cut. 

Potassium is the only ion continuing to show an increase at 

year 5 of the harvest lperiod. 

Nutrient Budgets , 

Changes in stream volume and ion concentrations after 

strip and block cutting caused streamflow outputs of nutrients to differ from values for uncut forests. For the stream 

water ions that showed relatively small changes in concentration after harvest, $uch as Mg2+, Na+, NH,+, and CI-, 

the outputs increased in direct proportion to increases in 

stream volume. To illustrate, over the 10-year period considered in this paper, streamflows were increased by 4 

percent by strip cutting and by 7 percent by block cutting 

(Table 1). Outputs for the nutrient ions listed previously 

were increased by about these same percentages. For 
Table 3.-Cation-anion relationships in stream water of the study watersheds (values are weighted, annual means) 

Item 

Total Total 

Ca2+ Mg2+ K+ Na+ NH4+ H+ cations S042- NO3- CI- anions All ions 

....................... ueq L - 7 - - - - - - - - - - - - - - - - - - - - - - - 

Strip cut 

Year 1 before harvest 100 35 6 53 2 3 208 133 39 16 188 396 

Year 2 after harvest 127 40 8 54 1 5 235 121 87 16 224 459 

Year 5 after harvest 94 31 11 , 49 1 1 187 123 31 12 166 353 

Block cut 

Year 1 before harvest 64 34 5 39 1 11 154 115 6 14 135 289 

Year 2 after harvest 139 55 21 42 0 14 271 90 211 17 318 589 

Year 5 after harvest 71 26 13 33 1 2 146 110 5 11 126 272 

Control 

Year 1 before harvest 77 32 6 41 2 14 172 129 34 16 179 351 

Year 2 after harvest 69 28 5 37 1 15 155 135 22 15 172 327 

Year 5 after harvest 67 27 5 34 1 12 146 127 37 14 178 324 

nutrient ions that showed greater changes in concentration, 

such as Ca2+, K+, NO3-, and S042-, changes in outputs 

were more variable. 

Calcium. The Ca2+ budget shows a sizeable net loss under 

forested conditions (Table 4). The input in precipitation for 

the 10 postharvest years was 11.5 kg ha-', while output in 

streamflow from the watersheds if they had not been cut 

Nas estimated as 165.5 kg ha-'. Strip cutting further 

ncreased the output by an estimated 26.6 kg ha-', or 16 

Iercent, while block cutting increased the output by 47.6 

(g ha-', or 29 percent. More than twoqhirds of the 

ncrease occurred in the first 3 years after initiation of strip 

Wing, and in the first 2 years after block cutting. 

'otassium. The K+ budget for uncut watersheds also 

ihows a net loss (Table 4). Over the 10 years of study, 

~~tputs of K+ in stream water were increased by 29.6 kg 

la-', or 135 percent, as a result of strip cutting, and 48.0 

.g ha-', or 218 percent, as a result of block cutting. The 

~ercentage increases are about 8 times greater than for 

:a2+. The changes in outputs were at a maximum in the 

rst few years after harvest, but increases have been conistent throughout the postharvest period. 

litrate. Nitrate values have been converted to NO3 - N for 

ie input-output budget summaries. This allows direct 

omparison of N losses in later discussions about N capital 

f the study sites. Comparison of inputs in precipitation 

with outputs if the watersheds had not been cut shows a 

slight accumulation of NO3 - N (Table 4). Input over the 

10-year study period was 52.9 kg ha-', and estimated 

output in the absence of cutting was 45.2 kg ha-'. The 

substantial variability in annual outputs, from undisturbed 

forests is thought to be related in part to the presence or 

absence of soil freezing (Likens et al. 1977). 

As a result of strip cutting, outputs for the 10 years after 

harvest were increased by 22.3 kg ha-', or about 50 percent. Block cutting caused NO3 - N outputs to be increased 

by 57.8 kg ha-', or 128 percent. The largest increases 

occurred in years 1 through 3 after the start of the stripcutting sequence, and in years 1 and 2 after block cutting. 

In years 6 through 10 after strip cutting, and 5 through 10 

after block cutting, the harvested watersheds lost smaller 

amounts of NO3 - N in streamflow than if they had not 

been cut. 

Sulfate. The SO4 - S budget shows a net loss on an annual 

basis (Table 4). The input in precipitation for the 10-year 

study period was 114 kg ha-' as opposed to an output in 

streamflow of 185.9 kg ha-' for the forested control watershed. Harvest resulted in relatively small changes, increasing SO4 - S output by 4.8 kg ha-' after strip cutting, and 

decreasing SO4- S output by 14.0 kg ha-' after block 

cutting. The small changes indicate that the declines in 

concentration of SOP- ions in streams were mostly compensated for by the increased volume of streamflow. 
Table 4.-Annual input-output budgets for Ca2+, K+, NO,-N, and SO& 

in kg haChanges in outputs due to: Water year Input in Output if 

after harvest precipitation uncut Strip cut Block cuta 

Total 

Total 5.6 22.0 + 29.6 48.0 

---------------- NOaN - - - - - - - - - - - - - - - - 

1 8.3 8.9 + 10.8* + 39.5 

2 5.9 4.6 + 9.3* + 17.9 

3 7.0 8.0 + 9.0* + 2.1 

4 4.1 4.8 + 0.2 0 

5 4.6 5.4 + 0.4 - 0.7 

6 5.0 4.8 -2.8 . - 0.4 

7 4.3 1.8 +1.1* 0 

8 5.0 1.5 -1.3" ; 0 

9 3.8 2.7 - 2.0* ' - 0.4 

10 4.9 2.7 - 2.4' - 0.2 

Total 52.9 45.2 + 22.3 + 57.8 

Continued 
Table 4.-Continued 

Changes in outputs due to: Water year Input in Output if 

after harvest precipitation uncut Strip cut Block cuta 

Total 114.0 185.9 + 4.8 - 14.0 

Significant at 0.05 level of probability. 

a Changes not tested for statistical significant because stream volumes for block cut 

were estimated by simulation. 

Biomass and Nutrients Removed by Harvest 

The harvesting operation removed an average of 50 metric 

t ha-' of biomass from the strip-cut watershed and 65 

metric t ha-' from the block clearcut (Table 5). Before 

cutting, the watersheds were estimated to support 133 and 

150 metric t ha-' of aboveground, living, woody biomass, 

respectively (Whittaker et al. 1974). The removals represent 

38 percent of woody biomass from the strip cut watershed 

and 43 percent of woody biomass from the block cut. The 

removal efficiency from the strip cut probably is lower 

because some trees on upper elevation strips were either 

unmerchantaBle or were on slopes too steep to log. In such 

cases the trees were felled, but left in place. 

For nutrient removals in harvested products, the rank was 

Ca ) N ) K ) S ) Mg ) P (Table 5). Total nutrient element 

contents of aboveground, woody biomass for Hubbard 

Brook forests have been estimated by Whittaker et al. 

(1979) and Likens et al. (1977). When compared with these 

values, Ca removed in harvest represented 28 percent and 

30 percent of aboveground total in woody biomass on the 

strip-cut and block-clearcut watersheds, respectively. Corresponding values for other nutrients were 26 and 30 percent 

for K, 31 and 33 percent for Mg, 21 and 25 percent for N, 

31 and 35 percent for S, and 18 and 19 percent for P 

(Table 5). 

Regeneration 

Natural regeneration has flourished after both block and 

strip cutting. The density and mix of species changed 

dynamically in the postharvest period (Table 6). Numbers 

of stems increased rapidly after harvest and peaked in year 

2 at about 1 million stems ha-'. The number of stems for 

year 2 after harvest reached a maximum on the third set of 

strips to be cut. This maximum count resulted mainly from 

increased numbers of herbaceous stems (Table 6), and 

probably reflects the abundance of seed sources in the 

previously cut strips. 

In terms of ground cover, the vegetation at year 2 after 

block cutting and each of the strip cuttings formed a dense 

tangle, averaging about 1.5 m in height. The only areas not 

revegetated were those under dense slash, or those 

severely gouged and rutted during logging. Such areas 

were sampled as part of the regeneration survey and 

amounted to less than 3 percent of the total watershed 

area. Dominance in terms of numbers of stems (Table 6) 

and biomass (Fig. 10) was shared by herbaceous species, 

especially Aster acuminatus, Dennstaedtia punctilobula, and 

Uvularia sessilifolia; by species of Rubus; by advanced 

regeneration of Acer; and by stump sprouts of Fagus 

grandifolia . 
Table 5.-Biomass and nutrient removal in harvested stems 

Harvest Biomass Ca K Mg N S P 

Oven-dry ---------- kg ha-' -? - - - - - - - - 

metric t ha - ' 

STRIP CUT' 

Preharvesta 133 383 155 36 351' 42 34 

Removed 50 107 40 11 74 13 6 

010 Removed 38 28 26 31 21 31 18 

BLOCK CUT 

Preharvesta 150 466 176 43 392 51 36 

Removed 65 139 52 14 97 18 7 

0'0 Removed 43 30 30 33 25- 35 19 

a From Whittaker et al. (1974, 1979) and Likens et al. (1977). 

Between years 2 and 10 the canopy closed and tree species gained dominance in both height and biomass (Fig. 

10). Although the ratio between total numbers of trees, 

herbs, and shrubs showed no drastic changes, competition 

reduced total stems at year 10 to several hundred thousand ha-' (Table 6). Also by year 10, some tree species 

had achieved sufficient diameter growth to move into the 

lower diameter classes (Table 7). The three most common 

northern hardwood species, Betula alleghaniensis, Acer 

saccharum, and Fagus grandifolia, became prominent in 

terms of total numbers of stems by year 10. Prunus 

pensylvanica, an exploitive species (Bormann and Likens 

1979), occurred in moderate numbers on the strip cutting 

and in large numbers on the block cutting, and usually 

dominated in terms of biomass as a result of having far 

more stems in the larger diameter classes (Table 7). 

Total biomass was between 34 and 53 metric t ha-' at 10 

years after the cuttings (Table 8). These values represent 

25 to 40 percent of the aboveground biomass before harvest. As mentioned previously, most of the biomass at 10 

years was dominated by tree species, especially Prunus 

pensylvanica. For example, on the block clearcutting, the 

51 metric t ha-' of biomass at year 10 (Table 8) consisted 

of 29 t ha-' of Prunus pensylvanica, 11 t ha-' of Betula 

alleghaniensis, 4 t ha-' of Fagus grandifolia, and 2 t ha-' 

of Acer saccharum. The biomass for Prunus pensylvanica 

actually was beginning to show a decline, having peaked at 

31 t ha-' at year 7 after harvest. This decline is in line with 

the usual growth pattern followed by Prunus pensylvanica 

(Bormann and Likens 1979). 

Discussion 

Changes in Water Yield 

The most important effect of strip and block cuttings on 

water yield at Hubbard Brook included: 

1. Increases in annual water yield, most of which 

occurred in the growing season months of June through 

September. 

2. Changes in timing of spring flows due to a speedup in 

snowmelt on the harvested watersheds. 

These are the same effects that occurred after an earlier 

experiment on Hubbard Brook Watershed 2, which was 

clearfelled and then treated with herbicides (Hornbeck et 

al. 1970). In that experiment, for a 3-year period in which 

vegetation was controlled with herbicides, annual increases 

in streamflow averaged 288 54 mm. For the first water 

year after the block clearcutting, the simulated increase in 

water yield was a comparable 278 mm (Table 1). For the 

first year after strip cutting, with only one-third of the watershed harvested, the increase in water yield was 22 mm. 

The increases in water yield from the strip-cut watershed 

were not as large as might have been anticipated. Hibbert 

(1967) and Douglass and Swank (1972) suggest that for the 

Eastern United States, increases in water yield for the first 

year after forest cutting are roughly proportional to percentage reduction in basal area. Thus, increases in water yield 
Table 6.-Number of trees, shrub, and herbaceous stems at 2 and 10 years after individual harvests (elevation ranges are low, 440 to 

550m; mid, 550 to 650m; and high, 650 to 750 m; block cut spanned elevations 470 to 600 m, or closest to mid-elevation range 

on strip cut) 

First strip Second strip Third strip Block cut 

Species Low Mid Upper Low Mid Upper Low Mid Upper Mid 

Year Year Year Year Year Year Year Year Year Year Year Year Year Year Year Year Year Year Year Year 

2 10 2 10 2 10 2 10 2 10 2 10 2 10 2 10 2 10 2 10 

................................. Thousands of stems ha - 7 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 

Treea 593 132 521 99 221 89 253 54 282 49 155 40 428 74 310 49 198 67 661 231 

Shrubb 165 53 32 92 93 220 111 16 130 27 76 55 204 11 216 20 117 67 51 33 

HerbaceousC 340 282 733 226 535 622 501 129 463 90 338 228 832 195 1160 108 772 542 297 183 

All species 1098 467 1286 417 849 931 865 199 875 166 569 323 1464 280 1686 177 1087 676 1009 447 

a Major tree species include: Abies balsamea, Acer pensylvanicum, A. rubrum, A. saccharum, A. spicatum, Betula alleghaniensis, B.papyrifera, Fagus grandifolia, 

Fraxinus americana, Picea rubens, Populus spp., and Prunus pensylvanica. 

Major shrub species include: Rubus spp., Sambucus canadensis, and Viburnum alnifolium. 

Major herbaceous species include: Aster acuminatus, Dennstaedtia punctilobula, Dryopteris spinulosa, Lycopodium lucidulum, Maianthemum canadense, Oxalis 

rnontana , Trillium spp., Uvularia sessilifolia , and Viola spp . 
Year I 

HM L B 

Year 2 

- 

HMLB 

Year 5 

Figure 10.-Proportions of biomass occupied by trees, shrubs, and herbs on the 

second strip (H, M, and L are high-, medium-, and low-elevation zones) and the block 

clearcut (B). 

after cutting the first set of strips may have been expected 

to be about 90 mm, or one-third of that occurring from that 

block cutting. The actual yield increase in year 1 from the 

strip cutting was less than one-tenth that from the block 

cut. And increases through the 10 postharvest years from 

the strip cuts were only 60 percent of those from the block 

cut (Table 1). 

The explanation for the smaller than anticipated increases 

lies in the cutting configuration. A strip cut increases the 

crown exposure and transpiration rate of the residual trees 

that border the cut strips (Federer and Gee 1974). A portion of the added transpiration may be drawn from the 

extra water available in the cut strips, or from soil water 

moving downslope from cut into uncut strips. As a result, 

increases in streamflow are smaller than they would have 

been if the area had been cut in one large block. The 

larger increases for the first water year after cutting of the 

second and third sets of strips (Table 1) support this 

explanation. 

Thus, it appears that strip cutting compared with block 

cutting is an inefficient form of forest harvest if augmentation of water yield is the most important consideration. The 

increases are small in relation to total area cut over. On the 

other hand, the smaller increases in water yield mean that 

there is less opportunity for nutrients to be transported 

from the watershed in dissolved and particulate forms. 

Year 10 

Regarding the changes in timing of streamflow during 

snowmelt, the advances in snowmelt runoff that occurred 

after strip and block cutting were sizeable. However, when 

cutting is a small portion of a larger watershed, these 

advances quickly become unrecognizable when joining with 

streams from completely forested areas (Hornbeck and 

Pierce 1969). If the timing changes after cutting are to have 

a practical significance with regard to downstream flooding, 

thousands of hectares within individual, regional watersheds would have to be harvested. There seems little 

likelihood that clearcutting will ever be of sufficient scale in 

New England to bring about significant changes in downstream spring floods. 

The rate at which water yield returns to preharvest levels 

should be strongly correlated with regrowth of vegetaiion. 

This is illustrated for the. blo'ckclearcut by plotting annual 

increases in water yield in relation to increases in stand 

biomass (Fig. 11). Increases in water yield declined steadily 

with accumulating biomass, and were minimal when 

biomass reached 50 metric t ha-', or about one-third of 

the biomass found before harvest. 

Erosion Losses in Streamflow 

For undisturbed forests at Hubbard Brook, losses of nutrient elements via streamflow are greater in dissolved form 

than in sediment or particulate form (Bormann et al. 1969, 

1974). The ratio for individual elements varies, but in terms 
Table 7.-Stems ha-', by diameter class, for six major tree species occurring at year 10 after harvest 

First strip Second strip Third strip Block clearcut 

D.b.h. class D.b.h. class D.b.h. class D.b.h. class 

Species Elevation (2.5 2.5-4.9 5.0-7.5 7.6-9.9 (2.5 2.5-4.9 5.0-7.5 7.6-9.9 (2.5 2.5-4.9 5.0-7.5 7.6-9.9 (2.5 2.5-4.9 5.0-7.5 7.6-9.9 

Betula alleghaniensis Low 25,300 743 57 0 3,800 1,467 200 67 8,800 2,067 467 0 

Mid 19,000 560 80 0 1,200 2,467 267 0 1,800 1,600 743 114 144,000 1,450 42 8 

Upper 23,500 629 171 57 5,000 3,257 229 0 13,700 2,333 267 0 

Acer saccharum Low 

Mid 

Upper 

Fagus grandifolia Low 

Mid 

Upper 

Prunus pensylvanica Low 

Mid 

Upper 

Acer pensylvanicum Low 

Mid 

Upper 

Acer spicatum Low 

Mid 

Upper 
I Table 8.-Aboveground, living biomass at various 

years after strip cutting and block 

clearcutting 

Year after 

harvest 

First Second Third Block 

strip strip strip clearcut 

of gross export of mass, dissolved substances average 

about 165 kg ha-' yr-I, or about 5 times the amount lost 

in sediment or particulate form (Likens et al. 1977). 

Our study did not determine sediment losses directly. 

However, the very small changes in the many turbidity 

readings obtained during and after harvests (Table 2) and 

in the material trapped in the weir basins indicate minimal 

changes in sediment or particulate losses resulting from 

harvest. 

Of the two harvested watersheds, the block clearcut was 

thought to have the greater potential for erosion losses. 

Increases in water yield were greater after block clearcutting, increasing the chances for streambank and channel erosion, and no buffer strip was left. However, the 

turbidity data (Table 2) indicate that erosion losses after the 

block clearcut remained at the same low levels as from the 

strip cutting. The results confirm an earlier conclusion from 

the clearfelling and herbicide experiment on Hubbard 

Brook Watershed 2 (Bormann et al. 1974): northern hardwood ecosystems have an inherent resistance to erosion 

that can withstand cutting disturbances so long as the 

forest floor is not abused. 

To protect the forest floor and maintain low erosion losses, 

known precautions were taken during logging. For example, logging was conducted in early autumn when chances 

for erosion and sedimentation are least. A buffer strip of 

trees was left along the stream channel in the strip cut, and 

efforts were made to avoid streamside zones in both the 

clearcut and strip cut. Skidroads were kept at lowest possible grades, and water bars were installed. These efforts, 

together with rapid revegetation, prevented serious erosion 

and resulted in minimal changes in nutrient losses in suspended or particulate form, and preservation of the high 

quality of forest streams at Hubbard Brook. 

Concentrations of Stream Water Ions 

The changes in concentration of various stream water ions 

during our study paralleled those reported for other studies 

in northern hardwood stands in New England. The 

increases in Ca2 + , K + , Mg2 + , and NO3- and decreases in 

Sod2- occurred after clearfelling and herbicide applications 

on Hubbard Brook Watershed 2 (Likens et al. 1970); after 

clearcuttings in the White Mountains of New Hampshire 

(Pierce et al. 1972; Martin and Pierce 1980); after a variety 

of clearcuttings located in Maine, New Hampshire, and 

Vermont (Martin et al. 1984); and after a whole-tree harvest 

in New Hampshire (Hornbeck and Kropelin 1982). The 

causes of the changes in concentrations are reasonably 

well understood, though not completely quantified. 

Mechanisms affecting concentrations. Several mechanisms 

may be responsible for the changes in ion concentrations 

after harvest. 

1. Blocking of uptake. Uptake of available nutrients by 

living vegetation can be sizeable. For example, annual 

uptake of Ca2+ by Hubbard Brook forests is estimated at 

62 kg ha-' (Likens et al. 1977). Clearcutting temporarily 

blocks uptake while decomposition goes forward and 

increases the amount of available nutrients in the dissolved 

inorganic fraction of the soil solution. The greater amounts 

of soil water resulting from reduced interception and transpiration provide a means of transport to streams. Calcium ' 

;- 200- 

k 

F 

E 

k 150- 

8 

s 

s 

9 loo- 

.? s. 

1 

$ 50- 

0 

10 20 30 40 50 

Aboveground living blornass -metric t ha-' 

Figure I1 .-Relationship of annual increases in water 

yield (the curve is hand-fitted). 
probably is the best example of this mechanism, increasing 

to maximums in the first 1 to 2 years after harvest, then 

declining with regrowth (Fig. 5). Potassium shows this 

same pattern initially (Fig. 6), but does not fully decline with 

regrowth, indicating that other mechanisms are involved. 

The decline with regrowth may involve other mechanisms. 

For example, in the Hubbard Brook Watershed 2 experiment in which the area was kept free of vegetation for 3 

years, declines in concentrations began in the third year 

without revegetation. This suggests that exhaustion of 

easily decomposed substrate also plays a role in decreases 

in ion concentrations. 

2. Critical element shunt. This mechanism is proposed 

by Bormann and Likens (1979) to operate as follows: in the 

first year after harvest, when C:N and element:P ratios of 

decaying organic matter are high, dissolved nutrients in soil 

solution are taken up by the increased numbers of microorganisms. As the C:N and element:P ratios decrease, and 

demands by microorganisms decline, nutrient ion export to 

streams increases. The critical element shunt may explain 

why nutrient ion concentrations are highest in the second 

year after harvest (Figs. 5, 6, 8, 9). 

3. Accelerated nitrification. Nitrification rates in soils of 

undisturbed forests in New England are low, seldom 

exceeding 3 kg ha-' mo-' during the growing season 

(Federer 1983). However, the nitrification rate increases 

dramatically after cutting of northern hardwoods (Likens et 

al. 1970; Vitousek and Melillo 1979). The result is a flush of 

available NO3- and H+, and, in turn, a mobilization of 

cations. The transport to streams is rapid, as indicated by 

the quick response of stream NO3- to cutting (Fig. 8). The 

fact that NO3- concentrations in streams fell below 

preharvesting levels in the fifth or sixth year of regrowth 

suggests several possibilities, including a corresponding 

decline in nitrification rates to levels below those in undisturbed forests, a greater uptake of N by the rapidly growing 

new stand, increased immobilization of N by soil organisms, or an increase in denitrification. These possibilities 

have not been tested for our study areas. 

4. Accelerated decomposition of organic matter. Canopy 

removal exposes the forest floor and mineral soil to greater 

amounts of light, heat, and moisture, and accelerates 

decomposition and mineralization of organic materials 

(Bormann and Likens 1979). Covington (1981) showed that 

the forest floor in northern hardwood stands declines by 

about 50 percent in weight, or an average of 31 t ha-' in 

the 15 years after clearcutting. One-third of this decline 

was estimated to occur in the first 3 years following cutting. 

During the 15-year degrading phase, it was estimated that 

net nutrient releases from mineralization of forest floor 

material were 35 kg Ca ha-', 31 kg Mg ha-', 44 kg K 

ha-', and 808 kg N ha-'. These releases are a source for 

increased ion concentrations of soil water and streams. 

5. Accelerated weathering of inorganic materials. Compared to decomposition of organic matter, weathering of 

mineral soil and rocks generally is a less active source of 

nutrients at Hubbard Brook (Likens et al. 1977). The 

increased exposure to heat and moisture that accelerates 

decomposition also should speed weathering rates, though 

this effect has not been quantified. 

While these mechanisms occur after both strip and block 

cutting, increases in concentrations of stream ions due to 

strip cutting were less than one-third of those for block 

cutting. The small responses after strip cutting can be 

explained in part by mobile ions being intercepted and 

used by uncut or regenerating strips or the stream buffer 

zone. Also, the strip-cutting configuration should reduce 

decomposition and weathering by better protecting the cut 

sites from light and excessive heat. Thus, the availability of 

nutrients for leaching from the cut strips would be less than 

in the larger opening created by block clearcutting. 

Although the increases were smaller after strip cutting, the 

progression of three harvests caused them to last up to 2 

to 3 times longer than increases after the block clearcutting. 

Sulfate. (I variety of hypotheses have been suggested for 

explaining the decrease in concentrations of S042- in 

streams after cutting. After the clearfelling of Hubbard 

Brook Watershed 2, Likens et al. (1970) attributed the 

decreases in S042- partly to dilution by the increased 

water yields and partly to the reduction of S042- generation by sources internal to the ecosystem. Fuller et al. 

(1986) suggested the same hypotheses for streams from a 

whole-tree harvest at Hubbard Brook and added the possibilities of decreased dry deposition and increased S042- 

adsorption by soils. Regarding this latter possibility, Nodvin 

(1983) proposed that excess acid production by elevated 

nitrification rates increases the net positive charge on soil 

surfaces, and enhances adsorption of S042- ions. The 

theory was tested in the laboratory and found applicable for 

the Hubbard Brook Watershed 2 experiment involving 

clearfelling and herbicides, and would seem equally applicable for the strip-cut and block-clearcut watersheds. 

Hydrogen. Changes in H+ are of special interest in relation 

to effects of acid precipitation. The forest canopy at 

Hubbard Brook at least temporarily reduces H+ in precipitation from 0.08 mg L-' above the canopy to 0.01 mg L-' 

beneath (Eaton et al. 1973). Felling of the canopy during 

harvest allows acid precipitation to fall directly on soils and 

streams and possibly have more impact. Also, as mentioned earlier, the increased nitrification rates accompanying harvest are acidifying and could combine with acid 

precipitation to accelerate acidification of soils and 

streams. The amount of H generated by this mechanism is 

substantial. Based on output of NO3 - N in stream water, 

increased nitrification in the first year after harvest resulted 

in H production of 2.8 kg ha-' on the block clearcut and 
i 

1 0.6 kg ha-' on the strip cutting. These values can be 

compared with the average annual input of H + in precipitation of 1 .O kg ha-' (Likens et al. 1977) and the annual total 

of 2.5 kg ha-' generated by all Hf sources within an 

undisturbed Hubbard Brook watershed (Driscoll and Likens 

1982). 

Thus, it is not surprising that there were small increases in 

stream water H+ of 0.001 - 0.002 mg L-' after strip cutting 

and 0.004 mg L-' after block clearcutting (Fig. 7). The 

increases were short lived, and after year 2 of the block 

clearcut, the H+ fell 0.008 mg L-' below preharvest levels. 

Such changes are barely detectable and any impacts on 

stream chemistry and biota would be extremely difficult to 

quantify. Concerns should not be totally dismissed as 

changes in H+ of soils and soil solution could be more 

pronounced and of greater significance than those occurring in streams (Federer and Hornbeck 1985). 

t Management implications. Changes in concentrations of 

nutrient ions in streamflow raise at least three 

concerns: (1) importance as a loss from site nutrient capital, (2) potential for harming water quality, and (3) adverse 

or beneficial effects on stream biota. A later section relates 

the importance of dissolved ions to nutrient capital. 

Regarding water quality, no measured ion concentrations 

exceeded standards or guidelines established for protecting 

water for domestic or recreational use. Nitrate came closest, reaching a maximum of 26 mg L-' after block clearcutting versus the established standard of 45 mg L-' for 

drinking water. Relationships of changing ion concentrations to stream biota have had only minimal study. Noel et 

al. (1986) and Likens et al. (1970) reported increases in 

stream periphyton and macroinvertebrates after clearcutting northern hardwoods, but they did not separate effects 

of stream chemistry from those of light and temperature. 

Where there is concern about stream biota or water quality, 

our study shows that changes in stream ions resulting from 

even-age management practices can be moderated substantially by using strip cutting rather than block 

clearcutting. 

Evaluation of Nutrient Removals and Leaching 

Losses 

Nutrient removals and leaching losses for the strip-cut and 

block-clearcut watersheds are summarized in Table 9. The 

table also shows nutrient pools, which serve as one basis 

for evaluating the importance of nutrient removals and 

losses. Such evaluations are not straightforward as there 

are still many unknowns. To illustrate, Figure 12 shows 

hypothetical curves of nutrient fluxes that would have to be 

quantified to fully evaluate harvest effects on site productivity. Such data would be needed for all nutrients likely to 

become growth limiting, and for stages of stand development beyond the critical 10-year regeneration period shown 

in Figure 12. While forest ecosystem studies at many locations are gradually providing these kinds of data and information, detailed evaluations of harvest impacts cannot yet 

be made. 

(DIuolwd md particulate) 

Abom ground. biomass accretion 

Rwt audatu - Wkw pind bi- occretlon 

. Bulk mipitation 

Forest floor acretim 

100 12345678910 

CU1 

Stand age 

Figure 12.-Hypothetical curves of changes in fluxes of nutrient elements, such as 

Ca, K, and Mg, in years 1 through 10 after harvest. 
1 Table 9.-Summary of nutrient removals, leaching losses, and nutrient pools 

Ca K Mg N S P 

Strip Block Strip Block Strip Block Strip Block Strip Block Strip Block 

Item cut clearcut cut clearcut cut clearcut cut clearcut cut clearcut cut clearcut 

10-year dissolved ion 27 48 30 48 3 7 22 58 5 -14 Oe Oe 

losses in streamflow 

attributed to harvest 

Total losses due 134 187 70 100 14 21 96 155 18 4 6 7 

to harvest 

----------- Estimated Preharvest Nutrient Pools, kg ha- '- - - - - - - - - - - 

Vegetation 

Roots 

Forest floor 

Mineral soil: 

Available 

Totalf 

Total 10,456 5368 7746 5232 743 2645 

--------------- Control Watershed, kg ha-' yr7- - - - - - - - - - - - - - - 

Dissolved ion input 

precipitation 1 .7b 0.8b 0.5b 6.5b 1 1 .gb .04e 

Dissolved ion output 

streamflow 1 2.Sb 1 .gb 2.gb 3.7b 17.2b .02e 

Net - 1 0.8b -l.lb - 2.4b 2.8b - 5.3b .02e 

Weathering release 21.1a 7.1a 3.5a Od 0.8a 1 .5e 

Net mineralization 42.6a 20.1a 6.1a 69. 6d 5.7a 1 0.6e 

a Likens et al. (1977) and Whittaker et al. (1979). 

Mean for 1963 through 1981. 

' Hornbeck and Kropelin (1982). 

Bormann et el. (1977). 

Wood (1980) and Wood et al. (1984). ' Includes available soil elements. 

In the interim, several studies have evaluated nutrient 

removals and leaching by comparing them with both plantavailable and total nutrient capitals of the harvest site 

(Freedman et al. 1981; Weetman and Webber 1972; 

Weetman and blgar 1983; Johnson et al. 1982; Hornbeck 

and Kropelin 1982). At least two of these studies point out 

that a more realistic value for such comparisons, and one 

that might ultimately prove useful to forest managers, lies 

somewhere between available and total capitals (Freedman 

et al. 1981; Hornbeck and Kropelin 1982) 

In the evaluations that follow we compare nutrient removals 

and leaching losses with both available and total nutrient 

capitals. We used an approach developed by Bormann and 

Likens (1979) that incorporates some of the more important 

nutrient fluxes from Figure 12. This approach can be used 

only for the first 4 years after harvest as data are not yet 

available for additional years. Even so, evaluations now are 

far more thorough than was possible at the height of the 

clearcutting controversy in the early 1970's. 
Calcium. Before harvest, estimated total and available 

capitals for Ca were 10,456 and 510 kg ha- ' respectively 

(Table 9), the largest values for any of the nutrient elements studied. Losses of Ca of 134 kg ha-' due to strip 

cutting and 187 kg ha-' due to block clearcutting (Table 9) 

represent 1.3 and 1.8 percent of total site nutrient capital, 

and 26 and 37 percent of available capital. The nutrient 

losses obviously are more impressive as proportions of 

available capital than of total capital. The major concern 

would seem to be that the available pool does not become 

limiting to regrowth during present and future rotations. 

Using the approach from Bormann and Likens (1979), we 

compared some of the major fluxes of available Ca in the 

years immediately following harvest. The sum of Ca2+ 

losses in stream water plus Ca stored in regrowing 

biomass.ranged from 45 to 61 kg ha-' yr-' the first 4 

years after block clearcutting (Fig. 13). Mineralization of Ca 

from the forest floor (Covington 1981) could supply as 

much as one-third of the Ca2+ needed to satisfy streamwater losses and storage in biomass. The remainder, or at 

least 25 to 40 kg ha-' yr-', may have to be drawn from 

other sources, especially mineral soil. The available pool in 

the mineral soil is maintained by several processes including weathering, which supplied 21 kg Ca2+ ha-' yr-' 

before harvest (Table 9), and should supply even greater 

amounts immediately after harvest. Mineralization in the 

mineral soil also should supply increased amounts of available Ca2+ after harvest. As another source, logging slash 

contains more than 200 kg ha-' of Ca2+, some of which 

should mineralize quickly in the years after harvest. Thus, it 

seems tharat least initially there should be no major 

decline in the available pool. There are mechanisms to 

adequately replace stream water losses and biomass 

storage. 

Potassium. The preharvest pools for K were estimated at 

5,368 kg ha-' for total capital and 75 kg ha-' for available 

(Table 9). The combined losses due to harvest of 70 kg 

ha-' for strip cutting and 100 kg ha-' for block clearcutting represent 1.3 and 1.9 percent of the total capital and 93 

and 133 percent of available. Concerns about K losses in 

relation to the available pool may be even greater than for 

Ca. 

In the 4 years immediately after block clearcutting, the sum 

of K+ losses in stream water plus K stored in biomass 

showed a linear increase (Fig. 13). Since estimated mineralization of K from the forest floor is relatively constant 

immediately after harvest (Covington 1981), contributions of 

K from other sources become increasingly more important 

with time. Combined mineralization and weathering before 

harvest were estimated to contribute 27 kg K ha-' yr-' to 

the available pool. As with Ca, there would seem to be a 

continued, adequate pool of available K after harvest. 

However, in contrast to Ca, increased losses of K+ in 

stream water have not subsided completely. Continued 

evaluation will be required as more data are obtained. 

- Combined loss in streamwater 

and biomass storage 

- - - Mineralized from forest floor 

: Other sources f ................ 

Years after harvest 

Figure 13.-Nutrient flux and sources in the initial 4 years after block clearcutting. 

Data on forest floor and biomass storage from Bormann and Likens (1979). 
Magnesium. Magnesium pools before harvest were 7,746 

kg ha-' total and 41 kg ha-' available (Table 9). Total 

losses due to strip cutting were 14 kg ha-' or 0.2 percent 

of total and 34 percent of available. For block clearcutting, 

losses were 21 kg ha-' or 0.3 percent of the total and 51 

percent of available. The proportionally smaller losses for 

Mg compared with K reflect a tighter nutrient cycle for Mg. 

For undisturbed forests, combined weathering and mineralization for Mg is estimated at about 10 kg ha-' yr -' 

(Table 9). It seems unlikely that the Mg losses due to harvest would adversely affect regrowth. The losses of Mg are 

small and the reserve pool is large, and increased losses of 

Mg2+ in streamflow did not last beyond the second growing season after harvest. 

Nitrogen. Nitrogen is of special interest because of concerns that it may be limiting to plant growth, even before 

harvest. Losses due to harvest of 96 kg ha-' from the strip 

cut and 155 kg ha-' from the block clearcut represent 1.8 

and 3.0 percent of the estimated total capital of 5,232 kg 

ha-' (Table 9). In terms of available capital of 26 kg ha-', 

the losses represent 369 percent for strip cutting and 596 

percent for block clearcutting. 

In contrast to Ca2+ and K+ , estimated mineralization of N 

from the forest floor after harvest is more than double the 

combined loss in stream water plus storage in biomass 

(Fig. 13). The fate of N lost from the forest floor is uncertain, but translocation to mineral soil and denitrification are 

possibilities (Bormann and Likens 1979). There have been 

large increases in NO3- in soil solution of mineral horizons 

after harvest of northern hardwoods (Hornbeck and 

Kropelin 1982), but it is not clear if the increases resulted 

from translocation out of upper horizons or from localized 

nitrification. The evaluation of denitrification has only 

recently been initiated at Hubbard Brook as part of a 

whole-tree harvesting experiment. 

Increased nitrification and decomposition of the forest floor 

should provide adequate supplies of available N for 

regrowth immediately after harvest. However, there is some 

question as to whether available N is sustained through the 

regrowth period. To illustrate, Hornbeck and Kropelin 

(1982) found that NO,- in mineral soil solution increased 

25-fold in the first 2 years after a whole-tree harvest of 

northern hardwoods. However, NO3- concentrations then 

declined rapidly, and by the fourth year after harvest were 

at levels below those in undisturbed forests. This pattern 

was similar in streamflow after harvest of our study watersheds at Hubbard Brook, indicating a potential for critical 

levels of available N by 4 to 5 years after harvest. 

Covington and Aber (1980) suggested that limited N at 

years 6 to 11 after clearcutting may be responsible for a 

decline in leaf production found in the exploitive species, 

Prunus pensylvanica. More research is needed on the N 

cycle to fully evaluate impacts on regrowth. 

Losses of N resulting from harvesting may be replaced in 

part from atmospheric sources. The inputs of N in precipitation exceed outputs in streams by an average of about 3 

kg ha-' yr-' (Table 9). Also, the only positively identified 

substrate for fixation of atmospheric N at Hubbard Brook is 

deadwood more than 2 cm' in diameter (Roskoski 1980). 

Large amounts of this size material were left as slash on 

the harvested watershed. Roskoski (1980) estimated that 

about 2 kg N ha-' yr-' may be fixed in this material at 

year 4 after clearcutting. 

Finally, there seems to be a mechanism for minimizing 

leaching losses of N after harvest. As shown in Figure 8 

and Table 6, N losses in streamflow at 5 to 6 years after 

completion of harvest fell below those for undisturbed 

forests. Depending on how long this effect lasts, and 

assuming that N is not being lost in some other, unknown 

manner such as denitrification, N losses after harvest could 

be replaced by atmospheric sources in as little as 20 to 30 

years. At the average net gain of 2.8 kg ha-' for undisturbed forests (Table 9), the replacement time would be 34 

to 55 years. This period could be even shorter if N fixation 

is found to be greater, a possibility suggested by the calculated mass balance of N for Hubbard Brook (Bormann et al. 

1977). 

Sulfur. Harvesting removed relatively small amounts of S 

and had little effect on S lost in stream water (Table 9). 

Sulfate4 occurs in high concentrations in streams (Fig. 9) 

and in soil solution (Hornbeck and Kropelin 1982) in our 

study area, both before and after harvest, and there is no 

apparent reason for concern about availability of S during 

regrowth. 

Phosphorus. Removals of P in harvested products represented 0.2 percent of the preharvest P capital (Table 9). On 

the basis of research by Wood et al. (1984), we estimated 

that strip and block cutting did not increase losses of P in 

streamflow. 

Total losses of P to harvest are small compared with the 

overall site capital. However, harvest may cause an important redistribution of soil P. Wood et al. (1984) point out 

that P is biologically conserved in the surface soil horizons 

of undisturbed forests at Hubbard Brook by the close coupling between decomposition and uptake. They suggest 

that harvest disrupts biological control of P and allows 

large amounts of P to move downward from the forest floor 

to B horizons. The time required to restore the P that 

moved from the forest floor is unknown. 

Management implications. Overall, the nutrient losses 

resulting from strip cutting and block clearcutting at 

Hubbard Brook do not seem a major concern. Combined 

losses to increased leaching and product removal did not 

exceed 3 percent of total capital for any of~the nutrients 
studied. In terms of available capital, the losses were more 

impressive, ranging from 26 to 596 percent. However, it 

appears that replacement mechanisms will be able to 

maintain the available pools at adequate levels. Nitrogen 

and K may be exceptions, particularly beyond the fifth year 

of regrowth. We are continuing to monitor K losses, and 

the nitrogen cycle is a central focus of a whole-tree harvest 

study in progress at Hubbard Brook. 

Losses to harvest were less for strip cutting than for block 

clearcutting (Table 9)-partly because strip cutting moderated leaching losses, and partly because less material was 

harvested from the strip cut (Table 5). Management prescriptions for these watersheds call for harvesting again for 

sawtimber is not less than 70 years, and more likely in 

about 110 to 120 years (Leak et al. 1969; Solomon and 

Leak 1969). This sho,uld be adequate time to replenish the 

nutrients and organic matter lost as a result of harvest 

(Likens et al. 1978). 

While the actual nutrient removals and increased leaching 

losses may not be a problem, transformations and redistribution of nutrients remaining on site could affect regrowth. 

As discussed, N may become limiting around year 5 of 

regrowth when nitrification declines to very low levels. The 

redistribution of P from organic to mineral soil also could 

affect regeneration. Strip cutting might moderate some of 

these effects, but more information is needed. 

Regarding nutrient removals in harvested products, 

although our study watersheds were completely clearcut, 

the use of biomass was not intensive by current standards. 

The increasing use of newly designed, mechanized logging 

and processing equipment, and rising demands for wood 

as pulp and an energy source, have greatly increased 

biomass harvesting. Nutrient removals for whole-tree harvesting of northern hardwoods may be 2 to 3 times the 

values reported here (Hornbeck 1977; Hornbeck and 

Kropelin 1982). In such cases, and especially when coupled with projections for significantly shorter period betwen 

harvests, nutrient removals may be of much greater concern. 

Regeneration 

Regeneration on both the strip and block cuts is following 

the pattern outlined by Bormann and Likens (1979). Outgrowth, or occupation of the sites by exploitive and existing 

species, especially herbs and shrubs, peaked at about year 

2 after harvest (Table 6). By year 10, upgrowth by tree 

species was well along and a closed canopy had formed. 

Dominant species at 10 years were Prunus pensylvanica 

and the three major northern hardwoods, Betula alleghaniensis, Acer saccharurn, and Fagus grandifolia. Prunus 

pensylvanica usually dies at about 30 years, by which time 

the stands should be wholly dominated by northern hardwood species. 

As mentioned at the outset, a prime objective of strip cutting is to regenerate high proportions of Betula and Acer in 

the new stand. It is difficult at this stage of regrowth to 

evaluate whether strip cutting has resulted in a more desirable species mix than block clearcutting. Little is known 

about what the species composition and stocking levels 

must be at age 10 to produce a commercially valuable 

northern hardwood stand. Strip cutting certainly appears 

successful in terms of total stems. Betula alleghaniensis 

and Acer saccharurn were the most frequently occurring 

tree species on the strips at age 10 (Table 7). 

Species composition differed markedly among the sets of 

strips (Table lo), partly because of environmental factors 

such as light, temperature, and moisture, and partly 

because of abundance of seed. Through year 10, stand 

development was optimum on the second and third strips, 

which had a favorable mix of species, especially in the 

2.5-4.9, and 5.0-7.5 cm d.b.h. classes, and fewer Prunus 

Table 10.-Species densities for trees more than 2.5 cm d.b.h. on harvested and control watersheds; 

observations for the strips and control stand are for the middle elevation range 

First strip Second strip Third strip Block clearcut Controla 

Species (10 years) (1 0 years) (10 years) (10 years) (60 years) 

- - - - - - - - - - - - - - - - - - stems ha -1- - - - - - - - - - - - - - - - - - 

Betula alleghaniensis 640 2734 2457 1500 167 

Acer saccharurn 320 1800 2058 358 543 

Fagus grandifolia 160 2533 743 442 387 

Prunus pensylvanica 3760 2657 971 7625 11 

Acer pensylvanicurn 640 1800 1143 250 62 

a Data for control stand from Bormann et al. 1970. 
pensylvanica than on strip 1 or the block clearcut (Tables 7, 

10). All strips had a more desirable mix of Betula and Acer 

compared with the undisturbed stand on the control watershed (Table 10). However, the current mix on the strips can 

be expected to undergo marked changes in the ensuing 

years. In other 15 years, regrowth on our study sites will be 

reaching an age for which more is known about species 

composition and stand development (Leak et al. 1969; 

Solomon and Leak 1969), and a more thorough evaluation 

of strip cutting will be possible. 

Betula alleghanienis occurred in maximum numbers on the 

block clearcut, but Prunus pensylvanica was the second 

most numerous species (Table 7) and had by far the greatest biomass. Competition from Prunus pensylvanica may 

result in a lag in productivity of commercial species on the 

block clearcut compared with the strip cut. Regeneration 

strategies for Prunus pensylvanica are complex (Marks 

1974; Marks and Bormann 1972), but the higher density of 

this species in the block cutting may be partly in response 

to a higher initial nutrient release after block cutting. Safford and Filip (1974) reported that fertilization greatly stimulated Prunus pensylvanica to the detriment of other commercial species in a 4-year-old northern hardwood stand. 

The regrowth on both watersheds has other important 

roles, such as preventing erosion and curbing nutrient 

losses. The low turbidities in streams coupled with visual 

observations throughout the watersheds show that 

regrowth has stabilized all soil disturbance and that erosion 

will not be prolonged. Several Hubbard Brook studies have 

shown the important role reproduction plays in recovery of 

nutrient cycles immediately after harvest or other disturbances (Dominski 1971 ; Marks and Bormann 1972; Likens 

et al. 1978). 

The density and rapidity of regrowth also are advantageous 

in helping to reduce the visual impacts of cutting. With 

regard to the visual or esthetic impact, strip cutting'may be 

less displeasing than other forms of clearcutting. The uncut 

strips can be used to shield the cut areas from view, and 

break the openness created by large clearcut blocks and 

patches (Fig. 14). 

Conclusion 

Commercial clearcutting of northern hardwoods, whether . . 

by progressive strips or blocks, is a severe disturbance to 

the forest ecosystem. However, our study indicates that if 

care is taken during logging, and if sawtimber rotation 

lengths are followed, there should not be major -adverse 

impacts on site nutrient capital, stand regeneration, or 

productivity. By the 10th year after harvest, hydrologic and 

nutrient budgets had returned nearly to preharvest levels, 

and a closed canopy had formed. Compared with block 

clearcutting, progressive strip cutting moderates effects on 

hydrologic and nutrient cycles, and may result in a more 

desirable mix of commercial species in the new stand. 

Acknowledgment 

Vincent Levasseur, forest technician at the Hubbard Brook 

Experimental Forest, maintained instruments and installations and collected much of the basic hydrologic and& 

matic data used in this paper. 

Figure 14.-Summer and winter views across block clearcut '(foregroundx strip cutting 

(center), and clearfelling (far right). 
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Department of Agriculture, Forest Service, Northeastern Forest Experiment Station; 1987 30 p. 

Two even-age management systems, progressive strip cutting and block 

clearcutting, have been studied since 1970 on small watersheds at the 

Hubbard Brook Experimental Forest, New Hampshire. In the strip cutting, 

all merchantable trees were harvested in a series of three strips over 4 

years (1970-74). In the block clearcutting, all trees were harvested in a 

single operation in 1970. This paper contrasts progressive strip cutting and 

block clearcutting for the 10-year period after initiation of harvest in terms 

of hydrologic response, erosion losses, stream water ions, nutrient leaching, nutrient removals in harvested products, and natural regeneraion of 

vegetation. 

ODC 1 16.38 

Keywords: water yield; watershed; hydrology; soil nutrients; nutrient 

cycling; nutrient budget; stand regeneration; Hubbard Brook 
Headquarters of the Northeastern Forest Experiment Station are in Broomall, Pa. 

Field laboratories are maintained at: 

0 Amherst, Massachusetts, in cooperation with the University of Massachusetts. 

0 Berea, Kentucky, in cooperation with Berea College. 

0 Burlington, Vermont, in cooperation with the University of Vermont. 

Delaware, Ohio. 

0 Durham, New Hampshire, in cooperation with the University of New Hampshire. 

0 Hamden, Connecticut, in cooperation with Yale University. 

0 Morgantown, West Virginia, in cooperation with West Virginia University, 

Morgantown. 

0 Orono, Maine, in cooperation with the University of Maine, Orono. 

0 Parsons, West Virginia. 

0 Princeton, West Virginia. 

0 Syracuse, New York, in cooperation with the State University of New York 

College of Environmental Sciences and Forestry at Syracuse University, 

Syracuse. 

0 University Park, Pennsylvania, in cooperation with the Pennsylvania State 

University. 

e Warren, Pennsylvania. 

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should be reported to the Secretary of ~griculture, Washington, DC 20250. 

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