The relation of harvesting intensity to

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Forest Ecology and Management 261 (2011) 1510–1519

Contents lists available at ScienceDirect

Forest Ecology and Management
journal homepage: www.elsevier.com/locate/foreco

The relation of harvesting intensity to changes in soil, soil water, and stream
chemistry in a northern hardwood forest, Catskill Mountains, USA
Jason Siemion a,∗ , Douglas A. Burns a , Peter S. Murdoch a , Rene H. Germain b
a
b

U.S. Geological Survey, Troy, NY, United States
State University of New York, College of Environmental Science and Forestry, Syracuse, NY, United States

a r t i c l e

i n f o

Article history:
Received 9 September 2010
Received in revised form 27 January 2011
Accepted 29 January 2011
Available online 20 February 2011
Keywords:

Stream water quality
Nitrate
Aluminum
Calcium
Partial harvest

a b s t r a c t
Previous studies have shown that clearcutting of northern hardwood forests mobilizes base cations,
inorganic monomeric aluminum (Alim ), and nitrate (NO3 − -N) from soils to surface waters, but the effects
of partial harvests on NO3 − -N have been less frequently studied. In this study we describe the effects
of a series of partial harvests of varying proportions of basal area removal (22%, 28% and 68%) on Alim ,
calcium (Ca2+ ), and NO3 − -N concentrations in soil extracts, soil water, and surface water in the Catskill
Mountains of New York, USA. Increases in NO3 − -N concentrations relative to pre-harvest values were
observed within a few months after harvest in soils, soil water, and stream water for all three harvests.
Increases in Alim and Ca2+ concentrations were also evident in soil water and stream water over the
same time period for all three harvests. The increases in Alim , Ca2+ , and NO3 − -N concentrations in the
68% harvest were statistically significant as measured by comparing the 18-month pre-harvest period
with the 18-month post-harvest period, with fewer significant responses in the two harvests of lowest
intensity. All three solutes returned to pre-harvest concentrations in soil water and stream water in the
two lowest intensity harvests in 2–3 years compared to a full 3 years in the 68% harvest. When the results

of this study were combined with those of a previous nearby clearcut and 40% harvest, the post-harvest
increases in NO3 − -N concentrations in stream water and soil water suggest a harvesting level above
which the relation between concentration and harvest intensity changes; there was a greater change
in concentration per unit change in harvest intensity when basal area removal was greater than 40%.
These results indicate that the deleterious effects on aquatic ecosystems previously demonstrated for
intensive harvests in northern hardwood forests of northeastern North America that receive high levels
of atmospheric N deposition can be greatly diminished as harvesting intensity decreases below 40–68%.
These results await confirmation through additional incremental forest harvest studies at other locations
throughout the world that receive high levels of atmospheric N deposition.
Published by Elsevier B.V.

1. Introduction
Although nitrogen (N) is considered a growth-limiting nutrient
in forests at a global scale (Magnani et al., 2007), many regions
receive atmospheric N deposition in excess of biological demand,
leading to elevated rates of net nitrification and leaching of nitrate
(NO3 − -N) through soils to adjacent surface waters (Aber et al.,
1989). These regions of excess N deposition include forested lands
in Europe, North America, and Asia that receive atmospheric N
deposition that originates from NOx emissions of coal-fired power

plants, ammonia (NH3 ) emissions from agricultural sources, and
NOx emissions from mobile sources (Gundersen et al., 2006; Elliott
et al., 2007; Stephen and Aneja, 2008). Many of these forested

∗ Corresponding author. Tel.: +1 518 285 5623; fax: +1 518 285 5601.
E-mail address: jsiemion@usgs.gov (J. Siemion).
0378-1127/$ – see front matter. Published by Elsevier B.V.
doi:10.1016/j.foreco.2011.01.036

regions have been receiving elevated atmospheric N deposition for
decades resulting in large N stores and decreased C/N ratios in these
ecosystems, particularly in soils (Aber et al., 1989; Johnson, 1992;
Gundersen et al., 2006).
Intensive harvests such as clearcuts or whole-tree harvests
in forests that receive elevated levels of atmospheric N deposition often induce large releases of NO3 − -N from soils, commonly
resulting in about 3–5 years of elevated NO3 − -N concentrations
in surface waters (Hornbeck and Kropelin, 1982; Reynolds et al.,
1995; Martin et al., 2000; Gundersen et al., 2006; Fukushima and
Tokuchi, 2008). This release of NO3 − -N is believed to result largely
from a lack of uptake of N by the vegetation that was removed; once

a secondary forest is established, stream NO3 − -N concentrations
generally diminish rapidly (Likens et al., 1969; Burns and Murdoch,
2005). Numerous other processes such as decreased N immobilization by microbes due to decreased litterfall rates also contribute
to the response observed in surface water NO3 − -N concentrations

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J. Siemion et al. / Forest Ecology and Management 261 (2011) 1510–1519

(Prescott, 1997). In upland areas with steep slopes, thin soils, and
resistant bedrock, the post-harvest period of elevated surface water
NO3 − -N concentrations is often accompanied by elevated losses of
nutrient base cations such as calcium (Ca2+ ), magnesium (Mg2+ ),
and potassium (K+ ) from soils, and increased soil water and surface
water acidity as evidenced by decreased pH and acid-neutralizing
capacity (ANC) (Hornbeck et al., 1990; Dahlgren and Driscoll, 1994).
Harvesting-induced increases in stream acidity and accompanying increased aluminum (Al) concentrations in these upland forests
can be detrimental to the survival of many species of aquatic biota
such as brook trout for up to 2–3 years after harvesting (Baldigo
et al., 2005). Elevated Ca2+ concentrations in stream water can persist for more than a decade after harvesting is completed (Bailey
et al., 2003). Changes in stream and soil chemistry that result from

harvesting are of concern not only because of potential effects on
aquatic ecosystems, but also because the Catskill Mountain region
that is the focus of the current study shows evidence of soil Ca2+
depletion, which can slow regeneration and harm sugar maple (Acer
saccharum) stands (Wilmot et al., 1995; Long et al., 1997; Lawrence
et al., 1999).
Partial harvests offer a means of decreasing the effects of vegetation removal on soil and stream chemistry relative to those that
follow clearcutting; however, results indicate that the response of
stream chemistry to partial harvests can vary widely (Martin and
Pierce, 1980; Gilliam et al., 2004) because a diversity of partial harvesting strategies have been deployed in a wide variety of forest
types and climatic settings (Martin et al., 2000; Thompson and
Pitt, 2003; Lee et al., 2004; LaPointe et al., 2006). Often, harvests of
less than 20% biomass removal, such as a pre-commercial thinning,
result in little change in soil-water chemistry, stream chemistry,
or aquatic biota (Briggs et al., 2000; Baldigo et al., 2005). In contrast, moderate cuts that remove half or more of tree biomass can
result in large changes in water chemistry (Martin and Pierce, 1980;
Tremblay et al., 2008). These study results suggest that the relation between harvest intensity and nutrient export is not linear; a
threshold of harvest intensity may exist below which only small
increases in nutrient export occur (Knight et al., 1991; Prescott,
1997). However, few studies have identified a clear threshold

where the relation between harvest intensity and the response
variable changes sharply.
A previous study of harvesting effects in a northern hardwood
forest in the Catskill Mountains of southeastern New York found
that there was a non-linear relation between changes in stream
chemistry and timber harvest levels (Wang et al., 2006). Additionally, the return of stream chemistry to reference levels was more
rapid for the 40% harvest than for a previous clearcut. The decreased
changes and shortened recovery time of stream chemistry following this partial harvest were attributed to a rapid expansion of the
canopy crown into post-harvest gaps (Wang et al., 2006). Other
studies support the governing role of harvesting-induced canopy
gaps through direct storage of nutrients as well as through indirect
effects of reduced litterfall on soil microbial N-cycling processes
(Parsons et al., 1994; Prescott, 2002).
The study described in this paper was implemented on a model
forest designed to demonstrate environmentally sustainable harvesting practices at the Frost Valley YMCA in the Catskill Mountains,
New York, USA, providing an opportunity to readily link the
research described here with outreach and education activities for
foresters and land owners. Three forest harvests of varying intensity
were completed to identify whether changes in soil–water chemistry, stream chemistry, and indices of soil N availability showed
evidence of a level above which the relation between concentrations and forest harvest intensity changed. The results of this study

are also placed within the context of data from two nearby harvests:
(1) a 40% harvest as previously discussed by Wang et al. (2006) and
(2) a clearcut previously described by Burns and Murdoch (2005)

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Fig. 1. Map of the study area showing study watersheds, harvest blocks, the portions
of study watersheds which were harvested, and surface water sampling sites.

and McHale et al. (2007). Including data from these previous investigations allowed us to explore the effects of harvesting on soil and
stream chemistry in this region for a range of harvesting intensities
from unharvested to clearcut conditions.
2. Study area
The study area consisted of a 48-ha reference watershed and
three timber harvest blocks located in the Frost Valley Model Forest: the 8.9-ha FV-N, the 10.5-ha FV-G, and the 22.7-ha FV-R harvest
blocks (Fig. 1). The Frost Valley Model Forest is located in the
headwaters of the Neversink River basin in the Catskill Mountains of southeastern New York. The watersheds delineated in
Fig. 1 may not represent the actual area that drains to the sampling points. Subsurface runoff in the unharvested upper portions
of the delineated watersheds may exit the watersheds via shallow
bedrock fractures as previously discussed by Burns et al. (1998) for

the Catskills. Field observations indicated greater stream flow in
the 28% harvested area (watershed area 10.1 ha) than in the 22%
harvested area (watershed area 17.8 ha). Additionally, field observations indicated that the stream channels did not form until well
within the harvested area, generally 100–200 m above the sampling
point.
The climate is humid continental with a mean annual air
temperature of 5.2 ◦ C and mean annual precipitation of 161 cm
for the period 1970–2000 at the National Weather Service Slide
Mountain meteorological site approximately 8 km northeast
of the study area at an elevation of 808 m (Northeast Regional
Climate Center, 2009). The area receives some of the highest
acid deposition rates in North America with mean annual total

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Table 1
Pre- and post-harvest stand density statistics for each harvest block.

Block Basal area
(m2 /ha)

Pre-harvest
FV-R 30
FV-G 29
FV-N30
Post-harvest
FV-R 10
FV-G 21
FV-N23
a

Relative stand Stems per
densitya (%)
hectare

Mean
diameter
(cm)

Total above
ground
biomass
(ton/ha)

107
100
104

1329
1250
1294

12.9
12.7
11.9

245
254
284

30
72
84

106
911
921

33.0
13.0
12.4

111
180
227

Defined as the fraction of growing space occupied by trees.

N deposition of 8.12 kg N ha−1 year−1 and sulfur (S) deposition
of 8.82 kg S ha−1 year−1 during 2007–2008 as determined from
data collected at the Biscuit Brook National Atmospheric Deposition Program site and the Claryville Clean Air Status and Trends
network site ((http://www.epa.gov/castnet/sites/cat175.html,
accessed 12/06/10).
Soils in the area are developed from glacial till on steep slopes
and are predominately medium textured, well drained Inceptisols of the Arnot-Oquaga-Lackawanna association (Tornes, 1979)
with O horizons ranging in thickness from 3 to 6 cm (Burns and
Murdoch, 2005). Total soil thickness ranges from 0 to 1 m; in
a nearby catchment mean thickness is 0.33 m (Johnson et al.,
2000). These poorly buffered soils are naturally acidic, and have
become more acidic in recent decades through base cation depletion due to the high rates of acidic deposition (Lawrence et al.,
1999).
The forest overstory within the study area is dominated by
northern hardwoods including sugar maple, red maple (Acer
rubrum), American beech (Fagus grandifolia) and yellow birch
(Betula alleghaniensis), with small numbers of eastern hemlock
(Tsuga Canadensis).
3. Methods
3.1. Forest harvesting
The harvest blocks shared similar pre-harvest stand density
traits of basal area, relative density, and stems per hectare. Relative
stem density is defined as the fraction of growing space occupied by
trees (USDA Forest Service, 1984). Overall above-ground biomass
averaged just over 250 tons per hectare prior to silvicultural activities. However, in terms of acceptable growing stock (ability to
produce saw logs now and into the future), block FV-R was stocked
with much higher quality stems, notably sugar maple and black
cherry (Prunus serotina). Pre- and post-harvest stand statistics are
shown in Table 1.
Block FV-R received a shelterwood regeneration harvest, reducing the basal area and relative density by 68%. The residual stand is
dominated by high quality saw timber-sized seed trees at a 10-m
spacing, which provides plentiful light for seedling establishment.
Blocks FV-G and FV-N had been high-graded (harvested for high
quality timber only) in the past, creating low quality uneven-aged
stands. The silvicultural goal for these two blocks was to use the
single tree selection method to simultaneously balance the distribution of the age classes and improve the quality of the residual
stocking. The 22% reduction in basal area for FV-N was within
the desired target harvest range; however, unfavorable markets
for low quality roundwood resulted in a lower intensity harvest
(28%) in FV-G than the prescribed 40% reduction in basal area.
The timing of the harvests, block area, and percent basal area

removed are given in Table 2. This table also shows the percent of
pre-harvest basal area of the three dominant northern hardwood
species.
Block FV-A was harvested in 2002 as part of a previous investigation (Wang et al., 2006), and is discussed in the current paper.
This block is forested with northern hardwoods similar to the other
forest blocks described here with pre-harvest and post-harvest
basal areas of 31.7 m2 ha−1 and 21.4 m2 ha−1 , respectively, indicating removal of 33% of basal area from the watershed that drains
the site. However, this harvest removed 40% of tree basal area
from the lower part of the harvest block closest to and surrounding
the stream with no harvest in the upper parts of the watershed.
Assuming that outlying areas furthest removed from the stream
contribute minimally to stream chemistry because of deep losses
through fractured bedrock combined with the fact that subsurface
flow from upper areas had to pass through the harvest-impacted
soils (and would be expected to acquire the 40% harvest chemical
signature) down gradient and surrounding the stream, we consider
the stream in Block FV-A to have responded as though 40% of basal
area was removed from its watershed.

3.2. Surface water
Stream water samples were collected bi-weekly from streams
that drained each of the three harvest blocks and the reference
watershed. Generally, 4 or 5 storms were sampled annually with
automated samplers in the harvest blocks, and varying numbers
of samples were analyzed per storm depending on the magnitude of the discharge. Storm sampling was not conducted in
the reference watershed. The samples were collected in 500 mL
polyethylene bottles and stored on ice during transport to the laboratory. Storm samples were collected by automated samplers in
500 mL polyethylene bottles that were generally retrieved within
2–3 days after collection.

3.3. Soil water
Soil water samples were collected monthly from March through
November and every 6–8 weeks during the winter when weather
conditions permitted. Samples were collected from six locations
per harvest block and nearby reference locations along an elevation gradient using zero-tension lysimeters installed horizontally
in the B horizon beneath the root zone at a depth of 0.15–0.25 m.
The samplers consisted of 50 cm long pvc tubes with a diameter
of 5 cm, with 0.5 mm openings spaced 5 mm apart on half the circumference of the tube, and sealed on one end. Two of these tubes
were connected to a collection unit by tubing with an additional
tube from the collection unit to the surface.

Table 2
Date of harvest, area, and basal area removed for each harvest block. The percent
of pre-harvest total basal area for each of the three dominant northern hardwood
species is also shown.
Block

Date cut

Block
area
(ha)

Basal area
removed
from cut
area (%)

Sugar
maple
(%BA)

FV-R

February to
April 2006
February to
April 2005
February to
April 2005

22.7

68

53

6

23

10.5

28

22

35

20

8.9

22

28

38

27

FV-G
FV-N

Yellow
birch
(%BA)

American
beech
(%BA)

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Table 3
Significance of differences in pre-harvest and post-harvest concentrations of Alim , Ca2+ , and NO3 − -N in stream water and soil water, and between reference and post-harvest
concentrations of NH4 + and NO3 − -N in O horizon soils.
Harvest intensity

22%
28%
68%

Stream water

Soil water

O horizon soils

Alim

Ca2+

NO3 − -N

Alim

Ca2+

NO3 − -N

NH4 +

NO3 − -N

ns
ns

ns
ns

ns
ns

**

**

**

**

**

**

**

**

**

**

ns

*

ns

**

**

**

**

**

ns = no significant difference.
*
p < 0.05.
**
p < 0.005.

3.4. Soil N
Inorganic nitrogen was measured in soil samples using a potassium chloride (2 M KCl) extraction method (Bremner, 1965). Thirty
samples that represented the combined Oe + Oa horizons were collected 4–6 times per year during the snow-free months in each
harvest block with an additional 30 samples collected from a nearby
reference area. The samples were collected from evenly distributed
locations throughout the harvest blocks and reference area. Before
each field trip, 30 mL of KCl was placed in each of thirty 250 mL
polyethylene bottles per block, which were then weighed. While
in the field, approximately 5 g of O horizon soil was placed in each

bottle, and the bottle was capped and shaken vigorously. Approximately 1 kg of soil was also placed in a clean plastic bag and
sealed for later soil moisture and loss on ignition analysis. Bottles were kept on ice until returned to the laboratory where they
were refrigerated. Approximately 18 h after sampling, the bottles
were weighed again, shaken, and the solution poured off and filtered through a glass fiber filter (GF/F). The filtrate was then stored
frozen until analyzed.
Samples for soil moisture analysis were stored in sealed plastic
bags until returned to the laboratory for analysis. Approximately
5 g of soil were weighed before and after drying in an oven at 65 ◦ C
for approximately 24 h. The oven dried soil was then placed in a

Fig. 2. Ca2+ , NO3 − -N, and Alim concentrations in stream water in reference, 22%, 28%, and 68% harvested watersheds in the Catskill Mountains of southeastern, NY. Vertical
line represents timing of the timber harvest in each watershed.

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J. Siemion et al. / Forest Ecology and Management 261 (2011) 1510–1519

muffle furnace at 450 ◦ C for approximately 24 h after which it was
weighed and the loss on ignition calculated (Blume et al., 1990).
3.5. Laboratory methods
Stream water and soil water were analyzed by ion chromatography for NO3 − -N, by inductively coupled plasma-emission
spectrometry for Ca2+ , by flow injection analysis for total
monomeric aluminum (Almono ) and organic monomeric aluminum
(Alorg ), by electrode for pH, and by a Gran titration for ANC
(Lawrence et al., 1995). Inorganic monomeric aluminum (Alim ), the
fraction that is toxic to aquatic biota, was calculated by subtracting
Alorg from Almono . KCl extracts from soils were analyzed for NO3 − N and NH4 + by automated flow injection analysis (Lawrence et al.,
1995).
3.6. Statistical methods
Comparisons of pre-harvest and post-harvest soil, soil water,
and stream water chemistry were conducted using a one-tailed
Wilcoxon rank sum test (Helsel and Hirsch, 1992) and results were
considered significant if p ≤ 0.05. The pre-harvest and post-harvest
periods were defined as all data collected 18 months prior to the
start of the harvests and 18 months after the harvests were completed. For soil analysis, the post harvest period was defined as all
data collected within 18 months after the harvest was completed.
These harvests were not replicated, and thus there is a risk that
the inferential statistical tests used here, while correctly identifying
whether significant differences exist among the treatments, cannot
identify with certainty that the observed changes were the result of
the harvests. We rely here on past harvest research performed by
some of the co-authors of this paper as well as researchers throughout the world that have identified responses of NO3 − -N, Ca2+ , and Al
to harvests and the biogeochemical processes responsible for these
responses. However, the results presented in the current paper
will require replication in other regions before harvesting response
thresholds can be generalized.
Regression analysis was used to investigate changes in the relation between harvest intensity and solute concentrations. Linear
regression relations were calculated for varying harvest ranges of
0–40%, 0–68%, and 0–97%, and for each of the three stream water
constituents (NO3 -N, Ca2+ , and Alim ). Slopes and confidence intervals of these regressions were compared to evaluate evidence for a
change in these relations with increased harvesting intensity.
4. Results
4.1. Stream water
Mean concentrations for constituents in stream water samples for the period October 1, 2003 through September 30,
2006 from the reference watershed were 0.7 ␮mol L−1 for Alim ,
43.3 ␮mol L−1 for Ca2+ , 14.2 ␮mol L−1 for NO3 − -N, and 5.78 for pH.
NO3 − -N concentrations showed seasonal variations typical of the
area—greater values during the dormant season and lower values
during the growing season. Evidence of episodic acidification was
also observed with elevated NO3 − -N concentrations and decreased
ANC and pH during storm events and spring melt; these data are
consistent with previous investigations that episodic acidification
in streams of this region is driven largely by nitric acid (Murdoch
and Stoddard, 1992). Concentrations of Alim , Ca2+ , and NO3 − -N
were higher during storm flow than during baseflow in the harvest
blocks.
A Kruskal–Wallis test was applied to annual daily mean temperatures and annual monthly precipitation totals for the four time
periods covered by the harvests (1997, 2002, 2005, and 2006) to

Fig. 3. Increase in mean concentrations of Alim , Ca2+ , and NO3 − -N in stream water
from 18 months prior to harvesting to 18 months post harvesting for the 22, 28,
and 68% harvest blocks from this study and nearby 40% (Wang et al., 2006) and 97%
(Burns and Murdoch, 2005) harvests. Also shown are linear regression lines and 90%
confidence intervals.

investigate whether differences in climatic conditions during the
periods that the harvests were conducted may have affected the
results of the study. There was no significant difference ( > 0.1) for
the precipitation data between the four time periods. There was
a significant difference for the daily mean temperatures, but the
difference was minimal (1997 was cooler than the other years by
approximately 1.5–2.0 ◦ C). A Kruskal–Wallis test was also applied
to the Alim , Ca2+ , and NO3 − -N data from the reference stream for
the four time periods covered by the harvests. All three chemical constituents were significantly higher during 1997 (p < 0.005).
The differences in median values between 1997 and the later harvests were approximately 12 ␮mol L−1 for Ca2+ and 10 ␮mol L−1
for NO3 − -N, while a 0.2 ␮mol L−1 increase in Alim was observed for
the year 2006. These greater concentrations of Ca2+ and NO3 − -N in

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J. Siemion et al. / Forest Ecology and Management 261 (2011) 1510–1519

samples from the reference stream during 1997 may have been due
to leakages of water through shallow bedrock fractures from the
adjacent 97% harvest. The NO3 − -N concentration timeline for the
97% harvest of 1997 given by Burns and Murdoch (2005) shows that
the changes in concentrations in the reference stream appear to be
coincident with changes in concentrations in the stream draining
the 97% harvest.
Increases in chemical concentrations in stream water in
response to the timber harvests were first evident 5 to 6 months
after the harvests were completed, with peak concentrations generally occurring within 1–2 months after the initial increase (Fig. 2).
Concentrations of Alim , Ca2+ , and NO3 − -N in the 22% and 28% harvest blocks remained elevated for 26–28 months, while in the 68%
harvest block concentrations remained elevated for 36 months.
The results of comparisons between pre-harvest and post-harvest
concentrations are shown in Table 3. Comparisons between the reference watershed and the harvest blocks were not made due to the
lack of storm sampling in the reference watershed.
The relations between changes in stream chemistry and harvest intensity are shown in Fig. 3, building on the work of Wang
et al. (2006). The mean response (difference between pre-harvest
period mean and post harvest period mean) of NO3 − -N in stream
water to the various harvesting intensities was not linear (Fig. 3A).
Above the harvesting range of 0–40% basal area removal, the mean
response of NO3 − -N concentrations rose sharply. The slope of the
linear regression line (r2 = 0.89) for the harvests in the range of
0–40% was 1.08, indicating an increase of 1.08 ␮mol L−1 of NO3 − -N
for every percent increase in basal area harvest removal, whereas
the slope of the linear regression line (r2 = 0.94) for harvests in
the range of 0–97% was 2.80, more than twice the response rate.
The mean NO3 − -N concentrations for the 68% and 97% harvests lie
above the 90% confidence interval for the linear regression based
on the 0–40% harvest intensities, further indicating a change in
response for harvests greater than 40%. A similar change in the
linear relation between harvest intensity and the mean response
in the 0–40% range was not evident for Alim and Ca2+ as the mean
concentrations for 68% basal area removal fell within the 90% confidence intervals for the 0–40% regression (Fig. 3B and C). However,
the relations with these constituents did show a clear change in
the slope of the linear regression at a harvest intensity greater than
68%. For Alim concentrations, the linear regression slope for the
0–68% harvest range increased more than fourfold for the 0–97%
range, and Ca2+ concentrations increased nearly twofold for the
same comparison of regression relations. Furthermore, the mean
values for each of these constituents at a harvesting intensity of
97% were both greater than the upper limit of the 90% confidence
interval for the 0–68% harvesting range.
4.2. Soil water
Responses in soil water chemistry were generally observed
within 5–7 months of completion of the harvests (Fig. 4), with
peak concentrations observed 10–20 months after completion of
the harvests. The results of comparisons between pre-harvest and
post-harvest concentrations are shown in Table 3. Post harvest Ca2+
and NO3 − -N concentrations in soil water in the 22% and 28% harvest
blocks not only returned to pre-harvest values, but decreased below
pre-harvest values 29 months after the harvests were completed.
Similarly to the stream water results, Alim , Ca2+ , and NO3 − -N concentrations in the 68% harvest block returned to pre-harvest levels
36 months after the harvest was completed.
4.3. O-horizon soil nitrogen
Mean NH4 + concentrations in O-horizon soils of the reference area varied between 60 and 670 mg N kg−1 soil (Fig. 5).

1515

The results of comparisons between the reference area and
post-harvest concentrations are shown in Table 3. Mean NH4 +
concentrations in O-horizon soils from the 22%, 28%, and 68%
harvest blocks were all significantly greater than those of the
reference area during the post harvest period (p < 0.005). The variability of NH4 + concentrations in the 22% harvest block decreased
14–16 months after the harvests were completed. However, the
68% harvest block NH4 + concentrations had much greater variability after the harvest was completed than before. Maximum
NH4 + concentrations occurred 14 months after harvesting in the
22% harvest block, 4 months after harvesting in the 28% harvest block, and 5 months after harvesting in the 68% harvest
block.
Mean NO3 − -N concentrations in O-horizon soils from the
22%, 28%, and 68% harvest blocks were all significantly greater
than those of the reference area during the post harvest period
(p < 0.005). The mean NO3 − -N concentrations in O-horizon soils
of the reference area were below 20 ␮mol L−1 for all sampling
trips. Maximum NO3 − -N values occurred 14 months after the
harvest was completed in the 22% and 28% harvest blocks and
5 months after the harvest was completed in the 68% harvest
block.

5. Discussion
The responses in soil water chemistry, stream water chemistry, and soil N availability were broadly consistent with previous
harvesting studies in the Catskills, in other northern hardwood
forests of northeast North America, and in forests in Europe and
Asia (Hornbeck and Kropelin, 1982; Martin et al., 2000; Burns and
Murdoch, 2005; Gundersen et al., 2006; Wang et al., 2006; McHale
et al., 2007; Fukushima and Tokuchi, 2008). Elevated Alim , Ca2+ ,
and NO3 − -N concentrations in streams and soil water during the
first two growing seasons after harvest are largely the result of an
increased supply of NO3 − -N in soils. A previous study in a nearby
clearcut in the Catskills suggested that these chemical changes are
largely driven by decreased vegetation N uptake following harvesting, and most likely not by increased net rates of N mineralization
and nitrification (Burns and Murdoch, 2005). Other factors may also
contribute to increased NO3 − -N availability such as NO3 − -N leaching from remaining slash, death and decay of roots, physical soil
disturbance and mixing, and reduced litter inputs that might induce
C-limitation and decreased N immobilization in microbial communities (Fahey et al., 1991; Staaf and Olsson, 1994; Prescott, 2002).
Several factors likely contributed to the post-harvest increases in
Alim , Ca2+ , and NO3 − -N concentrations observed in the Catskills
such as high rates of atmospheric N deposition and resulting large
soil N stores with low C:N, as well as thin, acidic soils; these
soils have high rates of net nitrification even in the absence of
disturbance (Dahlgren and Driscoll, 1994; Lawrence et al., 1999,
2000).
The mean NO3 − -N response for the partial harvests conducted in this study did not describe a linear relation between
the reference watershed and the previously conducted clearcut
(Fig. 3). The response increased markedly above 40% basal
area removal. We recognize that results from only 5 harvests are presented and used for the regression analysis, thus
confirmation of these results from other studies is needed.
Additionally, the pre- and post-harvest characteristics of these
stands were not identical. For example, Block FV-R had a
higher proportion of sugar maple and lower proportion of
yellow birch than Blocks FV-G and FV-N (Table 2) as well
as the previously harvested Block FV-A and clearcut. Furthermore, the shelterwood harvest in FV-R left much larger
trees than did the harvests in the other blocks, and either

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J. Siemion et al. / Forest Ecology and Management 261 (2011) 1510–1519

Fig. 4. Mean seasonal concentrations of Alim , Ca2+ , and NO3 − -N in soil water from sets of 6 zero tension lysimeters collected every 4–6 weeks in reference, 22%, 28%, and 68%
harvested watersheds in the Catskill Mountains of southeastern, NY (vertical line represents timing of the timber harvest in each watershed, error bars 1 standard deviation,
year label indicates position of winter season followed by spring, summer, and fall).

of these factors may have affected the results described
herein.
An additional consideration is that only concentration results
and not loads are presented here for the streams, and that increases
in streamflow following forest harvesting have been documented at
numerous study sites throughout the world driven largely driven
by decreased transpiration (Jones and Post, 2004; Robinson and
Dupeyrat, 2005). We did not calculate loads in this study, however, because two of the streams (22% and 28% harvests) showed
intermittent flow with evidence of water leaving the watershed via
shallow bedrock fractures, and the partial harvests were conducted
in limited portions of the watersheds. Although full watershed harvests were not performed, the stream water results were similar to
those obtained from soil water and soils, indicating that the unharvested portions of the watersheds located at the greatest distance
from the streams minimally influenced the stream water results.
Our expectation is that patterns of temporal change in loads as a
function of harvesting intensity for Alim , Ca2+ , and NO3 − -N would
have been similar to the patterns we observed for changes in concentration, but we cannot evaluate these patterns in the current
study. Therefore, we used concentrations to examine the concept
of harvesting thresholds above which negative effects of harvesting
were measured. Additionally, slight changes in solute concentra-

tions resulting solely from changes in transpiration rates cannot be
ruled out, but were unlikely to be a major driver of the concentration changes we observed.
Four methods were used to explore forest harvest intensity
thresholds: (1) the harvest intensity at which the relation between
the mean response (the difference between pre-harvest mean and
post-harvest mean concentrations of Alim , Ca2+ , and NO3 − -N) and
harvest intensity changed (Fig. 3); (2) the harvest intensity at
which maximum concentrations in stream and soil water exceeded
known biological thresholds; (3) the harvest intensity at which
stream water concentrations exceeded human health criteria; and
(4) the duration of elevated concentrations of Alim , Ca2+ , and NO3 − N in soils, soil water, and stream water.
The mean response in stream water NO3 − -N concentration
increased substantially at harvest intensities greater than 40%. For
Alim and Ca2+ , the mean response was linear across the partial harvest intensities described in this study and by Wang et al. (2006),
but was relatively greater for the previous clearcut (97% basal area
removal) suggesting greater increases in Alim and Ca2+ concentrations at harvesting intensities greater than 68%. A likely reason
why Alim did not respond in the same manner as NO3 − -N can
be explained by the typical behavior of Al in forested watersheds.
Alim concentrations in soils and streams show little increase until

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J. Siemion et al. / Forest Ecology and Management 261 (2011) 1510–1519

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Fig. 5. Mean seasonal concentrations of NH4 + and NO3 − -N in O-horizon soils from sets of 30 samples collected every 4–6 weeks in reference, 22%, 28%, and 68% harvested
watersheds in the Catskill Mountains of southeastern, NY (vertical line represents timing of the timber harvest in each watershed, error bars 1 standard deviation, year label
indicates position of winter season followed by spring, summer, and fall).

the sum of acid anion concentrations (AA) exceeds the sum of
base cation concentrations (BC), above which a linear relation
is commonly observed (Driscoll, 1985). In these Catskill streams,
AA/BC was generally about 0.7–0.9 prior to harvesting, and
generally increased in all streams where harvest occurred because
NO3 − -N concentrations increased to a greater extent than those of
the base cations. The clearcut stream showed the greatest increase
and had the highest mean value during the post-harvesting period
(1.03) among these harvests. This increase in AA/BC resulted
in an increasing response in Alim concentrations with harvesting
intensity that was proportionally greater at the greatest harvest
intensity. Stream Ca2+ concentrations may have shown a similar
response to those of Alim because exchange of Al for Ca2+ in soils
tends to become dominant as soil base saturation declines in acidic
soils, reflected by increased Alim concentrations in soil solution and
nearby streams (McHale et al., 2007).
Studies have shown that brook trout experience high mortality rates when exposed to stream water Alim concentrations in
the 3.7–7.4 ␮mol L−1 range (Baldigo et al., 2005). Alim concentra-

tions in the 68% harvest block reached or exceeded this range on
multiple occasions in the year following completion of the timber
harvest. Wang et al. (2006) reported that total dissolved Al concentrations in stream water in a 40% timber harvest exceeded a
suggested mortality threshold for brook trout (Gagen and Sharpe,
1987).
The USEPA 710 ␮mol L−1 maximum allowable concentration
for drinking water for NO3 − -N (10 mg L−1 , USEPA, 2010) was
approached but not exceeded by the maximum observed concentrations in the 68% harvest (642 ␮mol L−1 ). Total dissolved
Al concentrations exceeded the USEPA secondary drinking water
standards (7.4 ␮mol L−1 ) in post harvest stream water of both the
22% and 68% harvest blocks.
The responses of stream and soil water to the timber harvests
in all three blocks were noted within 5–7 months of completion of
the harvests. This delay in observed chemical response is typically
observed after harvesting in northeastern North America (Burns
and Murdoch, 2005), and likely reflects the winter timing of the
harvests and the time lag necessary for sufficient excess NO3 − -N

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J. Siemion et al. / Forest Ecology and Management 261 (2011) 1510–1519

to build in the soils and to be later flushed into lysimeters and
streams. Also, the mean transit time of baseflow stream water in
this region is about one year (Burns et al., 1998) indicating that
hydrologic transport lags alone may in part be responsible for the
lag observed from the period of harvesting to the first appearance of
changes in soil water and stream water chemistry. The post-harvest
elevated concentrations of Alim , Ca2+ , and NO3 − -N in stream and
soil water of the 22% and 28% harvests returned to pre-harvest
levels approximately 2 years after the harvests were completed.
Post-harvest concentrations of Alim , Ca2+ , and NO3 − -N in stream
and soil water of the 68% harvest remained elevated above preharvest levels 3 years after the harvest was completed, and the
elevated levels of NO3 − -N in stream and soil water of the nearby
97% harvest persisted for 4 years (Burns and Murdoch, 2005). These
results indicate that increasing the basal area removed during timber harvests leads to increasingly prolonged periods of elevated
Alim , Ca2+ , and NO3 − -N in stream and soil water post-harvest as
suggested previously by Wang et al. (2006). We hypothesize that
the faster recovery of stream chemistry in less intensive harvests
may result from the rapid closure of the small canopy gaps (and consequent uptake of nitrogen) that form after these harvests; inverse
exponential closure rates have been measured in northern hardwood forests (Beaudet and Messier, 2002). The larger and expansive
openings created by more intensive harvests and clearcuts likely
require regeneration to fill gaps, a slower process.
KCL-extractable NO3 − -N in soil samples showed a significant
post-harvest increase over levels found in the reference area. The
responses in the 22 and 28% harvest blocks were less than in the
68% harvest block and lasted only 18 months, while the response in
the 68% harvest block was approximately fourfold greater and was
prolonged. The range of NH4 + concentrations in soils of the harvest
blocks were mostly within the range measured in the reference
area; however, greater mean post-harvest NH4 + concentrations
were noted in all of the harvest blocks relative to the reference
area. These results are consistent with harvest-driven increases in
the availability of NO3 − -N that acidifies soils and soil solution and
mobilizes Ca2+ and Alim to local streams.

6. Conclusions
The evidence gathered during this study suggests that timber harvests with a basal area removal of greater than 40–68%
may lead to negative effects on the forest ecosystem. At levels above 40% basal area removal, the mean response of stream
water NO3 − -N concentrations increased substantially. Above 68%
basal area removal NO3 − -N concentrations approached the USEPA
710 ␮mol L−1 standard for drinking water and Alim concentrations
exceeded a known brook trout mortality threshold and reached levels where root uptake of Ca2+ may be impaired. The results of this
study also indicate that greater percentages of basal area removal
lead to longer periods of elevated Alim , Ca2+ , and NO3 − -N concentrations in post-harvest stream water. Soil water showed responses
to the harvests that were similar to those of stream water.
A sound forest management or timber harvest plan needs to
consider the long-term health of the forest ecosystem in order
to assure future productivity. Soil base cation status and species
composition, particularly sugar maple, are major concerns in this
regard (Long et al., 2009). Maintaining soil, soil water, and stream
water chemical concentrations below known ecological thresholds, above which negative consequences exist for the ecosystem,
is also a major concern. These results suggest that limiting timber
harvests in this region to a harvest intensity of less than 40–68%
basal area removal will assist in maintaining the long-term viability of the forest ecosystem, reduce the risk to downstream aquatic
ecosystems, and help ensure future timber productivity. The actual

percent basal area removal identified for this region may not apply
to other regions. Soil type, soil chemistry, forest type, and forest
health all affect the response to forest harvesting. Nonetheless, it is
likely that the general conclusion of this study is transferable—that
above a certain percent basal area removal there will be large
increases in the mean chemical response to harvesting. However,
this result awaits confirmation by other forest harvesting experiments in other regions throughout the globe that receive high levels
of atmospheric N deposition.
Acknowledgments
The authors thank Michael R. McHale of the U.S. Geological Survey, John Campbell of the U.S. Forest Service, and two anonymous
reviewers for their helpful comments on earlier versions of this
manuscript. The authors also thank the field and laboratory staff
at the U.S. Geological Survey’s New York Water Science Center
for field assistance and chemical analyses. Funding for this project
was provided by the New York City Department of Environmental
Protection and the U.S. Geological Survey. The cooperation of the
Frost Valley YMCA, the landowner of the study sites, is also greatly
appreciated.
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