Long-term effects of forest management on nutrient cycling in spruce-fir forests

Forest Ecology and Management 138 (2000) 285±299

Long-term effects of forest management on nutrient cycling in spruce-®r forests$ R.D. Briggsa,*, J.W. Hornbeckb, C.T. Smithc, R.C. Lemin Jr.d, M.L. McCormack Jr.e a

SUNY College of Environmental Science and Forestry, 350 IIlick Hall, One Forestry Drive, Syracuse, NY 13210, USA b USDA Forest Service, Northeastern Research Station, P.O. Box 640, Durham, NH 03824, USA c Department of Forest Science, Texas A&M University, College Station, TX 77843-2135, USA d Timberland Enterprises Inc., 10 Commercial Parkway, Old Town, ME 04468, USA e P.O. Box 295, Deer Isle, ME 0462, USA

Abstract Nutrient dynamics and soil disturbance have been monitored since 1979 on paired control and intensively managed watersheds in central Maine, USA. The mature spruce-®r stand was harvested by whole-tree clearcutting in 1981. Triclopyr was aerially applied to most of the same watershed 4 years after harvest to control hardwoods competing with conifer regeneration. In 1991, a series of plots on the treated watershed were precommercially thinned to stimulate growth of selected crop trees. Then in 1993, nitrogen fertilizer was applied to a subset of thinned plots to further stimulate crop tree growth. Disturbance induced changes in soil solution chemistry differed by soil drainage class. Soil solution NO3-N concentrations increased from near zero before harvest to 20 mg/l the second growing season following harvest on moderately well drained soils, more than two times corresponding values observed on somewhat poorly drained soils. Net nutrient losses resulting from harvest were <5% of total capital for the nutrients studied. Nitrate-N concentrations on poorly drained soils did not differ from those on the uncut watershed. This same temporal pattern was repeated following application of triclopyr in 1985, although peak concentrations were not as high as those following harvest. Elevated concentrations of nutrients in soil solution following both harvest and herbicide application disappeared within 3 years, concurrent with regeneration. Precommercial thinning (PCT) reduced stem density approximately 12-fold, increasing crop tree DBH for both balsam ®r (4 cm on control plots versus 6 cm on PCT plots) and red spruce (4 cm on control plots versus 5.5 cm on PCT plots). Although 34 Mg/ha of thinning slash remained after PCT (pre-harvest forest ¯oor dry weight averaged 64 Mg/ha), soil solution chemistry was not affected and nutrients were apparently conserved following treatment. Soil solution nitrate and cation concentrations increased following N fertilization. The fertilizer treatment further increased balsam ®r DBH (8 cm on fertilized plots) but not red spruce. Soil disturbances associated with harvesting may be problematic. Compaction and rutting from the road system and repeated trips of the feller-forwarder were still highly evident. Much of this area remains out of production and likely will be characterized by poor tree establishment and reduced growth through the current rotation. # 2000 Elsevier Science B.V. All rights reserved. Keywords: Whole-tree harvest; Soil solution chemistry; Precommercial thinning

$

Paper presented at the ninth North American Forest Soils Conference, Lake Tahoe, 9±14 August 1998. Corresponding author. Tel.: ‡1-315-470-6989; fax: ‡1-315-470-6954 E-mail address: [email protected] (R.D. Briggs). *

0378-1127/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 0 0 ) 0 0 4 2 0 - 5

286

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

1. Introduction Almost two decades have passed since the Symposium on the Impact of Intensive Harvesting on Forest Nutrient Cycling (Leaf, 1979). There is still a great deal of professional concern about potential for reduced productivity resulting from intensive harvesting practices (Kershaw et al., 1996). We cannot yet answer with certainty the questions posed by Stone (1979) regarding levels of nutrient removal that our systems can sustain with no impact on long-term productivity. Although our understanding of forest management impacts on site productivity is still incomplete, there has been signi®cant progress. Several large-scale watershed studies initiated in the late 1970s continue to advance our knowledge of ecosystem response to forest management (Mann et al., 1988; Pierce et al., 1993; Johnson and Todd, 1998). This paper focuses on a paired watershed study in Maine, a state where industry and large private land management companies manage 3.2106 ha of forest. Forestry is a signi®cant component of the economy. Analysis of economic data reported for Maine's forestry sector indicated that the total value of products generated was US $5.076 billion in 1990.1 Red spruce (Picea rubens Sarg.), black spruce (P. mariana (Mill.)B.S.P.), balsam ®r (Abies balsamea (L.)Mill.) and white spruce (P. glauca (Moench)Voss) are the primary species utilized by Maine's pulp and paper industry. The 1970s spruce budworm (Choristoneura fumiferana) epidemic was a major factor contributing to intensi®cation of forest management. Accelerated harvesting of damaged stands led to projected shortfalls in the spruce-®r wood supply, anticipated sometime between 2010 and 2050 (Seymour and Lemin, 1989). In order to alleviate projected shortfalls, management intensity has increased during the past 15 years. Until recently, a `typical' sequence of management activities in spruce-®r forests was initiated with whole-tree clearcutting. Following harvest, aerial application of herbicide is used to control hardwood

Fig. 1. Area in Maine treated with aerial application of herbicides from 1980 to 1996. Data compiled by M.L. McCormack, Jr.

and shrub vegetation competing with conifers. Stem density is often excessive, slowing development of individual stems and lengthening the time required for a stand to reach merchantable limits. Precommercial thinning (PCT) may be used to concentrate site resources on select crop trees, accelerating stand development. Approximately 200,000 ha of Maine forest land have been aerially treated with herbicide since initiation of the competition control program (Fig. 1). Precommercial thinning has also increased, with 30,000 ha treated during the period 1980±1992 (Seymour, 1993). Although fertilization of mature spruce-®r stands has not produced dramatic increases in growth,2 fertilization of thinned stands (currently not an operational practice) has the potential to further boost productivity. There is ample evidence that intensive management on moderate and high quality sites substantially increases yields and reduces rotation age (Seymour and McCormack, 1989). Harvesting, a form of vegetation management, alters nutrient cycling in forested ecosystems, potentially affecting site productivity as well as water quality. In addition to removal of nutrients and organic matter in biomass, organic matter decomposition rates may increase while stand capacity for water and nutrient uptake is temporarily reduced as a result of harvesting. One consequence is increased nutrient leaching to streams and groundwater. Effects of harvesting on nutrient cycling in forested ecosystems have been quanti®ed for a number of sites, including

1

Unpublished report based on Micro-IMPLAN analysis of 1990 data by Dr. David B. Field, Dept. of Forest Management, Univ. of Maine, 10 February 1995.

2 Unpublished data of Dr. Robert Shepard, Dept. of Forest Management, University of Maine, January 1999.

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

Weymouth Point in central Maine (Mann et al., 1988; Pierce et al., 1993). However, with the exception of Smith et al. (1988), impacts of subsequent operations (i.e., controlling competition, thinning, fertilization) on nutrient dynamics have not yet been widely reported. Continued monitoring of these long-term study sites is critical as the issue of sustainable forestry is debated. Paired watersheds that have been monitored over decades provide an excellent opportunity to unravel the temporal and spatial impacts of vegetation disturbance on nutrient cycling (Sidle and Hornbeck, 1991; Sidle and Sharpley, 1991). Our paper addresses effects of management practices on nutrient cycling at a spruce-®r forest in Maine over a 15-year period following harvest. Practices include whole-tree harvest, control of competing vegetation, precommercial thinning, and fertilization. 2. Methods and materials The study area consists of a pair of adjacent watersheds at Weymouth Point in Piscataquis County, north central Maine (458570 N, 698190 W), ranging in elevation from 287 to 315 m. The soils are coarse, loamy, mixed frigid Typic and Aquic Haplorthods that formed in basal till. Somewhat poorly drained (SPD) soils, located on gentle slopes and characterized by redoxymorphic features within the B horizon, dominate the treated watershed (41% of the area). Poorly drained (PD) soils, which occupy the extensive ¯ats and are characterized by the presence of redoxymorphic features in the upper 20 cm of mineral soil, occupy 34% of the watershed area. Moderately well drained (MWD) soils occupy the remaining 25% of watershed area, and occur on convex knolls and shoulders. These three drainage classes are interspersed across the gently rolling topography of the watersheds. The sequence of treatments evaluated begins in 1979 with collection of stream water samples from a 73 ha control (uncut) watershed and the adjacent 48 ha treatment watershed. The spruce-®r stand on the treatment watershed (3079 stems/ha, basal area 48 m2/ ha) was whole-tree harvested in June and July, 1981 by either large, rubber-tired feller-forwarders, or track mounted feller-bunchers working with rubber-tired grapple skidders. All merchantable stems (>14 cm DBH) were cut, transported to landings, mechanically

287

delimbed and topped to a 10 cm diameter. A buffer strip was left along the lower 450 m of a stream draining the treated watershed. Biomass and nutrient removals were estimated with biomass equations and nutrient concentration data (Smith et al., 1986). Post-harvest site disturbance on the treated watershed was measured using line transects (Martin, 1988). In addition, post-harvest disturbance on an adjacent 97 ha watershed that had been whole-tree harvested in April and May 1984 was reported by Turcotte et al. (1991). Stand/site conditions, as well as harvest equipment used on the latter site, were similar to those at Weymouth Point. A conifer release operation was conducted with herbicides on the treated watershed in August 1985, the fourth year following harvest. Hardwood competition interfering with conifer development on the harvest watershed was controlled by aerial application of triclopyr (butoxyethyl ester formation, 2 kg ae/ha) (Smith et al., 1988). Effects of precommercial thinning (PCT) on soil solution chemistry and crop tree growth were assessed on 27 plots (10 m10 m) located in areas of dense regeneration distributed across drainage classes. Three treatments were evaluated: control, PCT alone at a nominal spacing of 1.8 m1.8 m in October 1991 (10 years after harvest), and in combination with nitrogen fertilization (200 kg N/ha as ammonium nitrate in split applications, May and June, 1993). These three treatments were replicated 2, 3, and 4 times, respectively, on moderately well (MWD), somewhat poorly (SPD), and poorly drained (PD) soils. On each sample plot, 25±30 crop trees with well-developed crowns were identi®ed to result in an approximate residual spacing of 1.81.8 m. Crop tree total height and DBH were measured at the end of each growing season. Soil solution was sampled monthly (June±November) from 1979±1988 on both control and treated watersheds to assess effects of harvesting and herbicide application (period 1). Soil solution was sampled periodically on the treated watershed from 1991±1996 (period 2) to assess effects of PCT and N fertilizer application. Samples were collected monthly from September±October 1991, June±October 1992± 1993, June±August 1994, July 1995, and bimonthly from June±October 1996. Soil solution was extracted with porous, ceramiccup tension lysimeters installed 25 and 50 cm below

288

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

the soil surface. Samples collected during period 1 were drawn from pairs of lysimeters located on 12 plots (20 m20 m) distributed across the treated watershed, and from four plots located on the control watershed (originally installed in 1979). Samples collected during period 2 were drawn from three pairs of lysimeters (newly installed in 1991) 25 and 50 cm below the soil surface, located on each of 27 (10 m10 m) plots distributed across the treated watershed so as to sample across drainage classes, PCT and fertilizer treatments. Streamwater was sampled biweekly from May to November and monthly from December through April during period one and approximately monthly in the growing season during period 2. Streamwater and soil solutions were analyzed for major inorganic ions including NO3-N, NH4-N, SO4, Cl, PO4, K, Ca, Mg, Na, Al, Mn, and pH. Detailed laboratory methodology for samples collected during period 1, performed at the USDA Forest Service Laboratory in Durham, is provided by Hornbeck et al. (1990). Samples collected during period 2 (except for Cl and SO4) were analyzed at the University of Maine Analytical and Technical Laboratory. Concentrations of NO3ÿ and NH4‡were determined colorimetrically using ¯ow injection analysis. Concentrations of K and Na were determined using ¯ame emission spectrophotometry; remaining cations and P were determined by inductively coupled plasma spectrophotometry (ICP). Stream¯ow volume was estimated with the BROOK3 hydrologic model, which was calibrated with measured stream¯ow data from spruce-®r watersheds at the Nashwaak Experimental Forest in New Brunswick, Canada. Precipitation and temperature data for the BROOK model were obtained from a nearby NOAA cooperating weather station at Ripogenus Dam. Streamwater losses of nutrients were estimated from the product of simulated water volume and nutrient concentrations for each watershed, as described by Hornbeck et al. (1990). Likewise, nutrient inputs were estimated from the product of bulk precipitation volume and nutrient concentration (Hornbeck et al., 1990). Bulk precipitation was sampled as described by Likens et al. (1977) in a 3

Federer, 1995.

single collector located at the approximate center of the watershed. 3. Results We present our ®ndings in three components. First, we present management impacts on soil solution chemistry. Increased nutrient mineralization may lead to nutrient leaching and hydrologic loss from the site. Second, we assess the nutrient budget by comparing net gains or losses with total site capitals. Third, we consider impacts of physical site disturbances resulting from harvesting operations. 3.1. Solution chemistry We selected NO3-N (macronutrient anion) and Ca (macronutrient cation) to illustrate impacts of management activities on nutrient cycling. Nitrogen is the element most often limiting to tree growth and NO3-N usually responds to forest harvest. Calcium has been suggested as potentially limiting to growth in the long term due to harvest removals and leaching losses (Federer et al., 1988; Likens et al., 1996). Of the ions measured, these two showed the most dramatic changes in response to treatment. Soil solution concentrations of NO3-N and Ca decreased as sampling depth increased from 25 to 50 cm (Figs. 2 and 3), consistent with decreasing levels of biological activity with depth. Both nutrients increased immediately following whole-tree harvest in 1981 and returned to preharvest levels 3 years later. The pattern was the same for both soil depths but increases at 50 cm were only one-half that at 25 cm. The magnitude of the response varied by soil drainage class. The increases in NO3-N and Ca concentrations became less as soil drainage class became progressively wetter. A similar response was observed following triclopyr application in 1985. However, increases in NO3-N and Ca concentrations were 12% lower than post-harvest increases. Species composition also played a role in the effects of the conifer release treatment. Lower NO3-N and Ca concentrations were observed from lysimeters located in dense patches of conifer regeneration, whereas higher concentrations were observed in areas dominated by herbaceous

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

289

Fig. 2. Soil solution NO3-N concentrations from lysimeters located 25 cm (top) and 50 cm (bottom) below soil surface at Weymouth Point. (Uncut refers to control watershed; PD, poorly drained; SPD, somewhat poorly drained; MWD, moderately well drained; CON, unthinned; PCT, precommercial thinning; FRT, fertilized following PCT). Note change in scale from upper to lower graph.

Fig. 3. Soil solution Ca concentrations from lysimeters located 25 cm (top) and 50 cm (bottom) below soil surface at Weymouth Point. (Uncut refers to control watershed; PD, poorly drained; SPD, somewhat poorly drained; MWD, moderately well drained; CON, unthinned; PCT, precommercial thinning; FRT, fertilized following PCT). Note change in scale from upper to lower graph.

and hardwood vegetation, which was killed by the herbicide. The PCT treatment of October 1991 reduced stem density 12-fold, from 38,000 (80% of which were comprised of balsam ®r) to 3000 stems/ha. In contrast to the impacts of the harvest and herbicide treatments, soil solution concentrations of NO3-N and Ca were not affected by PCT (Table 1). In fact, NO3-N was below detection limits (0.05 mg/l). Although there were no treatment effects, soil solution concentrations of several elements (other than NO3-N and Ca) at 25 cm depth did vary signi®cantly by drainage class before and during the ®rst growing season following PCT (Table 1). We focus on the 25 cm lysimeters because decreasing elemental concentrations with depth reduce effects of soil drainage

class. Concentrations of K‡ on MWD soils were generally twice as large as on PD and SPD soils (Table 2). The opposite trend with drainage class occurred with Na and Mn, which had higher concentrations (50% greater) on PD soils compared to SPD and MWD. Magnesium was inconsistent, with higher concentrations on PD soils prior to thinning, reversing after thinning. The application of N fertilizer in 1993 had an immediate effect on soil solution chemistry. Concentrations of NO3-N and Ca (Figs. 2 and 3, respectively) on fertilized plots increased (a<0.05) relative to control and PCT plots for both sampling depths. Concentrations of NO3-N and Ca dropped to low levels 1 month after the ®rst application then increased again following the second application in June 1993.

290

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

Table 1 Summary of significance tests from ANOVA testing the null hypothesis of no effect of drainage class (D), precommercial thinning treatment (T), or the interaction (TD) on soil solution concentrations 25 cm below soil surfacea Nutrientb

NH4-N K Ca Mg Mn Fe Al Na SO4 Cl pH

1991c

1992

9/24

10/15

6/4

D

D

T

*

**

* **

*

**

** * *

6/30 D

TD

T

7/22 D

* **

TD

T

9/4 D

TD

T

10/28 D

**

*

*

**

* *

** *

* * *

** * * *

TD

T

D

TD

** ** *

*

**

a

Single asterisks denotes rejection of null hypothesis at aˆ0.05; double asterisks denotes rejection of null hypothesis at aˆ0.01; blank denotes failure to reject of null hypothesis. b Nitrate and P were below detection limits (0.05 mg/l). c PCT treatments applied after 1991 sample collection.

Elevated NO3-N persisted for 1993 and 1994, while elevated Ca was observed only during 1993. Other elements were affected by the fertilizer treatment (Mg, Mn, and Na). Increased concentrations of cations can be attributed to the combination of increased anion available for leaching, increased H‡ generated from nitri®cation displacing cations on exchange sites, and the priming effect of fertilization accelerating the rate of nutrient cycling. Those differences were more pronounced at 25 cm depth than at 50 cm depth (Figs. 2 and 3). 3.2. Crop tree response Crop trees responded positively to treatment, and the response varied by species (Table 3). DBH and height of these young trees have not yet been affected by soil drainage class. Although the treatmentdrainage class interaction was statistically signi®cant for balsam ®r height, there was no consistent pattern among the means. The main effects of treatment (PCT alone and in combination with fertilization) were striking. Average DBH at the end of the 1996 growing season for balsam ®r crop trees on PCT and PCT‡N plots was 6.0 and 8.0 cm, respectively, compared to 4.0 cm DBH in control plots. Red spruce

crop tree DBH on control plots averaged 4.1 cm, compared to 5.5 cm for trees on PCT and PCT‡N plots. Analysis of data collected the ®rst three growing seasons after fertilization showed that DBH increment had responded to the PCT treatment but not to fertilization (Briggs et al., 1999). Four growing seasons after fertilization, DBH of fertilized trees exceeded DBH of PCT only trees. 3.3. Nutrient budgets and streamwater chemistry Based on a summary of nutrient pools, removals of N, P, K, Ca, and Mg in trees harvested from the treatment watershed were 5% or less of total site capitals (Table 4). The proportion of nutrient removals attributed to increased leaching was small (Table 5) and resulted from a combination of increased stream¯ow and elevated concentrations for some nutrients. Stream¯ow was estimated to have increased 63% above that on the control watershed the ®rst year following harvest (Table 5). Increased stream¯ow gradually declines with regrowth, completely disappearing 10±12 years following clearcutting. Streamwater NO3-N concentrations for the control watershed were always low (Fig. 4) and mirrored soil solution patterns. Streamwater NO3-N concentrations

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

291

Table 2 Effects of soil drainage class on mean soil solution concentrations (mg/1) and pH at 25 cm prior to N fertilizer applicationa Nutrient

Drainb

1991c

1992

9/24

10/15

6/4

6/30

7/22

9/4

10/28

K

PD SPD MWD

0.59 0.53 1.26**

0.40 0.46 1.27**

2.02 2.24 2.70*

1.71

0.34 0.42 0.89

0.61 0.70 1.38*

0.38 0.40 l.16**

Mg

PD SPD MWD

1.07* 0.77 0.92

1.10 0.77 0.95

0.70

0.75

0.76

0.86 0.66 1.00*

0.90

Na

PD SPD MWD

1.24* 0.92 0.86

1.16** 0.86 0.93

0.79

1.05** 0.82 0.77

1.22 0.88 0.82

1.95** 1.42 1.16

1.24* 0.97 0.81

Mn

PD SPD MWD

0.57** 0.26 0.20

0.47

0.42** 0.15 0.16

0.41** 0.14 0.12

0.42** 0.14 0.11

0.37 0.13 0.10*

0.38* 0.07 0.10

SO4

PD SPD MWD

5.87

1.73

5.33

6.28* 4.83 7.28*

5.99 4.46 7.18*

5.80 4.47 8.14*

6.31

Cl

PD SPD MWD

2.33

6.99** 4.81 6.11

0.94

1.01

1.02

1.13 0.94 1.68*

1.40

pH

PD SPD MWD

5.26

5.26.** 5.85 5.51

5.06

5.43

5.22* 5.63 5.05*

479* 5.24 4.88

5.23

a

Single mean is presented for all three drainage classes when ANOVA failed to reject hypothesis of equality among soil drainage classes. PD, poorly drained; SPD, somewhat poorly drained, and MWD, moderately well drained. c Single and double asterisks for MWD indicate statistically significant difference from SPD by linear contrast at aˆ0.05 and 0.01, respectively; Single and double asterisks for PD indicate statistically significant difference from SPD by linear contrast at aˆ0.05 and 0.01, respectively. Single mean reported when drainage class was statistically non-significant. b

were elevated relative to the control watershed for three growing seasons following harvest and for two growing seasons following herbicide application (Fig. 4). This resulted in small increases in annual outputs of NO3-N (Table 5). Treated watershed stream concentrations dropped below those on the control watershed from 1991 to 1994, consistent with rapid N uptake by the vigorously developing young conifer stand. The fertilizer treatment of 1993 was not re¯ected in streamwater concentrations, due to the small size of the plots. In contrast to NO3-N, there were no apparent patterns in streamwater Ca relative to management treatments (Fig. 5). Calcium concentrations were consistently higher on the treated watershed even before harvest. Likely this re¯ects variation in the local geology rather than any treatment effect. The

unweathered basal till in the treated watershed is high in Ca. Mean Ca concentrations in groundwater obtained from seven wells drilled into the basal till (depths from 2 to 7 m) ranged from 13 to 28 mg/l during the period 1991±1994. Thus, basal till appears to provide a source of Ca for groundwater and streams for the watershed. 3.4. Physical site disturbance Soil disturbance at the Weymouth Point treatment watershed was evaluated by Martin (1988). He classi®ed disturbance into 10 categories along 100 randomly located transects 2.5 m in length. Approximately 92% of the treated watershed was physically disturbed following whole-tree clearcutting (Table 6). Relatively light disturbance (organic horizon scari®-

292

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

Table 3 Summary of analysis of variance results testing null hypotheses that the effects of treatment and drainage class on crop trees differ from zero at the end of the 1996 growing season Source

df

Treatment (T) Drainage Class (D) TD Contrasts PCT vs. CON FRT vs. PCT

2 2 4

Treatment (T) Drainage Class (D) TD Contrasts PCT vs. CON FRT vs. PCT

1 1

F-statistic Red spruce

Balsam fir

DBH 6.18* 0.56 0.22

26.22** 0.65 1.09 13.91** 12.33**

2 2 4

9.66** 0.00 Total height 0.69 1.98 0.53

1 1

0.09 1.31

12.40** 3.32

14.75** 1.88 3.80*

cation), associated with shaking of stumps during harvest by the feller-forwarder impacted 23% of the treatment watershed. Mineral ruts, the most severe form of disturbance on these soils, occupied 13% of the treatment watershed. Turcotte et al. (1991) assessed physical disturbance on a nearby site that was whole-tree harvested in the spring of 1984. Soils were members of the same catena as Weymouth Point, and the harvesting was done with same type of large feller-forwarders used at Weymouth Point. Turcotte et al. (1991) classi®ed disturbance into nine categories on ®ve 25 m long transects established in each of ®ve plots distributed across soil drainage classes (PD, SPD, and MWD). There was considerable overlap in the categories with those used by Martin (1988). The fact that the Turcotte et al. (1991) study assessed disturbance by drainage class warrants inclusion in this analysis.

Table 4 Summary of nutrient pools for treatment and control watersheds at Weymouth Point (adapted from Smith et al., 1986) Ca (kg haÿ1) Removal by harvest Increases in stream outputs summed for 11 years Total losses due to harvest Estimated preharvest nutrient pools Above-ground vegetation Roots Soil organic horizonsb Extractablec Totald Soil mineral horizonse Extractablec Totalf Total site capital

Control watershed Dissolved ion input, precipitation Dissolved ion output, streamflow Net a

K (kg haÿ1)

Mg (kg haÿ1)

N (kg haÿ1)

P (kg haÿ1)

494 66 560

224 35 259

52 21 73

376 9 385

54 ±a 54

537 186

245 85

57 20

410 142

59 20

208 384

23 69

66 70

n.a. 919

51 76

184 10,332 11,439

136 10,001 10,400

145 36,450 36,591

n.a. 5833 7304

166 2697 2852

Ca (kg haÿ1 per year)

K (kg haÿ1 per year)

Mg (kg haÿ1 per year)

N (kg haÿ1 per year)

P (kg haÿ1 per year)

1 12 ÿ11

1 2 ÿ1

1 3 ÿ2

4 1 ‡3

±a ±a ±a

Below detection levels (assumed to be <1). Oi, Oe, and Oa horizons. c Ca, K, and Mg extracted with mix of 0.05 N HCl and 0.025 N H2SO4. d Ash from dry ash procedure digested in concentrated HCl. Ca and Mg concentrations determined by inductively coupled plasma spectrophotometry (ICP); K determined by flame emission; N and P determined colorimetrically by block digestion and automated colorimetric analysis. e E and/or A and B horizons. f K, Ca and Mg determined after extraction with nitric-perchloric digest. Ca and Mg concentrations determined by ICP and K by flame emission. N and P determined by block digestion and autoanalyzer. b

Table 5 Impact of harvest and stand improvement on annual nutrient outputs and streamflowa If uncut

Actual

Change

Ca 1 2 3 4 5 6 7 8 11 12 13

20 14 15 8 6 13 17 21 17 23 23 NH4-N

1 2 3 4 5 6 7 8 11 12 13

0 0 0 0 0 0 0 0 0 0 0 a

If uncut

Actual

Change

K 43 27 22 16 14 22 21 20 21 16 21

‡23 ‡13 ‡7 ‡8 ‡8 ‡9 ‡4 ÿ1 ‡4 ÿ7 ÿ2

1 1 0 0 0 0 0 0 0 0 0

‡1 ‡1 0 0 0 0 0 0 0 0 0

1 2 2 1 1 1 1 2 2 3 1 NO3-N 0 0 0 0 0 0 0 0 0 0 0

If uncut

Actual

Change

Mg 18 10 6 2 2 3 2 2 2 2 2

‡17 ‡8 ‡4 ‡1 ‡1 ‡2 ‡1 ‡1 0 ÿ1 ‡1

1 2 1 0 2 1 0 0 0 0 0

‡1 ‡2 ‡1 0 ‡2 ‡1 0 0 0 0 0

If uncut

Actual

Change

Na

If uncut

Actual

Change

11 8 6 3 3 3 2 3 3 2 2

‡4 4 ‡2 ‡1 ‡1 0 0 ÿ2 0 0 ÿ2

Cl

5 4 4 2 2 3 3 6 5 7 7 S04-S

11 8 7 5 4 7 4 6 6 5 6

‡6 ‡4 ‡3 ‡3 ‡2 ‡4 ‡1 0 ‡1 ÿ2 ÿ1

5 10 3 6 4 6 2 4 2 4 4 7 3 4 5 4 5 5 8 5 6 6 Streamflow (mm)

9 6 7 3 3 4 4 6 4 4 7

12 8 9 5 4 6 5 6 6 4 9

‡3 ‡2 ‡2 ‡2 ‡1 ‡2 ‡1 0 ‡2 0 ‡2

490 330 400 200 150 280 180 310 360 300 440

800 620 610 380 300 460 270 350 380 300 440

‡5 ‡3 ‡2 ‡2 ‡2 ‡3 ‡1 ÿ1 0 ÿ3 0

7 4 4 2 2 3 2 5 3 2 4

‡310 ‡290 ‡210 ‡180 ‡150 ‡180 ‡90 ‡40 ‡20 0 0

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

Year after harvest

The nutrient values are kg haÿ1 and stream flow is millimeter depth for the entire watershed. Data were not collected for years 9 and 10 after harvest.

293

294

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

Fig. 4. Streamwater NO3-N concentrations for the control and treatment watersheds at Weymouth Point. (PCT denotes precommercial thinning treatment; PCT‡N denotes nitrogen fertilization to PCT plots).

Fig. 5. Streamwater Ca concentrations for the control and treatment watersheds at Weymouth Point. (PCT denotes precommercial thinning treatment; PCT‡N denotes nitrogen fertilization to PCT plots).

The area of undisturbed land reported by Turcotte et al. (1991) was three to six times greater than that reported by Martin (1988). The higher disturbance reported by Martin (1988) may be partly due to efforts made to minimize physical disturbance within the lysimeter plots. During the harvest at Weymouth Point, the feller-buncher maneuvered around the exterior of the lysimeter plots, reaching inward to harvest the trees. No such effort was made at the site sampled by Turcotte et al. (1991).

In any case, the impact of drainage class on site disturbance documented by Turcotte et al. (1991) is important. As soil drainage class improved from PD to MWD, the proportion of undisturbed area increased from 28 to 45% of the harvested site (Table 6). The incidence of severe rutting generated from the large feller-forwarder increased from 7% on MWD soils to 14% on PD soils. Imperfectly drained soils offer no resistance to large tires when there is a perched water table. These ruts persist today on the treatment

Table 6 Percentage of area in each of several disturbance classes for the Weymouth Point clearcut watershed and for an adjacent whole-tree harvested watershed categorized by soil drainage classa Disturbance Undisturbed Dead wood (slash) Bare rocks Depressed Organic scarification Organic mound Organic rut Mineral scarification Mineral mixed Mineral mound Mineral rut side Mineral rut a b

Weymouth Point (Martin, 1988) 7.7 8.8 0.5 7.6 23.1 6.7 27.7 1.3 ± 3.7 ± 12.9

Adjacent watershed (Turcotte et al., 1991)b PD

SPD

MWD

28.5a 5.0a ± ± ± 20.3 4.3 4.2 6.6 9.1 8.0 14.0b

35.5ab 4.6b ± ± ± 15.3 7.8 3.3 3.4 11.6 5.6 12.9b

45.0b 13.lb ± ± ± 11.1 11.4 0.8 1.2 8.4 2.4 6.6a

Means reported by Turcotte et al. (1991) within a row followed by different letter differ statistically. Drainage classes are PD, poorly drained, SPD, somewhat poorly drained, MWD, moderately well drained.

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

watershed, extending to the compact basal till. Repeated freeze-thaw cycles have not resulted in amelioration of the ruts that criss-cross the treatment watershed. The negative impacts of these ruts extend well beyond the area directly removed from production (Table 6). The ruts often contain standing water and impede lateral water movement, further reducing site aeration. This is particularly problematic on the PD soils, which are already characterized by low productivity (Briggs and Lemin, 1994). Current work underway to assess differences in CO2 ef¯ux between the control and treatment watershed may provide insight into the degree of impact that these ruts continue to exert on site productivity. Measurement of CO2 ef¯ux may indicate if the capacity for gas exchange between the soil and the atmosphere has been reduced by disturbance. 4. Discussion The patterns of elevated nutrient concentrations in soil solution after whole-tree harvest at Weymouth Point are similar to those summarized by Pierce et al. (1993) for whole-tree harvested sites in New Hampshire and in Connecticut. Nitrate-N and Ca concentrations at Weymouth Point increased following whole tree harvest and returned to pre-harvest levels after 3 years. Post-harvest patterns of streamwater NO3-N parallel those observed in soil solution (Fig. 4), returning to pre-harvest levels within 3 years as vegetation reoccupied the site. Streamwater Ca concentrations did not re¯ect the responses observed in soil solution at 25 cm (Fig. 5). The relatively high Ca background concentrations (which on occasion exceeded 12 mg/l) in streamwater may have masked any effects of harvest. Elevated soil solution and stream water nutrient concentrations recurred following herbicide application. However, peak NO3-N and Ca concentrations were 12% lower than those following harvest. Remaining conifers eventually utilized site resources liberated by elimination of competing vegetation. Increased shade and reduced soil moisture associated with the expanding conifer canopy and increased plant uptake substantially reduced nutrient export from the site, re¯ected in lower streamwater NO3-N concentra-

295

tions and decreased outputs in streamwater (Fig. 4, Table 5). As was the case following harvest, streamwater Ca concentrations showed no apparent response to herbicide application. However, Ca losses in streamwater continued to be elevated due to increased volume of stream¯ow (Table 5). The effects of herbicide release on soil solution nutrient concentrations at Weymouth Point are consistent with results reported for the Fallingsnow Ecosystem Project in Ontario, Canada, an operational scale long-term replicated study (Lautenschlager et al., 1998). Simpson et al. (1997), studying nutrient movement response to competition control at the Fallingsnow Project, documented slightly higher (relative to untreated plots) soil NO3-N concentrations 75 cm below the soil surface following herbicide release of planted black spruce and white spruce. Because of the high variance, those differences were not statistically signi®cant. It is interesting to note that their soils were imperfectly drained and that they sampled soil solution at 75 cm, deeper than the 50 cm depth used at Weymouth Point. Organic matter, aeration, and biological activity all decrease with depth below soil surface. Imperfect drainage combined with the 75 cm depth (reducing nutrient concentrations relative to the surface) likely contributed to Simpson et al. (1997) failure to detect statistically signi®cant treatment effects. The pattern of response for solution NO3-N chemistry indicates that the Weymouth Point watershed is a functioning ecosystem; nutrient cycling continues. Organic matter decomposition and nutrient mineralization are aerobic processes, decreasing in rate as progressively wetter soil conditions restrict soil O2 levels. Elevated concentrations of NO3-N and Ca associated with better drained soils are consistent with an intact mineralization system. Although we did not measure denitri®cation, it likely contributes to the lower levels of NO3-N observed in the wetter soils. Based on examination of nutrient budgets alone, whole-tree clearcutting and subsequent herbicide release have not exerted a major impact at Weymouth Point. Net nutrient removals associated with harvest of the 70-year-old spruce-®r stand combined with hydrologic losses represent 5% or less of total site capital. Hydrologic losses are a minor component of total nutrient removals (Table 4). At this site, the loam textured soils hold more nutrients than sandy soils and

296

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

appear capable of supporting the level of biomass and nutrient removals imposed by this study. The basal till, which will weather, albeit slowly into soil, also appears element-rich. Corti et al. (1998) pointed out that the soil skeleton, which consists of rock fragments, may serve as an important source of nutrients for plant growth. Although these large pools of basal till and coarse fragments are not available for immediate plant nutrient uptake, they represent the ultimate capital that can be made available through weathering of primary and secondary minerals. Unfortunately, mineral-rich soil and parent material is not characteristic of all sites. Assessment of potential management impacts on nutrient cycling and long-term productivity must be evaluated on a site-speci®c basis. Management activities have potential to impact water bodies fed by streams that pass through the treated area. Lake productivity is primarily a function of available P (Allan, 1995), which was not affected by the treatments applied at Weymouth Point. The absence of a harvesting effect on streamwater P levels was noted by Yanai (1998) for northern hardwoods at Hubbard Brook. Phosphorus is relatively insoluble and readily ®xed by soil colloids (Brady and Weil, 1999). However, Allan (1995) points out that for N:P ratios between 10:1 and 20:1, which characterize streamwater chemistry at Weymouth Point, algal growth in lakes may be limited jointly by either nutrient. Therefore, increased streamwater nitrate-N concentrations following harvest and herbicide application raise the issue of the potential for eutrophication. The spatial and temporal separation of clearcuts, coupled with the 3-year recovery of stream nitrate to pre-disturbance levels, minimize the potential for signi®cant eutrophication. The peak streamwater nitrate-N concentrations observed after clear cutting (0.9 mg/l) and herbicide (0.7 mg/l) were relatively low, in addition to being short-lived. Biotic effects of clearcutting on stream systems have been measured in the northeast. Noel et al. (1986) found that streams in clearcuts exhibited signi®cantly higher algae and macroinvertebrate populations relative to uncut stands in ME, NH and VT. However, cutting had minimal impact on streamwater chemistry. Consequently, Noel et al. (1986) attributed higher algal populations to increased light and temperature resulting from canopy removal.

The long-term impact of a net Ca loss of 11 kg/ha/ year from the control watershed is uncertain. Considered over a 70-year rotation, there is a potential loss of 770 kg/ha (7% of total site capital above the basal till) in the absence of operations. Given a base rich till and bedrock, it is not clear what proportion of streamwater Ca originates from the stream bed incised into basal till versus that dissolved in water ¯owing above the basal till. The latter would be more cause for concern than the former because our estimate of site nutrient capital in the mineral soil is derived from the solum above the basal till. Both sources likely make a contribution to streamwater Ca concentration. Earlier work suggested that Ca depletion could be a potential long-term problem. Hornbeck et al. (1990) reasoned that although Ca losses were small relative to total site capital, removal from the available pool could result in shortages of plant available Ca in the years immediately following harvest. However, the positive impacts of annual cycling of nutrients through uptake by deep roots, ®ne root turnover, and above-ground litter deposition act to maintain fertility in the solum. Longer rotations may be encouraged to limit interruptions in annual cycling and redistribution of nutrients. Weathering, one of the most poorly quanti®ed components of nutrient budgets, also acts to ameliorate loss of Ca from the system. It is interesting to note that Johnson et al. (1998), contrary to expectations based on earlier results, reported no decline in exchangeable Ca for a whole-tree harvested mixed oak forest in Tennessee. This non-impact was observed in spite of annual leaching losses of 8.6 kg/ ha/year combined with vegetation uptake (225 kg/ha). They cautioned that nutrient budget approaches overestimated the rate of Ca depletion. In light of these observations, the case for Ca as a potentially limiting nutrient at Weymouth Point is not compelling. The lack of any response in soil solution chemistry to the PCT was surprising, given increased inputs of organic matter. We estimated biomass inputs from PCT to be 34 Mg/ha using equations of Briggs (1982). The input is signi®cant in light of forest ¯oor biomass on the control watershed (64 Mg/ha) reported by Smith et al. (1986). We expected increased soil solution nutrient concentrations on PCT plots due to the increased soil temperature, moisture, and organic matter input combined with reduced nutrient uptake. Increased solar radiation on the forest ¯oor was

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

visually apparent. Although we did not measure soil temperature, we found that it was impossible to draw samples from lysimeters in control (unthinned) plots until June because water remained frozen. In contrast, we were able to draw samples from thinned plots in May. Increases in summer soil temperatures been reported in monitored whole-tree harvested sites (Donnelly et al., 1991; Mahendrappa and Kingston, 1994). Our results indicate that the young ®r-spruce system conserves nutrients following PCT. We refer to these ®r dominated stands as ®r-spruce, following the suggestions of Meng and Seymour (1992). Although the PCT treatment produced a signi®cant organic input on thinned plots, much of that material was not in direct contact with the forest ¯oor. The high stem density acted to support cut trees in semi-standing position. Balsam ®r, which retains needles for several years after cutting, dominated the regeneration and effectively limited direct foliar inputs to the forest ¯oor. This combination of factors, at least temporarily, conserves nutrients by limiting decomposition and mineralization rates at or below vegetation uptake capacity. From the perspective of nutrient uptake, the absence of soil solution response to PCT coupled with the positive response of crop tree DBH suggest that 3000 stems/ha of conifer crop trees represents full site occupancy at this stage of stand development. Crop tree utilization of site resources released by removing 90% of the standing trees was expressed through increased DBH. Unlike the harvest and herbicide treatments, which increased soil solution nutrient concentrations for 3 and 2 years, respectively, the PCT treatment did not affect soil solution nutrient concentrations. The application of N fertilizer to PCT plots further increased DBH of balsam ®r but not red spruce. Differential tree growth response by species in young stands was documented by Meng and Seymour (1992). Their work in regenerating ®r-spruce stands treated with herbicide to control hardwood competition showed that balsam ®r height growth was greater on MWD soils compared to PD soils. Height growth of red spruce did not differ between PD and MWD soils. On poorly drained soils, height growth of spruce and balsam ®r was similar. Although we did not observe any effects of drainage class on height or

297

DBH at Weymouth Point, it is possible that the overwhelming effect of the PCT treatment completely overshadowed any potential drainage class effect, which may become pronounced in the future. Physical disturbance associated with harvesting continues to be readily apparent on the PD and SPD soils, where deep ruts penetrate to the depth of compact basal till. Disturbance prevented establishment of regeneration, reducing stocking. From a practical perspective, reduced stocking has an immediate, measurable impact on productivity. Available growing space not occupied by trees represents unallocated site resources. Nutrients in soil solution where vegetation is poorly distributed or lacking may be potentially lost from the site by leaching. 5. Conclusions The impacts on nutrient cycling of intensive management (harvesting, competition control with herbicide, and PCT) have been relatively small and short in duration at Weymouth Point, similar to other sites in the northeast (Pierce et al., 1993; Lautenschlager et al., 1998). Nutrient removals due to harvesting and hydrologic loss did not exceed 5% of total site capital. From the perspective of nutrient capital, sites similar to Weymouth Point should be able to support the degree of intensive management that was used. From the perspective of nutrient cycling, the system continues to function. The largest problem that we observed was associated with physical site disturbance, exacerbated by operating large machines on imperfectly drained soils under wet conditions during harvest. The deep ruts that persist almost 20 years following harvest have likely further reduced the low productivity associated with poorly drained mineral soils (Briggs and Lemin, 1994). Disturbance of the forest ¯oor and removal of organic material negatively impacts tree growth. Turcotte (1988) showed that nitri®cation potential on disturbed, exposed mineral soil was substantially lower than on intact forest ¯oor. Visual evidence of planted spruce in compacted skid trails and disturbed areas compared to undisturbed areas on the harvested watershed points out a noticeable decline in growth and vigor. Management practices in Maine continue to undergo signi®cant change and improvement. The

298

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299

larger feller-forwarders having several cord capacities are no longer widely used (with the exception of one or two private contractors), signi®cantly reducing the possibility of inappropriate use on imperfectly drained soils. There is greater attention to scheduling the harvest of stands located on imperfectly drained soils during the dry season or winter under cover of snow. Several large companies use soil maps to assist in this decision making. Following a recent assessment of forestry best management practices (BMPs) in Maine (Briggs et al., 1998), more effort is being devoted BMP application. Clearcutting has declined substantially in the past 3 years, partly in response to the public debate following a ballot initiative in 1996 to ban clearcutting in Maine. The recently developed cutto-length harvesters working in conjunction with a forwarders, technology introduced from Sweden, have proved to be excellent systems for operating in spruce®r stands on imperfectly drained soils. Individual stems are delimbed at the point where they are felled. The forwarder that collects the cut stems drives over the slash, and has minimal impact on the forest ¯oor. An additional bene®t is that tops remain in the woods. It may be appropriate to ask if the signi®cant investment in time and money for paired watershed studies has been cost effective; we believe the answer to be a quali®ed yes. Although unequivocal assessment of the impacts of intensive harvesting on site productivity cannot be made until a complete rotation has passed, studies such as Weymouth Point have provided the necessary foundation. Certainly, the data collected over the past 15 years provides assurance that intensive management has not seriously degraded the productive potential of this site. During the late 1970s, it was not possible to make that statement. The high costs of study establishment and initial assessment of nutrient pools are behind us. Continued monitoring will require a fraction of the initial cost of establishment. With the passage of time, the scienti®c value of this site continues to increase, providing a contextual data framework to assess potential effects of global climate change. Acknowledgements The Weymouth Point site is owned and maintained by Bowater Great Northern Paper Co. Funding for this

study was provided by the Cooperative Forestry Research Unit at the University of Maine. The precommercial thinning study was supported by a grant from USDA Cooperative States Research Service Water Quality Program. The USDA Forest Service has been an important cooperator. The technical assistance of Rick Dionne, Anthony Guay, Brad Catling, Peter Caron and Jane Hislop is gratefully appreciated. References Allan, J.D., 1995. Stream Ecology: Structure and Function of Running Waters. Chapman & Hall, NY, pp. 91±93. Brady, N.C., Weil, R.W., 1999. The Nature and Properties of Soils, 12th Edition. Prentice Hall. Briggs, R.D., 1982. The Effects of fertilization on the nutrient distribution and biomass of the above-ground components of Abies balsamea (L.) Mill. M.S. thesis, SUNY Coll. Environ. Sci. and Forestry, Syracuse, NY, 160 pp. Briggs, R.D., Cormier, J., Kimball, A., 1998. Compliance with forestry best management practices in Maine. North. J Appl. For. 15, 57±68. Briggs, R.D., Lemin Jr., R.C., 1994. Soil drainage class effects on early response of balsam fir (Abies balsamea (L.)Mill.) to precommercial thinning. Soil Sci. Soc. Am. J. 58, 1231±1239. Briggs, R.D., Lemin, R.C., Jr., Hornbeck, J.W., 1999. Impacts of precommercial thinning and fertilization on water quality. Misc. Report 408, Coll. of Natural Sci., Forestry, and Ag., Maine Ag. and Forest Exp. Stn., Univ. of Maine, 80 pp. Corti, G., Ugolini, F.C., Agnelli, A., 1998. Classing the soil skeleton (greater than two millimeters): proposed approach and procedure. Soil Sci. Soc. Am. J. 62, 1620±1629. Donnelly, J.R., Shane, J.B., Yawney, H.W., 1991. Harvesting causes only minor changes in physical properties of an upland Vermont soil. North. J. Appl. For. 8, 33±36. Federer, C.A., Hornbeck, J.W., Tritton, L.M., Martin, C.W., Pierce, R.S., Smith Jr., C.T., 1988. Long-term depletion of calcium and other nutrients in eastern US forests. Eviron. Manage. 13, 593± 601. Federer, C.A., 1995. BROOK90: a simulation model for evaporation, soil water, and streamflow, Version 3.1. Computer freeware and documentation, USDA Forest Service, PO Box 640, Durham, NH. Hornbeck, J.W., Smith, C.T., Tritton, L.M., Pierce, R.S., 1990. Effects of intensive harvesting on nutrient capitals of three forest types in New England. For. Ecol. Manage. 30, 55±64. Johnson, D.W., Todd Jr., D.E., 1998. Harvesting effects on longterm changes in nutrient pools of mixed oak forest. Soil Sci. Soc. Am. J. 62, 1725±1735. Kershaw, K.M., Jeglum, J.K., Morris, D.M., 1996. Long term productivity of boreal forest ecosystems II. Expert opinion on the impact of forestry practices. NODA/NFP Tech. Rept. TR23. Natural Resources Canada, Great Lakes Forestry Centre, Sault Ste. Marie, Ontario, 21 pp.

R.D. Briggs et al. / Forest Ecology and Management 138 (2000) 285±299 Lautenschlager, R.A., Bell, F.W., Wagner, R.G., Reynolds, P.E., 1998. The Fallingsnow Ecosystem project: documenting the consequences of conifer release action. J. For. 96, 20±27. Leaf, A.L. (program chair), 1979. Proc. Impact of Intensive Harvesting on Forest Nutrient Cycling, SUNY Coll. Environ. Sci. and Forestry, Syracuse, NY, 421 pp. Likens, G.E., Bormann, F.H., Pierce, R.S., Eaton, J.S., Johnson, N.M., 1977. Biogeochemistry of a Forested Ecosystem. Springer, New York, 146 pp. Likens, G.E., Driscoll, C.T., Busco, D.C., 1996. Long-term effects of acid rain: response and recovery of a forest ecosystem. Science 272, 244±245. Mann, L.K., Johnson, D.W., West, D.C., Cole, D.W., Hornbeck, J.W., Martin, C.W., Riekerk, H., Smith, C.T., Swank, W.T., Tritton, L.M., Van Lear, D.H., 1988. Effects of whole tree and stem-only clearcutting on postharvest hydrologic losses, nutrient capital, and regrowth. For. Sci. 34, 412±428. Mahendrappa, M.K., Kingston, D.G.O., 1994. Intensive harvesting impacts on soil temperature and solution chemistry in the Maritimes region of Canada. NZ J. For. Sci. 24, 402±414. Martin, C.W., 1988. Soil disturbance by logging in New England: review and management recommendations. North. J. Appl. For. 5, 30±35. Meng, X., Seymour, R.S., 1992. Influence of soil drainage on early development and biomass production of young, herbicidereleased fir-spruce stands in north central Maine. Can. J. For. Res. 22, 955±967. Noel, D.S., Martin, C.W., Federer, C.A., 1986. Effects of forest clearcutting in New England on stream macroinvertebrates and periphyton. Environ. Manage. 10, 661±670. Pierce, R.S., Hornbeck, J.W., Martin, C.W., Tritton, L.M., Smith, C.T., Federer, C.A., Yawney, H.W., 1993. Whole-tree clearcutting in New England: Manager's guide to impacts on soils, streams, and regeneration. USDA Forest Service, NE For. Exp. Stn., Gen. Tech. Rept. NE-172, Radnor, PA, 23 pp. Seymour, R.S., 1993. Production silviculture in northeastern North America. In: Proc. of the 1992 Society of American Foresters Annual Convention, Richmond, VA, 25±28 October, SAF, Bethesda, MD, pp. 227±232. Seymour, R.S., Lemin, R.C., Jr., 1989. Timber supply projections for Maine, 1980±2080. College of Forest Resources, Maine Ag. Exp. Stn., University of Maine, Orono, Misc. Rept. 337, 39 pp.

299

Seymour, R.S., McCormack Jr., M.L., 1989. Having our forest and managing it too: the role of intensive silviculture in resolving forest land use conflicts. In: Briggs, R.D., Krohn, W.B., Trial, J.G., Ostrofsky, W.D., Field, D.B. (Eds.), Forest and wildlife management in New England Ð what can we afford, Proc. of a Joint Meeting of the Maine Division of NESAF, Maine Chapter of TWS, and the M Chapter of AFS. 15±17 March 1988, Portland, ME, Maine Ag. Exp. Stn. Misc. Rept. 336, Univ. of Maine, Orono, pp. 207±213. Sidle, R.C., Hornbeck, J.W., 1991. Cumulative effects: a broader approach to water quality research. J. Soil Water Conserv. 46, 268±271. Sidle, R.C., Sharpley, A.N., 1991. Cumulative effects of land management on soil and water resources: an overview. J. Environ. Qual. 20, 1±3. Simpson, J.A., Gordon, A.M., Reynolds, P.E., Lautenschlager, R.A., Bell, F.W., Gresch, D., Buckley, D., 1997. Influence of alternative conifer release treatments on soil nutrient movement. For. Chron. 73, 69±73. Smith Jr., C.T., McCormack Jr., M.L., Hornbeck, J.W., Martin, C.W., 1986. Nutrient and biomass removals from a red sprucebalsam fir whole-tree harvest. Can. J. For. Res. 16, 381± 388. Smith Jr., C.T., Hornbeck, J.W., McCormack Jr., M.L., 1988. Changes in nutrient cycling following aerial application of triclopyr to release spruce-fir. Northeastern Weed Sci. Soc. 42, 94±99. Stone, E.L., 1979. Nutrient removals by intensive harvest Ð some research gaps and opportunities. In: Leaf, A.L. (Program Chair), Proc. Impact of Intensive Harvesting on Forest Nutrient Cycling, SUNY Coll. Environ. Sci. and Forestry, Syracuse, NY, pp. 366±386. Turcotte, D.E., 1988. Mechanically disturbed forest soil on three drainage classes: spatial distribution and effects on potential nitrogen availability. M.S. thesis, Dept. of Natural Resources, Univ. New Hampshire, 88 pp. Turcotte, D.E., Smith, C.T., Federer, C.A., 1991. Soil disturbance following whole-tree harvesting in north-central Maine. North. J. Appl. For. 8, 68±72. Yanai, R.D., 1998. The effect of whole-tree harvest on phosphorus cycling in a northern hardwood forest. For. Ecol. Manage. 104, 281±295.