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TECHNICAL REPORTS
Landscape and Watershed Processes

Ion Cycling in Hemlock–Northern Hardwood Forests of the Southern Lake Superior Region

A Preliminary Study

Department of Soil Science, Univ. of Wisconsin, 1525 Observatory Dr., Madison, WI 53706-1299

* Corresponding author (bockheim{at}facstaff.wisc.edu)

Received for publication December 13, 2001.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Upland forests of the southern Lake Superior region are diverse and contain a shifting mosaic of eastern hemlock [Tsuga canadensis (L.) Carr.] and northern hardwood forests dominated by sugar maple (Acer saccharum Marsh.). In this study, we survey the relative effects of management practice (old growth vs. managed), forest cover type (hemlock vs. northern hardwood), and soil great group (Entic Haplorthod vs. Alfic Oxyaquic Fragiorthod) on ion cycling as a precursor to a longer-term, more detailed study. Bulk precipitation, throughfall, and soil leachates at three depths were collected for two growing seasons in eight stands on the Ottawa National Forest in the Upper Peninsula of Michigan. A total of 1210 solutions were analyzed for pH, Na, K, Mg, Ca, Cl, NO₃, and SO₄. Losses of base cations (Ca, Mg, K) and SO₄ from the bottom of the rooting zone generally were greater in old-growth than in managed northern hardwoods on both fragic and nonfragic soils. Leaching losses of base cations and NO₃ usually were greater beneath old-growth northern hardwoods than beneath old-growth hemlock on both soil types and for both forest cover types and management practices on fragic than nonfragic soils. Management practice, forest cover type, and soil type all appear to affect ion cycling within these forests. All of the stands featured striking losses of base cations that probably are influenced strongly by NO₃ and SO₄ in atmospheric deposition.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
NUTRIENT ACCUMULATION IN biomass, nutrient input from atmospheric sources, nutrients cycled in throughfall and stemflow, nutrient retranslocation within trees, and nutrient transfer by litterfall and leaching from the soil all affect forest productivity (Mahendrappa et al., 1986).

Ion cycling has been examined in second-growth northern hardwood ecosystems of the upper Great Lakes region, including the Turkey Lakes watershed in central Ontario (Foster et al., 1989; Morrison et al., 1992), Plastic and Harp Lakes in south-central Ontario (Neary and Gizyn, 1994), and along an acid deposition gradient extending from northern Minnesota through Michigan to northern Ohio (MacDonald et al., 1992; Liechty et al., 1993). According to these studies, net losses of base cations from northern hardwood ecosystems are exacerbated by high levels of NO₃ and SO₄ from atmospheric deposition.

For the past 3200 yr, the Southern Lake Superior Uplands physiographic province of the upper Great Lakes region has featured a shifting mosaic of small patches (1 to 20 ha) of hemlock, northern hardwood, and hardwood–hemlock cover types (Frelich et al., 1993; Davis et al., 1998). The complexity of ecosystems in the Southern Lake Superior Uplands makes it difficult to study biogeochemical processes as they relate to forest productivity and human disturbance effects.

This study examines the influence of (i) forest cover type (hemlock vs. northern hardwood), (ii) soil great group (Entic Haplorthod vs. Alfic Oxyaquic Fragiorthod), and (iii) management practice (old-growth vs. managed) on ion cycling in hemlock–northern hardwood ecosystems in western Upper Peninsula of Michigan. The study provides background information for developing a more detailed sampling strategy for future studies.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Experimental Sites
The study was conducted in southwestern portion of the Upper Peninsula of Michigan (Fig. 1) . The study sites are all in the Winegar Moraine Subsection of the Southern Superior Uplands Section (Keys et al., 1995). The old-growth northern hardwood and hemlock sites are in the Sylvania Wilderness, an unlogged area containing trees with a maximum age of 240 yr (Frelich et al., 1993). The managed stands are in the Ottawa National Forest and include uneven-aged (selection) stands and even-aged stands. The uneven-aged stands were previously managed by a selection system on a cutting cycle of 8 to 15 yr, a minimum residual basal area of 16 m² ha^-1, and a maximum residual tree diameter >45 cm at breast height (Goodburn and Lorimer, 1998). Even-aged, second-growth northern hardwoods have a predominant age of 56 to 75 yr. They have not been thinned and are essentially unmanaged since stand initiation. They contain only scattered trees from the former stand.

View larger version (26K): [in this window] [in a new window]   Fig. 1. Location of the study area.

Sugar maple comprised about 60% of the basal area of the old-growth northern hardwood stands, with basswood (Tilia americana L.) accounting for an additional 20 to 25% (Table 1). In the managed northern hardwoods, sugar maple comprised 65 to 96% of the basal area and basswood 2% or less. Hemlock accounted for 40% of the basal area in hemlock–hardwood stands with either yellow birch (Betula alleghaniensis Britton) or sugar maple making up most of the remainder. Aboveground biomass at these sites is approximately 190 Mg ha^-1 in old-growth hemlock (Campbell, 1998), 330 in old-growth northern hardwoods (Gries, 1995), and 118 Mg ha^-1 (Crow, 1978) in managed northern hardwoods. Aboveground net primary production is 4.8 Mg ha^-1 yr^-1 in old-growth hemlock (Campbell, 1998), 8.7 in old-growth northern hardwoods (Gries, 1995; Campbell, 1998), and 7.6 Mg ha^-1 yr^-1 in managed northern hardwoods (Crow, 1978). Leaf area index is approximately 10 m² m^-2 under old-growth hemlock, 5.0 m² m^-2 under old-growth northern hardwoods, and 5.0 to 5.7 m² m^-2 (Gries, 1995) under managed northern hardwoods (Crow, 1978). All of the sites have a Acer–Tsuga–Dryopteris (maple–hemlock–fern) habitat type (Natzke and Hvizdak, 1988).

The dominant feature of the region, the Winegar Moraine, was deposited by the south-flowing Ontonagan Lobe during the Late Wisconsinan approximately 10 000 yr ago (Peterson, 1982). The moraine is hummocky and contains till and debris flow sediments. Elevations range from 500 to 545 m.

Two soils were selected for the analysis: a sandy, mixed, frigid Entic Haplorthod and a coarse-loamy, mixed, frigid, superactive Alfic Oxyaquic Fragiorthod. Alfic Oxyaquic Fragiorthods generally have textures of fine sandy loam or medium sandy loam in the upper 130 cm (Table 2). In contrast, Entic Haplorthods have an upper sequum of fine or medium sandy loam from 0 to 52 cm thick over a sandy or coarse sandy lower sequum. The fragipan in Alfic Oxyaquic Fragiorthods begins at a depth of 34 to 61 cm and ranges between 36 and 91 cm in thickness. The argillic horizon in Alfic Oxyaquic Fragiorthods was obvious but weakly developed. Both soil great groups have maximum clay concentrations less than 10%, pH <5.6, organic C <52 g kg^-1, high exchangeable acidity and Al saturation, and low base saturation in the upper 100 cm. Despite the coarse textures, the soils contain a high percentage of weatherable minerals in the subsoil, particularly orthoclase and plagioclase feldspars (Whittig and Jackson, 1956).

The center 10- by 100-m section of each plot was divided further into three 10- by 33-m subplots. A random point within each subplot was selected for installation of a throughfall collector consisting of a 20-cm-diameter polyethylene funnel mounted on a stake 1.4 m above the ground surface. Along a 2- to 3-m radius from the throughfall collector, a porous-cup soil-water sampler (Soilmoisture Equipment Corp. [Santa Barbara, CA] Model 1900)¹ was installed at each of three depths, including the bottom of the E horizon at a depth of 5 to 18 cm (referred to as "shallow"), within the Bs horizon at 48 cm (referred to as "medium"), and either within the fragipan (70 cm) for Alfic Oxyaquic Fragiorthods or within the BC or C horizon (70 to 120 cm) for Entic Haplorthods (referred to as "deep"). Therefore, each stand had three throughfall collectors and nine soil-water samplers.

The E horizon is a zone of eluviation from which dissolved organic C, nutrients, and Fe and Al oxides and hydroxides are leached; the Bs horizon is a zone of illuviation where these constituents accumulate; the fragic horizon limits root penetration; and the BC or C horizon, which is also below the rooting zone, represents the base of the soil profile. For the purpose of this study, the ecosystem boundary extended from the atmosphere above the forest canopy to the bottom of the horizon from which the deep leachate was sampled.

Bulk precipitation collectors, following the design of the throughfall collectors, were installed in open areas. Three bulk precipitation collectors were installed at Sylvania 2A/2B, three at Sylvania 14/15, three at Tamarack Lake 1, two at Taylor Lake 1, and three each at Coral Lake 2 and Sucker Lake 2 (Fig. 1). Bulk precipitation and throughfall collectors were rinsed and scrubbed between collection intervals with deionized water. Soil water samplers were evacuated between collection periods with a hand vacuum pump to a negative pressure of 70 kPa.

Solutions from all collectors were sampled every 1 to 3 wk depending on the amount and intensity of rainfall events. Samples were collected over two growing seasons including 27 June to 12 Oct. 1996 and 16 May to 28 Sept. 1997. A total of 1210 solutions were recovered during 15 intervals. All solutions were kept on ice until they were returned to the laboratory where they were stored at a temperature of 0 to 5°C until analyzed.

Laboratory Procedures
Solutions were passed through a 0.45-µm membrane Millipore (Bedford, MA) filter. The pH of each solution was determined with a Hanna Instruments (Woonsocket, RI) HI 9023C pH meter and HI 1230 electrode. Cations (Ca, Mg, K, and Na) were analyzed by mass spectrophotometry at the University of Wisconsin Soil and Plant Analysis Laboratory. The limit of detection for Ca, Mg, K, and Na was 0.50, 0.04, 0.51, and 0.22 µmol_c L^-1, respectively. Anions were detected in the University of Wisconsin Forest Soils Laboratory on a Dionex (Sunnyvale, CA) 2000i ion chromatograph with an AGA4 cation analytical column, with a limit of detection of 1.6, 2.1, and 2.8 µmol_c L^-1 for NO₃, SO₄, and Cl, respectively. Hydrogen ion (H) and bicarbonate (HCO₃) concentrations were estimated from pH values.

Soil samples were returned to the laboratory, air-dried at 22°C, and passed through a 2-mm screen. The samples were sent to the University of Missouri Soil Characterization Laboratory, where all analyses were performed on the <2-mm fraction with methods established by the Soil Survey Staff (1996), including particle-size distribution (Method 3A), pH in distilled water (8C1a), organic C (6A1c), NH₄OAc-extractable bases (5B1), BaCl₂–triethanolamine–extractable acidity (6H1), base saturation by summation (5C3), and KCl-extractable Al (5B3).

For each solution, cation to anion ratios were used to check for potential contamination of the samples (Liechty et al., 1993). If a solution sample had a cation to anion ratio greater than 1.75 or less than 0.25, the sample was considered contaminated and removed from the database. This eliminated 6.6% of the bulk precipitation samples, comparable with the 8.4% recorded by Liechty et al. (1993). Concentrations were averaged for a given collector and then for replicate collectors of a given type over the 15 sampling intervals.

Although the volumes of bulk precipitation and throughfall samples were determined, we chose to report ion concentrations (µmol_c L^-1) rather than fluxes because (i) solutions were only sampled during the growing season and (ii) we were unable to determine the volume of water moving through the soil.

Data Interpretation
The lack of replication of treatments and an insufficient number of collectors precluded statistical comparisons among treatments.

	RESULTS

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Bulk Precipitation and Throughfall
The amount of precipitation collected during the first growing season (mid-June to mid-October 1996) and averaged among the sites in the Ottawa National Forest (including the Sylvania Wilderness) was 345 mm, compared with 359 mm collected at the National Atmospheric Deposition Program site at Trout Lake, which is 15 km to the southwest of the Sylvania Wilderness. We collected 377 mm of precipitation on the Ottawa National Forest during the second growing season (May through September 1997), compared with the 477 mm at Trout Lake. Over the two growing seasons, an average of 84% of the bulk precipitation at the eight sites passed through the canopy as throughfall. The old-growth hemlock canopy intercepted about 5% more precipitation than the old-growth northern hardwood canopy. There were no obvious differences in throughfall volume between the old growth and managed northern hardwood canopies.

The ranking of ions in bulk precipitation over all of the sites and collection periods was Ca > H > K > Mg > Na for cations and SO₄ > NO₃, Cl > HCO₃ for anions (Table 3). The mean ion concentrations are comparable with those from other studies in the upper Great Lakes region (Foster et al., 1989; Liechty et al., 1993; Neary and Gizyn, 1994; National Atmospheric Deposition Program, 2002). We did not measure NH₄; based on the cation to anion ratios from central Ontario (Foster et al., 1989; Neary and Gizyn, 1994), NH₄ may account for 20% of the cations.

Throughfall concentrations of all ions except HCO₃ were about twofold greater beneath old-growth hemlock than beneath the northern hardwood canopies on both soil great groups (Table 3). Throughfall concentrations generally were greater beneath old-growth northern hardwoods than beneath managed hardwoods, especially on the nonfragic soils. Soil type had no apparent effect on throughfall chemistry (Table 3), despite reports that differences in soil fertility may affect throughfall quality (Parker, 1983).

Soil Solution Chemistry
The ranking of cations in soil solutions was Ca > Mg > Na > K > H except in the shallow soil leachate where Na was usually higher than Mg; the ranking of anions in soil leachates was NO₃ > SO₄ > Cl > HCO₃ except in the deep soil leachate where SO₄ usually was greater than NO₃ (Table 3). Ion concentrations in soil leachates were comparable with values reported by Foster et al. (1989). The mean concentrations of all ions except HCO₃ decreased with depth.

The concentrations of base cations (Ca, Mg, and K) and NO₃ generally were greater in deep soil leachates beneath old-growth northern hardwoods than beneath old-growth hemlock on both fragic and nonfragic soils (Table 3). The concentrations of base cations (Ca, Mg, and K) and SO₄ usually were greater in deep soil leachates beneath old-growth northern hardwoods than under managed northern hardwoods on both fragic and nonfragic soils. The concentrations of base cations and NO₃ in deep soil leachates generally were greater in fragic than nonfragic soils (Table 3). Concentrations of SO₄ and NO₃ were up to fourfold greater in the deep soil leachate than in bulk precipitation, and concentrations of Ca, Mg, and Na were sixfold greater.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
The greater amount of K in throughfall than in bulk precipitation most probably was due to canopy leaching (Parker, 1983; Morrison et al., 1992); Ca and Mg probably are derived from canopy leaching but also from washoff of dry deposition (Lovett et al., 1996); and Na and Cl are derived largely from dry deposition. The concentrations of NO₃ and SO₄ were considerably higher for throughfall than for bulk precipitation, especially for hemlock, suggesting that dry deposition rates are in excess of any assimilation of these anions from precipitation (Liechty et al., 1993; Neary and Gizyn, 1994). The lower concentration of H in throughfall than in bulk precipitation implies buffering by the canopy; northern hardwood species were more effective in buffering than hemlock (Table 3). Parker (1983) and Neary and Gizyn (1994) reported similar findings.

The greater concentrations of all ions except HCO₃ in throughfall beneath old-growth hemlock than beneath the northern hardwood canopies reflect the greater leaf area indices and leaf-on period for hemlock than northern hardwood species. The greater concentrations of ions in throughfall of old-growth stands than in managed stands suggests that old-growth stands may be more susceptible to foliar leaching; younger, vigorously growing trees retain foliar nutrients more effectively than older trees (Tukey, 1970; Parker, 1983). Greater canopy leaching especially of K from the old-growth stands may also be related to greater amounts of dead branches than in the managed stands. Dying and dead tissues release ions more readily than younger, more vigorous plant parts (Tukey, 1970).

The decrease in mean concentrations of all ions except HCO₃ in the soil solutions may be due to lower uptake of nutrients and reduced weathering and mineralization with depth. The greater concentrations of base cations and NO₃ in deep soil leachates beneath old-growth northern hardwoods than beneath old-growth hemlock are noteworthy in that throughfall contributions of these ions were greater beneath hemlock, and uptake rates of base cations probably are greater by northern hardwoods (Bockheim, 1997). In northern hardwood ecosystems, litter decomposition (McClaugherty, 1983), mineralization of soil organic matter (Mladenoff, 1987), and fine-root turnover (Hendrick and Pregitzer, 1993) typically contribute larger amounts of nutrients to the soil than throughfall.

The greater concentrations of base cations and SO₄ in deep soil leachates beneath old-growth northern hardwoods than under managed northern hardwoods may reflect lower leaching losses under old growth than aggrading stands because of lower net primary production and lower nutrient uptake (Vitousek and Reiners, 1975). The greater concentration of base cations and NO₃ in deep soil leachates of fragic soils than nonfragic soils may imply that the fragipan concentrates water and nutrients within the rooting zone (Bockheim, 1997).

The greater concentration of base cations (SO₄, and NO₃) in the deep leachate than in bulk precipitation suggests that all of the ecosystems are susceptible to cation leaching by the mobile anions (SO₄ and NO₃) that arrive as atmospheric inputs. Stottlemyer and Hanson (1989) and MacDonald et al. (1992) reached similar conclusions in northern Michigan.

	SUMMARY AND CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
There was a net loss of most ions in most stands from deep leaching, particularly in Ca, Mg, Na, NO₃, and SO₄. Soil acidification appears to be due partly to internal sources such as sequestering of base cations by the vegetation and partly to external sources (i.e., acidic deposition).

Leaching losses of most ions were greater in old-growth stands than in aggrading, managed northern hardwood stands. We anticipated greater leaching losses in old-growth hemlock stands than in old-growth northern hardwood stands because of differences in nutrient uptake and retention. However, losses were greater in northern hardwoods possibly because of more rapid turnover due to litter decomposition, mineralization of soil organic matter, and fine-root turnover than in hemlock. Nutrient losses generally were greater in fragic soils than in nonfragic soils, possibly because the fragipan restricts rooting and allows for subsurface flow of water and nutrients. Therefore, management practice, forest cover type, and soil great group all influence ion cycling in hemlock–hardwood ecosystems of the upper Great Lakes region and should be considered in future studies.

	ACKNOWLEDGMENTS

 
The authors gratefully acknowledge financial support from the Wisconsin Dep. of Natural Resources and the USDA Cooperative State Research and Extension Service. Permission to work in the Ottawa National Forest and the Sylvania Wilderness Area was granted by Jeff Larson and Bob Evans of the U.S. Forest Service.

	NOTES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
¹ Mention of company and/or product does not constitute endorsement by the University of Wisconsin.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Bockheim, J. G. Articles by Crowley, S. E. Search for Related Content PubMed PubMed Citation Articles by Bockheim, J. G. Articles by Crowley, S. E. Agricola Articles by Bockheim, J. G. Articles by Crowley, S. E. Related Collections Watershed and Landscape Processes Ecosystem Management Other Environmental Contamination Nutrient Cycling Forest Soils