Leaf element concentrations and soil properties

in first- and second-rotation stands of red alder

(Alnus rubra)

Jana E. Compton, Dale W. Cole, and Peter S. Homann

Abstract: Successive rotations of nitrogen-fixing red alder (Alnus rubra Bong.) may alter soil properties, potentially

influencing future tree growth and nutrition. We examined the effects of red alder on soil properties and next-rotation alder

leaf and leaf litter element concentrations. A conversion experiment was initiated in 1984 by clearcutting a 50-year-old red

alder stand and an adjacent 50-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stand. Both areas were replanted

with red alder, yielding first- and second-rotation alder plots. Prior to conversion, the 50-year-old alder plot had higher total

soil C, N, and extractable Ca, Mg, and Al, while pH and available P were lower. The second-rotation plot had lower leaf P,

Ca, and Mg concentrations than the first-rotation plot in 1988 and 1989; it also had lower leaf K, Mn, and Fe concentrations in

1989. The second-rotation plot had lower leaf litter N, P, K, Mg, and Fe concentrations, and litter-fall mass and element

transfer rates were 30–49% those of the first rotation. The findings indicate a potential decrease in availability of most

macronutrients when growing repeated rotations of red alder on glacial till derived soils.

Résumé: Les révolutions successives d’aulne rouge (Alnus rubra Bong.), une espèce fixatrice d’azote, peuvent modifier les

propriétés du sol et influencer la nutrition et la croissance future des arbres. Les auteurs ont examiné les effets de l’aulne rouge

sur les propriétés du sol et la concentration des éléments dans les feuilles et la litière de feuilles des aulnes de la révolution

subséquente. Une expérience de conversion a été initiée en 1984 par la coupe à blanc d’un peuplement d’aulne rouge de

50 ans et d’un peuplement adjacent de Douglas taxifolié (Pseudotsuga menziesii (Mirb.) Franco) de 50 ans. Les deux endroits

furent replantés avec de l’aulne rouge pour constituer des parcelles de première et de seconde révolution. Avant la conversion,

la parcelle qui contenait de l’aulne rouge de 50 ans avait des valeurs de C et N total et de Ca, Mg et Al extractibles plus

élevées tandis que les valeurs du pH et de P disponible étaient plus faibles. Les parcelles de seconde révolution avaient des

concentrations foliaires de P, Ca et Mg plus faibles que les parcelles de première révolution en 1988 et 1989. En 1989, les

concentrations de K, Mn et Fe étaient également plus faibles. Les parcelles de seconde révolution avaient des concentrations

de N, P, K, Mg et Fe dans la litière de feuilles plus faibles ainsi qu’une masse de chute de litière et des taux de transfert des

éléments qui représentaient 30–49% des valeurs observées dans le cas de la première révolution. Ces résultats montrent qu’il

peut y avoir une diminution de la disponibilité de la plupart des macronutriments après plusieurs révolutions d’aulne rouge sur

des sols dérivés d’un till glaciaire.

[Traduit par la Rédaction]

Introduction

Early successional nitrogen-fixing alder species strongly mod-ify soil properties during primary succession, increasing soilorganic matter, nitrogen, and mineral weathering (Bormannet al. 1994). However, continued N inputs by N fixers duringsecondary succession can result in accelerated nitrate leaching(Van Miegroet and Cole 1984), with rates ranging from 3 to40 kg NO3-N⋅ha–1⋅year–1 in mixed and pure red alder (Alnusrubra Bong.) stands (Binkley et al. 1992; Johnson andLindberg 1992). Reaching this N-saturated condition may not

be commonly observed because N fixers often do not naturallyreplace themselves or grow in continuous stands. Coppicing orplanting successive rotations of N fixers may substantially in-crease soil acidity and is considered to be risky in acid soils forthis reason (Bormann et al. 1994). Although interplanting withN fixers may increase N availability and biomass accumula-tion of nonfixing species in mixed stands (Côté and Camiré1987), the complex effects of rotations on soil fertility are notwell understood.

Where red alder invades after disturbance, soil N availabil-ity often increases, and pH and base saturation decrease (sum-marized by Bormann et al. 1994). Decreases in soil pH aregenerally accompanied by increased soil solution and ex-tractable Al3+ (Reuss and Johnson 1986) and could result indecreased soil P availability (Sanyal and De Datta 1991).Available P has been shown to be higher (Giardina et al. 1995)and lower (Cole et al. 1990) under alder; given the importanceof pH and available P in the growth, nodulation and fixationin symbiotic N-fixing plants (Sprent 1988), any change overthe course of succession could be important in their ecologyand management.

Previous study in the Cedar River watershed of westernWashington found that red alder was less productive when

Received June 6, 1996. Accepted January 2, 1997.

J.E. Compton1 and D.W. Cole.College of Forest Resources,University of Washington, Seattle, WA 98195, U.S.A.P.S. Homann.Center for Environmental Science, MS 9181,Huxley College, Western Washington University, Bellingham,WA 98225-9181, U.S.A.

1 Author to whom all correspondence should be addressed.Present address: Department of Natural Resources Science,University of Rhode Island, Woodward Hall, Kingston, RI02881, U.S.A.

Can. J. For. Res. 27: 662–666 (1997)

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grown in repeated rotations, as compared with growth on anadjacent site previously occupied by 50-year-old Douglas-fir(Pseudotsuga menziesii (Mirb.) Franco). The second-rotationalder had 33% less height growth and 75% less abovegroundbiomass 5 years after planting (Cole et al. 1995). The objectiveof this study was to examine the relationship between potentialchanges in soil properties under red alder and subsequent aldernutrition at this site. We expected the initial lower soil pH, basesaturation, and available P in the alder soil to yield lower basecation and P concentrations in the leaves and leaf litter of thesecond-rotation alder stand than in alder grown on a formerDouglas-fir site.

Methods

Site descriptionThe study was conducted at the Thompson Research Center, locatedat the southwestern end of the Cedar River watershed, 56 km south-east of Seattle, Wash. The elevation is 220 m in the western foothillsof the Cascade Mountains. Mean annual air temperature was 10°Cfrom 1987 to 1992; the January mean was 4°C; and the July mean was17°C. Average annual precipitation was 135 cm, a large proportion ofwhich fell as rain between October and March.

The soil underlying the study site is the Alderwood series, pre-viously classified as a dystric Entic Durochrept, recently reclassifiedas a mesic ortstein Aquic Haplorthod (USDA Soil Survey Staff 1986).It is a gravelly sandy loam, derived from ablation till overlying indu-rated basal till. The earliest documented forest, mature Douglas-fir,was logged between 1910 and 1920 (Turner et al. 1976). After a seriesof wildfires passed through the area, most of the site was planted withDouglas-fir in 1931. Areas not planted, or where Douglas-fir wasdestroyed by subsequent fire, were invaded by red alder over the next10 years.

At the initiation of this study, the adjacent stands of Douglas-fir(basal area 50 m2⋅ha–1) and red alder (36 m2⋅ha–1) were approximately50 years old (Van Miegroet et al. 1992). In September 1984, all treesin a 50 × 100 m (0.5-ha) plot within each of the two stands wereharvested and removed with cables to minimize soil disturbance. InFebruary 1985, 2-year-old red alder seedlings from gravelly areas10 km southeast of the site were planted at 2 × 2.5 m spacing, yieldingfirst-rotation alder on the former Douglas-fir plot and second-rotationalder on the former alder plot.

Soil sampling and analysisIn July 1984, prior to harvesting, mineral soil was collected from the0–15, 15–30, and 30–45 cm depths from eight 15 × 15 m subplots ineach plot. For each subplot, soil was composited from three pits andair-dried. The <2 mm fraction was analyzed for pH by glass electrodeon a 2:1 water–soil extract; for N by modified Kjeldahl digest (Park-inson and Allen 1975) followed by NH4

+ analysis (TechniconAutoAnalyzer II); for total C by combustion (LECO); and forBray-extractable P (Olsen and Sommers 1982). Samples were ex-tracted with 1 M NH4Cl, and the extract was analyzed by flameatomic absorption spectrophotometry for Ca, Mg, and K and bygraphite furnace for Al. The NH4

+ was then displaced by 1 M NaCl todetermine cation exchange capacity (CEC). Differences betweenplots were examined by two-way ANOVA using SYSTAT (Wilkin-son 1989).

Leaf and litter sampling and analysisFrom four adjacent living trees within each of the eight subplots oneach plot, 15 alder leaves with petioles were collected on 22 September1988 from 1 to 2 m above the ground. At the same locations, alder leaflitter was collected on 18 November 1988 by picking 60 leaves off theground.

From three trees within each subplot, leaves were stripped fromthree branches 1–2 m from the top of the canopy on 12 July,16 August, and 19 September 1989. A caterpillar (Archips sp.) attackin May and June 1989 prevented earlier sampling of the upper canopy.Alder leaf litter was collected in each subplot from 14 October 1989through 5 January 1990 in a 0.53 × 0.61 m plastic tray lined withnylon mesh. The litter was removed from the trays at 1- to 4-weekintervals.

The fresh leaves were measured for leaf area (LI-COR, Lincoln,Nebr.). Leaves and litter were dried at 75°C and weighed. Ground(<0.4 mm, 40 mesh) samples were digested by the modified Kjeldahlmethod (Parkinson and Allen 1975). Digest solutions were analyzedfor NH4

+ by the indophenol blue method (Technicon AutoAnalyzerII) and for P, K, Ca, Mg, Al, Fe, Cu, Mn, and Zn by inductivelycoupled plasma emission spectroscopy (Thermo-Jarrell Ash). Recov-eries for N, P, K, Ca, Mg, Al, Fe, Cu, Mn, and Zn were 132, 80, 82,68, 90, 68, 107, 122, 114, and 157%, respectively, based on NationalInstitute of Standards and Technology pine or citrus leaf standards.Coefficients of variation for these same elements were 4, 16, 13, 13,16, 21, 18, 14, 19, and 26%, respectively, for three replicate analysesof each standard.

Concentration differences between plots and sampling dates weretested by two-way ANOVA using SYSTAT (Wilkinson 1989). Alu-minum concentrations were log transformed to achieve a normal dis-tribution. Litter-fall mass for each period was multiplied by elementconcentration to yield litter-fall element transfer for 1989. Averagelitter fall was determined by summing litter fall within subplots for allsampling periods, then averaging the subplots.

Results

The second-rotation alder plot had higher initial soil C, N,CEC, and extractable Ca, Mg, and Al than the first-rotationplot (Table 1). It also had lower soil pH and Bray P.

The first-rotation plot had higher leaf P, Ca, and Mg in 1988and 1989, lower K, Mn, and Fe in 1989, and higher Al in 1988compared with the first-rotation plot (Table 2). In spite of thesedifferences, growing season trends for both plots were similarfor most elements (Fig. 1). The second-rotation plot had higherspecific leaf mass (9.4 mg⋅cm–2) than the first-rotation plot(5.8 mg⋅cm–2).

The second-rotation plot had lower leaf litter N, Ca, Mg,and Fe concentrations in 1988 and 1989 and higher Al in 1988(Table 2). In combination with much lower litter-fall mass, thisyielded litter-fall element transfers 30–49% of those in thefirst-rotation plot (Table 3).

Discussion

The differences in initial soil properties between the first- andsecond-rotation alder plots are generally consistent with thegreater soil C and N, higher CEC, and lower pH previouslyfound under alder (Binkley et al. 1992; Bormann et al. 1994).The experimental design is unreplicated, and therefore, standhistory may be confounded with previous differences in soilproperties. However, similarities to previous studies, and prox-imity and similar topography of the plots, support our conten-tion that the differences in initial soil properties were the resultof differences in the vegetation. In addition to the commonfindings, we also found lower Bray-extractable P in the initialsoil of the second-rotation plot. In contrast, increased P avail-ability was associated with alder in primary succession andalder interplantings on different soil parent materials(Bormann and Sidle 1990; Giardina et al. 1995).

Compton et al. 663

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The second-rotation plot had lower leaf concentrations ofP, Ca, and Mg in 1988 and 1989, indicating a potential long-term impact of changing soil properties under alder on futurestand nutrition. The similarity of the results for 1988 and 1989suggests that neither the differences in sampling nor the 1989defoliation affected this overall trend. Higher specific leafmass in the second-rotation stand could be related to greaterN availability; N fertilization can increase specific leaf mass(Kozlowski et al. 1991).

Lower P concentrations in the second-rotation alder leavesreflect the lower soil Bray-extractable P (Tables 1 and 2);comparison with critical levels indicates a deficiency in thesecond-rotation plot (1600 mg P⋅kg–1; as determined by

Hughes et al. (1968)). Nitrogen-fixing species appear to havehigh requirements for P (Sprent 1988) and may be especiallyaffected relative to other species when P is limiting.

Leaf N levels were the same or higher in the second-rotationplot, indicating that soil acidification and lower P availabilitydid not reduce alder’s ability to acquire sufficient N. At thissite, the leaves of Douglas-fir (Brozek et al. 1990) and fire-weed (Epilobium angustifolium L.; Van Miegroet et al. 1990)had lower P concentrations when grown on areas previously oc-cupied by alder, supporting our finding that the second-rotationplot had lower plant available P. Other studies have shown aconnection between high soil N and P deficiency (Mohrenet al. 1986; Teng and Timmer 1995).

Depth

(cm)

pH

(H2O)

Total C

(g⋅kg–1)

N

(g⋅kg–1)

Exchangeable components (cmol[+]⋅kg–1) Bray P

(mg⋅kg−1)CEC Ca Mg K Al

First rotation0–15 5.3 38 1.5 9.2 0.72 0.07 0.13 0.28 64

15–30 5.3 26 1.1 8.6 0.90 0.07 0.10 0.01 32

30–45 5.3 21 1.1 7.0 0.36 0.04 0.12 0.01 28

Second rotation0–15 4.5 110 5.5 16.6 1.32 0.34 0.17 1.89 20

15–30 4.9 68 3.5 14.1 0.68 0.08 0.08 0.35 12

30–45 4.9 67 3.6 13.3 1.36 0.12 0.10 1.29 8

Effects (p values)Stand (S) ≤0.001 ≤0.001 ≤0.001 ≤0.001 ≤0.01 ≤0.05 ≤0.05 ≤0.001

Depth (D) ≤0.05 ≤0.001 ≤0.001 ≤0.05 ≤0.10 ≤0.05 ≤0.001

S×D ≤0.05 ≤0.10 ≤0.05 ≤0.05 ≤0.10

Note: Values are for eight composite samples collected in 1984. Significant effects of stand, soil depth, and the interaction were determined by

two-way ANOVA.

Table 1. Initial soil properties in first- and second-rotation alder.

Samplea N P K Ca Mg Mn Fe Al Cu Zn

Leaf 1988

First rotation 30 800 1250 5130 6930 1930 229 67 69 9 20

Second rotation 29 400 1150 4560 5400 1640 211 57 98 12 23

S effect ≤0.10 ≤0.01 ≤0.05 ≤0.10 ≤0.001

Litter 1988

First rotation 28 100 817 4124 6775 1660 294 101 180 10 23

Second rotation 24 547 761 3883 5441 1350 352 99 266 12 24

S effect ≤0.01 ≤0.01 ≤0.05 ≤0.10 ≤0.05

Leaf 1989

First rotation 29 500 1710 7230 4610 1730 243 153 189 10 43

Second rotation 31 200 1480 6000 3480 1520 188 138 208 14 41

D effect ≤0.05 ≤0.001 ≤0.001 ≤0.001 ≤0.001 ≤0.001 ≤0.001 ≤0.01 ≤0.05

S effect ≤0.001 ≤0.001 ≤0.001 ≤0.05 ≤0.001 ≤0.01 ≤0.001

D×S effect ≤0.001 ≤0.10 ≤0.01

Litter 1989

First rotation 30 800 922 3130 6680 1710 450 250 436 16 66

Second rotation 27 500 611 2180 6220 1280 450 221 477 16 58

D effect ≤0.001 ≤0.001 ≤0.001 ≤0.01 ≤0.001 ≤0.001 ≤0.001 ≤0.001 ≤0.001 ≤0.001

S effect ≤0.001 ≤0.001 ≤0.001 ≤0.10 ≤0.001 ≤0.10 ≤0.01

D×S effect ≤0.01 ≤0.05 ≤0.001 ≤0.001

Note: Effects (p-values) are from one-way ANOVA for 1988 and two-way ANOVA for 1989.aS, stand; D, date.

Table 2.Mean leaf and litter nutrient concentrations (mg element⋅kg tissue–1) and effects of stand and sampling date.

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The second-rotation plot had lower leaf Ca and Mg, whilesoil extractable concentrations were higher in this plot, indi-cating that uptake may not be directly related to soil extractablenutrients. The second-rotation plot had higher extractable andleaf Al; high levels of Al in solution culture can inhibit Ca andMg uptake (Sucoff et al. 1990). Nitrogen-fixing plants may beespecially sensitive to soil solution Al (Sucoff et al. 1990),although Alnus glutinosa (L.) Gaertn. was more tolerant ofhigher solution Al concentrations than other species(McCormick and Steiner 1978).

Lower leaf litter P, K, and Mg in second-rotation alder(Table 3) may have long-term implications for nutrient distri-bution and availability. The production of litter with lowernutrient concentrations may result in the accumulation ofslowly decomposing soil organic matter, which has a longerperiod of nutrient immobilization. Leaf litter from the second-rotation plot decomposed 8% more slowly than litter from thefirst-rotation plot (Cole et al. 1995). Lower leaf litter concen-

trations in the second-rotation alder plot also indicate that thisstand is more proficient (sensu Killingbeck (1996)) at resor-bing P, K, and Mg, perhaps in response to lower availability.

The future growth of red alder may also be negatively im-pacted by changes in soil properties observed after 50 years ofalder growth. Aboveground woody biomass increment in thefirst-rotation plot was 52% that of the first-rotation (Coleet al. 1995). Replicated studies on different soil types are re-quired to determine whether our conclusions extend beyondthe till-derived soil of this study. Although our design does notallow us to conclusively demonstrate the effect of successivealder rotations on soil fertility, the second-rotation plot hadslower growth and lower element concentrations in leaves andleaf litter, provoking further investigation into the relationshipbetween repeated rotations of red alder and soil fertility. It isalso raises the possibility that during its tenure, red alder pro-duces soil conditions that negatively impact its own growth,explaining its short but dramatic role in plant succession.

Acknowledgments

The authors thank Helga Van Miegroet for providing the 1984soils data, and P. Jay Kuhn and Jacquie Fenning for assistancewith the laboratory analyses. We also appreciate suggestionsfor improvement of the manuscript from Dennis Knight,Alan White, and two anonymous reviewers.

References

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Site Mass N P K Ca Mg Mn Fe Al Cu Zn

Second rotation 740 21 0.5 1.9 4.5 1.1 0.32 0.17 0.33 0.011 0.042

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Table 3.Mass and element content (kg⋅ha–1) of litter fall in 1989, collected from 14 October 1989 through 6 January 1990.

Fig. 1. Element concentrations in alder leaves and leaf litter in

1989. All y-axis units are milligrams element per kilogram of tissue.

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