The influence of red alder patches on light, litterfall, and soil nutrients in adjacent conifer stands

The influence of red alder patches on light,litterfall, and soil nutrients in adjacent coniferstands

John M. Lavery, Philip G. Comeau, and Cindy E. Prescott

Abstract: To evaluate the distance over which red alder patches influence adjacent conifer stands, we measured lighttransmission and nutrient contents of soil and litterfall along transects crossing the boundary between alder and coniferstands at three sites (10–15, 20–25, and ≥40 years old) in coastal British Columbia. Light levels were higher in theunderstory of alder stands than in adjacent conifer stands. In simulated openings, light levels rapidly increased withdistance from the alder edge, reaching 60% of full sunlight at south-facing edges, 5 m from north-facing edges, and2–3 m from east- and west-facing edges. Soil N, NH4-N, NO3-N, and mineralizable N remained elevated for about10 m from the alder boundary. Nitrogen contents of Douglas-fir seedlings grown in soil from the alder stand were ele-vated and correlated to soil N concentrations. Nutrient inputs in alder litterfall were positively related to concentrationsof total C; total, extractable, and mineralizable N in soils; and the N, P, and B concentrations of seedlings. Alderlitterfall drift extended 8–18 m into adjacent conifer stands. The optimal arrangement for alder–conifer mixtures wouldbe alder patches or strips at least 10 m wide and about 20 m apart oriented north to south.

Résumé : Dans le but d’évaluer jusqu’à quelle distance les bouquets d’aulne rouge influencent les peuplements adja-cents de conifères, nous avons mesuré la transmission de la lumière et le contenu en nutriments du sol et de la chutede litière le long d’un transect passant par la limite entre des peuplements d’aulne et de conifères dans trois stations(10–15, 20–25 et ≥40 ans) situées dans la zone côtière en Colombie-Britannique. Le niveau de lumière était plus élevéen sous-étage des peuplements d’aulne que dans les peuplements adjacents de conifères. Dans des ouvertures simulées,le niveau de lumière augmentait rapidement à mesure qu’on s’éloignait de la limite des aulnes, atteignant 60 % duplein ensoleillement du côté de l’ouverture exposée au sud, à 5 m de la bordure exposée au nord et à 2–3 m des bor-dures exposées à l’est ou à l’ouest. Le contenu en azote du sol, sous forme de NH4, de NO3 et de N minéralisable, de-meurait élevé sur environ 10 m à partir de la limite des aulnes. Le contenu en N de semis de douglas cultivés dans lesol provenant de peuplements d’aulne était élevé et corrélé à la concentration de N dans le sol. L’apport de nutrimentsdans la chute de litière d’aulne était positivement relié à la concentration de C total et de N total, extractible et minéra-lisable dans le sol ainsi que de N, P et B dans les semis. La chute de litière d’aulne était emportée jusqu’à 8–18 mdans les peuplements adjacents de conifères. La configuration optimale des mélanges d’aulne et de conifères seraitconstituée de bouquets ou de bandes d’aulne d’au moins 10 m de largeur distants de 20 m et orientés nord-sud.

[Traduit par la Rédaction] Lavery et al. 64

Introduction

Indications that growing red alder (Alnus rubra Bong.) inan intimate mixture with conifers can contribute to long-term sustainability (Comeau and Sachs 1992) and enhancenon-timber resource values (McComb 1994; Hibbs and De-Bell 1994) has stimulated interest in management of red

alder in British Columbia (B.C.) and the Pacific Northwest.Managing red alder in mixedwood stands requires striking abalance between the detrimental effects of overtopping alderon light reaching understory conifers and the nutritionalbenefits of the alder. Growth of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco var. menziesii) when in mixturewith red alder is typically lower than in pure stands (Coleand Newton 1986), as a result of lower light transmittancelevels in stands with alder (Shainsky and Radosovich 1992;Shainsky et al. 1994; Comeau 1996).

The competitive effects of alder on light are counterbal-anced by increased N availability because of fixation ofatmospheric N. Nitrogen fixation rates in alder stands usu-ally range between 20 and 85 kg·ha–1·year–1 (Binkley et al.1994), but rates up to 320 kg·ha–1·year–1 have been reported(Van Miegroet et al. 1989). Soil total N content can increaseby 20%–50% over periods of 30 years or more, and annualN turnover rates for soil in alder stands can reach eight timesthose of neighbouring conifer stands (Binkley 1992; Binkleyet al. 1992). Nutrient return via leaf litterfall has been sug-

Can. J. For. Res. 34: 56–64 (2004) doi: 10.1139/X03-194 © 2003 NRC Canada

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Received 19 June 2003. Accepted 8 August 2003. Publishedon the NRC Research Press Web site at http://cjfr.nrc.ca on22 December 2003.

J.M. Lavery1,2 and C.E. Prescott. Department of ForestSciences, The University of British Columbia, 3041-2424 Main Mall, Vancouver BC V6T 1Z4, Canada.P.G. Comeau. Department of Renewable Resources,University of Alberta, 442 Earth Sciences Building,Edmonton AB T6G 2E3, Canada.

1Corresponding author (e-mail: [email protected]).2Present address: Forest Research, Private Bag 3020, SalaStreet, Rotorua, New Zealand.

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gested as the primary mechanism by which fixed N is trans-ferred to the soils in alder stands (Bormann et al. 1994).Radwan et al. (1984) reported average nutrient returns inalder litter (in kg·ha–1·year–1) of 82 for N, 41 for Ca, 19 forK, 8 for Mg, 7 for S, 4 for P, 1 for Fe, 1 for Mn, 1 for Al,0.2 for Zn, and <0.1 for Cu. Litterfall cycling of N is gener-ally three to eight times greater in mixed stands of alder andconifer than in pure conifer stands (Binkley et al. 1992),while cycling of P, S, Ca, Mg, and K is often two to tentimes greater in mixed stands (Radwan et al. 1984). Litter-fall N inputs relate well with rates of N accretion in soil(Van Miegroet et al. 1989; Binkley et al. 1992).

One option for minimizing competition for light whilemaintaining the nutritional benefits of a red alder – Douglas-fir mixture is to plant the alder in patches or strips inter-spersed within conifer-dominated stands. A successful patchmixture requires that the influence of alder on soil nutrientsupply extend further into the conifer stand than its shadingeffects. The nutritional benefits of alder (based on measuresof conifer growth) have been reported to extend 8–15 mfrom the edge of mixed stands (Miller and Murray 1978;Miller and Reukema 1993), with the effect extending fartherdownslope than upslope (Rhoades and Binkley 1992). Theextent to which alder reduces light levels in an adjacent co-nifer plantation depends on the height and leaf density of thesurrounding stand, the orientation of the stand boundary, lat-itude, and size of the opening (Berry 1964; Nyland 1996;Lieffers et al. 1999). In general, the amount of light reachingthe center of an opening increases as the size of the openingincreases (Groot et al. 1997; Lieffers et al. 1999).

In this study, we examine the spatial effects of red alderon light and soil nutrients by measuring these factors atpoints along transects crossing the boundary between alderstands and adjacent conifer stands. We also determine if soilnutrient availability along the transects is related to nutrientinputs in litter. These observations are used to recommendthe optimal arrangement for mixtures of alder and conifersthat would maximize the improved nutrient availability andminimize light competition between the conifers and thealder.

Materials and methods

Three sites in coastal B.C. were used in the study. At eachsite, two transects were established across the boundary be-tween the red alder and conifer stands, extending 25 m intothe conifer stand and 10 m into the alder stand. TheChilliwack transects (CH1 and CH2) were located in a10-year-old, 12 m tall stand near Chilliwack (49°15′N,121°95′W, 380 m a.s.l.), in the Dry Maritime variant of theCoastal Western Hemlock (CWH) biogeoclimatic zone(Meidinger and Pojar 1991). The soil was a Humo-FerricPodzol derived from glacial till, with a sandy loam to loamysand texture with 10%–30% coarse fragments. The site waslogged and windrowed in 1982 and planted with grand fir(Abies grandis (Dougl. ex D. Don) Lindl.) in 1983; alder es-tablished naturally. Transect CH1 had a bearing of 62° and<2° slope, but occupied a northern aspect of the mountain-side. Transect CH2 also had a bearing of 62° and a 5° slopein separate alder and fir stands nearby. The alder stands hadan understorey dominated by unidentified grasses (Poaceae),

Rubus ursinus Cham. & Schlechtend., and Mahonia nervosa(Pursh) Nutt. syn. Berberis nervosa Pursh; the conifer por-tions were mostly devoid of understory vegetation.

The Malcolm Knapp transects (MK1 and MK2) were lo-cated in a 25-year-old stand comprising 15 m tall red alderand Douglas-fir in the Malcolm Knapp Research Forest ofThe University of British Columbia, near Maple Ridge(49°23′N, 122°62′W, 175 m a.s.l.), in the Submontane VeryWet Maritime variant of the CWH zone (Meidinger andPojar 1991). The soils was a Humo-Ferric Podzol derivedfrom colluvium and glacial till, with a loamy sand texturewith 20%–50% coarse fragments. Transects MK1 and MK2extend outward from an alder stand (approximately 50 m ×20 m) into a Douglas-fir stand that surrounded the alder. TheMK1 transect had a bearing of 180° and an 8°–10° slope,while the MK2 stand, originating in the same alder stand,had a bearing of 45° and an 8°–10° slope. The understoreyin the alder stand was dominated by Rubus spectabilis Purshand Polystichum munitum (Kaulf.) C. Presl.; in the Douglas-fir stands, it was P. munitum, M. nervosa, and R. spectabilis.

The Nanaimo Lakes transects (NM1 and NM2) werelocated in a 45-year-old stand comprising 10 m tall alder(most of which had top damage) and 30 m tall conifers,10 km west of Nanaimo (49°16′N, 123°93′W, 220 m a.s.l.)in the Very Dry Maritime subzone of the CWH zone(Meidinger and Pojar 1991). The soil varied from Humo-Ferric Podzol to Ferro-Humic Podzol in the center of the al-der stand where there was a small ephemeral stream. Thesoil was silty loam to loamy sand in texture with 5%–40%coarse fragments. The alder stand was irregularly shaped,approximately 150 m × 30 m, with the conifer stand sur-rounding it. Transect NM1 extended on a bearing of 110°from the alder stand into an adjacent stand of Douglas-fir,western white pine (Pinus monticola Dougl. ex D. Don),western hemlock (Tsuga heterophylla (Raf.) Sarg.), and asmall amount of alder, with a slope <2°. Transect NM2 ex-tended from the same alder stand on a bearing of 55° up a10°–12° slope into a relatively pure Douglas-fir stand. Therewas an understory of R. spectabilis and P. munitum underthe alder and Gaultheria shallon Pursh. under the conifers.The top damage to the alder appeared to have been causedby a freezing episode and affected approximately 50% of thetrees, reducing them from a height of approximately 15 m to10 m.

Ten sample points were located along each transect: at thedripline boundary between stands; at 3, 6, 9, 12, 15, 20, and25 m into the conifer stand; and at 3 and 10 m into the alderstand. The points were numbered 1 through 10; point 1 was10 m into the alder stand, point 3 was at the boundary, andpoint 10 was 25 m into the conifer stand. The location, spe-cies, diameter at breast height (DBH), and height of all treesin a 20 m × 55 m area centered on each transect weremapped.

LightHemispherical photographs were taken during the summer

of 1998 at each of the 10 points along each transect. Thephotographs were taken on overcast days or near dawn ordusk to avoid solar penumbral effects. A Nikon F601 camerawith a Nikorr 8mm f/2.8 fisheye lens (Nikon Canada, To-ronto, Ont.) and Kodak TMAX 100 black and white film

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(Kodak Canada, Vancouver, B.C.) was mounted on a tripod1.4 m above the ground. The negatives were digitized usingan Olympus ES-10 scanner (Olympus America Inc., Mel-ville, N.Y.) and saved as Windows Bitmaps (*.BMP), com-patible with the spot light interception and transmittanceestimator (SLIM) (Comeau et al. 2001a) and light intercep-tion and transmittance estimator (LITE) (Comeau et al.2001b) analysis software.

SLIM software was used to process digitized hemispheri-cal photographs for subsequent use by the LITE model andto provide estimates of average monthly transmittance. Opensky data from the MK site was coupled with stand mappingand tree measurement data for each transect. The LITEmodel generates a canopy consisting of 1-m3 cells, based onspatial gap fraction data generated from hemispherical pho-tographs and information on tree location, species, and topheight (Comeau et al. 1998). Tree heights, crown radius, andcrown length were generated by LITE. After generating thecanopy, the LITE model was used to estimate light penetra-tion through the canopy in 1-h increments over the period ofinterest. Average photosynthetic photon flux density (PPFD)and transmittance were calculated for each point along thetransects for the period July 1–31, 1998, based on the gener-ated canopy and open sky readings from the Malcolm Knappsite.

To evaluate the spatial influence of red alder on lighttransmission, LITE model simulations were completed usingonly the alder component of each stand (i.e., with all coni-fers removed). For these simulations, alder canopies weregenerated from tree measurement data (location, DBH,height, crown dimensions). We also used the model with thisalder-only data set to evaluate the effect of stand boundaryorientation by artificially altering the bearing of the transectto each of the four cardinal directions while keeping otherfactors constant. For these simulations, the area exclusive ofthe alder stands was treated as being open.

Soil nutrientsOne soil sample was collected to a 10 cm depth at all 10

sample points along each transect during mid-June 1998.The samples were transported on ice to The University ofBritish Columbia for processing. All samples were trans-ferred to paper bags and dried in a forced air oven for 48 hat 70 °C. Dry soils were passed through a 0.5-mm sieve,transferred to plastic bags, and shipped to the B.C. Ministryof Forests, Glyn Road Analytical Laboratory in Victoria,B.C., for analysis.

Total N was measured by dry combustion using a LecoCNS instrument (Leco Corporation, St. Louis, Mo.). Soilsamples were extracted with 2 mol·L–1 KCl, then NH4-N andNO3-N in the extracts were measured colorimetrically with aTechnicon DP-1000 autoanalyzer (Bayer Healthcare, To-ronto, Ont.) (Kalra and Maynard 1991). Mineralizable Nwas determined by incubating soil samples under anaerobic,waterlogged conditions for 2 weeks at 30 °C, then displacingNH4-N with 1 mol·L–1 KCl extractant and colorimetric mea-surement with the autoanalyzer (Kalra and Maynard 1991).Bray P1-extractable phosphorus was analyzed using an anti-mony-phospho-molybdenum (Kalra and Maynard 1991). pHwas measured in water.

A bioassay was conducted to compare the nutrient supplycapacities of soils along each transect. In early April 1998,12 gallons (1 gallon = 4.546 09 L) of mineral soil (0–30 cmdepth) were collected adjacent to each transect point at thethree sites (60 samples total). The samples were passedthrough a 1.0-mm sieve, mixed with an equal volume ofperlite, and left in large open buckets. Four hundredDouglas-fir seedlings (Fdc 1+0 PSB 415B, seedlot #32401)from Pelton Nursery in Haney, B.C., were used in the bio-assay. Seedling root systems were rinsed to remove all grow-ing medium residue and planted in 4-L plastic pots (ListoProducts Inc., Surrey B.C.) containing equal volumes of thesoil mixture on April 29, 1998. Nine trees that were notplanted were dried and ground to determine initial nutrientconcentrations. On November 15, the seedlings were har-vested, the roots washed thoroughly, separated into root andshoot, and dried for 48 h at 70 °C. The samples were thenground to <0.05 mm using a Wiley mill (Thomas Scientific,Swedesboro, N.J.). N and P concentrations in the shoot por-tion of each seedling were measured using a microwave aciddigestion method, a variant of the protocol by Kalra andMaynard (1991).

LitterfallLitterfall was collected for 1 year from each of the six

transects and from six additional transects. The six addi-tional transects (two at each of three sites) allowed us to in-crease the range of stand ages in which we measuredlitterfall mass. The additional sites were (i) a 4-year-oldstand at East Wilson Creek near Sechelt, B.C. (49°47′N,123°75′W), (ii) a 5-year-old stand at Gough Creek also nearSechelt, and (iii) a 26-year-old stand at the Malcolm KnappResearch Forest (49°23′N, 122°61′W). Three litter trapsmeasuring 25 cm × 50 cm (0.125 m2) were placed at eachmeasurement point along each transect; one was centered onthe transect, and the others were 5 m to either side. Thetraps were installed in July 1998, and litter in the traps wascollected every 2 weeks from mid-August until mid-November and then monthly through the winter, spring, andsummer of 1999. Litter was dried for 48 h at 70 °C, sepa-rated into leaf and needle components, and composited, sothat each sample represented the annual litterfall from eachtrap. For both litter types, three 1-g samples from each sitewere ground and analyzed for N, P, K, Ca, Mg, S, Cu, Fe,Mn, Zn, and B concentrations using a modified microwaveacid digestion process followed by spectral analysis at theB.C. Ministry of Forests, Glyn Road Analytical Laboratory(Kalra and Maynard 1991). Nutrient concentrations weremultiplied by annual litterfall mass to calculate litterfall nu-trient inputs at each sample point.

Statistical analysesTrends in light levels and differences in soil, litterfall, and

seedling nutrient concentrations among the 10 sample pointsin each transect were tested using simple linear regressionand polynomial regression. Differences among samplepoints in mass and nutrient concentrations of litterfall andseedlings were tested for significance using a one-wayANOVA, while differences between the two litter types weretested using paired t tests. All relationships among soils,litterfall, and seedlings were analyzed using linear regression

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techniques. S-PLUS version 6.1 statistical software was usedfor all analyses (Insightful Corporation 2002).

Results

LightThe quantity of light reaching the understorey beneath

alder stands varied with age, canopy cover, and structure(Fig. 1). More light reached the understorey in the alderstands than in the conifer stands, but neither understoreylight regime was above the minimum level required forgrowth of Douglas-fir seedlings (40% PPFD, Mailly andKimmins 1997). When conifers were removed and lighttransmittance was modeled from the alder stand into theadjacent opening (Fig. 2), light levels above the 40% PPFDminimum for Douglas-fir growth were reached within 6 m,and the 60% PPFD level considered acceptable for Douglas-fir growth (Carter and Klinka 1992) was reached within 9 m.Simulated changes in stand boundary orientation of eachtransect revealed a substantial effect of orientation. Lightlevels above 60% PPFD occurred 0–2 m inside the alderstand for south-facing boundaries, 3.5–5.5 m into the open-ing for north-facing boundaries, 1–3 m into the opening foreast-facing boundaries, and 1–6 m into the opening for west-facing boundaries. The height of the stands also influencedthe distance to which alder influenced light transmission inthe adjacent opening.

Soil nutrientsSoil total C, total N, mineralizable N, NH4-N, and NO3-N

were all higher in the alder stand than in the adjacent coniferstand at the oldest site (NM, Fig. 3). The regressions indi-cated significant differences (p < 0.05) along the transects inthe NM stand, but there were no significant differences atthe youngest site (CH) and occasional, smaller differencesat the intermediate-aged site (MK). The decline in pH andNO3-N at NM2 was significant at p = 0.05.

All of the variables related to soil C and N remainedelevated for 6–10 m beyond the stand boundary into the ad-jacent conifer stands; nitrogen concentrations remained ele-vated for 3–9 m, mineralizable N for 9 m, NO3-N for 6 m,and NH4-N for 6–10 m.

Shoot N concentrations in Douglas-fir seedlings grown inalder soils were significantly higher than the conifer soils fortransects NM1 (R2 = 0.50, p = 0.02), NM2 (R2 = 0.61, p =0.008), and MK1 (R2 = 0.44, p = 0.04). Elevated shoot Nconcentration occurred in soils from positions up to 7 m intothe Douglas-fir stand. Seedlings grown in alder soils fromthe NM site also had significantly higher shoot P concentra-tions (p = 0.02) than those grown in soil from the coniferstands, despite observations of low extractable P in the aldersoil.

Seedling shoot N concentration was significantly relatedto soil N and NO3-N concentrations at the NM site (Ta-ble 1). Shoot concentrations of B were significantly relatedto soil NO3-N concentration for NM1 and CH2. P concentra-tions in Douglas-fir seedlings were positively related to soilN concentration (R2 = 0.70, p < 0.05) for all seedlings com-bined at NM.

LitterfallLitterfall mass of red alder reached a maximum of 4000–

6000 kg·ha–1·year–1 between 15 and 20 years of age (Fig. 4),which is consistent with results presented by Zavitkovskiand Newton (1971) and Radwan et al. (1984). Litter produc-tion was lower in the NM stand than in the other sites, prob-ably as a consequence of the obvious top damage to thealders at this site.

Alder leaf litter had significantly higher concentrations ofN, P, K, Ca, Mg, and B than conifer needle litter and signifi-cantly lower concentrations of cellulose, lignin, Cu, Fe, andZn (Table 2). Mass of leaf litterfall was significantly greater

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Fig. 1. Estimated percent transmittance at 1.5 m along sixtransects from alder stands into adjacent conifer stands as calcu-lated by the light interception and transmittance estimator (LITE)model for July 1998. CH, Chilliwack site; MK, Malcolm KnappResearch Forest site; NM, Nanaimo site.

Fig. 2. Estimated percent transmittance along six transects fromalder stands into adjacent openings (conifers removed) as calcu-lated by the light interception and transmittance estimator (LITE)model for July 1998. Dashed lines represent important lightthresholds from other studies. CH, Chilliwack site; MK,Malcolm Knapp Research Forest site; NM, Nanaimo site.



in alder stands than in conifer stands (Table 3). Greatermasses of N, P, K, Ca, Mg, S, and B were returned annuallyin leaf litter in the alder stands (Table 3), while greatermasses of Fe, Cu, Mn, and Zn were returned in the coniferstands.

The distance that alder litter traveled into adjacent coniferstands increased with stand age, from 0 m in the young (0-to 5-year-old) stands to 20–25 m in the oldest (≥40 years.)stands (Fig. 5). The maximum litterfall distance, defined asthe sample point nearest to the alder stand that received less

than 300 kg of alder litter per hectare per year, was significantlyrelated to the logarithm of alder stand age (y = –7.7425 + 18.59log(age), R2 = 0.80, p < 0.001).

The mass and nutrient content of alder litter at eachtransect point was positively correlated with several of themeasured indices of soil nutrient supply (Table 4). Most sig-nificant relationships occurred in the NM stands.

Migration of alder litterfall into the conifer stand and theresulting inputs of N and P can be seen in Fig. 6. Althoughthe patterns were complicated by the occasional presence of

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Fig. 3. Concentrations of NO3-N, pH in H2O, Bray-extractable P, total N, total C, NH4-N, and mineralizable N in the upper 10 cm ofmineral soil at each point along the six transects from alder into conifer stands. Lines represent significant regressions. Dashed linescorrespond to open symbols. The vertical line at 10 m represents the alder–conifer stand boundary. CH, Chilliwack site; MK, MalcolmKnapp Research Forest site; NM, Nanaimo site; 1, Transect 1; 2, Transect 2.

Statistics

Relationshipa Transectb Equation R2 p value

Soil total N and bioassay %N NM1 0.6572 + 0.2535x 0.41 0.048NM2 0.5342 + 0.1092x 0.45 0.034

Soil NO3-N and bioassay %N NM1 0.6625 + 0.0190x 0.42 0.040NM2 0.5358 + 0.0064x 0.67 0.004CH2 0.8006 + 0.0023x 0.60 0.008

Soil NO3-N and bioassay %B NM1 9.2326 + 85.77x 0.68 0.003CH2 8.536 + 65.2326x 0.68 0.003

aTotal N is in %; soil NO3-N is in g·m–3.bNM, Nanaimo Lakes site; CH, Chilliwack site.

Table 1. Significant relationships between soil and seedling indicators of nutrient supply.



alder in the conifer stand at CH1, CH2, and NM1, alder leaflitter and associated inputs of N and P extended between 8and 18 m into the conifer stands.

Discussion

Our light measurements and modeling simulations indi-cate that red alder stands cast shade for only a short distanceinto adjacent openings. Although there was some variationattributable to stand height, light reached levels consideredto be acceptable for Douglas-fir growth within 6 m of thealder stand edge. Alder litterfall extended 8–18 m into theadjacent conifer stands, which is consistent with other stud-ies (Miller and Murray 1978; Rhoades and Binkley 1992;Miller and Reukema 1993).

The measures of soil N and P availability indicated a clearinfluence of alder at the 45-year-old site (NM), but no appar-

ent influence at the 10-year-old site (CH) and occasionalsignificant effects at the 25-year-old site (MK). Binkley etal. (1994) reported influences of alder on soil N at severalsites in the Pacific Northwest, most of which were olderthan 25 years. Two exceptions are notable: a 23-year-oldstand near Nanaimo (Binkley 1983), at which a soil N effectwas evident, and a 50-year-old stand at Cascade Head,Washington, which did not show a significant increase insoil N. The 23-year-old stand was on a very infertile site,while the 50-year-old stand was on a very rich site. Thesefindings suggest that the alder effect on soil N will be de-tectable sooner on poor sites and may be undetectable onvery rich sites. The higher levels of mineralizable N in theconifer stand at NM1 probably reflect the presence of alderin this stand. The lack of NO3-N in the alder stand at NM2may be the result of inhibition of nitrification because of wetsoil conditions.

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Fig. 4. Amount of leaf litterfall (kg·ha–1·year–1) in alder standsof various ages. Circles represent data collected in this study; di-amonds are values from Radwan et al. (1984); squares are valuesfrom Zavitkovski and Newton (1971); triangles are values fromCole et al. (1995).

Alder Conifer

Nutrient Mean SE p value Mean SE

Cellulose (%) 30.03 0.67 0.001 33.35 0.62Lignin (%) 27.86 0.72 <0.001 39.64 1.32N (%) 2.29 0.07 0.001 1.46 0.05P (%) 0.08 0.01 0.046 0.07 0.00K (%) 0.24 0.02 0.004 0.10 0.01Ca (%) 1.26 0.10 <0.001 0.90 0.08Mg (%) 0.14 0.01 0.006 0.08 0.00S (%) 0.13 0.00 0.007 0.12 0.00Cu (g·m–3) 9.12 0.14 0.061 28.04 7.84Fe (g·m–3) 418.04 132.21 0.021 1709.16 377.55Mn (g·m–3) 266.56 32.89 0.307 303.42 11.60Zn (g·m–3) 33.88 1.41 0.153 39.35 4.26B (g·m–3) 17.16 3.43 0.045 10.62 1.22

Table 2. Carbon and nutrient concentrations in leaf litter of redalder and conifers and p values for differences between alder andconifer litter as determined by a paired t test.

Alder Conifer

Content Mean SE p value Mean SE

Mass 3986.44 423.65 0.013 2661.84 124.39N 93.91 11.37 <0.001 39.92 1.87P 3.99 0.42 <0.001 1.86 0.09K 8.88 1.19 <0.001 2.66 0.12Ca 51.92 4.75 <0.001 23.96 1.12Mg 6.29 0.54 0 2.05 0.10S 3.99 0.42 0.042 3.19 0.15Cu 0.04 0.004 0.010 0.08 0.003Fe 1.93 0.53 0.001 4.86 0.23Mn 1.04 0.17 0.175 0.80 0.04Zn 0.15 0.02 0.045 0.11 0.005B 0.07 0.004 0.001 0.03 0.001

Table 3. Mass and nutrient content of annual leaf litterfall(kg·ha–1·year–1) in adjacent alder and conifer stands and p valuesfor differences between alder and conifer stands as determinedby a paired t test.

Fig. 5. The relationship between the age of the alder stands andthe distance to which alder litter migrated from the alder standboundary. The line shown is described by the equation y =–7.7425 + 18.59log(age) (R2 = 0.80, p < 0.001).



The effect of alder on soil extractable P was less clear.Past studies have also shown substantial variation in theinfluence of red alder on soil P, with P both increasing(Giardina et al. 1995) and decreasing (Compton and Cole1998) in alder stands. These differences may be related todifferences in understory vegetation. The site at which P in-creased in the alder stand was dominated by R. spectabilis,whereas the site at which P declined in the alder stand wasdominated by P. munitum. Polystichum munitum and otherferns have high concentrations of P compared with other

understory vegetation (Turner et al. 1976), and its litter isnot preferred by first-order detritivores and other decom-posers (Carcamo et al. 2000). Thus, sequestration of P byP. munitum may inhibit expression of higher soil available Pin some alder stands. The absence of P. munitum in alderstands at Nanaimo Lakes may have contributed to the higheravailable P measured in soil in these stands. Polystichummunitum was more abundant at Malcolm Knapp, which mayhave contributed to the lack of increase in extractable soil Pin the alder stands at this site.

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62 Can. J. For. Res. Vol. 34, 2004

Fig. 6. Annual leaf litterfall mass, N content, and P content at points along transects from alder into adjacent conifer stands. The verti-cal line at 10 m represents the alder–conifer stand boundary. Significant (p < 0.05) differences were found for all transects exceptNM2. CH, Chilliwack site; MK, Malcolm Knapp Research Forest site; NM, Nanaimo site; 1, Transect 1; 2, Transect 2.

Statistics

Relationshipa Transectb Equation R2 p value

Litterfall mass and soil total C NM1 0.9797 + 0.00001x 0.80 0.004NM2 2.6048 + 0.00001x 0.80 <0.001

Litterfall N content and soil NO3-N NM1 0.1655 + 0.0001x 0.75 0.001NM2 0.2284 + 0.0002x 0.90 <0.001MK2 0.1655 + 0.001x 0.61 0.007

Litterfall P content and soil Bray P MK2 3.9211 + 0.0494x 0.73 0.002Litterfall P content and seedling %P NM1 0.5655 + 0.0046x 0.73 0.002Litterfall N content and seedling %N NM (comb.)c 0.4823 + 0.0066x 0.74 <0.001Litterfall B content and seedling %B NM (comb.)c 7.2346 + 99.55x 0.56 <0.001

aMass and nutrient contents are in kg·ha–1·year–1; total C is in %; NO3-N and Bray P are in g·m–3.bNM, Nanaimo Lakes site, MK, Malcolm Knapp Research Forest site.cTransects 1 and 2 combined.

Table 4. Significant relationships between litterfall and indices of soil nutrient supply.



The trends in N concentrations of the Douglas-fir seed-lings grown in soils from the transects mirrored the other es-timates of N availability in the soils. However, the trends inseedling P concentration did not correlate with estimates ofavailable P in soil measured using the Bray P1 method. Thissupports Cade-Menun and Lavkulich’s (1997) suggestionthat available P tested with the Bray P1 method is not agood measure of P availability in podzolic soils. Also, be-cause the Bray P1 technique does not include whole leavesand humus in the mineral soils extraction, some of the plant-available P will not be measured (Curran 1984).

Although soils under alder stands are prone to cationleaching owing to increased acidity, which has been attrib-uted to nitrification under the alder (Van Miegroet et al.1989; Binkley and Sollins 1990), we found only a smalleffect on soil pH and only in the oldest stands.

The correlations between inputs of N, P, and B in litterfalland indices of their availability in soil (i.e., extractable andmineralizable N or nutrient contents of Douglas-fir seedlingsgrown in soil from the same locations) suggest that thegreater nutrient supply in alder soils are the result of greaterinputs in alder litter. The results of the seedling bioassayalso indicate that the enhancement of nutrient supply underalder may extend into the next generation of trees, as hasbeen observed by Brozek (1990) and Compton and Cole(1998) in their studies of an alder cutover replanted withDouglas-fir.

The larger differences in nutrient supply between alderand conifer components in the older stands and greater spa-tial extent of the influence of alder litter with age may relateto changes in the distribution of alder and conifer crowns asstands age. In the 15-year-old stand (CH), migration of alderlitterfall into adjacent conifer stands was constrained toabout 5 m, probably because of the height of the alder. In the25-year-old stand (MK), canopy density and resistance ofthe neighbouring stand may have constrained litterfall to10 m. At this stage, leaf litter could penetrate the adjacentconifer stand by being blown in from underneath or overthe tops of the trees. As the conifers reach pole stage(~20 years) and the crowns lift, the adjacent alder canopy islower than the base of the conifer crown, allowing for morealder litter ingress from below. This was reflected in themigration of litter (>10 m) in the 45-year-old stands (NM).

Management implicationsThe results of this study indicate that reductions in light

levels adjacent to a patch of red alder create conditions thatare unfavourable for Douglas-fir (at a height of 1.4 m) forless than 6 m from the alder stand edge, whereas improvedsoil nutrient supply extends about 10 m from the stand. Al-der strips or patches should be at least 10 m wide to promotegood stem form (Peterson et al. 1996). Therefore, the opti-mal arrangement for mixtures of alder and conifer would bealder patches or strips at least 10 m wide and about 20 mapart. A north–south orientation of such strips would mini-mize shading effects, although such shading effects appearedto be minor. Such a system would maximize the improvednutrient availability due to alder, provide good stem formwithin each alder patch, and minimize light competition be-tween the conifers and the alder.

Changes in soil nutrient supply along alder–conifertransects were closely related to the distribution of alderlitterfall. Thus, the beneficial effect of alder on soil nutrientsupply can be predicted by the spatial distribution of itslitter. Some management practices that would encouragemovement of alder litter into adjacent conifer stands are(i) planting conifers downslope of alder or on the lee side ofprevailing winds, (ii) planting conifers within 10 m of thealder stand, and (iii) early stem pruning of conifers to facili-tate influx of alder litter.

Acknowledgements

We thank Clive Dawson and David Dunn at the B.C. Min-istry of Forests’ Glyn Road Analytical Laboratory for assis-tance with soil and tree tissue analysis. We also thank SarahHarper, Ben Andrew, Angela Plautz, Christina Cockle, andHolger Wernsdorfer for their assistance in the field and thelaboratory. Funding support by Forest Renewal British Co-lumbia (research project HQ96400-RE) and support fromthe B.C. Ministry of Forests is gratefully acknowledged.

References

Berry, A.B. 1964. Effect of strip width on proportion of daily lightreaching the ground. For. Chron. 40: 130–131.

Binkley, D. 1983. Ecosystem production in Douglas-fir plantations:interaction of red alder and site fertility. For. Ecol. Manage. 5:215–227.

Binkley, D. 1992. Mixtures of N2-fixing and non-N2-fixing treespecies. In The ecology of mixed species stands of trees. 1.Edited by M.G.R. Cannell, D.C. Malcolm, and P. Robertson.Blackwell Scientific Publishing, Boston. pp. 99–123.

Binkley, D., and Sollins, P. 1990. Factors determining differencesin soil pH in adjacent conifer and alder-conifer stands. Soil Sci.Soc. Am. J. 54: 1427–1433.

Binkley, D., Sollins, P., Bell, R., Sachs, D., and Myrold, D. 1992.Biogeochemistry of adjacent conifer and alder–conifer stands.Ecology, 73: 2022–2033.

Binkley, D., Cromack K., Jr., and Baker, D.D. 1994. Nitrogen fixa-tion by red alder: biology, rates, and controls. In The biologyand management of red alder. 1. Edited by D.E. Hibbs,D.S. DeBell, and R.F. Tarrant. Oregon State University Press,Corvallis, Ore. pp. 57–72.

Bormann, B.T., Cromack K., Jr., and Russell, W.O. 1994. Influ-ences of red alder on soils and long-term productivity. In Thebiology and management of red alder. 1. Edited by D.E. Hibbs,D.S. DeBell, and R.F. Tarrant. Oregon State University Press,Corvallis, Ore. pp. 47–56.

Brozek, S. 1990. Effect of soil changes caused by red alder (Alnusrubra) on biomass and nutrient status of Douglas-fir (Pseudo-tsuga menziesii) seedlings. Can. J. For. Res. 20: 1320–1325.

Cade-Menun, B.J., and Lavkulich, L.M. 1997. A comparison ofmethods to determine total, organic and available phosphorus inforest soils. Commun. Soil Sci. Plant Anal. 28: 651–663.

Carcamo, H.A., Abe, T.A., Prescott, C.E., Holl, F.B., and Chan-way, C.P. 2000. Influence of millipedes on litter decomposition,N mineralization, and microbial communities in a coastal forestin British Columbia, Canada. Can. J. For. Res. 30: 817–826.

Carter, R.E., and Klinka, K. 1992. Variation in shade tolerance ofDouglas-fir, western hemlock, and western red cedar in coastalBritish Columbia. For. Ecol. Manage. 55: 87–105.

© 2003 NRC Canada

Lavery et al. 63



Cole, D.W., Compton, J.E., Edmonds, R.L., Homann, P.S., and VanMigroet, H. 1995. Comparison of carbon accumulation inDouglas-fir and red alder forests. In Carbon forms and functionsin forest soils. Edited by W.W. McFee and J.M. Kelly. Soil Sci-ence Society of America Inc., Madison, Wis. pp. 527–546.

Cole, E.C., and Newton, M. 1986. Nutrient, moisture, and lightrelations in 5-year-old Douglas-fir plantations under variablecompetition. Can. J. For. Res. 16: 727–732.

Comeau, P.G. 1996. Why mixedwoods? In Silviculture of temper-ate and boreal broadleaf–conifer mixtures. 1. Edited byP.G. Comeau and K.D. Thomas. B.C. Ministry of Forests, Victo-ria, B.C. pp. 1–7.

Comeau, P.G., and Sachs, D. 1992. Simulation of the consequencesof red alder management on the growth of Douglas-fir usingFORCYTE-11. B.C. Ministry of Forests, Victoria, B.C. ForestResources Development Agreement (FRDA) Rep. 187.

Comeau, P.G., Gendron, F., and Letchford, T. 1998. A comparisonof several methods of estimating light under a paper birchmixedwood stand. Can. J. For. Res. 28: 1843–1850.

Comeau, P.G., Macdonald, R., Bryce, R. 2001a. SLIM — spotlight interception and transmittance estimator version 2.1. B.C.Ministry of Forests, Victoria, B.C.

Comeau, P.G., Macdonald, R., Bryce, R. 2001b. LITE — light in-terception and transmittance estimator version 2.1. B.C. Minis-try of Forests, Victoria, B.C.

Compton, J.E., and Cole, D.W. 1998. Phosphorus cycling and soilP fractions in Douglas-fir and red alder stands. For. Ecol. Man-age. 110: 101–112.

Curran, M.P. 1984. Soil testing for phosphorus availability to someconifers in British Columbia. Ph.D. thesis, The University ofBritish Columbia, Vancouver, B.C.

Giardina, C., Huffman, S., Binkley, D., and Caldwell, B.A. 1995.Alders increase soil phosphorus availability in a Douglas-firplantation. Can. J. For. Res. 25: 1652–1657.

Green, R.N., Trowbridge, R.L., and Klinka, K. 1993. Towards ataxonomic classification of humus forms. For. Sci. Monogr. 29:1–49.

Groot, A., Carlson, D.W., Fleming, R.L., and Wood, J.E. 1997.Small openings in trembling aspen forest: microclimate and re-generation of white spruce and trembling aspen. Natural Re-sources Canada, Sault Ste. Marie, Ontario. Northern OntarioDevelopment Agreement / National Forest Programme(NODA/NFP) Tech. Rep. TR-47.

Hibbs, D.E., and DeBell, D.S. 1994. The management of youngred alder. In The biology and management of red alder. 1.Edited by D.E. Hibbs, D.S. DeBell, and R.F. Tarrant. OregonState University Press, Corvallis, Ore. pp. 202–215.

Insightful Corporation. 2002. S-Plus 6.1 for Windows statisticalsoftware. Seattle, Wash.

Kalra, Y.P., and Maynard, D.G. 1991. Methods manual for forestsoil and plant analysis. Can. For. Serv. North. For. Res. Cent.Inf. Rep. NOR-X-319.

Lieffers, V.J., Messier, C., Stadt, K.J., Gendron, F., and Comeau,P.G. 1999. Predicting and managing light in the understory ofboreal forests. Can. J. For. Res. 29: 796–811.

Mailly, D., and Kimmins, J.P. 1997. Growth of Pseudotsugamenziesii and Tsuga heterophylla seedlings along a light gradi-ent: resource allocation and morphological acclimation. Can. J.Bot. 75: 1424–1435.

McComb, W.C. 1994. Red alder: interactions with wildlife. In Thebiology and management of red alder. 1. Edited by D.E. Hibbs,D.S. DeBell, and R.F. Tarrant. Oregon State University Press,Corvallis, Ore. pp. 131–140.

Meidinger, D., and Pojar, J. 1991. Ecosystems of British Columbia.B.C. Ministry of Forests, Victoria, B.C.

Miller, E.K., and Murray, M.D. 1978. The effects of red alder ongrowth of Douglas-fir. U.S. Dep. Agric. For. Serv. Gen. Tech.Rep. PNW-70.

Miller, R.E., and Reukema, D.L. 1993. Size of Douglas-fir trees inrelation to distance from a mixed red alder – Douglas-fir stand.Can. J. For. Res. 23: 2413–2418.

Nyland, R.D. 1996. Silviculture — concepts and applications.McGraw Hill, Boston, Mass.

Peterson, E.B., Ahrens, G.R., and Peterson, N.M. 1996. Red aldermanager’s handbook for British Columbia. B.C. Ministry ofForests, Victoria, B.C. Forest Resources Development Agree-ment (FRDA) Rep. 240.

Radwan, M.A., Harrington, C.A., and Kraft, J.M. 1984. Litterfalland nutrient returns in red alder stands in western Washington.Plant Soil, 79: 343–351.

Rhoades, C.C., and Binkley, D. 1992. Spatial extent of impact ofred alder on soil chemistry of adjacent conifer stands. Can. J.For. Res. 22: 1434–1437.

Shainsky, L.J., and Radosovich, S.R. 1992. Mechanisms of compe-tition between Douglas-fir and red alder seedlings. Ecology,733: 30–45.

Shainsky, L.J., Yoder, B.J., Harrington, T.B., and Chan, S.S.N.1994. Physiological characteristics of red alder: water relationsand photosynthesis. In The biology and management of redalder. 1. Edited by D.E. Hibbs, D.S. DeBell, and R.F. Tarrant.Oregon State University Press, Corvallis, Ore. pp. 73–91.

Turner, J., Cole, D.W., and Gessel, S.P. 1976. Mineral nutrient ac-cumulation and cycling in a stand of red alder (Alnus rubraBong.). J. Ecol. 64: 965–974.

Van Miegroet, H., Cole, D.W., Binkley, D., and Sollins, P. 1989.The effect of nitrogen accumulation and nitrification on soilchemical properties in alder forests. In Effects of air pollutionon western forests. Edited by R. Olson and A. Lefohn. Air andWaste Management Association, Pittsburgh, Pa. pp. 515–528.

Zavitkovski, J., and Newton, M. 1971. Litterfall and litter accumu-lation in red alder stands in western Oregon. Plant Soil, 35:257–268.

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The influence of red alder patches on light, litterfall, and soil nutrients in adjacent conifer stands