Growth and Survival of Jack Pine Exposed to Simulated Acid Rain as SeedlingsNeil W. MacDonald* and Brandon J. Ducsay

ABSTRACTIn a previous study, jack pine (Pinus banksiana Lambert) seedlings

grown under pH 2.5 simulated rain had larger shoot/root ratios andaltered nutrition compared with seedlings grown with pH 4.7 rain.The objective of this study was to determine if these differences ininitial seedling characteristics produced long-term effects on survivalor growth of outplanted seedlings. Significantly (P < 0.05) greaterdiameter increment (4.3 vs. 4.0 cm) between ages 6 and 10 of jackpine treated with pH 2.5 rain as seedlings was consistent with acarryover effect from the initial treatments. However, no differencesbetween treatments in jack pine diameter, height, or survival persistedto age 14. Results support recent recommendations that extendedmeasurement periods may be necessary to fully assess the long-termeffects of pollutant increases or decreases on growth of immaturetrees.

EARLY RESEARCH into the effects of atmospheric pollut-ants on forest ecosystems focused on the short-term

impacts of acutely acidic simulated rain applied to seeds,seedlings, and soils under greenhouse conditions (Woodand Bermann, 1977; Lee and Weber, 1979; McColl andJohnson, 1983). One difficulty encountered with studiesof this type was the inability to infer long-term, chroniceffects of moderately acidic precipitation (pH 4.3 to 4.5)on mature forests from the results of short-term, acutelyacidic treatments on seedlings (Peterson and Mickler,1994). While a few studies have investigated the growthof seedlings immediately following the cessation of ex-perimental treatments (Jacobsen et al., 1990; Sasek etal. 1991; Sheppard et al., 1993), Peterson and Mickler(1994) recommended multi-year observations followingcessation of treatments to assess the long-term effects ofacute pollutant stress experienced only during the seed-ling stage. Given the large number of studies that haverelied on seedlings as test subjects to assess pollutantimpacts, the absence of literature on the long-term growthof surviving seedlings is remarkable.

When jack pine seedlings were germinated and grownwith simulated acid rain at pH levels 2.5 to 4.7, seedlingtop weights were greatest and root weights were leastfor seedlings grown at pH 2.5 (MacDonald et al., 1986).Foliar nutrient relations also were altered by these treat-ments, with seedlings grown at pH 2.5 being higher inN, K, and Ca but lower in P and Mg than seedlingsgrown at pH 4.7. MacDonald et al. (1986) hypothesizedthat because of larger shoot/root ratios (2.1:1 vs. 1.3:1) and altered nutrition, the seedlings grown at pH 2.5would be less well adapted to moisture stresses or nutrientlimitations than the seedlings grown at pH 4.7. If thiswas true, growth or survival of seedlings raised at pH2.5 would be less than that of seedlings grown at pH

Natural Resources Management Program, Dep. of Biology, Grand ValleyState Univ., AJlendale, MI 49401-9403. Received 9 Jan. 1996. "Corre-sponding author (macdonan@gvsu.edu).

Published in Soil Sci. Soc. Am. J. 61:295-297 (1997).

4.7. To test this hypothesis, surviving seedlings fromthe experiment were outplanted. The objective of thisstudy was to determine if survival or growth of outplantedjack pine during a 12-yr period differed as a result ofexposure to different acid rain treatments during theseedling stage.

A detailed description of the methods and results of theoriginal study of simulated acid rain effects on jack pine seedlingestablishment, seedling nutrition, and seedbed soil propertiesis contained in MacDonald et al. (1986). Seedlings were raisedfrom seed representing genotypes found in northern lowerMichigan (MacDonald et al., 1986). Following the completionof the greenhouse study in September, 1981, surviving seed-lings were maintained in their seedbed soils without furthertreatment in a shade house at the Michigan State UniversityTree Research Center (East Lansing, MI). In October, 1982,the seedlings were outplanted in Section 4, T6N R15W, OliveTownship, Ottawa County, MI (elevation 190 m). Seedlingswere not remeasured prior to planting.

The study site is located within the native range of jackpine near its southern extent (Fowells, 1965). Mean annualprecipitation totals 802 mm, with =57% of the total fallingbetween April and September (Pregitzer, 1972). Annual pollut-ant deposition rates, estimated from monitoring sites in nearbycounties (MacDonald et al., 1993), are =21 kg SOS" ha~',15 kg NO3~ ha"1, and 4 kg Nrtf ha~'. These deposition ratesclosely approximate S and N input rates experienced by seed-lings raised at pH 4.7. Annual hydrogen ion deposition is 0.36kg H+ ha"1, with a mean rain pH of 4.35.

Soils at the study site are sandy, mixed, mesic Entic Haplor-thods (Grattan series). The plantation was laid out in a random-ized complete-block design, with a total of six blocks eachcomprising two adjacent plots. Blocks were located to be assimilar as possible in topography, surface soil characteristics,and potential for shading by adjacent plantations. Becausedifferences in seedbed soil (A/E or Bwl horizon) in the green-house study had produced differences in growth of seedlings(MacDonald et al., 1986), differences among groups of seed-lings in seedbed soils also were incorporated as a block effect.Groups of 16 seedlings initially exposed to either pH 2.5 orpH 4.7 rain then were randomly assigned to plots within blocks.Seedlings were planted on a 2 by 2 m spacing, with eachexperimental plot surrounded by one row of nonexperimentalseedlings, and the entire plantation was surrounded by anadditional row of nonexperimental seedlings.

In early May, 1995, we measured the diameters of allsurviving trees to the nearest 0.05 cm at 1.3 m above theground with a diameter tape. We measured total heights tothe nearest centimeter with a telescoping fiberglass measuringpole. Repeated measurement errors, determined from replicatemeasurements of two trees per plot, were 0.5% for diameterand 0.6% for total height. Survival was determined by thenumber of experimental trees alive on each plot. To examinethe progression in growth since 1982, we identified the fourcodominant trees on each plot closest to plot mean height anddiameter and randomly selected one tree per plot from these

Abbreviations: *, ** Significant at the 0.05 and 0.01 probability levels,respectively.

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296 SOIL SCI. SOC. AM. J., VOL. 61, JANUARY-FEBRUARY 1997

groups for stem analysis. We cut cross sections at locationsalong the stem at 0.1, 0.15, 0.5, 1.0, 2.0, 3.0, and 4.0 mabove the ground. Inside-bark diameters, determined as thegeometric mean of the major and minor diameters of samplecross sections (Husch et al., 1972), were measured to thenearest 0.5 mm at the outer edges of rings corresponding totree ages of 6, 10, and 14 yr. Diameter increments betweenthese ages were determined for each cross section as thedifference between successive inside-bark diameters.

We sampled the upper 15 cm of mineral soil on each plotby collecting four composite samples per plot, each composedof three randomly located 4.5-cm-diameter cores. We alsosampled the O- to 50-, 50- to 100-, and 100- to 150-cm soildepths at two locations on each plot using a bucket auger. Allsoil samples were analyzed for pH (1:1 soil/water), organicC (H2SO4-K2Cr2O7 oxidation), and texture (hydrometer). Re-peated measurement errors, based on 17% sample replication,were 0.5% for pH, 7.2% for organic C, and 12.3% forpercentage silt + clay.

Analyses of variance for current growth, survival, and soilproperty data were performed using unweighted plot means.We analyzed stem diameter data by height and soil propertydata by depth using repeated measures analysis (SYSTAT;Wilkinson, 1989). We tested all data for homogeneity of vari-ance using Bartlett's test and for normality using Lilliefors'test (Wilkinson, 1989). No serious departures from the assump-tions of equal variance and normality were detected, exceptfor diameter increments between ages 10 and 14 and inside-barkdiameters at age 14. Non-normality in these data was relatedto rapid growth after age 10 of one tree sampled from a pH4.7 plot with very low tree density (56% survival). Removalof the data from this tree from analyses of variance did notproduce or diminish any significant effects compared withstatistical analyses incorporating all data, so results based onanalyses of the complete data set have been reported. Pearsoncorrelations, based on plot means (n = 12), were used toassess the degree of association among growth measures, plottree densities, and soil properties. Based on results of correla-tion analyses, pH, organic C, and silt + clay at various depthswere tested as covariates in analyses of growth measures.

RESULTS AND DISCUSSIONSoil physical and chemical properties did not differ

significantly between plots allocated to the two treatments(Table 1). Similarly, results of repeated measures analy-ses indicated no significant (P = 0.29 to 0.93) treatmentX depth or block X depth interactions for pH, organicC, and percentage silt + clay, suggesting that differencesin soil properties did not affect treatment means forjack pine growth and survival. Soils on all plots werecoarse-textured, acidic, and low in organic C, typicalof the poorer soils occupied by jack pine (Fowells, 1965).The overall range in soil properties (Table 1) did confirmthe need to investigate selected soil properties as covari-ates in analyses of growth and survival data.

Mean tree diameter, height, and survival at age 14did not differ significantly between treatments (Table 2).We did not observe any stumps or dead trees at the sitein 1995, consistent with early seedling mortality andpersistence of remaining trees once established. Theprobability level for block effects (Table 2) suggests thatsurvival was associated with environmental conditionsrelated to block locations or soil characteristics. Soilproperties did not serve as significant covariates for

Table 1. Soil property means and ranges at jack pine seedlingoutplanting site in Section 4, T6N R15W, Ottawa County,Michigan.

Soil propertyand depth

Silt + Clay, %0-15 cm0-50 cm50-100 cm100-150 cm

Organic C, %0-15 cm0-50 cm50-100 cm100-150 cm

pH2.5plots

3.53.26.55.1

0.410.250.250.13

++±±

±±+±

0.510.72.21.7

0.040.030.070.06

pH4.7plots

3.44.96.65.1

0.440.330.200.14

±+±+

±+±±

0.61.92.62.0

0.050.120.070.09

Ranget

3.0-4.52.5-7.53.8-10.52.0-8.0

0.35-0.530.20-0.520.11-0.360.07-0.28

P-T*

0.770.100.930.98

0.200.200.300.87

P-B§

0.210.480.870.25

0.430.720.620.76

PH0-15 cm 4.26 ± 0.07 4.23 ± 0.07 4.16-4.36 0.20 0.010-50 cm 4.34 + 0.10 4.34 ± 0.07 4.20-4.50 1.00 0.0250-100 cm 4.51 + 0.13 4.55 ± 0.31 4.30-5.15 0.77 0.29100-150 cm 4.93 + 0.26 4.89 ± 0.32 4.50-5.40 0.83 0.29

t Range in plot means.t Significance probability from ANOVA related to treatments (T).§ Significance probability from ANOVA related to blocks (B).1 Mean + standard deviation, n = 6 plots per treatment.

survival, diameter, or height at age 14, since most vari-ability in soil properties already was incorporated as ablock effect.

Stem analysis did not reveal any significant differencesbetween treatments in early diameter growth except fordiameter increment between ages 6 and 10, which wasgreater in jack pine treated with pH 2.5 rain as seedlings(Table 2). This effect did not persist, as there were nosignificant differences between treatments in diameterincrement between ages 10 and 14 or in inside-barkdiameters at age 14 (Table 2). Mean inside-bark diame-ters at ages 6 and 10 tended to be positively correlatedwith plot plus buffer tree densities (r = 0.37 to 0.65*)but were not correlated with soil properties. In contrast,mean diameter increments between ages 10 and 14 andmean inside-bark diameters at age 14 were negativelycorrelated with plot plus buffer tree densities (r = — 0.67 *to -0.88**). These relationships are consistent withstand density becoming a factor restricting diametergrowth only after canopy closure became complete. Be-tween ages 6 and 10, significantly greater mean diameterincrement in seedlings treated with pH 2.5 rain (Table2) was consistent with a carryover effect from earlysimulated rain treatments. No soil property variable was asignificant covariate in the analysis of diameter incrementdata, suggesting that significant treatment effects werenot attributable to underlying variation in soil properties.

Seedlings treated with pH 2.5 rain initially had largertops with higher N concentrations, both related to greaterN input from acidified rain (75-d input of 29.8 kg Nha~' compared with 2.2 kg N ha"1; N.W. MacDonald,1995, unpublished data). Resulting seedling characteris-tics appear to have had a positive effect on early growth,in contrast to the originally hypothesized negative effectsof higher shoot/root ratios and altered nutrition. In oneof the few studies examining carryover rain chemistrytreatment effects, Sheppard et al. (1993) found that expo-sure of red spruce (Picea rubens Sarg.) seedlings to acidicmists containing N significantly increased the weightand length of shoots the summer following cessation of

MACDONALD & DUCSAY: JACK PINE SEEDLING SURVIVAL AND GROWTH 297

Table 2. Growth and survival of jack pine exposed to differentlevels of simulated acid rain as seedlings.

Initial treatment pH

Variable pH2.5 pH 4.7 P-Tf P-BJ

Diameter, cm§Height, mttSurvival, %DIBtt, age 6, cmDIM, age 6 to 10DIB, age 10DI, age 10 to 14DIB, age 14

8.47 ± 0.6014.61 ± 0.1871.9 ± 15.21.36 ± 0.294.26 ± 0.224.91 ± 0.383.84 ± 0.356.99 ± 0.40

8.30 ± 0.754.53 + 0.2678.1 ± 11.71.27 ± 0.304.02 ± 0.204.66 ± 0.364.09 ± 1.197.00 ± 0.83

0.710.650.280.650.040.250.580.99

0.690.970.090.690.150.350.230.56

t Significance probability from ANOVA related to treatments (T).t Significance probability from ANOVA related to blocks (B).§ Diameter outside bark measured at 1.3 m, age 14.1 Mean ± standard deviation, n = 6 plots per treatment.tt Total height, age 14.tt Diameter inside bark (DIB), means based on repeated measures of stem

cross sections within trees, n = 4 per tree at age 6, n = 5 per tree atage 10, and n = 7 per tree at age 14.

tt Diameter increment (DI), means based on repeated measures of stemcross sections within trees, n = 4 per tree for age 6 to 10, and n = 5per tree for age 10 to 14.

treatments, supporting the plausibility of the carryoverresponse observed in jack pine.

Peterson and Mickler (1994) note that changes indiameter are less important than changes in height forearly seedling competitiveness. In this study, the absenceof significant differences in growth measures at age 14illustrates this point in that differences in early diametergrowth did not improve competitiveness as jack pineattained sapling size. The absence of negative effectsrelated to initially greater shoot/root ratios demonstratedthat jack pine exposed to acutely acidic deposition asseedlings readily adjusted to local site conditions afteroutplanting and equalization of pollutant exposure. Simi-larly, Archibold (1978) reported that the growth of sap-ling lodgepole pine (Pinus contorta Douglas ex. Loudon)in British Columbia, severely reduced by 25 yr of SC»2fumigation, resumed normal rates after levels of emis-sions were substantially reduced. Similar resilience ofseedlings or saplings in forest ecosystems experiencingreductions from extremely elevated pollutant stresswould not be expected where ecosystem properties havebeen irrecoverably affected by previous pollutant deposi-tion (e.g., smelter-derived SO2, acidic precipitation, andheavy metal contamination, as reported by Freedmanand Hutchinson, 1980).

The positive carryover effects in this study were subtle,were not fully expressed until several years after cessationof original treatments, and were contrary to the originallyhypothesized negative effects. The persistence of signifi-cant effects 9 yr after cessation of original treatmentssuggests that experiments designed to assess the effectsof pollutant reductions on seedling or tree growth mayneed to be longer than commonly used intervals of severalyears (Thornton et al., 1992). Results of this study sup-port the conclusions of Kelly et al. (1993) that short-termstudies of seedling growth may be of only limited valuein prediction of long-term responses to atmospheric pol-

lutant increases or decreases. Our results also supportthe recommendation made by Peterson and Mickler(1994) that multi-year observations of seedlings follow-ing initial periods of pollutant exposure may be necessaryto fully assess long-term treatment effects.

ACKNOWLEDGMENTSThis study was supported by the Summer Undergraduate

Research Program of the GVSU Science and MathematicsDivision. James B. Hart, Roy Prentice, and Randall Kuipersprovided advice and assistance during the initial phases of thisstudy. We thank the Ottawa Soil and Water ConservationDistrict and the Ottawa County Parks and Recreation Depart-ment for their cooperation.