Dendroecology of American chestnut in a disjunctstand of oak–chestnut forest

Ryan W. McEwan, Carolyn H. Keiffer, and Brian C. McCarthy

Abstract: American chestnut (Castanea dentata (Marsh.) Borkh.) was once an important hardwood species in the for-ests of eastern North America. Following the chestnut blight fungus (Cryphonectria parasitica (Murrill) Barr) pandemicof the early 20th century, C. dentata remains only as sprouts throughout much of its range. We conducted a dendroecologicalanalysis of a large naturalized stand of mature C. dentata to evaluate the species’ growth capacity, ecology, and restora-tion potential. Eestablishment of C. dentata was sporadic in the first 40 years of our chronology, followed by a disturbance-associated recruitment pulse. The species appears to be tolerant of suppression in the understory, but responded to releasewith rapid radial growth (>10 mm·year–1). Although its climate–growth relationships are similar to those of other hard-wood species, mean radial growth of C. dentata was nearly twice that of other hardwood species found in the stand(4.7 ± 0.21 vs. 2.5 ± 0.16 mm·year–1). Chestnut blight has recently infected this stand, resulting in a sharp depressionin the growth chronology of C. dentata, even when outward signs of infection were not yet visible. Observed establish-ment and growth patterns suggest that blight-resistant C. dentata is likely to attain dominance rapidly in forests whererestoration efforts include canopy manipulations that increase light availability.

Résumé : Le châtaignier d’Amérique (Castanea dentata (Marsh.) Borkh.) fut à une certaine époque une espèce feuillueimportante dans les forêts de l’est de l’Amérique du Nord. Depuis l’épidémie de la brûlure du châtaignier (Cryphonec-tria parasitica (Murrill) Barr) du début du 20e siècle, C. dentata est demeuré seulement à l’état de rejets presque par-tout dans son aire de répartition. Les auteurs ont réalisé une étude dendroécologique dans un vaste peuplementnaturalisé de C. dentata mature pour évaluer le potentiel de croissance, l’écologie et la possibilité de restauration de C.dentata. L’établissement de C. dentata a été sporadique pendant les 40 premières années de la chronologie suivi par unregain de recrutement associé à une perturbation. L’espèce semble être tolérante à la suppression en sous-étage mais aréagi au dégagement avec une croissance radiale rapide (>10 mm·an–1). Bien que les relations entre le climat et lacroissance soient semblables à celles des autres essences feuillues, la croissance radiale moyenne de C. dentata étaitprès de deux fois plus élevée que celle des autres espèces présentes dans le peuplement (4,7 ± 0,21 versus 2,5 ± 0,16mm·an–1). La brûlure du châtaignier a récemment infecté ce peuplement causant une diminution abrupte dans la chro-nologie de la croissance de C. dentata avant même que des signes évidents d’infection soient visibles. Les patronsd’établissement et de croissance observés indiquent qu’un C. dentata résistant à la brûlure deviendrait probablement ra-pidement dominant dans les forêts où les efforts de restauration incluent des manipulations de la canopée qui augmen-tent la disponibilité de la lumière.

[Traduit par la Rédaction] McEwan et al. 11

Introduction

One of the most important biological events in the historyof the postglacial Eastern Deciduous Forest was the demiseof the American chestnut (Castanea dentata (Marsh.) Borkh.)caused by the exotic and pathogenic fungus Cryphonectriaparasitica (Murrill) Barr (chestnut blight). When C. parasiticawas introduced in the early 1900s, C. dentata was a domi-nant species in many forests of eastern North America (Russell1987), comprising more than 50% of the basal area of somestands (Braun 1950; Nelson 1955). By 1950, chestnut blight

had spread throughout much of eastern North America andby the 1960s, C. dentata had been all but extirpated (Keever1953; Good 1968; McCormick and Platt 1980). Throughoutmost of its native range, C. dentata is currently representedonly by seedling and stump sprouts, which grow until theyreach approximately 10 cm DBH (diameter at 1.37 m) andare then killed back by the blight (Paillet 1984, 1988).

The loss of C. dentata had a substantial influence on theforests of eastern North America. In effect, this loss createda vacuum in canopy dominance which initiated dynamicsthat are likely still important and ongoing (Keever 1953;McCormick and Platt 1980). Because of the historical im-portance of C. dentata, breeding programs have been devel-oped that aim to create a blight-resistant hybrid possessingthe ecological attributes of C. dentata (Hebard 1994; Hebard2001). These programs are coming to fruition and blight-resistant planting stock may be available within the next de-cade. Experimental C. dentata restoration is already underway(Brosi 2001; McCament and McCarthy 2005). The successof these efforts may be constrained by our ecological under-standing of how C. dentata functions in a forest setting.

Can. J. For. Res. 36: 1–11 (2006) doi:10.1139/X05-218 © 2006 NRC Canada

1

Received 15 March 2005. Accepted 16 September 2005.Published on the NRC Research Press Web site athttp://cjfr.nrc.ca on 12 January 2006.

R.W. McEwan1 and B.C. McCarthy. Department ofEnvironmental and Plant Biology, 315 Porter Hall, OhioUniversity, Athens, OH 45701, USA.C.H. Keiffer. Department of Botany, 4200 E UniversityBoulevard, Miami University, Middletown, OH 45042, USA.

1Corresponding author (e-mail: ryan.w.mcewan.1@ohio.edu).

Ecological understanding of how C. dentata performs rel-ative to potential competitors in a forest setting has beenlimited by the fact that the blight occurred before the adventof modern ecological techniques. For instance, much of ourunderstanding of C. dentata ecology comes from observa-tional studies (Braun 1950), or studies that took place instands where chestnut blight already had a significant influ-ence (Keever 1953; Good 1968; McCormick and Platt 1980;McEwan et al. 2005). Studies of C. dentata seedling andstump sprouts have provided much of our current knowledgeof the species (Paillet 1984, 1988, 2002). Remnant standscontaining C. dentata can still be found; however, these standshave been strongly influenced by blight infection (Brewer1995; Tindall et al. 2004). Perhaps the largest remainingstand of mature C. dentata is a forested site in West Salem,Wisconsin (Paillet and Rutter 1989). This stand originatedfrom a few transplanted propagules and is separated fromthe native range of C. dentata by several hundred kilometres.Because this distance was greater than the natural dispersalrange of blight inoculum, the site remained blight-free untilthe late 1980s (Paillet and Rutter 1989). This area also con-tains many of the hardwood species that are found within thenative range of C. dentata. Therefore, this stand represents aworkable facsimile of preblight forests and offers an unusualopportunity for the study of C. dentata growing as a canopytree in a forest setting (Paillet and Rutter 1989).

We used tree-ring analysis, or dendroecology, in the WestSalem stand to investigate the ecology of C. dentata. Dendro-ecology is a proven method for reconstructing forest dynamicsand elucidating the ecology of individual species and eco-systems (Henry and Swan 1974; Kipfmueller and Swetnam2001; Soulé et al. 2004). Dendroecological analysis is par-ticularly useful in the West Salem stand because it allows forthe quantification of ecological relationships prior to the ar-rival of chestnut blight in the stand. The objectives of ourstudy were to (i) compare establishment dynamics betweenC. dentata and other hardwood species, (ii) test the com-monly held notion that C. dentata grows faster than otherhardwood species, and (iii) examine the relationship betweenC. dentata growth parameters and climatic variables.

Materials and methods

Study-site descriptionThe study site in West Salem (43°53′N, 91°04′W) is located

more than 600 km west of the natural range of C. dentata(Paillet and Rutter 1989). Soils of the study area are sandyand mildly acidic and exposed sandstone is found in severalareas of the stand (Paillet and Rutter 1989). These conditionsare similar to those found in areas of maximum C. dentatadominance throughout its native distribution (Keever 1953;Russell 1987). Mean annual precipitation and summer tem-perature at the study site (75 cm and 21 °C, respectively) aresimilar to those found at the northernmost limits ofC. dentata’s native distribution; however, the mean wintertemperature is 6 °C lower (–16 vs. –10 °C; Paillet and Rutter1989). The study site is classified as dry-mesic upland forestin the prairie–forest floristic province of Curtis (1959).These are generally closed-canopy forests in which Quercusalba L., Quercus rubra L., and Quercus velutina Lam. arecanopy dominants and Carya ovata (Mill.) K. Koch, and

Populus grandidentata Michx., among others, are minorcomponents (Curtis 1959).

In 1907, a resident of West Salem planted approximatelynine C. dentata propagules that had been collected in thecentral Appalachian region (Paillet and Rutter 1989). Be-cause West Salem is far outside C. dentata’s native range, itwas outside the initial range of the chestnut blight fungus.Therefore, these propagules grew into large, sexually maturetrees and began seeding into the surrounding woodlands.Castanea dentata currently comprises 37% of the basal areain these woodlands (B.C. McCarthy and C.H. Keiffer, un-published data), and the native oaks (Quercus spp.) andhickories (Carya spp.) were being “replaced” prior to the ar-rival of chestnut blight in the late 1980s (Paillet and Rutter1989). The vegetation of the site is characterized in detail byPaillet and Rutter (1989). Botanical nomenclature followsGleason and Cronquist (1991).

Field and laboratory methodsIn the summer of 2001, 30 permanent plots (500 m2) were

established throughout the West Salem stand using a stratifiedrandom sampling scheme. At each plot, all stems ≥2.5 cm indiameter were identified to species, tagged, measured, andmapped. In late February of 2002, at each plot, a single in-crement core was collected at a height of 1.37 m from thelargest C. dentata, a randomly chosen healthy C. dentata, asymptomatically blight-infected C. dentata, and the largestnon-C. dentata tree. This sampling scheme was designed toallow comparison of non-C. dentata hardwood species withC. dentata and also comparison of healthy and diseasedC. dentata stems. Of the 30 plots, 16 did not contain repre-sentatives of all three C. dentata categories, and on 3 plots,more than one of the samples was collected from an infectedstem, owing to the unavailability of healthy specimens.Characteristics used to identify blight-infected C. dentatastems included cankers or abnormal fissures on the trunk,profuse epicormic branching, dark orange pustules on thestem, wilted or brown leaves attached to branches in the can-opy, and patches of dieback in the crown. Cores were storedin paper straws and transported to Ohio University for pro-cessing and data collection.

Each core was first glued into a slotted wooden mount fol-lowing the general procedure outlined by McCarthy (2001).Cores were then sanded with increasingly fine grit sandpaperto obtain a clean surface upon which anatomical features werevisible with the use of a dissecting microscope (Stokes andSmiley 1996; McCarthy 2001). Cores were cross-dated using“pointer years” (Fritts 1976; Yamaguchi 1991; Stokes andSmiley 1996). Annual increments were measured to the near-est 0.01 mm using an Olympus SZ40 boom dissecting micro-scope (40×), Velmex unislide stage (Velmex Inc., Bloomfield,New York), Acu-Rite linear encoder (Acu-Rite CompaniesInc., Jamestown, New York), and Quick-Check digital read-out device (Metronics Inc., Bedford, New Hampshire).

Analytical methodsThe accuracy of assigned dates on cores was then verified

using the COFECHA program (Holmes 1983; Grissino-Mayer2001). Samples were pooled and analyzed in COFECHA®

using a cubic smoothing spline. Because the mean serieslength was 38.5 years, the segment length was set at 20 years

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2 Can. J. For. Res. Vol. 36, 2006

lag 10. Though necessary given the constraints of the dataset, this segment length is problematically short and createda multitude of flagged segments (approximately 25% of thesegments). Cores with flagged segments were examined toensure dating accuracy and the final COFECHA® values(mean sensitivity 0.212, series intercorrelation 0.415) werewithin an acceptable range given a multispecies data setwith an unusually short mean series length.

Once dates were verified, temporal patterns of establishmentwere examined by employing the commonly used graphicaltechnique of plotting the pith date (the first year of growth at1.37 m) of all trees in the stand against each stem’s diameterat 1.37 m (Shumway et al. 2001). Regression analysis wasthen used to provide a more precise understanding of theage–diameter relationship for C. dentata (Loewenstein et al.2000). A best fit regression line (Zar 1999) was constructedusing the PROC GLM procedure of SAS® (SAS InstituteInc. 1999).

Growth of C. dentata was compared with that of otherhardwoods using both mean annual ring width (RW; themean annual linear growth increment) and basal-area increment(BAI; the area of wood produced at DBH within a given year).Initial comparisons were made across all samples, includingall years of the growth chronology. To negate the influence ofage-related growth trends, comparisons were then made betweenthe first 20 years of growth in C. dentata and in other hard-woods. Because of skewed distributions, all comparisons weremade using the non-parametric Wilcoxon’s t test (Zar 1999).

The relationships between climatic variables and the growthrates of C. dentata and non-C. dentata hardwoods were exam-ined using correlation analysis. Because endogenous standdisturbances can obscure the climate signal in eastern hard-wood forests, growth measurements for both groups were

standardized using the ARSTAN® program prior to correlationanalysis (Cook and Holmes 1997; International Tree-RingData Bank Program Library, Rubino and McCarthy 2000).This standardization was conducted using a cubic smoothingspline with a 40-year length for C. dentata and a 60-yearlength for hardwoods (Cook and Peters 1981; Cook andHolmes 1997). A 50% variance cutoff was used for bothgroups (Cook and Peters 1981; Cook and Holmes 1997). Weconducted correlation analyses of the standardized chronologyfor both groups and mean monthly temperature, precipitation,and the Palmer Drought Severity Index (PDSI). We then definedthe growing season as May through September (Universityof Wisconsin–Extension 2005) and performed correlations ofmean growing-season temperature, precipitation, and PDSIwith the standardized chronology. To examine a possible lagrelationship with climate variables, we also conducted correla-tion analyses on the previous year’s mean monthly and meangrowing-season temperature, precipitation, and PDSI. All datawere screened for normality prior to correlation analysis usingD’Agostino’s omnibus test (D’Agostino et al. 1990). Pearson’sproduct–moment correlation was used for normally distributeddata, and Spearman’s correlation was used for non-normaldata (Zar 1999). Correlations were performed using theNumber Cruncher Statistical System (NCSS) 2001 (Hintze2001). All climate data were downloaded from the ClimateVisualization System (CLIMVIS) archive (Wisconsin Divi-sion 4) of the National Climate Data Center (National Oce-anic and Atmospheric Administration 2005).

Results

We collected cores from 105 stems belonging to nine species.The majority of cores (76) were collected from C. dentata;

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1840 1860 1880 1900 1920 1940 1960 1980 20000

20

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80

BepaCaovCADEPogrQualQucoQuruQuveUlam

Pith date (year)

Stem

dia

met

er (

cm)

Fig. 1. Establishment patterns as indicated by relationships between age and diameter (at 1.37 m) for trees in a forest stand in WestSalem, Wisconsin, containing Castanea dentata (CADE). Other hardwood species are as follows: Betula papyrifera (Bepa); Caryaovata (Caov); Populus grandidentata (Pogr); Quercus alba (Qual); Quercus coccinea (Quco); Quercus rubra (Quru); Quercus velutina(Quve); Ulmus americana (Ulam).

the remainder of the collection comprised the following:Betula papyrifera Marsh. (4), C. ovata (4), P. grandidentata(1), Q. alba (4), Quercus coccinea Muenchh. (1), Q. rubra (8),Q. velutina (6), and Ulmus americana L. (1). The hardwoodspecies other than C. dentata (hereinafter referred to as “otherhardwoods” (OH)) possess a variety of life-history charac-teristics (Burns and Honkala 1990). Nevertheless, we reportresults for OH collectively because analyses of subsectionsbased on life history or even genus (e.g., only Quercus spp.) didnot yield substantively different results. Of the 76 cores col-lected from C. dentata, 33 were from stems that were visuallyassessed in the field as being infected with chestnut blightand 43 were from stems lacking visible evidence of blight.

Initial graphical analysis of the data revealed an episodicrecruitment pattern for C. dentata (Fig. 1). The oldest stems

in the sample were oaks (Quercus spp.), and the only specieswith initiation dates prior to 1900 were Q. alba and Q. rubra(Fig. 1). A mix of species enter the record after 1900, andthe earliest date recorded in the C. dentata samples was1935 (Fig. 1). Castanea dentata stems enter the record spo-radically throughout the mid-1900s, ending with the entry ofa pulse of stems into the record beginning ca. 1973. Stemsthat entered the record during this period were variouslysuccessful, as several reached diameters of more than 40 cmDBH over the years prior to our sampling (in 2001), whileothers reached less than 20 cm DBH (Fig. 1).

Growth comparison between C. dentata and OHCastanea dentata generally exhibited faster growth than

OH in the stand; however, its growth was variable. RW,which is a measure of wood production along a radius fromthe pith to the bark, was significantly (p < 0.0001) greaterfor C. dentata than for OH. BAI, which is an estimator ofannual wood production, however, was not significantly dif-ferent (p = 0.31). BAI of forest trees is influenced by treeage, because of both the biology of the trees and the fact thatBAI is strongly influenced by stem size; large trees that aregrowing slowly can have a greater BAI than smaller fast-growing stems. Because the C. dentata sample populationwas younger (29.3 ± 1.3 years (mean ± SE)) than the OHsample population (75.3 ± 4.9 years), we corrected for age-related bias by conducting the analysis using only the first20 years of growth in each sample. In this analysis, as in theoverall comparison, C. dentata exhibited significantlygreater RW than did OH (p < 0.0001; Fig. 2). When only thefirst 20 years of growth are considered, C. dentata also ex-hibited a significantly greater BAI than did OH (p = 0.03),which suggests the capacity to produce significantly morewood per unit time (Fig. 2). When either metric is consid-ered, C. dentata exhibited more variability in growth thandid OH (Fig. 2). For instance, the coefficient of variation ofBAI across all years for all samples was approximately twiceas large in C. dentata (81.6 cm2·year–1) as in OH (40.8cm2·year–1).

Temporal patterns in the growth chronologies were readilyapparent and the relationship of C. dentata growth to that ofOH was clearly linked to recruitment in the stand (Fig. 3).For most of the RW chronology, C. dentata exhibited substan-tially faster growth than did OH (Fig. 3A). The C. dentataRW chronology was characterized by considerable variationand large fluctuations in growth during the 1940s; however,this was likely due to a small sample size (Fig. 3C). Oncethe C. dentata sample size was larger than 10, the two chro-nologies exhibited consistent separation. Indeed, throughoutmuch of the chronology, C. dentata exhibited a mean RWthat was more than twice that of OH (Fig. 3A). The BAIchronology is generally characterized by greater wood pro-duction in C. dentata; however, there is not consistent sepa-ration between the chronologies (Fig. 3B). Two periods ofseparation were apparent. The first occurred in the mid-1970s and the second began in the late 1980s and continuedthroughout the remainder of the chronology (Fig. 3B). Thesetwo periods were characterized by low levels of recruitment,while the period of greatest C. dentata recruitment into thesample population was also a period during which the BAIchronology of OH surpassed that of C. dentata in magnitude

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Other hardwoods

p < 0.0001

0

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p = 0.03

Castanea dentata0

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Castanea dentata Other hardwoods

(A)

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t (c

m·y

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)2

–1M

ean

annu

al r

ing

wid

th (

mm

·yea

r)

–1

Fig. 2. Box-and-whisker plots of mean annual ring widths (A)and mean annual basal area increments (B) for the first 20 yearsof growth in C. dentata and other hardwoods from a forest standin West Salem, Wisconsin. Whiskers represent the 5th and 95thpercentiles and the center line of the box is the median. Proba-bility values are derived from non-parametric Wilcoxon’s t tests.

(Figs. 3B, 3C). We attributed this “switch” during the expo-nential increase in the sample size of C. dentata (Figs. 3B, 3C)to the fact that BAI is sensitive to the mean stem diameter ofthe sample population. As small C. dentata stems enter the

sample population, mean stem diameter for the samplepopulation of C. dentata drops, while mature OH stems con-tinue growing and increasing in diameter. This interpretationis supported by the RW chronology, which does not exhibit

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1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Sam

ple

size

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nual

rin

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idth

(m

m·y

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0

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10Castanea dentataOther hardwoods

(A)

Fig. 3. Mean annual ring width (A) and basal area increment (B) chronologies (mean ± SE) for C. dentata and other hardwoods in a foreststand in West Salem, Wisconsin. Sample sizes (C) represent the accumulation of stems into the sample population over time. Note thatthree oak (Quercus spp.) stems that initiated prior to 1910 are not depicted, owing to the low information content in that section of the graph.

a drop in C. dentata growth. This indicates that the switch inthe chronology is an effect of stand dynamics and not evi-dence of slowed growth of C. dentata relative to that of OH.

Influence of chestnut blight on chronologyAn obvious feature of both the RW and BAI chronologies

for C. dentata is a sharp decline beginning ca. 1999 (Figs. 3A,3B). Because this substantial decline is neither associatedwith a climatic event nor reflected in the OH chronology, weinterpret it as a standwide reduction in C. dentata growth as-sociated with detrimental activity of chestnut blight. In thefield, we distinguished between stems that were apparentlyhealthy and stems that exhibited symptoms of blight. Growthchronologies developed separately from these two sets ofsamples are statistically indistinguishable throughout mostof the chronology (Fig. 4). The chronologies exhibited sepa-ration beginning ca. 1997 (Fig. 4), approximately 10 yearsfollowing the initial infection at the site (Paillet and Rutter1989). Statistical separation of the BAI chronologies for thehealthy and diseased stems began with a marginal differencein 1999 (p = 0.08) followed by statistically significant differ-ences in 2000 (p = 0.03) and 2001 (p < 0.01; Fig. 4). The in-fluence of chestnut blight was an obvious feature in thegrowth chronologies of individual stems as well. For exam-ple, a stem with one of the fastest growth rates in the sample(consistently producing annual rings >8 mm wide) exhibiteda sharp decline in growth beginning in 1998 (Fig. 5). Thisdecline was not apparent in other C. dentata stems recordedin the field as apparently healthy, nor was a growth declineobvious in the mean chronology of OH (Fig. 5).

Although the majority of stems identified as healthy in thefield exhibited normal growth throughout the chronology,20% exhibited apparently disease-related growth declines.The BAI chronology developed from “healthy” stems is marked

by a substantial decline in 2001 (Fig. 4), and the same de-cline is apparent in the RW chronology of “healthy” stemsas well (data not shown). In fact, RW in the “healthy” groupdeclined so sharply in 2001 that statistical separation fromthe diseased group was equivocal (p = 0.047; data not shown).This decline was not found in all of the “healthy” C. dentatastems in the sample (Fig. 5), there is no evidence of a de-cline in the OH chronology (Fig. 3), and this decline is notattributed to climatic variables. Although other factors couldbe involved, the most likely explanation for this decline inthe apparently healthy stems is detrimental activity of theblight fungus prior to the emergence of disease signs detect-able by field observation.

Climate–growth relationshipsThe C. dentata and OH standardized RW index (ARSTAN®

chronology; Cook and Holmes 1997) showed similar corre-lations with climatic variables (Table 1). Current-year tem-perature did not exhibit a significant relationship with eitherthe C. dentata or the OH chronology. Castanea dentata dif-fered from OH in that its chronology exhibited a highly sig-nificant positive correlation (p = 0.005) with current-yearAugust precipitation and the OH chronology did not (Ta-ble 1). PDSI exhibited a significant positive correlation for 9of the 12 months tested for both the C. dentata and the OHchronologies (p < 0.05). Growth of both C. dentata and OHwas also significantly correlated with mean growing-seasonprecipitation and PDSI (p < 0.05; Table 1). Previous-yearvariables also exhibited significant correlations with the stan-dardized chronologies. For instance, previous-year Augusttemperature was negatively correlated with the C. dentatachronology (p = 0.006), while the OH chronology did notexhibit any significant relationships with previous-year tem-peratures. Previous-year growing-season precipitation was

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1980 1985 1990 1995 20000

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60 Castanea dentata, healthyCastanea dentata, diseased

*

**

Bas

al a

rea

incr

emen

t (c

m·y

ear

)2

–1

Year

Fig. 4. Basal area increment chronologies (mean ± SE) for C. dentata stems in a forest stand in West Salem, Wisconsin, that wereidentified in the field as either apparently healthy (n = 43) or infected with chestnut blight (n = 33). Only the portion of the chronol-ogy during which the blight had an influence is shown. Note that both the apparently healthy and infected groups had a mean stemage of 29 years, and mean stem sizes were 31 and 30 cm DBH, respectively (*, p < 0.05; **, p < 0.01).

significantly correlated with the standardized chronologiesfor both groups (p < 0.05), as was precipitation in Septem-ber. Previous-year PDSI was positively correlated with theC. dentata standardized chronology for March (p = 0.04),September (p = 0.01), and October (p = 0.01). The OH stan-dardized chronology exhibited a significant positive correla-tion with previous-year PDSI for the growing season as awhole and also for all individual months from June throughDecember.

Relationship between diameter and age in C. dentataThe relationship between diameter and age (at 1.37 m) in

C. dentata was positive, as expected, although there wassome convolution in the relationship (Fig. 6). A straightleast-squares regression line (p < 0.001) yielded an R2 valueof 0.45 and was described by the model

[1] Age = 0.453(DBH) + 15.02

This model generally fit the data well; however, therewere important departures from the general relationship. First,the relationship was essentially “flat” for stems in the agerange 20–30 years which exhibited diameters from approxi-mately 10 to 45 cm. Second, the model generally underesti-mates the age of stems >45 cm DBH. Finally, note that twoof the largest stems in the sample were <40 years old (atDBH), suggesting the potential for extremely fast growth inC. dentata.

Discussion

Castanea dentata recruitment in the West Salem standwas episodic and apparently facilitated by disturbance. Theentry of an obvious pulse of stems into our sample was ex-hibited by C. dentata beginning ca. 1970. This pulse can be

linked to two land-use changes reported by Paillet and Rutter(1989) that occurred early in the 1970s. First, cattle were ex-cluded from the West Salem stand beginning in 1970. Pailletand Rutter (1989) suggest that grazing effectively restrictsC. dentata regeneration, as seedlings are preferentially grazedbecause they are often still attached to their perennating nut.Second, Paillet and Rutter (1989) documented logging onthe site in 1972. Based on the stem morphology of C. dentataon logged sites, Paillet and Rutter (1989) suggest that, oncereleased from light competition, C. dentata saplings can growstraight into the canopy, apparently overtopping neighboringcompetitors. Our data support this notion, as several stemsthat established in the 1970s grew rapidly and consistentlybeginning with the first year of record and reached diameterscomparable to those of canopy trees (i.e., >40 cm DBH) injust 30 years. These stems were likely released from grazingin areas where the canopy was subsequently removed duringthe logging operation. This positive relationship with distur-bance confirms the growth-rate patterns of C. dentata seed-lings observed by (McCament and McCarthy 2005). A positiveresponse to disturbance is shared by other members of theFagaceae and has been attributed to recruitment in Quercusspp. (Crow 1988). However, C. dentata differs from Quercusspp. in that if conditions are not ideal for growth and canopyrecruitment, it can exist as a “shrub” without notable loss ofvigor for substantial periods of time (Paillet 2002). This wasevident in our study, as many C. dentata stems, which likelywere released from grazing into a closed-canopy setting, re-mained relatively suppressed throughout the chronology andreached final diameters of <20 cm.

Castanea dentata in the West Salem stand exhibited remark-able radial growth. Based on measurements from C. dentatastumps, Paillet and Rutter (1989) hypothesized that C. dentatahad a maximum annual growth increment of approximately

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1965 1970 1975 1980 1985 1990 1995 20000

2

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12 Castanea dentata, infected ca. 1998Castanea dentata, healthyOther hardwoods

Rin

g w

idth

(m

m)

Year

Fig. 5. Ring-width chronologies of two representative C. dentata stems (one healthy and one infected) from a forest stand in West Sa-lem, Wisconsin. The health status of each stem was determined in the field (see Materials and methods for details). A mean annualring width chronology (mean ± SE) developed from other hardwoods found in the stand is also shown.

10 mm·year–1. This hypothesis is supported by our findingsand several stems exhibited radial growth of >12 mm withina single year. Mean radial growth of C. dentata greatly ex-ceeded that of OH in the West Salem stand and is considerablymore than mean values reported elsewhere for Liriodendrontulipifera and Nyssa sylvatica (Orwig and Abrams 1994). Infact, radial growth of C. dentata (4.7 ± 0.21 mm·year–1

(mean ± SE)) was similar to the maximum growth reportedfor L. tulipifera (4.83 ± 0.48 mm·year–1; Orwig and Abrams1994), a well-known fast-growth species. Radial growth ofC. dentata was three times that of Q. alba (n = 10) from Dy-sart Woods, Ohio (1.5 ± 0.11 mm·year–1; Rubino and Mc-Carthy 1999), and even if we adjust the mean for Q. alba toinclude only the 20 largest rings from each sample, growth(2.8 ± 0.17 mm·year–1) was still much less than that exhib-ited by C. dentata in West Salem. Wood production (mea-sured as BAI) by C. dentata was not significantly greaterthan that by OH across all years and samples; however, thiscomparison was strongly influenced by the disturbance-related dynamics in the C. dentata chronology. Comparisonswhich corrected for age indicated that C. dentata gained

wood at a faster rate, and that the maximum mean BAI exhib-ited by individual C. dentata stems was vastly greater thanmaximums exhibited by OH, with many C. dentata stems ex-hibiting BAI of >50 cm2·year–1. Our results support those ofJacobs and Severeid (2004), who report that C. dentata sap-lings performed exceedingly well in a plantation setting andexhibited radial growth (4.15 mm·year–1) which greatly sur-passed that of Q. rubra and Juglans nigra. Although thegrowth of C. dentata has been shown here, and elsewhere(Jacobs and Severeid 2004), to greatly exceed that of otherhardwood species, the relationships of this growth to clima-tic conditions are similar. Growth of C. dentata stems in ourstudy was related to temperature, precipitation, and PDSI ina fashion similar to that of OH in the stand, with only a sug-gestion of increased importance of previous-year PDSI toOH. Climatic relationships were also similar to those reportedelsewhere for Q. alba (Rubino and McCarthy 1999).

The influence of chestnut blight was manifested as a stand-wide reduction in C. dentata growth. Growth declines havebeen attributed to invasive or pathogenic species in other sys-tems. For instance, the shoot pine beetle (Tomicus piniperda

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Castanea dentata Other hardwoods

Temp. Precipitation PDSI Temp. Precipitation PDSI

Current yearJanuaryFebruary 0.33S*March 0.30S* 0.27S*April 0.33S** 0.33*May 0.38*** 0.35**June 0.39*** 0.35**July 0.43*** 0.31*August 0.36S*** 0.45*** 0.33**September 0.37*** 0.30*October 0.27* 0.28*November 0.26*DecemberGrowing season 0.39*** 0.46*** 0.25* 0.38**

Previous yearJanuaryFebruaryMarch 0.27S*AprilMay 0.27*June 0.26*July 0.26*August –0.35** 0.34**September 0.33* 0.31* 0.30* 0.44***October 0.33* 0.44***November 0.31S*December 0.31*Growing season 0.28* 0.42*** 0.35**

Note: Coefficients are given only for significant correlations (p < 0.05). Correlations were performedusing either Pearson’s product moment test or Spearman’s rank correlation (indicated by a superscript“S”), depending on normality of the data (*, p < 0.05; **, p < 0.01; ***, p < 0.005). PDSI is thePalmer Drought Severity Index.

Table 1. Correlations between the ring width index for Castanea dentata and other hard-woods in a forest stand in West Salem, Wisconsin, and climate metrics from the currentand previous year.

L.) significantly suppressed radial growth of Pinus palustrisMill. (Czokajlo et al. 1997), radial-growth impacts of thepandora moth (Coloradia pandora Blake) are well docu-mented in Pinus ponderosa Dougl. ex P. Laws. & C. Laws.(Speer et al. 2001), and defoliation by gypsy moth (Lymantriadispar L.) has been detected in the growth chronologies ofoak (Muzika and Liebhold 1999; Naidoo and Lechowicz2001). These insect pests, though, are not necessarily mortalityagents, whereas the influence of chestut blight on C. dentatais more similar to that of dogwood anthracnose (Disculadestructiva Redlin) on Cornus florida L. (McEwan et al.2000) or Dutch elm disease (Ophiostoma ulmi (Buisman)Nannf.) on U. americana (Pipe et al. 2000). In these in-stances the infected stems are practically always killed. Be-cause exotic fungal pathogens are usually mortality agents,opportunities for documenting radial-growth depression havebeen limited. Notably, a sharp depression was apparent inthe growth chronology of stems, which we classified in thefield as healthy. Although other factors could be involved,we interpret this decline in growth of apparently healthystems as a disease symptom that is manifesting itself prior tothe emergence of outward signs. This supports the work ofPaillet and Rutter (1989), which isolated the chestnut blightfungus from a dead C. dentata stem that was free of blightsigns except for “a few epicormic sprouts”. These findingssuggest that external signs of blight infection may not ap-pear until years after a tree is infected with the fungus, andthat field delineation of “healthy” and “diseased” specimensis problematic.

Castanea dentata exhibited considerable flexibility in itsecological response. For instance, several C. dentata stemsresponded to apparent release from light competition by rap-idly growing to canopy size. This positive relationship todisturbance in a potentially long-lived canopy tree, and theability to grow quickly and potentially form monotypic stands,are reminiscent of L. tulipifera, a species found in much ofC. dentata’s eastern range (Skeen et al. 1980; Kalisz 1986).

However, C. dentata also exhibits the capacity to remain inthe understory for long periods of time (Paillet 2002) and,though suppressed, can respond with rapid apical elongationif light conditions become favorable (Paillet and Rutter 1989).This ability of a potential overstory dominant to maintain apositive carbon balance in the low-light environment of aforest understory over a long period of time is reminiscentof Fagus grandifolia, a congener of C. dentata belonging tothe Fagaceae, which also reproduces via sprouts and can re-spond to canopy gaps even after long periods of suppression(Canham 1990). This combination of growth strategies re-sembling those of both a rapidly growing early-successionalspecies and a late-successional shade-tolerant species mayhave contributed to C. dentata’s expansion and forest domi-nance in the late Holocene (Paillet 2002).

Restoration of C. dentata as a component of eastern for-ests may be facilitated by its growth characteristics. Our datasuggest sporadic regeneration punctuated by a pulse of re-cruitment associated with forest disturbance. This supportsPaillet and Rutter’s (1989) hypothesis that naturalization ofC. dentata in West Salem was a three-step process. First,“pioneer” trees established, likely taking advantage of lightgaps (Paillet and Rutter 1989). Second, a large pool of “oldseedlings” (sensu Paillet and Rutter 1989) established in theunderstory. Finally, these seedlings were released by distur-bance and assumed canopy dominance en masse (Paillet andRutter 1989). Restorationists may be able to take advantageof this process by establishing dispersed C. dentata colonies,particularly in forested settings where canopy disturbance hasrecently occurred or is anticipated (McCament and McCarthy2005). The rapid growth of some C. dentata stems in ourstudy suggests that establishment under enhanced light con-ditions, such as those available following partial forest cut-ting, may allow rapid assertion of C. dentata canopydominance on some sites (Paillet and Rutter 1989; Paillet2002; Jacobs and Severied 2004). The overall performanceof C. dentata on the West Salem site indicates that blight-

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McEwan et al. 9

0 10 20 30 40 50 60 70 800

10

20

30

40

50

60

70

Stem diameter (cm)

Stem

age

(ye

ars)

Fig. 6. Relationship of age to diameter (at 1.37 m) for C. dentata in a forest stand in West Salem, Wisconsin. See the text for the regression model.

resistant varieties should have the ecological capacity to suc-cessfully assume canopy dominance once they are reestab-lished in their preblight range.

Acknowledgements

We thank the American Chestnut Foundation, the OhioPlant Biotechnology Consortium, Ohio University, and Mi-ami University for providing funding and (or) support forthis research. Jane Cummings-Carlson of the Wisconsin De-partment of Natural Resources provided useful logistical in-formation. Jon Tyson and Gary Noll assisted with fieldcollection of increment cores. We thank R. Bockenhauer andthe Rhymes family for access to the study site. Thanks arealso extended to Rob Kaminski for aid in increment corepreparation. Amy L. Goff-Yates, Kim J. Brown, and threeanonymous reviewers provided comments that improved themanuscript considerably.

References

Braun, E.L. 1950. Deciduous forests of eastern North America.Blakiston, Philadelphia, Pa.

Brewer, L.G. 1995. Ecology of survival and recovery from blightin American chestnut trees [Castanea dentata (Marsh.) Borkh.]in Michigan. Bull. Torrey Bot. Club, 122: 40–57.

Brosi, S.L. 2001. American chestnut seedling establishment in theKnobs and Eastern Coalfields regions of Kentucky. M.S. thesis,University of Kentucky, Lexington, Ky.

Burns, R.M., and Honkala, B.H. 1990. Silvics of North America.Vol. 2. Hardwoods. U.S. Dep. Agric. Agric. Handb. 654.

Canham, C.D. 1990. Suppression and release during canopy re-cruitment in Fagus grandifolia. Bull. Torrey Bot. Club, 117: 1–7.

Cook, E.R., and Holmes, R.L. 1997. ARSTAN: chronology devel-opment. In The International Tree-Ring Data Bank Program Li-brary, Version 2.1. User’s manual. Edited by H.D. Grissino-Mayer, R.L. Holmes, and H.C. Fritts. Laboratory of Tree-RingResearch, The University of Arizona, Tuscon, Ariz. pp. 75–87.

Cook, E.R., and Peters, K. 1981. The smoothing spline: a new ap-proach to standardizing forest interior tree-ring width series fordendroclimatic studies. Tree-Ring Bull. 41: 45–53.

Crow, T.R. 1988. Reproductive mode and mechanisms for self-replacement of northern red oak (Quercus rubra) — a review.For. Sci. 34: 19–40.

Curtis, J.T. 1959. The vegetation of Wisconsin. The University ofWisconsin Press, Madison, Wis.

Czokajlo, D., Wink, R.A., Warren, J.C., and Teale, S.A. 1997.Growth reduction of Scots pine, Pinus sylvestris, caused by thelarger pine shoot beetle, Tomicus piniperda (Coleoptera,Scolytidae), in New York State. Can. J. For. Res. 27: 1394–1397.

D’Agostino, R.B., Belanger, A., and D’Agostino, R.B., Jr. 1990. Asuggestion for using powerful and informative tests of normal-ity. Am. Stat. 44: 316–321.

Fritts, H.C. 1976. Tree rings and climate. Academic Press, NewYork.

Gleason, H.A., and Cronquist, A. 1991. Manual of vascular plantsof northeastern United States and adjacent Canada. 2nd ed. TheNew York Botanical Garden, Bronx, N.Y.

Good, N.F. 1968. A study of natural replacement of chestnut in sixstands in the Highlands of New Jersey. Bull. Torrey Bot. Club,95: 240–253.

Grissino-Mayer, H.D. 2001. Evaluating crossdating accuracy: amanual and tutorial for the computer program COFECHA. Tree-Ring Res. 57: 205–221.

Hebard, F.V. 1994. The American Chestnut Foundation BreedingPlan: beginning and intermediate steps. J. Am. Chestnut Found.13: 16–21.

Hebard, F.V. 2001. Backcross breeding program produces blight-resistant American chestnuts (Virginia). Ecol. Restor. 19: 252–254.

Henry, J.D., and Swan, J.M.A. 1974. Reconstructing forest historyfrom live and dead plant material — an approach to the study offorest succession in southwest New Hampshire. Ecology, 55:772–783.

Hintze, J. 2001. NCSS and PASS [computer program]. NumberCruncher Statistical Systems, Kaysville, Utah.

Holmes, R.L. 1983. Computer-assisted quality control in tree-ringdating and measurement. Tree-Ring Bull. 43: 69–78.

Jacobs, D.F., and Severeid, L.R. 2004. Dominance in interplantedAmerican chestnut (Castanea dentata) in southwestern Wiscon-sin, USA. For. Ecol. Manage. 191: 111–120.

Kalisz, P.J. 1986. Soil properties of steep Appalachian old fields.Ecology, 67: 1011–1023.

Keever, C. 1953. Present composition of some stands of the formeroak–chestnut forest in the southern Blue Ridge Mountains. Ecol-ogy, 34: 44–54.

Kipfmueller, K.F., and Swetnam, T.W. 2001. Using dendrochronologyto reconstruct the history of forest and woodland ecosystems. InThe historical ecology handbook. Edited by D. Egan and E.A.Howell. Island Press, Washington, D.C. pp. 199–228.

Loewenstein, E.F., Johnson, P.S., and Garrett, H.E. 2000. Age anddiameter structure of a managed uneven-aged oak forest. Can. J.For. Res. 30: 1060–1070.

McCament, C.L., and McCarthy, B.C. 2005. Two-year response ofAmerican chestnut (Castanea dentata) seedlings to shelterwoodharvesting and fire in a mixed-oak forest ecosystem. Can. J. For.Res. 35: 740–749.

McCarthy, B.C. 2001. Introduction to dendrochronology [online].Available from http://www.plantbio.ohiou.edu/dendro [accessed20 February 2005].

McCormick, J.F., and Platt, R.B. 1980. Recovery of an Appala-chian forest following the chestnut blight. Am. Midl. Nat. 104:264–273.

McEwan, R.W., Muller, R.N, Arthur, M.A., and Housman, H.H.2000. Temporal and ecological patterns of flowering dogwoodmortality in the mixed mesophytic forest of eastern Kentucky. J.Torrey Bot. Soc. 127: 221–229.

McEwan, R.W., Rhoades, C., and Beiting, S. 2005. Americanchestnut (Castanea dentata) in the pre-settlement vegetation ofMammoth Cave National Park, central Kentucky, USA. Nat.Areas J. 25: 275–281.

Muzika, R.M., and Liebhold, A.M. 1999. Changes in radial incre-ment of host and nonhost tree species with gypsy moth defolia-tion. Can. J. For. Res. 29: 1365–1373.

Naidoo, R., and Lechowicz, M.J. 2001. Effects of gypsy moth onradial growth of deciduous trees. For. Sci. 47: 338–348.

Nelson, T.C. 1955. Chestnut replacement in the Southern High-lands. Ecology, 36: 352–353.

National Oceanic and Atmospheric Administration. 2005. CLIMVISarchive. Available from http://www.ncdc.noaa.gov/oa/climate/onlineprod/drought/xmgrg1.html [accessed 20 February 2005].

Orwig, D.A., and Abrams, M.D. 1994. Contrasting radial growthand canopy recruitment patterns in Liriodendron tulipifera andNyssa sylvatica: gap-obligate versus gap-facultative tree species.Can. J. For. Res. 24: 2141–2149.

© 2006 NRC Canada

10 Can. J. For. Res. Vol. 36, 2006

Paillet, F.L. 1984. Growth-form and ecology of American chestnutsprout clones in northeastern Massachusetts. Bull. Torrey Bot.Club, 111: 316–328.

Paillet, F.L. 1988. Character and distribution of American chestnutsprouts in southern New England woodlands. Bull. Torrey Bot.Club, 115: 32–44.

Paillet, F.L. 2002. Chestnut: history and ecology of a transformedspecies. J. Biogeogr. 29: 1517–1530.

Paillet, F.L., and Rutter, P.A. 1989. Replacement of native oak andhickory tree species by the introduced American chestnut(Castanea dentata) in southwestern Wisconsin. Can. J. Bot. 67:3457–3469.

Pipe, N.D., Braiser, C.M., and Buck, K.W. 2000. Evolutionary re-lationships of the dutch elm disease fungus Ophiostoma novo-ulmi to other Ophiostoma species investigated by restricted frag-ment length polymorphism analysis of the rDNA region. J.Phytopathol. 148: 533–539.

Rubino, D.L., and McCarthy, B.C. 1999. Tree-ring data, DysartWoods, Ohio. International Tree-Ring Data Bank, World DataCenter for Paleoclimatology, Data Contribution Series 199–011.Available from http://www.ncdc.noaa.gov/paleo/treering.html.National Oceanic and Atmospheric Administration / NationalGeophysical and Climate Data Centers Paleoclimatology Pro-gram, Boulder, Colo. [accessed 19 July 2005].

Rubino, D.L., and McCarthy, B.C. 2000. Dendroclimatologicalanalysis of white oak (Quercus alba L., Fagaceae) from an old-growth forest of southeastern Ohio, USA. J. Torrey Bot. Soc.127: 240–250.

Russell, E.W.B. 1987. Pre-blight distribution of Castanea dentata(Marsh.) Borkh. Bull. Torrey Bot. Club, 114: 183–190.

SAS Institute Inc. 1999. SAS® user’s manual. SAS Institute Inc.,Cary, N.C.

Shumway, D.L., Abrams, M.D., and Ruffner, C.M. 2001. A 400-year history of fire and oak recruitment in an old-growth oakforest in western Maryland, U.S.A. Can. J. For. Res. 31: 1437–1443.

Skeen, J.N., Carter, M.E.B., and Ragsdale, H.L. 1980. Yellow-poplar: the Piedmont case. Bull. Torrey Bot. Soc. 107: 1–6.

Soulé, P.T., Knapp, P.A., and Grissino-Mayer, H.D. 2004. Humanagency, environmental drivers and western juniper establishmentduring the late Holocene. Ecol. Appl. 14: 96–112.

Speer, J.H., Swetnam, T.W., Wickman, B.E., and Youngblood, A.2001. Changes in pandora moth outbreak dynamics during thepast 622 years. Ecology, 82: 679–697.

Stokes, M.A., and Smiley, T.L. 1996. An introduction to tree-ringdating. The University of Arizona Press, Tucson, Ariz.

Tindall, J.R., Gerrath, J.A., Melzer, M., McKendry, K., Husband,B.C., and Boland, G.J. 2004. Ecological status of Americanchestnut (Castanea dentata) in its native range in Canada.Can. J. For. Res. 34: 2554–2563.

University of Wisconsin–Extension. 2005. University of Wiscon-sin: frost dates for LaCrosse Wisconsin. Available from http://www.uwex.edu/ces/wihort/links/FrostDates.htm [accessed 10 Jan-uary 2005].

Yamaguchi, D.K. 1991. A simple method for cross-dating incre-ment cores from living trees. Can. J. For. Res. 21: 414–416.

Zar, J.H. 1999. Biostatistical analysis. Prentice Hall, Upper SaddleRiver, N.J.

© 2006 NRC Canada

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