Spatial Patterns of Juniperus virginiana and Lonicera maackii on a Kentucky road cutSteven M. Castellano & Richard L. Boyce

Department of Biological Sciences, Northern Kentucky University, Highland Heights, KY

Abstract

This study investigated the spatial patterns of several woody plantspecies on a road cut site in Northern Kentucky with particularfocus on eastern red cedar (Juniperus virginiana) and Amurhoneysuckle (Lonicera maackii). The site faced NW and consistedof nine 25-m2 quadrats. The positions of all woody plants 50 cmand taller were measured. For each woody plant, we alsomeasured height, soi l depth, and photosynthetically active radiation(PAR); the latter two measurements were taken at the four cardinalpoints. Ripley’s L showed that J. virginiana and Bradford pear(Pyrus cal leryana) were distributed randomly while the remainingspecies were clustered, especial ly L. maacki i. White ash (Fraxinusamericana), J. virginiana, and L. maackii distributions wereindependent of other species, while red panicle dogwood (Cornusracemosa) and P. cal leryana both showed a sl ight association withother woody plants. Mann-Whitney tests showed that L. maackiiwas found in areas of lower light than J. virginiana and that C.racemosa was found in deeper soils than J. virginiana. Smaller L.maacki i individuals clustered with larger ones, but this pattern wasnot seen in J. virginiana.

Introduction

Amur honeysuckle is a shrub native to the Amur River valley ineastern Asia that was first recorded in the United States in 1898(Luken and Thieret 1995) and was reported in southwestern Ohio byLucy Braun (1961) as “becoming abundant in pastures andwoodlands.” As of today this shrub is widespread throughout muchof the area (personal observation) and, in some cases, has come todominate the shrub layer of forest and fields (Hutchinson and Vankat1997). This invasive plant has shown to decrease the fecundity ofannual plants (Gould and Gorchov 2000) and adversely impactnative tree seedlings and herbaceous plants (Hutchinson and Vankat1997). Lonicera, like other troublesome plants, has been known tothrive in areas that have been disturbed by human activity, such asroad cuts (Luken and Thieret 1995).

Our study focused on the relationship that Lonicera shares withJuniperus virginiana, eastern red cedar, on a disturbed road cut site.Juniperus is a common tree of old fields and disturbed areas and hasshown the potential to facilitate natural succession and enhance thesuccess of native hardwood seedlings (Meiners and Gorchov 1998).The presence of Lonicera may disrupt this process and altercommunity structure and the populations of the native flora (Medley1997). Understanding of the relationships between invasive speciesand native competitors is an important factor in the management ofecosystems to prevent or remediate exotic plant invasions.

Our main questions for this study were:• What are the patterns of distribution for Lonicera and Juniperus andat what scales are these patterns most pronounced?• Is there a spatial association between these species?• Does the soil depth have an effect on the distribution of theseplants?• How does PAR relate to the patterns of distribution?• Are different size classes for each species distributed differently?

Methods and MaterialsOur site was on a northwest facing road cut and included nine contiguous 25 m2 quadrats (5 m x 5 m). All woody plants ≥50 cm tall were identified as tospecies and were assigned Cartesian coordinates relative to the site’s most south east corner (0 m north, 0 m east). Height was measured with a level ingrod to the highest living limb containing leaves.

PAR was measured for each plant using an Accupar light interceptor device (Decagon Devices, Pullman, WA) in four cardinal directions ≈1 m from theedge of the plants canopy. The soi l depth for each plant was measured in four cardinal directions 30 cm from the center of their trunk with a metal probe.

Nonparametric Mann-Whitney tests were used to analyze PAR and soil depth data (means, minimum, and maximum values). Ripley’s K function was usedto analyze the coordinate data to determine distribution, scale of distribution, and associations of each plant relative to other plants, with focus onJuniperus and Lonicera. Monte Carlo randomizations were run 1000 times for distribution determination and 5000 times for association determination. Thelibrary splancs was used in the program R for the analysis of these data (Rowlingson and Diggle 1993; R Development Core Team 2004). A more easilyinterpreted transformation of Ripley’s K uses an estimator L and is defined as (Goreaud & Pel issier 2000) :

L(r) = √K(r)/π-r ,

where r is the inter-plant distance. Ripley’s L was also used to compare distribution patterns of L. maackii and J. virginiana of three different size classes,50-100cm, 101-200cm, and 201-500cm for J. virginiana and 50-100cm, 101-200cm, and 201-275cm for L. maackii. Each size class was compared to othersize classes of the same species. Edge correction fol lowed Diggle’s (2002) method of treating the plots as tori so edges would be el iminated.

Conclusions• Lonicera showed a clumped distribution at all scales ≤ 5 m withpeak aggregation at 2 m.

• Juniperus showed a mostly random distribution with a slightindication of clumping at 1 m.

• Lonicera mean PAR ratio was lower than the mean PAR ratio forJuniperus. Lonicera was more likely to be found in lower light thanJuniperus (p=0.01)

• There was only a slight indication that Juniperus was found inthinner soils than Lonicera, but this was not strong, statistically(p=0.07).

• Lonicera and Juniperus did not show a significant association withother species of woody plants (Lonicera p=0.733 & Juniperusp=0.704).

• Smaller Lonicera were shown to cluster with medium sizeLonicera (p=.0228) and medium Lonicera clustered with largeLonicera (p<0.0001).

• Different size classes of Juniperus did not cluster at any scale(p>0.10) (Data not shown).

Acknowledgements:

Northern Kentucky University-for use of its property for researchplots.CINSAM-FundingThe Council for Undergraduate Research- Funding for travelexpenses.Richard Boyce- for his guidance on the project.

Literature CitedBraun, E L. 1961. The woody plants of Ohio. Ohio State University Press, Columbus.

Diggle P L. 2002. Statistical Analysis of Spatial Point Patterns. Oxford UniversityPress, Oxford, p. 5-6

Goreaud F, Pelissier R. Spatial structure analysis of heterogeneous point patterns:examples of application to forest stands. URL ftp://pbil.univ-lyon1.fr/pub/mac/ADE/ADE4/DocThemPDFUS/Thema81.pdf

Gould A M, Gorchov D L. 2000. Effects of the exotic shrub Lonicera maackii on thesurvival and fecundity of three species of natives annuals. Am Midl Nat 144:36-50

Hutchinson T F, Vankat J L. 1997. Invasibility and effects of Amur honeysuckle insouthwestern Ohio forests. Conservation Biology 11(5):1117-24

Luken J O, Thieret J W. 1995. Amur honeysuckle (Lonicera maackii; Caprifoliacea):its ascent, decline, and fall. Sida 16(3):479-503

Medley K E. 1997. Distribution of the non-native shrub Lonicera maackii in KramerWoods, Ohio. Physical Geography 18(1):18-36

Meiners S J, Gorchov D L. 1998. Effects of distance to Juniperus virginiana on theestablishment of Fraxinus and Acer seedlings on old fields. Am Midl Nat 139:353-364

R Development Core Team (2004). R: A language and environment for statisticalcomputing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-00-3, URL http://www.R-project.org.

Rowlingson B S, Diggle P J. 1993. Splancs: Spatial point pattern analysis code in S-plus. Lancaster, UK: Lancaster University. URLhttp://www.maths.lancs.ac.uk/~rowlings/Splancs/

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Cornus Fraxinus Juniperus Lonicera Pyrus

Mean Soil Depth

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Site map showing distribution of Loniceraand Juniperus

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Cornus Fraxinus Juniperus Lonicera Pyrus

Mean PAR

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Juniperus virginiana on our site

L functions for Juniperus and Lonicera distribution. Red linesindicate confidence envelope after 1000 data randomizations. An Labove the envelope indicates clumping, within the envelope,random, and below, uniform. Distance from plant in meters shownby r.

L functions for associations of Lonicera and Juniperus (Kdot graphs) with other woody plants and relationships amoung Lonicera ofdifferent size classes (K12 graphs). Red lines indicate confidence envelope after 5000 data randomizations. L above the envelope showspositive association, L within the envelope,no association, and below the envelope, negative association. Size class data for Juniperus notshown.

PAR was measured with theAccupar

There is a weak indication thatLonicera was found at deeper soildepths than Juniperus (p=0.07)

Juniperus exhibited mean PAR ratios thatwere higher than Lonicera mean PAR ratios

(p=0.01).

View of interstate 275 from our site prior to spring leaf-out. Gray/brown shrubs on left and bottom-right show Lonicera invasion.

Typical Lonicera maackii shrub in leaf