tand 5 had more, low vigor trees before defoliation and stand density was above 100 percent stocking. During 1983, mortality reduced stocking to 89 percent, which increased to 105 percent by 1984. In Stand 5, most of the mortality occurred in stressed, overtopped and intermediate trees because physiological condition at the time of defoliation is the greatest contributor to mortality [1].

The additional TSI treatment in Stand 3 resulted in 95 fewer trees on the treatment area compared to Stand 4. With approximately equal losses to mortality, this difference still existed in 1986. In hardwood stands in northeastern North America, maximum individual tree growth occurs at about 30 percent stocking and individualtree growth benefits continue to accrue until densities approach 60 percent, or full stocking, where net growth equals gross growth [35]. As densities increase beyond 60 percent, competition begins to limit individual tree diameter growth until mortality becomes substantial above 80 percent stocking, and net growth drops signifycantly. Reductions in stand density from thinning and/or natural mortality increases physical growing space for crown expansion of residual trees, as well as increasing the availability of other site resources (e.g. light, water nutrients) [4-44]. The thinning treatments in this study targeted the removal of low vigor trees with smaller crowns and less stem taper. From 1981-1986, Stand 3 stocking remained at or below the 60 percent threshold for optimum growth. Except for 1983, Stand 4 stocking was always between 70 - 80 percent, possibly explaining why post-defoliation growth was more similar to Stand 5.

Most of the wood product volume and value in a typical Appalachian oak stand is concentrated in the largest, most dominant trees with the best stem form, especially if the stands are thinned [41]. Trees in dominant and codominant crown classes continue cambial activity longer than intermediate and overtopped trees of the same species and on the same site [42]. Both red and white oaks have shown increased diameter growth rates if their crowns are released from direct competition with adjacent trees [41-43]. Significant diameter growth rate increases are possible in crown-released older (50+ years) oaks, especially if the trees are in codominant/dominant canopy positions [44]. Post-thinning and post-defoliation stocking in Stand 3 remained within recommended limits to maximize growth. Stocking in Stand 4 was always higher, even with mortality.

Our study indicated that both EW and LW increment were reduced during defoliation, and red oaks were more affected than white oaks. During an average growing season mean ring widths for red oaks are typically greater than white oaks growing in the same sites [44]. Because EW production seasonally precedes gypsy moth defoliation, reduced starch storage from previous years of defoliation can lead to a reduction in EW production the following spring. Conversely, the effect of defoliation is manifested in reduced LW production during the year of defoliation, especially for white oaks, and during the year of defoliation and as a lag effect the following year, for red oaks [19]. A high positive correlation between EW width and LW width of the preceding year, points to a dependence of EW formation on the previous year’s growing conditions for oaks [45] and ring-porous Fraxinus sp. [46].

The ratio of EW:LW was only significantly affected by defoliation and not by treatment or species, supporting the common use of this metric for reconstructing historic insect outbreaks in ring-porous species. Earlywood width is strongly associated with total vessel areas so under favorable growing conditions earlywood is wider and vessels and total vessel area tend to be larger [47]. There is evidence that earlywood vessel area is reduced when the growing environments becomes less favorable [48]. Therefore, when defoliation causes proportionally more earlywood, with potentially reduced vessel area [25], wood density (specific gravity) and strength may be lower because the latewood vessels also have stiffer cell walls [49].

Gypsy moth defoliation caused major reductions in oak volume production during two years of active feeding and one year following. Data from increment cores were used in our whole-stem models to provide an estimate of the total merchantable stem volume lost for the 3-year period. Defoliation may also affect wood cellular and strength properties because in defoliated oaks, the proportion of earlywood and latewood was altered. Hence, variations in wood strength and appearance of the resulting oak lumber may reduce its potential for production of high value veneer and flooring. Future studies could utilize digital images of increment cores and stem sections to identify and measure earlywood vessel characteristics.

5. Acknowledgements

We thank Dave Feicht, Al Iskra, and Rod Whiteman (deceased) for field data collection and Darlene Mudrick for dendrochronolgy measurements.


  1. C. B. Davidson, K. W. Gottschalk and J. E. Johnson, “Tree Mortality Following Defoliation by the European Gypsy Moth (Lymantria dispar L.) in the United States: A Review,” Forest Science, Vol. 45, No. 1, 1999, pp. 74- 84.
  2. T. Tigner, “Gypsy Moth Impact on Virginia’s Hardwood Forests and Forest Industry,” Virginia Department of Forestry, Charlottesville, 1992.
  3. K. W. Gottschalk, “Silvicultural Guidelines for Forest Stands Threatened by the Gypsy Moth,” General Technical Report NE-171, USDA Forest Service, Northeastern Forest Experiment Station, Radnor, 1993, p. 49.
  4. P. M. Wargo and D. R. Houston, “Infection of Defoliated Sugar Maple Trees by Armillaria Mellea,” Phytopathology, Vol. 64, 1974, pp. 817-822. doi:10.1094/Phyto-64-817
  5. D. M. Dunbar and G. R. Stephens, “Association of TwoLined Chestnut Borer and Shoestring Fungus with Mortality of Defoliated Oaks in Connecticut,” Forest Science, Vol. 21, No. 2, 1975, pp. 169-174.
  6. R. W. Campbell and R. J. Sloan, “Forest Stand Responses to Defoliation by the Gypsy Moth,” Forest Science, Monograph 19, 1977.
  7. D. R. Houston, “Oak Decline and Mortality,” In: C. C. Doane and M. L. McManus, Eds., The Gypsy Moth: Research toward Integrated Pest Management, USDA Forest Service, Science and Education Agency, Technical Bulletin, No. 1584, 1981, pp. 217-219.
  8. J. Parker, “Effects of Defoliation on Red Oak Chemistry,” In: C. C. Doane and M. L. McManus, Eds., The Gypsy Moth: Research toward Integrated Pest Management, USDA Forest Service, Science and Education Agency, Technical Bulletin, No. 1584, 1981, pp. 219-225.
  9. P. M. Wargo, “Defoliation and Tree Growth,” In: C. C. Doane and M. L. McManus, Eds., The Gypsy Moth: Research toward Integrated Pest Management, USDA Forest Service, Science and Education Agency, Technical Bulletin, No. 1584, 1981, pp. 225-240.
  10. C. B. Davidson, K. W. Gottschalk and J. E. Johnson, “European Gypsy Moth (Lymantria dispar L.) Outbreaks: A Review of the Literature,” General Technical Report NE-278, USDA Forest Service, Northeastern Research Station, Newtown Square, 2001.
  11. F.M. Thomas, R. Blank and G. Hartman, “Abiotic and Biotic Factors and Their Interactions as Causes of Oak Decline in Central Europe,” Forest Pathology, Vol. 32, No. 4-5, 2002, pp. 277-307. doi:10.1046/j.1439-0329.2002.00291.x
  12. R. Rogers and T. M. Hinckley, “Foliar Weight and Area Related to Current Sapwood Area in Oak,” Forest Science, Vol. 25, 1979, pp. 298-303.
  13. R. L. Phipps, “Comments on Interpretation of Climatic Information from Tree Rings, Eastern North America,” Tree-Ring Bulletin, Vol. 42, 1982, pp. 11-21.
  14. D. W. Woodcock, “Climate Sensitivity of Wood-Anatomical Features in Ring-Porous Oak (Quercus Macrocarpa),” Canadian Journal of Forest Research, Vol. 19, No. 5, 1989, pp. 639-644. doi:10.1139/x89-100
  15. G. C. Varley and G. R. Gradwell, “Population Models for the Winter Moth,” In: T. R. E. Southwood Ed., Insect Abundance, Symposium, Royal Entomological Society, London, 1968, pp.132-142.
  16. A. H. Rose, “The Effect of Defoliation on Foliage Production and Radial Growth of Quaking Aspen,” Forest Science, Vol. 4, 1958, pp. 335-342.
  17. H. M. Kulman, “Effects of Insect Defoliation on Growth and Mortality of Trees,” Annual Review Entomology, Vol. 16, 1971, pp. 289-324. doi:10.1146/annurev.en.16.010171.001445
  18. G. R. Stephens, N. C. Turner and H. C. DeRoo, “Some Effects of Defoliation by Gypsy Moth (Porthetria dispar L.) and Elm Spanworm (Ennomos subsignarius Hbn.) on Water Balance and Growth of Deciduous Forest Trees,” Forest Science, Vol. 18, No. 4, 1972, pp. 326-330.
  19. R. M. Muzika and A. M. Liebhold, “Changes in Radial Increment of Host and Nonhost Tree Species with Gypsy Moth Defoliation,” Canadian Journal of Forest Research, Vol. 29, No. 9, 1999, pp. 1365-1373. doi:10.1139/x99-098
  20. R. Naidoo and M. J. Lechowicz., “Effects of Gypsy Moth on Radial Growth of Deciduous Trees,” Forest Science, Vol. 47, No. 3, 2001, pp. 338-348.
  21. D. A. Gansner and O. W. Herrick, “Estimating the Benefits of Gypsy Moth Control on Timberland,” USDA Forest Service Res. Note NE-337, 1987, Northeastern Forest Experiment Station, Broomall, p. 3.
  22. C. W. Minott and I. T. Guild, “Some Results of the Defoliation of Trees,” Journal of Economic Entomology, Vol. 18, No. 2, 1925, pp. 345-348.
  23. W. L. Baker, “Effect of Gypsy Moth Defoliation on Certain Trees,” Journal of Forestry, Vol. 39, No. 12, 1941, pp. 1017-1022.
  24. S. Kucherov, “The Reconstruction of Lymantria dispar Outbreaks by Dendrochronological Methods in the South Urals,” In: Y. N. Baranchikov, W. J. Mattson, F. P. Hain and L. Thomas, Eds., Forest Insect Guilds: Patterns of Interaction with Host Trees, Abakan, Siberia, 13-17 August 1989.
  25. F. Huber, “Determinisme de la Surface des Vaisseaux du Bois des Chenes Indigenes (Quercus robur L., Quercus petraea Liebl.): Effet Individuel, Effet de l’Appareil Foliaire, des Conditions Climatiques et de l’Age de l’Arbre,” Annals of Forest Science, Vol. 50, No. 5, 1993, pp. 509-524. doi:10.1051/forest:19930507
  26. A. Fratzian, “Growth and Vitality of Oak Stands after Being Eaten by Gypsy Moths, Lymantria dispar L., in Romania,” Anz. Schaedlingskd., Pflanz. Unweltschutz, Vol. 46, 1973, pp. 122-125.
  27. A. Magnober and A. Cambini, “Radial Growth of Cork Oak and the Effects of Defoliation Caused by Larvae of Lymantria dispar L. and Malacosoma neustria L. [Portuguese],” Boletin do Instituto dos Produtos Florestals, No. 413, 1973, pp. 53-59.
  28. M. J. Twery, “Changes in the Vertical Distribution of Xylem Production in Hardwoods Defoliated by Gypsy Moth,” Ph.D. Dissertation, Yale University, New Haven, 1987.
  29. M. A. Fajvan, J. S. Rentch and K. W. Gottschalk, “The Effects of Thinning and Gypsy Moth Defoliation on Wood Volume Growth in Oaks,” Trees, Vol. 22, No. 2, 2008, pp. 257-268. doi:10.1007/s00468-007-0183-6
  30. R. Kienholz, “Seasonal Course of Height Growth in Some Hardwoods in Connecticut,” Ecology, Vol. 22, No. 3, 1941, pp. 249-258. doi:10.2307/1929612
  31. M. H. Zimmerman and C. L. Brown, “Trees: Structure and Function,” Springer-Verlag, New York, 1974
  32. P. M. Wargo, “Variation of Starch Content among and within Roots of Red and White Oak Trees,” Forest Science, Vol. 22, 1975, pp. 468-471.
  33. P. M. Wargo, “Consequences of Environmental Stress on Oak: Predisposition to Pathogens,” Annals of Forest Science, Vol. 53, No. 2-3, 1996, pp. 359-368. doi:10.1051/forest:19960218
  34. P. R. Larson, “Some Indirect Effects of Environment on Wood Formation,” In: M. H. Zimmerman, Ed., Formation of Wood in Forest Trees, Academic Press, New York, 1964.
  35. S. F. Gingrich, “Measuring and Evaluating Stocking and Stand Density in Upland Hardwood Forests in the Central States,” Forest Science, Vol. 13, No. 1, 1967, pp. 38-53.
  36. D. M. Smith, B. C. Larson, M. J. Kelty and P. M. S. Ashton, “The Practice of Silviculture Applied Forest Ecology,” 9th Edition, John Wiley and Sons, New York, 1997.
  37. M. L. McManus, “In the Beginning: Gypsy Moth in the United States,” In: P. C. Tobin and L. M Blackburn Eds. “Slow the Spread: A National Program to Manage the Gypsy Moth,” USDA Forest Service General Technical Report NRS-6. Newtown Square, 2007, pp. 3-13.
  38. VoorTech Consulting. Measure J2X R. VoorTech Consulting, Northwood, 2000.
  39. H. D. Grissino-Mayer, R. L. Holmes and H. C. Fritts, “The International Tree-Ring Data Bank Program Library Version 2.1 User’s Manual,” Laboratory of Tree-Ring Research, University of Arizona, Tucson, 1997.
  40. SAS Institute Inc., “SAS/STAT 9.1 User’s Guide,” SAS Institute Inc., Cary, 2004.
  41. G. W. Miller, J. W. Stringer and D. C. Mercker, “Technical Guide to Crop Tree Release in Hardwood Forests,” Professional Forestry Note, University of Tennessee, 2007. http://www.sref.info/publications/online_pubs
  42. T. T. Kozlowski, “Growth and Development of Trees,” Academic Press, New York, 1971.
  43. D. L. Graney, “Ten-Year Growth of Red and White Oak Crop Trees Following Thinning and Fertilization in the Boston Mountains of Arkansas,” Proceedings of the 4th Biennial Southern Silvicultural Research Conference, Atlanta, 4-6 November 1986.
  44. J. S. Rentch, D. Fekedulegn and G. W. Miller, “Climate, Canopy Disturbance, and Radial Growth Averaging in a Second-Growth Mixed-Oak Forest in West Virginia, USA,” Canadian Journal of Forest Research, Vol. 32, No. 6, 2002, pp. 915-927. doi:10.1139/x02-016
  45. P. Nola, “Climatic Signal in Earlywood and Latewood of Deciduous Oaks from Northern Italy,” In: J. S. Dean, D. M. Meko and T. W. Swetnam, Eds. Tree Rings, Environment and Humanity, University of Arizona, Tucson, 1996, pp. 249-258.
  46. J. C. Tardiff, “Earlywood, Latewood and Total Ring Width of Ring-Porous Species (Fraxinus nigra Marsh) in Relation to Climatic and Hydrologic Factors,” In: J. S. Dean, D. M. Meko and T. W. Swetnam, Eds., Tree Rings, Environment and Humanity, University of Arizona, Tucson, 1996, pp. 315-324.
  47. J. C. Tardiff and F. Conciatori, “Influence of Climate on Tree Rings and Vessel Features in Red Oak and White Oak Growing Near Their Northern Distribution Limit, Southwestern Quebec, Canada,” Canadian Journal of Forest Research, Vol. 36, No. 9, 2006, pp. 2317-2330. doi:10.1139/x06-133
  48. P. Fonti and I. Garcia-Gonzalez, “Suitability of Chestnut Early Wood Vessel Chronologies for Ecological Studies,” New Phytologist, Vol. 163, No. 1, 2004, pp. 77-86. doi:10.1111/j.1469-8137.2004.01089.x
  49. A. P. Schniewind, “Transverse Anisotropy of Wood: A Function of Gross Anatomic Structure,” Journal Forest Products Research Society, Vol. 9, 1959, pp. 350-359.

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