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.

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