Growth of Sugar Maple (Acer saccharum Marsh.) after Ice Storm Damage and Forest Tent Caterpillar (Malacosoma disstria Hubner) Defoliation

The January 1998 ice storm broke off tree crowns across a wide geographic area in northeastern North America, and forest tent caterpillar (Malacosoma disstria Hubner) defoliated some of the same stands in 2004–2007. We assessed the post-event growth responses of upper canopy sugar maples (Acersaccharum Marsh.) in previously thinned and recently rehabilitated even-aged northern hardwood stands in New York State, USA. Cores from ice-storm-damaged trees showed an initial radial growth reduction, a recovery after one year, and an increase to or above pre-storm levels after three years. A later forest tent caterpillar defoliation in the same stand caused a second reduction of growth, and another recovery after one year. We observed greater post-storm radial growth on trees released by a post-ice storm rehabilitation treatment than in the untreated control, with growth exceeding pre-storm rates. Cores from another site thinned 38 years earlier and impacted only by the forest tent caterpillar showed a more moderate growth reduction, and a prompt but smaller post-defoliation growth response than among trees affected by both the ice storm and defoliation. Findings reflect the potential for growth of upper canopy sugar maple trees to recover after a single or two closely occurring crown disturbances, and provide guidance to managers who must decide about removing or continuing to manage stands after similar kinds of ice storm damage or defoliation.

The influence of stand and landscape characteristics on forest tent caterpillar (Malacosoma disstria) defoliation dynamics: the case of the 1999–2002 outbreak in northwestern Quebec

The forest tent caterpillar (Malacosoma disstria Hbn.) is an eruptive forest insect common across North America and an important defoliator of trembling aspen (Populus tremuloides Michx.). Forest stands having suffered severe defoliations by the forest tent caterpillar over multiple years are known to incur reduced tree growth and increased tree mortality. In this study, we developed a predictive model of forest tent caterpillar defoliation dynamics using local and contextual variables expressing forest composition and structure, and their heterogeneity, at different scales. Of all scales considered (500, 1000, 1500, and 2000 m), contextual variables at 1500 m were found to have the greatest effect on defoliation dynamics. At this scale, we found that a greater proportion of preferred host trees in the landscape increased defoliation severity, but duration was modulated by compositional heterogeneity, where persistence was reduced in highly heterogeneous landscapes. Indeed, the likelihood of a single year of defoliation was much greater in highly diverse landscapes than the likelihood of multiple years of defoliation. These findings are consistent with ecological theory. Contrary to the expected result that older trees would be most susceptible, we found that “middle-aged” trees (~50 years) were most likely to be defoliated.