A Forest Tent Caterpillar Outbreak Increased Resource Levels and Seedling Growth in a Northern Hardwood Forest

Abstract

In closed-canopy forests, gap formation and closure are thought to be major drivers of forest dynamics. Crown defoliation by insects, however, may also influence understory resource levels and thus forest dynamics. We evaluate the effect of a forest tent caterpillar outbreak on understory light availability, soil nutrient levels and tree seedling height growth in six sites with contrasting levels of canopy defoliation in a hardwood forest in northern lower Michigan. We compared resource levels and seedling growth of six hardwood species before, during and in the three years after the outbreak (2008–2012). Canopy openness increased strongly during the forest tent caterpillar outbreak in the four moderately and severely defoliated sites, but not in lightly defoliated sites. Total inorganic soil nitrogen concentrations increased in response to the outbreak in moderately and severely defoliated sites. The increase in total inorganic soil nitrogen was driven by a strong increase in soil nitrate, and tended to become stronger with increasing site defoliation. Seedling height growth increased for all species in the moderately and severely defoliated sites, but not in lightly defoliated sites, either during the outbreak year or in the year after the outbreak. Growth increases did not become stronger with increasing site defoliation, but were strongest in a moderately defoliated site with high soil nutrient levels. Growth increases tended to be strongest for the shade intolerant species Fraxinus americana and Prunus serotina, and the shade tolerant species Ostrya virginiana. The strong growth response of F. americana and P. serotina suggests that recurring forest tent caterpillar outbreaks may facilitate the persistence of shade intolerant species in the understory in the absence of canopy gaps. Overall, our results suggest that recurrent canopy defoliation resulting from cyclical forest insect outbreaks may be an additional driver of dynamics in temperate closed-canopy forests.

Reconstruction of Stand History and Impact Evaluation of an Invasive Bark Beetle in Siberian Fir Forests with the Help of Spatial Structure Analysis

“…At this stage, Polygraphus proximus is able to cause maximum damage and interrupt the forest-forming process of fir or, if there is a sufficient amount of viable undergrowth of fir, roll back the succession cycle of its dominance for several decades. In any case, the decrease in canopy cover stimulates the growth of saplings [38]. This shows how insect outbreaks can be a driver of forest dynamics.…”

Anatomical acclimation of mature leaves to increased irradiance in sycamore maple (Acer pseudoplatanus L.)

“…Although the scenario we tested was equivalent to a sudden gap formation, light availability may also change slightly and gradually throughout the growing season due to upper canopy defoliation (Rozendal and Kobe 2016 ) and to the changing leaf or solar angle. Such changes may not induce sudden stress and allow a more gradual anatomical and physiological acclimation.…”

Impacts Of The Invasive FourEyed Fir Bark Beetle (Polygraphus Proximus Blandf.) On Siberian Fir (Abies Sibirica Ledeb.) Forests In Southern Siberia

“…The impact of herbivorous insects on forest ecosystems has interested researchers around the world (Lyamtsev, Isaev 2005;Palnikova et al 2006;McCullough 2006;Bidart-Bouzat, Imeh-Nathaniel 2008;Rozendaal, Kobe 2016). Particular attention has been given to studying how invasive insects impact different tree species (Binimelis et al 2007;Hulme et al 2009;Bacon et al 2012).…”