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

Danaë M A Rozendaal,Richard K Kobe,Petr Heneberg

doi:10.1371/journal.pone.0167139

Danaë M A Rozendaal, Richard K Kobe + Show 1 more

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https://doi.org/10.1371/journal.pone.0167139

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Journal: PloS one	Publication Date: Nov 21, 2016
Citations: 8	License type: CC BY 4.0

Affiliation: Michigan State University

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.

Highlights

In temperate closed-canopy forests, gap formation and closure are thought to be major drivers of forest dynamics
Shade intolerant species benefit most from large canopy gap formation, as these species grow fast in high-light conditions at the expense of low survival in shade, while shade-tolerant species have high survival in shade, but do not grow fast in high light ([8], but see [9]). These differential responses to resource levels across tree species can play an important role in driving long-term patterns in forest dynamics [10,11]
We evaluate the effect of a forest tent caterpillar outbreak in 2009 on understory light availability, soil nutrient levels and seedling height growth for six tree species in a hardwood forest in northern lower Michigan, USA

Summary

Introduction

In temperate closed-canopy forests, gap formation and closure are thought to be major drivers of forest dynamics. Shade intolerant species benefit most from large canopy gap formation, as these species grow fast in high-light conditions at the expense of low survival in shade, while shade-tolerant species have high survival in shade, but do not grow fast in high light ([8], but see [9]). These differential responses to resource levels across tree species can play an important role in driving long-term patterns in forest dynamics [10,11]

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