Natural Resource Ecology and Management Natural Resource Ecology and Management Publications 2017 Landscape host abundance and configuration regulate periodic outbreak behavior in spruce budworm (Choristoneura fumiferana Clem.) Louis-Etienne Robert Universite de Montreal Brian R. Sturtevant U.S. Department of Agriculture Barry J. Cooke Ontario Ministry of Natural Resources and Forestry Patrick M. A. James Universite de Montreal MFoallorie-Jw othisees a Fndor taindditional works at: http://lib.dr.iastate.edu/nrem_pubs UnivPerasitrty ofof TtheoronEtonvironmental Indicators and Impact Assessment Commons, Forest Management Commons, Natural Resources and Conservation Commons, and the Natural Resources See next page for additional authors Management and Policy Commons The ompc lete bibliographic information for this item can be found at http://lib.dr.iastate.edu/ nrem_pubs/248. For information on how to cite this item, please visit http://lib.dr.iastate.edu/ howtocite.html. This Article is brought to you for free and open access by the Natural Resource Ecology and Management at Iowa State University Digital Repository. It has been accepted for inclusion in Natural Resource Ecology and Management Publications by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Landscape host abundance and configuration regulate periodic outbreak behavior in spruce budworm (Choristoneura fumiferana Clem.) Abstract Landscape-level forest management has long been hypothesized to affect forest insect outbreak dynamics, but empirical evidence remains elusive. We hypothesized that the combination of increased hardwood relative to host tree species, prevalence of younger forests, and fragmentation of those forests due to forest harvesting legacies would reduce outbreak intensity, increase outbreak frequency, and decrease spatial synchrony in spruce budworm (Choristoneura fumiferana Clem.) outbreaks. We investigated these hypotheses using tree ring samples collected across 51 sites pooled into 16 subareas distributed across a large ecoregion spanning the international border between Ontario (Canada), and Minnesota (USA). This ecoregion contains contrasting land management zones with clear differences in forest landscape structure (i.e., forest composition and spatial configuration) while minimizing the confounding influence of climate. Cluster analyses of the 76-years time-series generally grouped by subareas found within the same land management zone. Spatial nonparametric covariance analysis indicated that the highest and lowest degree of spatial synchrony of spruce budworm outbreaks were found within unmanaged wilderness and lands managed at fine spatial scales in Minnesota, respectively. Using multivariate analysis, we also found that forest composition, configuration, and climate together accounted for a total of 40% of the variance in outbreak chronologies, with a high level of shared variance between composition and configuration (13%) and between composition and climate (9%). At the scale of our study, climate on its own did not explain any of the spatial variation in outbreaks. Outbreaks were of higher frequency, lower intensity, and less spatially synchronized in more fragmented, younger forests with a lower proportion of host species, with opposing outbreak characteristics observed in regions characterised by older forests with more concentrated host species. Our study is the first quantitative evaluation of the long-standing "silvicultural hypothesis" of spruce budworm management specifically conducted at a spatio-temporal scale for which it was intended. Keywords spruce budworm; harvest disturbance; landscape ecology, forest management legacies, dendrochronology, outbreak synchrony Disciplines Environmental Indicators and Impact Assessment | Forest Management | Natural Resources and Conservation | Natural Resources Management and Policy Comments This is a manuscript of an article published as Robert, L.-E., Sturtevant, B. R., Cooke, B. J., James, P. M. A., Fortin, M.-J., Townsend, P. A., Wolter, P. T. and Kneeshaw, D. (2017), Landscape host abundance and configuration regulate periodic outbreak behavior in spruce budworm (Choristoneura fumiferana Clem.). Ecography. doi: 10.1111/ecog.03553. Rights Works produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The onc tent of this document is not copyrighted. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/nrem_pubs/248 Authors Louis-Etienne Robert, Brian R. Sturtevant, Barry J. Cooke, Patrick M. A. James, Marie-Josee Fortin, Philip A. Townsend, Peter T. Wolter, and Daniel Kneeshaw This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/nrem_pubs/248 Landscape host abundance and configuration regulate periodic outbreak behavior in spruce budworm (Choristoneura fumiferana Clem.). Louis-Etienne Robert1, Brian R. Sturtevant2, Barry J. Cooke3, Patrick M. A. James1, Marie- Josée Fortin4, Philip A. Townsend5, Peter T. Wolter6, Daniel Kneeshaw7 1Département de sciences biologiques, Université de Montréal, C.P. 6128, succursale Centre-ville. Montréal, Québec, Canada. H3C 3J7 2Institute for Applied Ecosystem Studies, Northern Research Station, USDA Forest Service, 5985, Highway K. Rhinelander, WI 5450 3Ontario Ministry of Natural Resources and Forestry, 70 Foster Dr., Sault Ste. Marie, Ontario, Canada. P6A 6V8 4Department of Ecology and Evolutionary Biology, University of Toronto. 25 Willcocks Street. Toronto, Ontario, Canada. M5S 3B2 5Russell Labs, 1630 Linden Drive, Madison, USA. WI 53706 6Iowa State University, Dept. of Natural Resource Ecology and Management. 339 Science II. Ames, USA. Iowa 50011 7Centre d’étude de la forêt (CEF). Université du Québec à Montréal, C.P. 8888, Succ. Centre-Ville. Montréal, Québec, Canada. H3C 3P8 Corresponding author: Louis-Etienne Robert , Département de sciences biologiques, Université de Montréal, C.P. 6128, succursale Centre-ville. Montréal, Québec, Canada. H3C 3J7. Email: [email protected] Decision date: 13-Nov-2017 This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: [10.1111/ecog.03553] ‘This article is protected by copyright. All rights reserved.’ Accepted Article Accepted Abstract Landscape-level forest management has long been hypothesized to affect forest insect outbreak dynamics, but empirical evidence remains elusive. We hypothesized that the combination of increased hardwood relative to host tree species, prevalence of younger forests, and fragmentation of those forests due to forest harvesting legacies would reduce outbreak intensity, increase outbreak frequency, and decrease spatial synchrony in spruce budworm (Choristoneura fumiferana Clem.) outbreaks. We investigated these hypotheses using tree ring samples collected across 51 sites pooled into 16 subareas distributed across a large ecoregion spanning the international border between Ontario (Canada), and Minnesota (USA). This ecoregion contains contrasting land management zones with clear differences in forest landscape structure (i.e., forest composition and spatial configuration) while minimizing the confounding influence of climate. Cluster analyses of the 76-years time-series generally grouped by subareas found within the same land management zone. Spatial nonparametric covariance analysis indicated that the highest and lowest degree of spatial synchrony of spruce budworm outbreaks were found within unmanaged wilderness and lands managed at fine spatial scales in Minnesota, respectively. Using multivariate analysis, we also found that forest composition, configuration, and climate together accounted for a total of 40% of the variance in outbreak chronologies, with a high level of shared variance between composition and configuration (13%) and between composition and climate (9%). At the scale of our study, climate on its own did not explain any of the spatial variation in outbreaks. Outbreaks were of higher frequency, lower intensity, and less spatially synchronized in more fragmented, younger forests with a lower proportion of host species, with opposing outbreak characteristics observed in regions characterised by older forests with more concentrated host species. Our study is the first quantitative evaluation of the long-standing “silvicultural hypothesis” of spruce budworm management specifically conducted at a spatio-temporal scale for which it was intended. Keywords: spruce budworm; harvest disturbance; landscape ecology, forest management legacies, dendrochronology, outbreak synchrony. ‘This article is protected by copyright. All rights reserved.’ Accepted Article Accepted Introduction Outbreaks of boreal forest insects are a major forest disturbance that have significant ecological and economic consequences. Insect outbreaks affect biogeochemical processes and can influence nutrient cycling, hydrology, and atmospheric carbon cycling, all of which can affect climate at a global scale (Kurz et al. 2008, Dymond et al. 2010). Insect outbreaks also affect forest landscape structure (i.e., stand species composition and spatial configuration) with consequences for forest succession (Baskerville 1975), timber production (Chang