Predicting balsam fir growth reduction caused by spruce budworm using large-scale historical records of defoliation

Abstract

-To predict the reduction in growth of balsam fir (Abies balsamea (L.) Mill.) subjected to spruce budworm (Choristoneura fumiferana (Clem.)) epidemics, tree-ring chronologies of dominant trees were related to historical records of defoliation collected in the province of Quebec, Canada. These trees were sampled on 136 sites and were harvested for stem analyses that allowed us to calculate indexed radial growth and tree volume increment for a period that covers the last insect outbreak. Defoliation variables explained 36% and 23% of the annual changes in ring width index and annual volume increment index, respectively. Defoliation that dated back by as much as six years affected current-year growth whereas current-year defoliation had limited impact. Several severe annual defoliation events reduced volume growth of dominant balsam fir by 50% over a 10-year period. These results can help predict future growth reduction among dominant balsam fir trees subjected to different scenarios of spruce budworm defoliation over broad areas.balsam fir / spruce budworm / defoliation class / growth reduction / stem analysis Résumé -Prédiction de la réduction de croissance du sapin baumier causée par la tordeuse des bourgeons de l'épinette en utilisant des relevés historiques de défoliation recueillis à grande échelle. Afin de prédire les pertes de croissance de sapins baumiers (Abies balsamea (L.) Mill.) soumis à des épidémies de tordeuse des bourgeons de l'épinette (Choristoneura fumiferana (Clem.)), les séries chronologiques de cernes annuels d'arbres dominants ont été reliées à des relevés historiques de défoliation recueillis dans la province de Québec, Canada. Ces arbres, échantillonnés sur 136 stations, ont été abattus pour faire des analyses de tige qui ont permis de calculer des indices de croissance radiale et d'accroissements en volume pour une période couvrant la dernière épidémie de cet insecte. Les variables de défoliation expliquent 36 % et 23 % de la variation interannuelle de l'indice de croissance radiale et de l'indice d'accroissement annuel en volume, respectivement. Les défoliations s'étant produites jusqu'à six ans auparavant ont affecté la croissance de l'année courante alors que les défoliations de l'année courante n'ont eu qu'un effet limité. Des défoliations sévères répétées pendant plusieurs années ont diminué de 50 % la croissance en volume des sapins baumiers dominants pendant une période de 10 ans. Ces résultats peuvent contribuer à prédire la future réduction de croissance de sapins baumiers dominants soumis à différents scénarios de défoliation par la tordeuse des bourgeons de l'épinette pour de grands territoires. sapin baumier / tordeuse des bourgeons de l'épinette / classe de défoliation / réduction de la croissance / analyse de tige

Natural root grafting in Picea mariana to cope with spruce budworm outbreaks

“…As the impact of budworm defoliation in stand development lengthens far beyond the outbreak (Colford-Gilks et al 2012), differential growth between potential dominant and suppressed trees (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) lagged 12 years behind the period of highest outbreak intensity (1973)(1974)(1975)(1976)(1977)(1978). Accordingly, the post-outbreak impact in balsam fir has been observed to persist during wide temporal spans, e.g., 6 years in relation to tree growth (Pothier et al 2005) and 11-15 years (Taylor and MacLean 2009) and up to 35 years in relation to tree mortality (MacLean and Andersen 2008). Enhanced carbon allocation to storage (Salomón et al 2016) and use of starch reserves to fuel metabolism over periods of limited carbon supply (Bhupinderpal-Singh et al 2003;Aubrey et al 2012) and to resprout in cases of canopy dieback is the life strategy of species subjected to frequent disturbance regimes (Bond and Midgley 2001).…”

“…Variability in tree growth and mortality following budworm defoliation remains largely unexplained; e.g., stand characteristics accounted for 40% of the variance in growth reduction in balsam fir (Bergeron et al 1995;Campbell et al 2008) and 47% of the total deviation in tree mortality in spruce and fir trees (Colford-Gilks et al 2012). Similarly, the coefficient of determination between ring-width index and defoliation intensity was below 0.4 and 0.2 in fir and spruce trees, respectively (Pothier et al 2005(Pothier et al , 2012, suggesting a relatively weak relationship between defoliation and tree growth, especially for the latter species (Pothier et al 2012). These observations point to overlooked factors that might influence tree performance to withstand budworm defoliation and could help to explain why some trees succumb to outbreaks whereas others survive.…”

“…Insect outbreaks have a periodicity of 30-40 years (Boulanger and Arseneault 2004;Boulanger et al 2012) and cause extensive mortality, e.g., the latest spruce budworm outbreak destroyed up to 238 million m 3 of softwood in Quebec (Boulet et al 1996). Larval feeding on foliage can cause tree growth reductions above 40% (Krause and Morin 1999;Pothier et al 2005) and, eventually, tree death. Canopy gaps are progressively filled by growth releases of surviving trees, and they trigger recruitment and post-outbreak colonization (Morin 1994).…”

“…Tree vulnerability to outbreaks is crucial to predict forest dynamics and timber yield in boreal forests (Pothier et al 2005;Bouchard et al 2007;Morin et al 2007); yet, knowledge on tree vulnerability is limited in comparison with our understanding of tree susceptibility to budworm outbreaks (Pothier and Mailly 2006;Campbell et al 2008). Variability in tree growth and mortality following budworm defoliation remains largely unexplained; e.g., stand characteristics accounted for 40% of the variance in growth reduction in balsam fir (Bergeron et al 1995;Campbell et al 2008) and 47% of the total deviation in tree mortality in spruce and fir trees (Colford-Gilks et al 2012).…”

Modelling natural disturbances in forest ecosystems: a review

“…loss of leaf area) based on stand and environmental descriptors (e.g., Davidson et al, 2001;Wolf et al, 2008: GUESS;Komonen and Kouki, 2008). Similar statistical approaches were used to directly model tree growth reduction in response to defoliation (e.g., Mason et al, 1997;Pothier et al, 2005;Campbell et al, 2008). With regard to insect herbivory on phloem rather than on foliage, the Westwide Pine Beetle Model (Smith et al, 2005;Ager et al, 2007: FVS) represents a processoriented approach in which the beetle occupation level necessary to kill one square foot of basal area is used as a proxy for the physiological effects of phloem feeding.…”