Event Title

Legacy of Insect Defoliators: Increased Wind-Related Mortality Two Decades After a Spruce Budworm Outbreak

Event Website

http://www.nafew2009.org/

Start Date

23-6-2009 10:30 AM

End Date

23-6-2009 10:50 AM

Description

The effects of spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks on growth and survival of balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea spp.) are well documented, but few studies extend beyond 10 years after defoliation ceased. We used inventory data from 106 permanent sample plots (PSP) in >50 year old balsam fir stands in northern New Brunswick, Canada, to determine legacy effects of the 1969-1993 budworm outbreak on stand development up to 29 years after defoliation ceased. Defoliation data were based on annual aerial surveys from 1945 to 1993 and PSP ground sampling from 1985 to 1993. PSPs were stratified into net stand volume development categories (decreasing, stable, and increasing stemwood volume from 1985-2005), and related to outbreak phases (outbreak, direct 1-10 years after defoliation ceased, and legacy >10 years), number of years of defoliation (1-4, 5-8, 9-12), and stand age (mature, overmature). Trend and rate of volume development over time was related to past outbreak severity (?2 = 6.681, df = 2, p<0.05). For example, 93% of 15 PSPs that had entered the stand break-up phase (i.e., <100 m3/ha live standing volume) experienced ?5 years of defoliation. Stand age was an important factor influencing outbreak severity (e.g., r2 = 0.383, p<0.01) and vulnerability to post-outbreak wind disturbance events. A pulse of post-outbreak wind-related mortality peaked at 11 m3/ha/yr 11-15 years after defoliation ceased. Hence, the compounding effect of post-outbreak wind disturbance drastically increased the impact and longevity of the spruce budworm disturbance event, especially in ageing post-outbreak stands. Our study demonstrates the need to consider the complexity of disturbance dynamics, as a single disturbance event rarely operates in isolation. Stand development projections and wood supply models need to take into account losses that result from the interaction of disturbances events to ensure the security of future wood supplies.

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Jun 23rd, 10:30 AM Jun 23rd, 10:50 AM

Legacy of Insect Defoliators: Increased Wind-Related Mortality Two Decades After a Spruce Budworm Outbreak

The effects of spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks on growth and survival of balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea spp.) are well documented, but few studies extend beyond 10 years after defoliation ceased. We used inventory data from 106 permanent sample plots (PSP) in >50 year old balsam fir stands in northern New Brunswick, Canada, to determine legacy effects of the 1969-1993 budworm outbreak on stand development up to 29 years after defoliation ceased. Defoliation data were based on annual aerial surveys from 1945 to 1993 and PSP ground sampling from 1985 to 1993. PSPs were stratified into net stand volume development categories (decreasing, stable, and increasing stemwood volume from 1985-2005), and related to outbreak phases (outbreak, direct 1-10 years after defoliation ceased, and legacy >10 years), number of years of defoliation (1-4, 5-8, 9-12), and stand age (mature, overmature). Trend and rate of volume development over time was related to past outbreak severity (?2 = 6.681, df = 2, p<0.05). For example, 93% of 15 PSPs that had entered the stand break-up phase (i.e., <100 m3/ha live standing volume) experienced ?5 years of defoliation. Stand age was an important factor influencing outbreak severity (e.g., r2 = 0.383, p<0.01) and vulnerability to post-outbreak wind disturbance events. A pulse of post-outbreak wind-related mortality peaked at 11 m3/ha/yr 11-15 years after defoliation ceased. Hence, the compounding effect of post-outbreak wind disturbance drastically increased the impact and longevity of the spruce budworm disturbance event, especially in ageing post-outbreak stands. Our study demonstrates the need to consider the complexity of disturbance dynamics, as a single disturbance event rarely operates in isolation. Stand development projections and wood supply models need to take into account losses that result from the interaction of disturbances events to ensure the security of future wood supplies.

http://digitalcommons.usu.edu/nafecology/sessions/disturbance/1