To improve understanding of the temporal aspects of looper outbreaks, we are developing methods for historical reconstruction of past outbreaks. In 2003-4 we successfully quantified a 'tree-ring signature' in western hemlock and western redcedar that is caused by looper defoliation. In this study, we targeted the Coquitlam Island where historical records indicate an outbreak defoliated stands between 1969 and 1973. Because these stands were located on the island, accessibility was limited and they were not salvaged logged during that outbreak. Dendroecological analyses showed that three of five sites on the island were impacted by the 1970s outbreak. Narrow marker rings in 1972 and 1973 were present on the island but not in chronologies from sites on-shore, indicating the suppression was due to a local disturbance rather than regional influences such as climate. Western redcedar is a secondary host to western hemlock looper and showed a growth-suppression during the early 1970s at one site on the island. In the next two field seasons, we will expand sampling to assess additional stands including mature forests dominated by western hemlock.
Lori D. Daniels.
Forest Investment Account (FIA). 2004. Western hemlock looper in coastal BC: disturbance regime and implications for forest management. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2004MR253