RESPONSE OF RED ALDER (ALNUS-RUBRA) SEEDLINGS TO A WOOLLY ALDER SAWFLY (ERIOCAMPA-OVATA) OUTBREAK

We monitored the effect of an outbreak of Eriocampa ovata L.on experim ental Alnus rubra Bong. seedlings during the year of the outbreak (199 3) and the following growing season. Seedlings planted on low-elevatio n sites had significantly more of their leaves damaged (>50% per tree) than plants on high-elevation sites (<25% per tree), with significant differences between low-elevation sites during the year of the outbre ak. There was a positive relationship between the amount of herbivore damage and plant relative growth rate early in the growing season and a negative relationship by August. This suggests that the sawflies att acked the largest and fastest growing plants, reducing their growth by midsummer. Plants with the highest degree of herbivore damage were th e largest by the end of the growing season with no effects on plant gr owth the following year. Leaves from plants that had previously been d efoliated were less palatable to E. ovata in 1994, but plants with a h igh degree of herbivore damage in 1994 were likely plants that had a h igh degree of damage in 1993.