Despite the widespread occurrence of dense stands of slow-growing trees stressed by competition and drought, the ponderosa pine forests around Flagstaff, AZ have not had a bark beetle epidemic in the past 100 years. There are many hypotheses for the underlying causes behind the lack of epidemic outbreaks. One hypothesis is based on the tree growth differentiation hypothesis and climate for Flagstaff. Flagstaff has hot, dry weather in May and June and receives summer rains during July and August. Tree growth is typically strongly limited by water stress in May and June. Bark beetles in northern Arizona may have peak flight times, i.e. host searching and colonizing, during May and June which coincides with greater host tree allocation of photosynthate to resin production (a major tree defense against bark beetles) versus growth. No previous studies in the Southwestern US have examined yearly phenology of bark beetle flights and tree growth and physiology in order to evaluate this hypothesis. We are assessing temporal variation in these characteristics between January and December 2002. Preliminary results show an increase in resin flow and beetle flights between January and June, higher photosynthesis in March than May and June, and little above- or below-ground growth in all months.
Species 1: Coleoptera Scolytidae Dendroctonus
Species 2: Coleoptera Scolytidae Ips pini
Keywords: Tree phenology, Host defense
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