RELATIONSHIP BETWEEN WEATHER PATTERNS, SITKA SPRUCE (PICEA-SITCHENSIS) STRESS, AND POSSIBLE TIP WEEVIL (PISSODES-STROBI) INFESTATION LEVELS

Vapor pressure deficit (VPD) regimes were determined for Sitka spruce (Picea sitchensis (Bong.) Carr.) plantations growing in coastal and inland sites of the Olympic Peninsula of Washington State. Relationships between VPD regimes on patterns of stomatal conductance, stem hydration, and xylem pressure potential were examined in Sitka spruce saplings growing on these two sites. These patterns and VPD regimes were analyzed in relation to areas known to sustain either low or high infestation levels of the tip weevil (Pissodes strobi (Peck) (Coleoptera: Curculionidae)). High VPD regimes of inland Sitka spruce plantations were frequently observed in the summers and were associated with clear days and on-shore breezes; in synchrony with high VPD regimes, the trees of these areas exhibited water stress and decreased photosynthesis. In turn, these factors might contribute to lowered host defenses against tip weevil attacks. Coastal sites generally experienced lower VPD regimes and, consequently, infrequent water stress and stomatal closure, and spruces growing near the coast were mostly associated with low tip weevil attack.