THE EFFECTS OF THE MOUNT ST. HELENS ERUPTION CLOUD ON FIR (ABIES SP.) NEEDLE CUTICLES: ANALYSIS WITH SCANNING ELECTRON MICROSCOPY.

Abstract

Dead fir needles were collected from standing trees of Abies amabilis in five sites at the margin of the blast zone and located progressively farther from the eruption crater of Mount St. Helens. Scanning electron microscope techniques were used to determine patterns of cuticular melting for these needles and for Abies grandis needles which were heated at specific temperatures for 2 min. Comparisons between cuticular appearances of oven-heated needles and needles from Mount St. Helens were made to determine air temperatures at the collection sites at the time of the eruption. Air temperatures at these sites are estimated to have ranged from about 50 C to about 250 C. Analysis of cuticular sulfur content showed these needles adsorbed little or no volcanic S02 . Conifer needles provided a record of maximum air temperatures during the eruption, and helped reveal the pattern of heat distribution from the eruption cloud. This technique may prove useful for ecological studies in other heat-stressed habitats.