Ants were surveyed in three habitats at Mount St. Helens in 2008. The area most impacted by the 1980 eruption is the Pumice Plain. Less impacted is the Blowdown Zone where trees were toppled due to the blast. Two habitats were surveyed in the Pumice Plain varying in vegetation density (Pumice Plain Low-Vegetation (PPLV) and Pumice Plain High-Vegetation (PPHV)), and one habitat was surveyed in the Blowdown Zone (BDZ). Ten ant species were collected with the most species collected from the BDZ habitat and the least from the PPLV habitat. Ant abundance was higher at the BDZ and PPHV habitats than at the PPLV habitat. Ant biodiversity was highest at the BDZ habitat than at the PPHV and PPLV habitats. Significant correlations between ant community parameters and plant community parameters were also found. Few plants in the PPLV habitat may contribute to the lack of ants. High ant species richness at the BDZ habitat may be due to complex plant architecture. Results from this study suggest that ants are important focal species in tracking biotic recovery following disturbances. 1. Introduction Mount St. Helens erupted on May 18, 1980, strongly impacting a 600？km2 area as a result of a northern lateral blast of the volcano [1]. The volcanic eruption began with a magnitude 5.1 earthquake, which dislodged the northern slope of the mountain leading to the largest landslide in recorded history [1]. Material from the landslide covered a 60？km2 area referred to as the Debris Avalanche [1]. Following the landslide a volcanic blast toppled forests within a 370？km2 area referred to as the Blowdown Zone because mature trees were snapped at the base as a result of the impact [1]. Pyroclastic flows emanating from the volcano covered 15？km2 of land immediately north of the volcano, which is now referred to as the Pumice Plain [1]. Organisms in the Pumice Plain were vaporized as a result of the volcanic blast [1]. Since 1980, numerous ecological studies have recorded the impact of the volcanic eruption on plant and animal communities and ecosystem dynamics [2]. Most impressive among the organismal responses was the discovery of pioneer arthropod colonists on the Pumice Plain within a year following the eruption [3, 4]. Even plants were quick to respond with a prairie lupine plant, Lupinus lepidus, being found on the Pumice Plain in 1981 [5]. Among the pioneer arthropod colonists found on the Pumice Plain were winged ants (Formicidae) [6]. Ants have been known to respond dramatically to changes in the environment and may be useful indicator species in assessing recovery of
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