Mount St. Helens erupted on May 18, 1980, demolishing an area of 600km2 and removing all fauna and flora in the area north of the mountain. The eruption converted the substrate in the area into a mixture of pumice pebbles and ash (Mullineaux & Crandell 1981). Research done by Parmenter et al. (2018) has shown that ground beetles (Coleoptera: Carabidae) comprise 14% of the total beetle diversity out of 39 families observed, making this the second most abundant family in the study area. Ground beetles are often used as bioindicators along disturbance gradients. Their well-known taxonomy and short reproductive cycle make them effective monitors of ecosystem changes. Carabids have unique sensitivity to the changes of microhabitats during succession, seen through the loss and gain of species in the population (Parmenter et al. 2018). My study aims to determine whether assemblages of ground beetles remain a model for relay successional patterns, as well as contribute to the ongoing monitoring of invertebrate biodiversity in this post-eruption landscape. Pitfall traps were used to monitor carabid diversity at three locations. Traps were put in transects of five, set 10m apart, checked weekly to capture phenology, and species diversity over time recorded.
Results/Conclusions
Over 300 carabid specimens and 20 carabid species were caught, with two species not previously recorded in the study area: Pterostichus lama(Ménétriés) and Agonum cupreum(Dejean). Agonum cupripenne(Say) was found in great abundance along Spirit Lake and in much higher numbers than previously recorded. Of the three trapping areas, Spirit Lake yielded the highest number of carabid species as well as the highest number of individuals. This could be due to this site having a much more developed understory and plant community compared to the other two. The soil type and moisture have also been known to produce differing distributions of carabids in this location. Drier soil and lack of shade in the pumice plains causes increased water loss through cuts in the beetles’ waxy cuticle as well as the need for more frequent grooming. The presence of new species, loss of previously recorded species, and increasing dissimilarity in species composition from historical data demonstrate the sensitivity carabids have to the changes the plant and other insect communities are undergoing post-eruption.