Carbon and Nitrogen Levels across Forest Soil Communities Impacted by Bark Beetle and Wildfire Disturbance in Western Montana

Abstract:

Global climate change has had extensive impacts on the forest ecosystems of the western US, namely by causing increases in mountain pine beetle numbers and wildfires. Mountain pine beetles experience higher survival rates due to milder winters, allowing for greater frequency and severity of attacks and in turn causing more widespread pine tree mortality. Meanwhile, the arid conditions created by this temperature increase have been conducive to a surge in wildfires. Although many investigations have been carried out on the soil biogeochemistry in areas hit by one or the other, no study to our knowledge has explicitly researched the compound effects of these disturbances. This study examined soil levels of carbon (C) and nitrogen (N) as well as the C/N ratios of pine and fir soil communities that have been affected by both beetle and fire disturbance. Our results show that no significant differences were found in the C/N ratios in response to all modes of disturbance. However, significant C losses from the O horizon, but not the M horizon, were observed following wildfire. Similarly, losses in N from just the O horizon were observed, but these were not significant. In conclusion, fire resulted in marked declines in soil C, and forests impacted by beetle infestation and fire experienced C losses similar to fire alone.