Impacts of Prescribed Burns and Severe Weather Events on Oak Wilt Transmission in Central Minnesota

Abstract

Ecological disturbances of a region shape the landscape and influence ecosystem structure and function. However, in a rapidly changing world, newly introduced disturbances such as diseases and pests interact with historical disturbance regimes in unknown ways. The purpose of this thesis was to identify relationships between oak wilt, a catastrophic disease of oak trees introduced to Minnesota in the 1940s, and two historical disturbances of central Minnesota: low intensity fires and severe weather events. 1. The relationship between fire frequency and oak wilt occurrence was explored using a prescribed burning program at Cedar Creek Ecosystem Science Reserve. Using data collected from a census of 1,700 oak trees located on 28 different burn plots, two descriptive models were created: a logistic regression model to describe the probability of oak wilt presence and a Poisson regression model to describe density of stems with oak wilt. High fire frequency plots had lower oak wilt probability and oak wilt stem density than low fire frequency plots. Oak wilt presence was lower in high fire frequency plots than low fire frequency plots as well. These results suggest there is a relationship between high fire frequency and reduced probability of oak wilt presence and oak wilt stem densities. This relationship provides preliminary support for the use of prescribed burning as a possible management tool in conjunction with existing control measures. 2. The relationship between severe weather events (wind speeds > 50 knots and/or recorded hail amounts) and new oak wilt infection site was examined using NOAA’s severe weather events database and Minnesota DNR oak wilt aerial surveys for Anoka County. New oak wilt pocket formation occurred more frequently in areas where a severe weather event occurred the previous year. These results suggest severe weather events increase the probability of aboveground transmission of oak wilt via insect vectors and the likelihood of new oak wilt pocket formation. This relationship can be used to prioritize recently storm-damaged areas for more focused surveying in order to increase the success of early oak wilt detection. The relationships between fire frequency, severe weather events, and oak wilt presented within this thesis provide a framework for future adaptations and research to further inform oak wilt detection and management practices.