Loss of wildfire – a 55 year sample of forest change in north-central Minnesota

Background/Question/Methods

Fire dependent pine forests in north-central Minnesota were maintained by natural and anthropogenic fire until Europeans settled the area in the early 1900’s. By the 1960’s researchers were concerned that this fire suppression was causing adverse effects to the fire dependent forests. In 1964, Vilas Kurmis, from the U. of Minnesota, installed monumented sample sites for long-term monitoring of change in the upland forest communities of Itasca State Park, Clearwater Co, Minnesota. These sites have been re-sampled approximately every 10 years since. Using the Minnesota DNR’s native plant community classification, we compared sites from 1965 with the same sites in 2021, to explore community change. Each site has eight circular plots (11.6 m diameter) of five nested rings. The outer four rings and inner circle are used for tree sampling, with dbh and species recorded. The inner circle also has heights for smaller woody plants; estimated cover of forbs and small shrubs (like blueberries); and estimated total cover for broad categories such as trees, tree reproduction, shrubs, forbs, graminoids, etc.

Results/Conclusions

Of the 30 sites, 18 were fire-dependent and 12 were mesic hardwood in 1965. Nine of the fire-dependent sites and only one of the mesic hardwood sites shifted toward more mesic conditions, so overall 10 sites shifted more mesic while 15 showed no shift, and the rest showed no clear trend. These patterns are consistent with our hypotheses that a disruption of fire processes would cause a mesic shift in the fire-dependent sites, and that mesic sites would remain mesic. According to the classification used, the 30 sample sites had a mix of northern and central floristic affinities. The few sites that shifted floristic affinities showed no clear signal of shifts being due to lack of fire, climate change or other disturbances.