Expanding the Tree Ring-Based Fire History Reconstruction of Itasca State Park

Abstract

Itasca State Park is among the most iconic and visited state parks in Minnesota, and was established to protect the headwaters of the Mississippi River as well as to preserve an example of the old growth pine forests that once characterized the region. The red pine-dominant, fire dependent forest communities of Itasca support a close association between frequent fire events and forest composition, with many fire-scarred trees and remnant stumps preserving the park’s fire history within their annual growth rings. This research uses remnant, fire-scarred red pine stumps to expand upon previous fire history research by enhancing spatial coverage of tree-ring sample collection, strengthening the temporal assignment of fire events, and providing the first assessment of historic fire seasonality across the entire park area. Increasing evidence has been better documenting the role of people as critical ignition sources in fire regimes of the Upper Great Lakes. To better understand the role people may have had in influencing the fire regime of Itasca State Park, I investigated the cultural history of the area to provide important contextual information.I reconstructed a conservative fire history in Itasca State Park, dating 98 of 129 total tree-ring cross-sections that were collected in 2019, 2020 and 2021. I recorded 27 fire events from 348 individual fire scars between 1649 and 2015 (366 years), with the earliest and latest tree-ring documented fires recorded in 1697 and 1920 respectively. During this time, shorter and longer fire intervals were noted, with intervals being similar to other red pine fire history reconstructions. Fires tended to be synchronous across the park, with four fire years being recorded by at least 70% of the recording samples. Other fires with lower replication still exhibit a synchronous nature, as many events were recorded by samples collected at spatially distant sites. Fire seasonality could be determined on 180 (51.7%) fire scars, 78% of which affected the earlywood of the associated tree ring, indicating the early-growing season as the primary season of fire occurrence in Itasca State Park. Superposed Epoch Analysis found a significant relationship between fire occurrence and dry conditions the year before, and the year of fire events. Written records for the broader park area, however, indicate that most forest fires were ignited by human activities, and occurred in the spring, prior to the usual period of lightning strikes and fire occurrence (June-August). It is possible for Native American agency to have played an important role alongside dry conditions and lightning as an ignition source of historic fire events. Findings from this research affirm previous findings that fires were influential to the park’s forest conditions before Euro-American intervention. Results also identify the possibility of influence on the fire regime by Native American peoples who lived in or visited the park in the past. This fire history research may be a place to begin discussions, relationships, and partnerships with Native American communities in the area, as well as with management personnel to explore how fire may be returned to the park landscape with consideration of the park’s cultural history, and the association between fire and climate.