Hunting for Hemlock: Locating, restoring, and expanding eastern hemlock (Tsuga canadensis (L.) Carr.) presence in Minnesota

Abstract

Eastern hemlock (Tsuga canadensis (L.) Carrière) is a charismatic, foundational conifer species that reaches its western range limit in Minnesota. Historical records from the late 19th century document populations as far west as Itasca County, MN. Almost 150 years later, due to natural and anthropogenic disturbances and low regeneration, eastern hemlock is considered an endangered species in Minnesota with only 40 - 50 wild trees remaining in the Duluth area. Professional land managers and private citizens are interested in increasing eastern hemlock populations in Minnesota. This project seeks to understand the restoration potential of planted eastern hemlocks around the state. To help determine where eastern hemlock can grow, we distributed a survey to land managers and the general public to collect site locations and conditions, tree height, maturity, and any known histories. Respondents reported 518 trees at 62 unique locations, the majority of which were planted. Sites were located throughout the state, from Lake County west to Beltrami County, and southeast to Winona County, with most participants describing their hemlock as doing well. A reported 94% of trees 20 feet or higher had evidence of cones, indicating these trees are well-adapted to Minnesota’s soils and climates. To develop planting recommendations, we installed a planting experiment in 2023. The four planting sites included locations within and beyond the historical range, with open and underplanted conditions. The seedlings were sourced from five different provenances in Wisconsin, Michigan, and Pennsylvania, and half received nurse blocks to influence microclimate. Data from the first growing season suggests that planting interventions that maximize soil moisture, such as underplanting or utilizing downed dead wood to reduce insolation, and planting larger seedlings result in higher survival. Growth trends were less clear, possibly due to droughty summer conditions. Further observation of experiment trees may reveal clearer trends in survival and growth, or the trees that survive may instead homogenize. Both studies suggest that eastern hemlock can successfully grow across many site conditions in Minnesota, but require active management to expand their range.