An evaluation of the relationship between fire history and cultural activities on Star Island, Cass Lake, Minnesota

Faculty advisor: Dr. Kurt KipfmuellerThis research was supported by the Undergraduate Research Opportunities Program (UROP)

The North American tree-ring fire-scar network

Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree-ring fire scars provide valuable perspectives on fire regimes, including centuries-long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree-ring fire-scar network (NAFSN), which contains 2562 sites, >37,000 fire-scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000-m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire-scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under-sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non-Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually- to sub-annually-resolved tree-ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America

An Assessment Of The Dendroclimatic Potential Of Three Conifer Species In Northern Minnesota

Ring-width chronologies from Pinus resinosa Ait., Pinus strobus L., and Thuja occidentalis L. were developed in two areas of the Boundary Waters Canoe Area Wilderness to assess their growth climate response and their potential for developing reconstructions of climate. New red pine chronologies were combined with existing chronologies to extend the ring-width record both into the past and into the present. Ring-width response to climate, assessed using correlation analysis and response functions, was broadly similar among all three species with relatively significant positive relationships with June–July precipitation and significant negative (but less consistent) associations with June–July temperatures (p < 0.05). White-cedar appeared to have a broader phenological window of response with a stronger spring influence when compared to other species included in this study. Comparisons with other nearby proxies showed relatively strong coherence overall but with some important regional differences. Overall, these species may be useful for placing current climatic patterns in the Boundary Waters within a longer term perspective but care should be taken with respect to identifying appropriate climatic records for calibration.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]

Tree rings detect earthworm invasions and their effects in northern hardwood forests

Invasions of European earthworms into the forests of northern North America are causing dramatic changes in forest floor structure, vegetation communities, biogeochemical cycling, and site hydrology. However, long-term studies on the effects of invasive earthworms are limited because little data exist on the timing and rate of earthworm invasion at specific sites. We successfully used tree rings to identify the timing of earthworm invasions and the effects of earthworm activity on the Acer saccharum overstory of two recently invaded sites in northern Minnesota, thereby establishing a method to date earthworm invasions at other sites. In addition to identifying a tree-ring signature related to earthworm invasion, we found trees growing in invaded conditions were more sensitive to drought than trees growing in earthworm-free conditions. Increased drought sensitivity by A. saccharum has important implications for possible range shifts under climate change scenarios that include increasing drought frequency and severity