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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.

Background The Lake States experienced unprecedented land use changes during Euro-American settlement including large, destructive fires. Forest changes were radical in this region and largely attributed to anomalous settlement era fires in slash (cumulation of tops and branches) following cutover logging. In this study, I place settlement era fires in a historical context by examining fire scar data in comparison to historical accounts and investigate fire-vegetation-climate relationships within a 400-year context. Results Settlement era fires (1851–1947) were less frequent than pre-settlement fires (1548–1850) with little evidence that slash impacted fire frequency or occurrence at site or ecoregion scales. Only one out of 25 sites had more frequent settlement era fires, and that site was a pine forest that had never been harvested. Settlement era fires were similar across disparate ecoregions and forest types including areas with very different land use history. Settlement fires tended to burn during significantly dry periods, the same conditions driving large fires for the past 400 years. The burned area in the October 8, 1871, Peshtigo Fire was comprised of mesic forests where fuels were always abundant and high-severity fires would be expected under the drought conditions in 1871. Furthermore, slash would not have been a major contributor to fire behavior or effects in the Peshtigo Fire when logging was still limited to relatively accessible pine forests. Conclusions Historical written accounts of fires and settlement era survey records provide a reference point for landscape changes but lack temporal depth to understand forest dynamics. Tree-ring analyses provide a longer (ca. 400 year) context and more mechanistic understanding of landscape dynamics. While settlement land use changes of Lake States forests were pervasive, fires were not the ultimate degrading factor, but rather likely one of the few natural processes still at work.

A key challenge to maintaining resilient landscapes is adapting to and maintaining dynamic ecological processes. In fire-dependent ecosystems, this includes identifying and defining mechanisms through which fire influences forest structure and functionality. Interpretations of tree patterns via land survey records in the Lake States have often highlighted the importance of infrequent moderate to extreme disturbance events. However, historical survey methods are limited to observing higher severity disturbances and over large landscapes, thus it is not clear if the origin, structure, and forcing factors for either patterns or processes are adequately quantified by these methods. We used dendrochronological methods to determine how fire history and stand structure, including cohort structure, tree density, and spatial patterning, are linked within Lake States mixed conifer forests in Wisconsin. We found relatively short mean fire return intervals (MFRIs) ranging from 6 to 13 yr with little variation in fire frequency among sites. Current densities of red-pine-dominated forests are 4–37 times historical (ca. 1860) densities (mean 12×) and almost entirely spatially random, whereas historically forests were spatially aggregated at stand scales. Stands also contained multiple and/or loosely defined cohort structures suggesting very different controls operating historically than currently. Heterogeneity that helped maintain ecosystem resilience in these ecosystems historically came from frequent fire disturbance processes that affected stand-scale forest resistance. This was likely the historical dynamic across fire-adapted transitional pine forests of the Lake States.

Background: Drivers of fire regimes vary among spatial scales, and fire history reconstructions are often limited to stand scales, making it difficult to partition effects of regional climate forcing versus individual site histories.Aims: To evaluate regional-scale historical fire regimes over 350 years, we analysed an extensive fire-scar network, spanning 240 km across the upper Great Lakes Region in North America.Methods: We estimated fire frequency, identified regionally widespread fire years (based on the fraction of fire-scarred tree samples, fire extent index (FEI), and synchronicity of fire years), and evaluated fire seasonality and climate–fire relationships.Key results: Historically, fire frequency and seasonality were variable within and among Great Lakes’ ecoregions. Climate forcing at regional scales resulted in synchronised fires, primarily during the late growing season, which were ubiquitous across the upper Great Lakes Region. Regionally significant fire years included 1689, 1752, 1754, 1791, and 1891.Conclusions: We found significant climate forcing of region-wide fire regimes in the upper Great Lakes Region.Implications: Historically, reoccurring fires in the upper Great Lakes Region were instrumental for shaping and maintaining forest resilience. The climate conditions that helped promote widespread fire years historically may be consistent with anticipated climate–fire interactions due to climate change.

Extensive changes in montane forest structure have occurred throughout the U.S. Southwest following Euro-American settlement. These changes are a product of confounding effects of disturbance, climate variability, species competition, and modern land use changes. Pronounced forest reproduction events in the Southwest have generally occurred in climatically wet periods but have also followed widespread fire exclusion. Understanding the ecological processes driving such events has important implications for forest restoration, although these efforts remain difficult due to confounding factors. Separation of these interacting factors was possible in the Sierra San Luis of northern Mexico where we investigated climate, fire, and tree recruitment in areas with continued frequent fires or where fire exclusion came relatively late (1940s). Fires were strongly tied to interannual wet-dry cycles of climate, whereas recruitment peaks were more closely tied to local processes, namely, fire-free periods, than to broad-scale climatically wet conditions. The greatest pulse of tree recruitment coincided with a pronounced mid-century drought (1942-1957) and a period of reduced fire frequency. The second largest pulse of recruitment (ca. 1900) preceded a well-documented period of recruitment (and an anomalously wet period) elsewhere across the Southwest in the 1910s-1920s, and also coincided with specific fire-free periods during below-average precipitation. We also found greater spatial dependence and clustering in older age classes of trees. This spatial pattern indicates a legacy of fire-induced mortality in shaping stand structure, underscoring the importance of frequent fire effects on spatial variability in forests.

In the Great Lakes Region, minor differences in soils and location (e.g., proximity to the Great Lakes) can lead to strong differences in vegetation; thus, the utility of broad-scale mapping often depends on capturing subtle landscape features and local processes. Similarly, vegetation patterns are in part a result of disturbances that have changed drastically over time, therefore mapping efforts must take into account vegetation–fire relationships to various biophysical settings (e.g., landtype associations, climate, and soils). Despite this, too little attention has been given to potential sources of mapping error, which include data limitations, ecological similarity, community classifications, locational error, sample quality, and lack of knowledge of systems—specifically natural disturbance regimes. We used ∼23,500 plots with detailed vegetation, soils, and classification information to (1) evaluate LANDFIRE (Landscape Fire and Resource Management Planning Tools) historical vegetation (Biophysical Settings or BpS) classifications, (2) refine these classifications based on detailed soil regime and plant associations, and (3) draft fuzzy set soil-classification gradient maps to evaluate uncertainty in mapping and sources of mapping errors. Locally derived reference plot data often did not agree with LANDFIRE BpS mapping even for classifications generalized broadly by Fire Regime Groups. Our fuzzy methodological approach improves decision-making processes by assessing mapping confidence and highlighting potential sources for errors including classifications themselves. Our mapping efforts suggest that soil drainage and productivity data helped to delineate BpS classifications, which may in turn help stratify Existing Vegetation Types into feasible options.

The occurrence of wildfire is influenced by a suite of factors ranging from “top‐down” influences (e.g., climate) to “bottom‐up” localized influences (e.g., ignitions, fuels, and land use). We carried out the first broad‐scale assessment of wildland fire patterns in northern Mexico to assess the relative influence of top‐down and bottom‐up drivers of fire in a region where frequent fire regimes continued well into the 20th century. Using a network of 67 sites, we assessed (1) fire synchrony and the scales at which synchrony is evident, (2) climate drivers of fire, and (3) asynchrony in fire regime changes. We found high fire synchrony across northern Mexico between 1750 and 2008, with synchrony highest at distances <400 km. Climate oscillations, especially El Niño‐Southern Oscillation, were important drivers of fire synchrony. However, bottom‐up factors modified fire occurrence at smaller spatial scales, with variable local influence on the timing of abrupt, unusually long fire‐free periods starting between 1887 and 1979 CE. Thirty sites lacked these fire‐free periods. In contrast to the neighboring southwestern United States, many ecosystems in northern Mexico maintain frequent fire regimes and intact fire–climate relationships that are useful in understanding climate influences on disturbance across scales of space and time.

We estimated fall (10 Sep-8 Nov) survival rates, cause-specific mortality rates, and determined the magnitude and sources of mortality of 1,035 radio-marked American woodcock (Scolopax minor) in Michigan, Minnesota, and Wisconsin during 2001-2004. In all 3 states, we radio-marked woodcock on paired study areas; 1 of which was open to hunting and expected to receive moderate to high hunter use and the other of which was either closed to hunting (Michigan and Minnesota) or was relatively inaccessible to hunters (Wisconsin). We used Program MARK to estimate fall survival rates, to evaluate a set of candidate. models to examine the effects of hunting and several covariates (sex, age, year, state) on survival, and to examine the relationship between survival rates and kill rates due to hunting. Hunting accounted for 70% of the 86 woodcock deaths in the hunted areas, followed by predation (20%) and various other sources of mortality (10%). Woodcock deaths that occurred in the non-hunted and lightly hunted areas (n = 50) were caused by predators (46%), hunting (32%), and various other sources (22%). Based on small-sample corrected Akaike's Information Criterion values, variation in fall survival of woodcock was best explained by treatment (i.e., hunted vs. non-hunted), year, and period (pre-hunting season intervals vs. hunting season intervals). The average fall survival estimate from our best model for woodcock in the non-hunted areas (0.893, 95% CI = 0.864-0.923) was greater than the average for the hunted areas (0.820, 95% CI = 0.786-0.854 [this estimate includes data from the lightly hunted area in Wisconsin]), and the average treatment effect (i.e., greater survival rates in non-hunted areas) was 0.074 (95% CI = 0.018-0.129). The kill rate due to hunting was 0.120 (95% CI = 0.090-0.151) when data were pooled among states and years. We detected a negative relationship between hunting kill rates and survival in our hunted areas, which suggests that hunting mortality was at least partially additive during fall. Our results illustrate the influence of hunting relative to other sources of mortality in Michigan, Minnesota, and Wisconsin, and indicate that managers may be able to influence fall survival rates by manipulating hunting regulations or access on public land.

The 20th century was a period of profound changes in climate, land-use, forest structure, and fires throughout much of western North America and few montane forests continue to function under historical influences of climate variations and uninterrupted fire regimes. Yet, if we are to manage for resilient forests, understanding these linkages is critical and will depend on both pre-1900 and 20th century observations. My research takes advantage of a unique opportunity in northern Mexico to study forest and fire dynamics before a century of fire exclusion. My research documented a shift in climate – fire relationships in the late 19th century toward an overwhelming importance of antecedent moisture, unlike that seen previously for > 200 years. Tree recruitment peaks were tied to local processes, not broad-scale climate conditions. Antecedent wet conditions that promote fire occurrence suggests that in arid regions of the Southwest, anomalously wet years, still functioning under frequent fire occurrence, may further limit tree recruitment. The importance of fire induced mortality in shaping stand structure underscores the spatial variability of forests and helps explain even-age patches in forests as an artifact of patch survival of seedlings that recruit into the overstory.

Investigation of bird migration has often highlighted the importance of external factors in determining timing of migration. However, little distinction has been made between short- and long-distance migrants and between local and flight birds (passage migrants) in describing migration chronology. In addition, measures of food abundance as a proximate factor influencing timing of migration are lacking in studies of migration chronology. To address the relationship between environmental variables and timing of migration, we quantified the relative importance of proximate external factors on migration chronology of local American woodcock (Scolopax minor), a short distance migrant, using event-time analysis methods (survival analysis). We captured 1,094 woodcock local to our study sites in Michigan, Minnesota, and Wisconsin (USA) during autumn 2002–2004 and documented 786 departure dates for these birds. Photoperiod appeared to provide an initial proximate cue for timing of departure. Moon phase was important in modifying timing of departure, which may serve as a navigational aid in piloting and possibly orientation. Local synoptic weather variables also contributed to timing of departure by changing the rate of departure from our study sites. We found no evidence that food availability influenced timing of woodcock departure. Our results suggest that woodcock use a conservative photoperiod-controlled strategy with proximate modifiers for timing of migration rather than relying on abundance of their primary food, earthworms. Managing harvest pressure on local birds by adjusting season lengths may be an effective management tool with consistent migration patterns from year to year based on photoperiod.