Contradictions and continuities: a historical context to Euro-American settlement era fires of the Lake States, USA


 
 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.
 
 
 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.
 
 
 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.



Introduction
The term unprecedented is often used to describe destructive wild res in recent years such as the 2020 res in western Oregon that burned close to a million acres and forced the evacuation of half a million people (Abatzoglou et al. 2021). While wild res in what are typically wet forests of the western Cascade mountains are unusual, neither the weather conditions that led to wild res (Abatzoglou et al. 2021), nor the 2020 res themselves were unforseen. Large wild res have shaped coastal ecosystems including the west Cascades of Oregon over millennia (Agee 1993;Weisberg and Swanson 2003;Weisberg 2009).
Historical context is essential not only to understanding rare events, but also past and potential climate change in uences on re frequency, severity, and scale. Understanding disturbance regimes in relation to climate and land use changes is vital for fostering resilient ecosystems that can accommodate an uncertain future (Landres et al. 1999). In the modern era, human-induced disequilibrium (e.g., re exclusion via landscape fragmentation, grazing, and re suppression) has weakened the relationships among re, vegetation, and climate (Marlon et al. 2012;Higuera et al. 2015). This limits our understanding of these interacting factors, thus necessitating longer-term historical perspectives (Parks et al. 2017). Despite these limitations, much of our understanding of re history comes from recent decades and periods when both climate and human activities have undergone rapid and unique transformations (Marlon et al. 2012;Meunier and Shea 2020).
Perhaps nowhere is the rapid and unique transformation of land illustrated better than the > 20 million hectare "Great Cutover" of the Lake States forests. While some logging preceded legal title, this era began primarily after the original public land surveys were carried out (Michigan: 1816-1856, Wisconsin: 1833-1866, Minnesota: 1848-1907 and was largely concluded by 1920 after the Lake States were denuded (Stearns 1997;Kates 2001). While the Cutover is sometimes reduced to a relatively discrete, singular event, it occurred in multiple phases over a period of 60 years. The initial phase of cutting, "river lumbering", was con ned to pine forests near rivers and streams as it was unpro table to haul logs any distance to water (Whitney 1987). It was not until the 1880s that railroad expansion in northern forests opened new areas for logging including more isolated softwood stands and especially hardwoods like maple (Acer spp), which could not be oated down rivers (Roth 1898;Larson and Larson 2016). After 1880 both the scale and intensity of logging expanded dramatically, ushering in one of the most intense periods of logging the temperate world has ever seen (Marquis 1975;Whitney 1990). The peak harvest of pine was ca. 1890 (in MI and WI, 1900 in MN) and by 1920 harvest of hardwoods exceeded pine (Stearns 1997). Weaver and Clements (1929) stated that the pine-hemlock forest of the Lakes States had been reduced to such small fragments that there were doubts as to its former existence (Whitney 1987).
While cutover logging was globally unprecedented in its speed and intensity (Whitney 1987;Williams 1989;Schulte et al. 2007) it was the repeated and often intense slash res (Zon and Cunningham 1931;Schulte et al. 2007) that followed, which "all the authorities agreed" were the instruments of change rather than logging itself (Roth 1905;Curtis 1959;Whitney 1987). In fact, res at the time were used to justify logging by timber barons who were depicted not as wasteful capitalists, but rather saving forests from waste by res (Stimson 1910). The sentiment of "more good pine timber was burned than ever reached the sawmills" was handed down as common knowledge among lumbermen at the time (Zon and Cunningham 1931;Dickman and Leefers 2003) and subsequently even by researchers examining the pro igate logging practices of the Cutover (Fries 1951;Whitney 1987). Fires fed by pine slash were viewed as the ultimate degradation of Lake States forests -along with the exorbitantly wasteful logging, clearing stumps for farmers (19 million pounds of explosives were used by the University of Wisconsin College of Agriculture alone; Gough 1997), nearly universally failed attempts at farming (Whitney 1987), and subsequent re suppression.
describe large re years. The res of October 8, 1871, for example, famously destroyed 9 km 2 of the city of Chicago, and killed several hundred people. At the same time, they burned > 10,000 km 2 and multiple cities (e.g., Holland, Lansing, Port Huron, Manistee) in lower Michigan (Dickmann and Leefers 2003). These res are sometimes collectively called "the great Midwest res of 1871". In Minnesota, the "Great Fires" denote the especially destructive re years of 1894, 1908, 1910, and 1918(Haines and Sando 1969Johnson 2020). During these destructive re years, tens of thousands of hectares also burned elsewhere in the Lake States. In Wisconsin, for example, 1894 is the year of the "Phillips Fire" which burned over eight counties in late July, destroying the town of Phillips and killing several hundred people. What these Euro-American settlement (hereafter settlement) res have in common is that they were, and remain to be, considered anomalies. Interestingly, 150 years after the fact, we still not only attribute the 1871 res to extraordinary and anomalous conditions, but also take solace in the belief that those conditions will not repeat themselves (Frelich 2002;NOAA NWS 2021). Yet in the Lake States region, we have only a nascent understanding of re regimes in relation to vegetation and climate (Meunier et al. 2019a). Thus far, there has been little effort to view settlement era res in greater historical and ecological context.
The rst systematic attempt to evaluate the problem of slash as a re hazard was led by the architect of research in the U.S. Forest Service, Raphael Zon. Zon and Cunningham (1931) found that settlement era res were a result of weather conditions, not slash, and that any impact on re intensity/severity would have been both localized, since slash covered a small proportion of cutover areas, and was short-lived (Cheyney 1939). Yet slash remained a primary culprit for uncontrolled wild res which posed a "serious problem to those concerned with re control" (Williams 1955), perpetuating the notion that settlement era res were unprecedented in intensity and frequency (Dickman andCleland 2002, White andHost 2008) and driven primarily by slash (Wells 1968;Brose et al. 2001;Frelich 2002). It was commonly held, for example, that re seldom swept into "virgin stands" for more than 10 rods in the absence of logging slash (Lorimer 1980).
In fuel-limited semi-arid regions the importance of fuel buildup in driving high-severity re is unequivocal (Parks et al. 2018). Yet, the relative importance of fuels on re behavior and effects in more mesic temperate forests are less clear (Steel et al. 2015). Interestingly, two of the largest wild res in Michigan history burned the same ground in 1871 and 1881. The more devastating res of September 1881 were blamed, in part, on dead timber from the 1871 res and slash, which popular accounts indicated had been "building up for decades" (Rummel 2003). Slash build up for decades is in direct contradiction to ndings by Zon and Cunningham (1931) though repeat high-severity res are not unheard of -at least in western US montane systems (Coppoletta et al. 2020). In Michigan, fuel loadings in mixed pine stands were found to be more closely tied to the cumulative impact of past res than stand composition and structure following harvesting (Drobyshev 2008). Repeated res in Michigan reduced woody debris and the duff layer resulting in less intense subsequent res (Drobyshev 2008).
As the environmental historian William Cronon (1983) stated, "an ecological history begins by assuming a dynamic and changing relationship between environment and culture, one as apt to produce contradictions as continuities." This is an attempt to try and ascertain the contradictions and continuities of our recent re history for the Lake States, a period of profound changes and importance that we are only beginning to critically evaluate after more than a century. In this study my objective was to evaluate res of the settlement era in a context of a longer re chronology and in relation to vegetation and climate. Speci cally, I evaluated re frequency and the similarity of re events between pre-settlement (prior to 1851), and settlement ( (2) Central Sands (CS), WI (7,068 km 2 ) -a glacial lakebed of well-drained outwash sands intermixed with wetlands, but with few natural lakes or rivers and very little topography. Currently, this landscape consists of a high proportion of dry pine-oak barrens and forest. Historically, the region had higher proportions of pine (62% of original land survey witness trees), including red and white pines (P. resinosa, P. strobus) in the northwest (Bruce Mound, Wildcat Ridge, Stoney Bluff sites) and jack pine (P. banksiana) in the central portions (Quincy Bluff site) of the ecoregion. A particularly destructive settlement era re in this landscape was "The Great Marsh eld Fire" in June 1887 (Wood and Marathon Counties, WI).
(3) Blu ands and Coulees (B&C), WI (23,004 km 2 ) -an unglaciated region of silt and loam soils with few natural lakes and wetlands, but complex ridge and valley topography. Within the Bluff and Coulee region I sampled a red pine relict (Pine Bluff) occurring on steep bluffs with an exposed sandstone outcrop in an otherwise hardwood-dominated landscape that was primarily white oak (Quercus alba) woodland in presettlement times.
(4) Northern Highlands (NH), WI (6,821 km 2 ) -a rolling topography with pitted-gravelly sands and abundant natural lakes, rivers, and streams. While sandy soils predominate, the soils tend to be more productive in this ecoregion and support dry-mesic mixed conifer forests which comprised ca. 56% of witness trees in the original survey notes. Historically this landscape was Wisconsin's greatest pinery, but also contained abundant eastern hemlock (Tsuga canadensis)-hardwoods, as well as aspen-birch (Populous-Betula). Notable settlement era res include a large re in 1904, again in 1907-08, and 1910 (WI Historical Society 2021).
(5) Northeast Sands (NES), WI (2,865 km 2 ) -deep, well-drained outwash sands with level to rolling topography and scattered, small lakes. This landscape had a high proportion of pine forests (62% of settlement survey witness trees). Notable settlement era res included 1900 (Chequamegon Bay and Menominee River). Two sampling sites in this ecoregion (Wolf Lane and Camp Bird) were old growth pine stands that were never harvested. (7) The Seney-Tahquamenon Sand Plain (SSP), UP (3,765 km 2 ) -primarily mixed conifer swamp, muskeg/bog, and patterned peatlands dominated by tamarack (Larix laricina) and black spruce (Picea mariana) on poorly-drained sand lake plains with mixed pine forests (red, jack, and white pines) on sandy ridges and dunes. Ramsey Lake typi ed this landscape and was a 900-ha patterned fen peatland.
(8) The Grand Marais Lakeshore (GML), UP (5,284 km 2 ) -red and jack pine ridges and dunes along Lake Superior with interior uplands containing scattered northern hardwoods and eastern hemlock-white pine forests. Peatlands occur in poorly drained lacustrine deposits and in western kettles. Sites in this ecoregion ranged from > 1200 ha peatland (Betchler Lake), pockets of pine along Lake Superior (Bay View), to more extensive interior forest (Corner Lake, Hwy 13).

Data collection and analysis
Within natural origin red pine-dominated stands, I collected sections from remnant stumps and partial sections from snags and re-scarred living trees at 10 cm height. Stands were either old-growth or had been harvested in the cutover period (ca. 1860-1920) but had minimal recent disturbance (e.g., post cutover logging) and contained pre-Euro-settlement era stumps. Multiple stands comprised a site which ranged in size from small pine stands within hardwood forests to more extensive pine forests with efforts to sample comparable areas (0.12-2.41 ha, µ = 0.76 ha). Samples were collected from randomly placed plots as well as opportunistically by searching within ~ 200m of plots for additional samples (Meunier et al. 2019b;Sutheimer et al. 2021).
In the laboratory, I sanded samples until the cellular structure of xylem was clearly visible with magni cation (Grissino-Mayer and Swetnam 2000) and assigned exact calendar dates to all re-scars. I compiled and analyzed re-scar chronologies for each site using Fire History Analysis and Exploration System software version 2.0 (FHAES, Brewer et al. 2019). I analyzed re return intervals (MFRI-the number of years between res) within sites in which res occurred on ≥ 10% of recorder trees by settlement and pre-settlement periods framed broadly by patterns of Euro-American settlement using 1850 as the cutoff (pre-settlement ≤ 1850). For pre-settlement chronologies, I included the years up to the time that a major disruption of re events was apparent (i.e., I excluded post-settlement res after effective re exclusion -prior to unusually long MFRI's). Most trees, once large enough to be protected by thick bark, are not injured by low-intensity res; however, once injured, trees are more susceptible to repeated injury in subsequent res and are considered "recording trees" (Swetnam and Baisan 1996). Filtering, based on scarring percentage, provides a relative index of re size (Farris et al. 2010). A 10% lter, for example, will only consider re years recorded on ≥ 10% of recorder trees, thus eliminating res that may have burned only one or few trees in a single lightning strike or localized incident (Meunier et al. 2014). I also calculated Weibull median probability (WMPI) which is a less-biased estimator of central tendency with skewed data (Grissino-Mayer 1999), but MFRI are more commonly reported (e.g., LANDFIRE 2016).
To test for differences in historical re frequency between settlement and pre-settlement periods I compared MFRI for re recorded on ≥ 10% of recorder trees between time periods (SigmaPlot Systat Software, 2010). I used two-tailed Student's t-test to compare MRFI when data were normally distributed with equal variance, and nonparametric Mann-Whitney rank sum tests to compare periods when data were not normally distributed. I compared re frequency by time periods for site (n = 25) and ecoregion (n = 8) and used MFRI distribution to compare median values and data spread (by site and ecoregion) for pre-settlement and settlement periods.
Composite re intervals (e.g., res on ≥ 10% recorder trees) are in uenced by the number of re-scarred trees sampled; the more trees sampled the lower the likelihood of missing a re (Lafon et al. 2017). MFRI's are also in uenced by the level of ltering; higher levels of ltering usually result in fewer, larger re years and longer MFRI. Therefore, I also evaluated temporal variations in re with a decadal re index (DFI) which does not depend on compositing and accounts for sample depth (Hoss et al. 2008). DFI is calculated by rst summing the number of res recorded during each decade and dividing by the number of recording trees that are represented during the decade (Lafon et al. 2017). Dividing by the number of recording trees standardized re sums and permitted comparison of decades with different sample sizes (Lafon et al. 2017). I regressed DFI against time for the entire pre-exclusion period (both settlement and pre-settlement eras) to test for trends (i.e., positive or negative slope) over time. Analyses of re frequency changes over time (or between periods) were done for each individual site (n = 25) as well as for sites pooled by region (n = 8). The Cutover generally followed an east-to-west progression (Maine to Michigan and Wisconsin, then Minnesota) with geographic factors playing an important role in settlement era lumber industry (Stearns 1997). I evaluated regionally composited re occurrence changes to detect broader spatial scale re patterns.
There is no robust way to compare historical written accounts of settlement era res to tree-ring re scar records. However, to try to ascertain general agreement between historical accounts and re-scar data, I compiled the proportion of regions recording well-known large re events. This allowed me to evaluate whether particularly large settlement era res, as depicted from historical written accounts, had a higher proportion of ecoregions with re scars recording the same re year (an indication of widespread re, Meunier and Shea 2020). I also composited re history among all sites (659 re-scar samples) into a single re chronology and used a more restrictive lter -res recorded on ≥ 15% of all recorder trees, with a minimum sample size of 10 recording trees -to compare how the largest re years, reconstructed with re-scar samples, compared to known settlement era res. Setting a minimum sample size of 10 recorder trees helps to reduce the in uence of early re years that scar a high proportion of trees due to small sample sizes. I compared the largest re years (recorded on ≥ 15% of recorder trees across all samples combined) across both pre-settlement and settlement periods with this composited re history. I used superposed epoch analysis (SEA) to understand climate drivers (average Palmer Drought Severity Index, PDSI, of four grid points across the region; Cook et al. 2007) for both widespread re years with ≥ 15% rate of scarring across all sites/samples and for notable settlement era res via historical accounts.
Generally, re perimeters for settlement era res are anecdotal and/or lacking detailed descriptions of spatial extent and patterns making re-vegetation characteristics di cult to ascertain. The 1871 Peshtigo Fire is an exception to this with reasonably well-documented re perimeter maps (Fig. 2). To evaluate revegetation characteristics in relation to land use changes (i.e., slash) I overlaid the approximate boundaries for the 4,856 km 2 Wisconsin portion of the October 1871 Peshtigo re and extracted all settlement era General Land O ce Public Land Survey (GLO) witness tree records that intersected the Peshtigo re boundary (Sickley et al. 2001). The survey, which was designed to form the basis of property boundaries and land records during the settlement era included notes on the species, diameter, and location relative to section corners of two to four "witness trees" (Stewart 1935). I overlayed the Peshtigo re footprint on a raster map of GLO witness trees and extracted all witness trees within the boundary of the Peshtigo Fire to evaluate forest composition of that landscape at the time of settlement using ArcMap 10.3 (ESRI 2014).

Results
This study included 659 crossdated re-scarred tree samples collected among the 25 sites spanning the period from 1548 (the rst re included in analyses) to 1947 when effective re exclusion was apparent among all sites. The temporal extent of tree-ring records varied among sites but, collectively, I identi ed 3,229 res from 1548-1947. Despite very different landscape contexts (i.e., ecoregions) and sites (e.g., forest composition), prior to the mid-1900s, res were historically frequent in all locations with MFRI ranging from 3 to 15 years (µ = 8) for res recorded on 10% of recorder trees (Table 1). When considering res that were recorded on ≥ 25% of recorder trees (larger re years) re frequency decreased slightly but were still frequent (MFRI = 5-34 years, µ = 12). In general, res were most frequent in the Central Sands, Blu ands and Coulees, and Northwest Sands ecological landscapes (MFRI = 4) and longest in the Keweenaw-Baraga Moraines (MFRI = 12) and Seney-Tahquamenon Sand Plain (MFRI = 11). Among the 25 different sites, re frequency was signi cantly different between pre-settlement and settlement periods at only three sites (Sand Lake, Pine Bluff, and Camp Bird; Table 2). Two sites (Sand Lake and Pine Bluff) had signi cantly shorter MFRI (P < 0.001, P = 0.008 respectively) in the presettlement period and one site (Camp Bird) had signi cantly shorter return intervals (P = 0.046) in the settlement (MFRI = 4) versus pre-settlement period (MFRI = 8). Results were similar by ecoregion. The Northeast Sands was the only region which had more frequent re in the settlement period (MFRI presettlement = 8, settlement = 4; P < 0.001). The Blu ands and Coulees ecoregion (Pine Bluff) had more frequent re in the pre-settlement (MFRI = 4) than in settlement (MFRI = 9); whereas there were no statistical differences in re frequency between periods in the other six ecoregions though intervals were longer during settlement (Fig. 3). When evaluating trends in re frequency with decadal re index (DFI) I found no sites that illustrated a signi cantly positive slope over time whereas six sites had signi cantly negative slopes illustrating reduced re frequency in the settlement period (Table 3). Most sites had no signi cant changes over time.
Similar trends were evident when evaluating DFI by ecoregion. Only the Northeast Sands ecoregion had a positive slope (Fig. 4)  level analyses. In general, there was greater evidence for reduced re frequency in the settlement period, as compared to pre-settlement, at both site (Table 3) and ecoregion (Fig. 4) scales.  Fig. 5). Interestingly, while 1894 was found in half of ecoregions (Table 4), re scar records include 1895 as a more widespread re year (Fig. 5). Both 1894 and 1895 were drought years (averaged PDSI = -2.008, -2.380 respectively). All but one historically documented re year, 1931, which was a severe regional drought year (PDSI = -3.424), were detected by re-scars. Fire scar evidence of 1871, one of the more destructive settlement era re years, did not indicate it as one of the more extensive re years. Notably, records of this re year, and all re years detected by re-scar methods, are limited to low-and/or moderate-severity res. High-severity res are more likely to kill trees that would otherwise record res and destroy evidence of past res (Kent 2014). It follows that more detailed maps of 1871 res illustrate a more extensive footprint of res (Fig. 2b), albeit lower-severity and less destructive. Both large re-scar reconstructed re years (Fig. 5) and notable res via historical accounts (Table 4) were signi cantly related to dry conditions (Fig. 6).  1965, Heinselman 1973, Stearns 1997, Pyne 2001, Dickmann and Leefers 2003, USFWS 2004, Brown 2009, Apps 2020.
The Peshtigo Fire is somewhat unique in that there are detailed re perimeter maps allowing at least qualitative analysis of re-vegetation-climate relationships. Settlement era witness tree maps of the Peshtigo Fire region indicated that portions of the 1871 res were a mesic "sugar bush" -a colloquial term for maple (Acer) forest used for syrup production (e.g., Lower, Upper, and Middle Sugarbush; Fig. 2a). The most abundant tree species out of 11,014 witness trees identi ed in the footprint of the Peshtigo Fire at the time of GLO Public Land Survey (ca. 10 years prior to the re) was hemlock (Tsuga canadensis; 21%), followed by cedar (Thuja occidentalis; 14%), beech (Fagus grandifolia; 12%), tamarack (Larix laricina; 8%), and sugar maple (Acer saccharum; 8%; Fig. 7). Less than 10% of witness trees in the footprint of the Peshtigo re were pine of any kind (most of which was white pine -a common component of mesic hardwoods ;Curtis 1959). This region was and remains dominated by mesic forests (WI DNR 2015) which were not harvested at any scale until a decade or more following the Peshtigo re (Stearns 1997).

Discussion
As climate and re regimes change, new understanding is needed of the inherent resilience of ecosystems and of the implications for human communities and ecosystem services (Hessburg et al.

2019)
. Following a period of rapid and intense land-use and associated ecosystem changes, forests of the Lake States are now more homogeneous, with less species diversity (Schulte et al. 2007) and less spatial and structural complexity (Meunier et al. 2019a), and are less coupled to local climate controls (Thompson et al. 2013), all of which lead to a loss of resilience in forest ecosystems (Drever et al. 2006).
It remains unclear what the relative contributions of logging, slash res, or subsequent re suppression were to changes in Lake States forests (White and Mladenoff 1994;Rhemtulla et al. 2009). It was assumed that settlement era res were anomalous, with more frequent and severe res resulting from cutover slash (White and Host 2008). Early laws were passed to require disposal of slash (Wright and Heinselman 2014) and the prevention of wild res at all costs formed the basis of forest conservation in the Lake States; yet, there is little evidence for slash as a widespread and prolonged re hazard (Zon and Cunningham 1931) and little or no evidence that re was more frequent in the settlement period (Tables 2-3, Figs. 3-5). Fuel type (e.g., forest composition), in addition to fuel loading (i.e., slash), needs to be considered in relation to re-severity particularly for destructive settlement era res like the October 1871 Peshtigo re. The assumption that res were another (or the) degrading force of forest following exploitative settlement era land-use changes (Johnson 2020) may be fundamentally awed and formed, in part, by ignorance of basic historical re regime characteristics in Lake State forests.
Several studies have suggested that the combination of logging and slash res followed by re suppression in the 1930s drastically altered forest composition in the Lake States (Miller et al. 2010) and led to a loss of coniferous species and increase in deciduous species in northern Wisconsin (Mladenoff and Howell 1980;White and Mladenoff 1994;Radeloff et al. 1999;Steen-Adams et al. 2007). Other studies have found that establishment dates in Lake States pine-oak forest peaked following logging and res, particularly between 1891 and 1911 (Cook 2000), which include some of the most widespread settlement era re years (e.g., 1891, 1894-95, and 1910Table 4, Fig. 5). Close coupling between tree recruitment and low-severity res, including in the settlement period, was also noted in the BWCAW (Heinselman 1973). In a study in western Oregon and Washington, effects of slash burning following clearcut harvesting had little effect on the quantity of natural stocking of conifers and subsequent hazard rating was lower on burned than unburned plots (i.e., lower spread rate and more easily controlled; 1970). Remarkably, while land use history varied across the disparate forests and ecoregions in this study (e.g., different composition, harvested or not, timing and intensity of harvest) two factors are common among all locations: re was historically frequent, and re was universally excluded by the mid-20th century (Table 1). It is likely that 100 years of re suppression, rather than a period of more frequent res, were primary drivers of expansive forest changes (Paulson et al. 2016).
From the perspective of high-severity wild res, slash is simply redistributed fuels where boles and branches that were in the canopy are in a different arrangement on the forest oor but with the same amount of available fuel (Evans and Wright 2017). However, cutting (and windthrow) can change fuel moisture of slash which can affect ame length potentially increasing re-severity (Evans and Wright 2017). Fuel moisture of slash increases with compaction over time which in uences combustion dynamics (Wright et al. 2019). Fuels also tends to decompose much faster in eastern forests with higher productivity (moisture and temperature) than in the western US (Graham and McCarthy 2006). It is known, at least in theory, that many Lake State conifer forests inherently have heavy fuel loads (canopy and ground) where re behavior is controlled more by weather at the time of re than by any other factor (Bessie and Johnson 1995;Frelich 2002). The relationship between settlement land use changes and re severity remains an unresolved issue; however, it seems that res in the Lake State likely had both abundant fuels and, periodically, extended drought conditions. Notably, the 1871 res in Wisconsin had been burning for many weeks prior to October with little rain since the early part of July and below average snowfall in winter of 1870-71 (Gess and Lutz 2003). Residents described a constant cracking of re at night and smoke was omnipresent (Pernin 1971). These res were primarily lower severity, much of which burned pine forests to the north of the October 8 Peshtigo Fire (northern Oconto and Marinette Counties) where presumably slash would have been present (Fig. 2b). These low-severity res of 1871 were detected across study sites in Wisconsin (NWS, CS, NES), the Menominee Indian Reservation to the northeast (Sand and Abrams 2011), and in the Huron Mountains in the Upper Peninsula of Michigan (Muzika et al. 2015). Schulte and Mladenoff (2005) in their analysis of GLO data found that stand-replacing res were never recorded by surveyors within the ecological landscapes associated with the October 8, 1871 Peshtigo Fire ( Fig. 2a). Wild re frequency and intensity are broadly inversely related (Pickett and White 1985;Turner et al. 1989). Fire regimes in many forested systems can be categorized as ranging from "fuel-limited" to "climate-limited" where the former are characterized by more frequent, lower-severity wild res and the latter by infrequent, more severe wild res (Steel et al. 2015). The mesic forests of the Peshtigo Fire region (Fig. 7) would be expected to burn infrequently and with high severity. It is not surprising that GLO survey data would not detect res in this landscape which would be characterized by infrequent res, nor is it surprising that this landscape would burn with the intensity and devastation that it did with abundant fuels (e.g., hemlock, cedar, larch forests). In 1871 logging was still restricted to river lumbering of pine and while land clearing was associated with settlement it would likely have been limited in comparison to the ca. 5,000 km 2 area burned, and very little logging and associated slash would have been present. Regardless of the contributions of settlement activities to the Peshtigo Fire, high-severity res would be expected to predominate in forests there. Notably, the high-severity Peshtigo Fire represents a relatively small proportion of area burned as low-severity re in that same year (Fig. 2b).
In 1871 there was prolonged regional drought (average PDSI 1871 = -2.364, 1870 = -2.470) where res had been burning for more than a month, which were then fanned by strong southeasterly winds (NOAA 2021) into an abnormally dry forest with abundant fuels. This story is not unique to the Peshtigo Fire or to 1871, but rather the way many large re years burned over the last 400 years in the Lake States . This is also the case in the 2020 Oregon res which had been burning for weeks prior to being pushed by strong downslope winds (Abatzoglou et al. 2021). While land use changes in relation to wild res occurring during settlement in the Lake States cannot be discounted, they also cannot explain scores of similar re years, over widely varying landscapes, and over centuries (Fig. 5).
Historical reference information is valuable for understanding how current conditions arose, as well as for developing a mechanistic understanding of ecosystem dynamics and predicting future conditions (Safford et al. 2012;Miller and Safford 2017). Historical data, like written accounts at the time of Euro-American settlement, or settlement era Public Land Survey data, can be useful in describing the magnitude of change in conditions relative to reference landscapes (Rhemtulla et al. 2009), but are not always useful in assessing the drivers of change or in forecasting future conditions (Frelich 2002).
Likewise, a single "settlement" reference is a static view of ecosystems that were and remain inherently dynamic. What becomes apparent when considering a longer history and greater context is that frequent res were one of few continuities within forests of the Lake States during settlement. This is a starting point for unraveling the effects of the myriad land abuses in the settlement period and for understanding the contradictions of de ning forest conservation in the Lake States on the premise of re suppression.
Although the nature of future forests will be determined in part by climate change and other exogenous variables, land use and re have been and are likely to remain the driving factors in shaping forests (Rhemtulla et al. 2009). The question is what type of land uses and what type of re will be part of those future forests.

Conclusions
Settlement era res (ca. 1851-1947) were believed to have been abnormally frequent and primarily a result of slash build up following extensive cut-over of Lake States forests. However, historically (over the last 400 years) res were always relatively frequent occurring on average every 8 years (MFRI = 3-15 years). Settlement res in the Lake States were not simply slash res, they were a combination of weather, climate, and fuel arrangements. Large res tended to be driven by extended drought conditions   Composite re chronology for all sites of large re years recorded on > 15% recording trees with > 10 recording trees. Top graph illustrates number of recorder trees (line) and percent of all recorder trees scarred (bars) over time.

Figure 6
Results of superposed epoch analysis (SEA) of the average Palmer Drought Severity Index (PDSI) across the region (Cook et al. 2007) for years prior and subsequent to re event years (year 0) for (a.) notable historical accounts of settlement era res (i.e., interval based on 1,000 Monte Carlo simulations of random distributions of annual PDSI (a. 1850PDSI (a. -1950PDSI (a. , b. 1600PDSI (a. -2000.