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Forests have always been more than just their trees. The forests in Michigan (and similar forests in other Great Lakes states such as Wisconsin and Minnesota) played a role in the American cultural imagination from the beginnings of European settlement in the early nineteenth century to the present. Our relationships with those forests have been shaped by the cultural attitudes of the times, and people have invested in them both moral and spiritual meanings.Author John Knott draws upon such works as Simon Schama'sLandscape and Memoryand Robert Pogue Harrison'sForests: The Shadow of Civilizationin exploring ways in which ourrelationships with forests have been shaped, using Michigan---its history of settlement, popular literature, and forest management controversies---as an exemplary case. Knott looks at such well-known figures as William Bradford, James Fenimore Cooper, John Muir, John Burroughs, and Teddy Roosevelt; Ojibwa conceptions of the forest and natural world (including how Longfellow mythologized them); early explorer accounts; and contemporary literature set in the Upper Peninsula, including Jim Harrison'sTrue Northand Philip Caputo'sIndian Country.Two competing metaphors evolved over time, Knott shows: the forest as howling wilderness, impeding the progress of civilization and in need of subjugation, and the forest as temple or cathedral, worthy of reverence and protection.Imagining the Forestshows the origin and development of both.

The regrowing forests of eastern North America have been an important global C sink over the past 100+ years, but many are now transitioning into late succession. The consequences of this transition are unclear due to uncertainty around the C dynamics of old-growth forests. Canopy structural complexity (CSC) has been shown to be an important source of variability in C dynamics in younger forests (e.g., in productivity and resilience to disturbance), but its role in late-successional forests has not been widely addressed. We investigated patterns of CSC in two old-growth forest landscapes in the Upper Peninsula of Michigan, USA, to assess factors associated with CSC and its influence on productivity and disturbance resilience (to moderate-severity windstorm). CSC was quantified using a portable below-canopy LiDAR (PCL) system in 65 plots that also had long-term (50-70+ years) inventory data, which were used to quantify aboveground net primary productivity (ANPP), disturbance history, and stand characteristics. We found high and variable CSC relative to younger forests across a suite of PCL-derived metrics. Variation in CSC was driven by species composition and size structure, rather than disturbance history or site characteristics. Recent moderate severity wind disturbance decreased plot-scale CSC, but increased stand-scale variation in CSC. The strong positive correlation between CSC and productivity illustrated in younger forests was not present in undisturbed portions of these late-successional ecosystems. Moderate severity disturbance appeared to reestablish the positive link between CSC and productivity, but this relationship was scale and severity dependent. A positive CSC-productivity relationship was evident at the plot scale with low-severity, dispersed disturbance, but only at a patch scale in more severely disturbed areas. CSC does not appear to strongly correlate with variation in productivity in undisturbed old-growth forests, but may play a very important (and scale/severity-dependent) role in their response to disturbance. Understanding potential drivers and consequences of CSC in late-successional forests will inform management focused on promoting complexity and old-growth conditions, and illustrate potential impacts of such treatments on regional C dynamics.

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.

Carbon accumulation in forests has been attributed to historical changes in land use and the enhancement of tree growth by CO2fertilization, N deposition, and climate change. The relative contribution of land use and growth enhancement is estimated by using inventory data from five states spanning a latitudinal gradient in the eastern United States. Land use is the dominant factor governing the rate of carbon accumulation in these states, with growth enhancement contributing far less than previously reported. The estimated fraction of aboveground net ecosystem production due to growth enhancement is 2.0 ± 4.4%, with the remainder due to land use.

Many ecosystems have been altered since European colonization, resulting in the loss of historical ecosystems along with information about historical ecosystems. Tree density estimation from historical land surveys with alignment to expert classifications of historical vegetation strengthen reconstructions of vegetation history through research triangulation. For the midwestern United States, we extended historical tree density estimates (≥12.7 cm in diameter) to contextualize expert classifications of vegetation types in Illinois and Minnesota, part of the historical Great Plains grasslands with very frequent fire exposure, and Indiana and southern Michigan, which were more protected from fire. We also identified a tree density threshold between grasslands and savannas and contrasted density estimates with two alternate density estimates. After refining expert-classified vegetation types, out of 14 major historical ecosystems in this region, 11 were grasslands, savannas, or woodlands. The three additional ecosystems were American beech (Fagus grandifolia) closed woodlands and forests in Indiana and American beech-oak (Quercus) closed woodlands and forests and tamarack (Larix laricina) and ash (Fraxinus) swamp forests in southern Michigan. Because tree densities in the grasslands of Illinois and Minnesota did not exceed 4 trees/ha and tree densities in the savannas of Indiana, Michigan, and Minnesota ranged from 23 trees/ha to 78 trees/ha, around 15 trees/ha may be a reasonable threshold between grasslands and savannas. Density estimates generally matched with two other sources of density estimates, despite using different approaches, supporting the reliability of density estimation. Anchoring density estimates from land surveys to other sources of historical vegetation establishes the validity of density estimation, while supplementing expert-classified ecosystems.

QUESTIONS: Do ecological sorting processes and functional diversity of forest ground‐layer plant communities vary among mature (65–85‐yr‐old) even‐aged, managed uneven‐aged and old‐growth forest stands? How does functional diversity relate to environmental variables within stands? LOCATION: Northern temperate deciduous forests of Wisconsin and the Upper Peninsula of Michigan, USA. METHODS: Ground‐layer species cover and light availability were measured at each of four old‐growth, even‐aged second‐growth, and managed uneven‐aged stands (n = 12 stands total). We used mixed‐effect models and fourth‐corner analysis to assess relationships among forest structure, species traits and the three components of functional diversity (functional richness, evenness, divergence) based on 32 leaf, reproductive and whole plant traits from 111 species. RESULTS: We identified differences in leaf phenology and morphology, life form and dispersal among stand types at the community level. Ground‐layer plant communities of even‐aged and uneven‐aged stands were at opposite ends of a spectrum of strategies aimed at tolerating stressful vs competitive environments, respectively. In even‐aged stands, communities were characterized by species adapted to relatively dark and closed conditions (heavy‐seeded tree saplings, spring ephemerals). In contrast, managed uneven‐aged stands were characterized by species with potential for quick returns on investment of nutrients and dry mass in leaves (i.e. early summer species with high specific leaf area, low leaf dry matter content and high phosphorus concentration). Old‐growth stands had fewer trait associations than managed stands, and were characterized by ferns and species with either ballistic or wind‐assisted seed dispersal. Functional diversity metrics were related in complex ways to light, management and soil texture. Managed stands had higher functional richness and divergence than old‐growth stands, which, instead, showed higher functional evenness. CONCLUSIONS: Even‐aged and managed stands support ground‐layer species with a distinct set of traits relative to those found in old‐growth forests. Although there is broad interest in uneven‐aged management as a means to restore the structures and functions of old‐growth forests, uneven‐aged management does not, at least initially, produce ground‐layer plant communities more similar to old‐growth forests than even‐aged management.

The concept of naturalness was developed to assess to what degree landscapes represent a natural state. Protected areas are often regarded as the remnants of untouched landscapes although many landscapes commonly perceived as pristine have a long history of human impact. Here, we introduced a historical perspective into the concept of naturalness and the analysis of the effectiveness of protected areas by analyzing historical trajectories in land-cover and forest communities for the Pictured Rocks National Lakeshore on Michigan’s Upper Peninsula (USA). Distribution of land-cover and forest community types was reconstructed for pre-settlement time (around 1850), the height of agricultural expansion (1928), and modern conditions (2000). Naturalness of the landscape was assessed by analyzing similarity between pre-settlement and current conditions and by assessing landscape continuity (1850–1928–2000). We compared changes in the strictly protected park core zone with those in the inland buffer zone with ongoing sustainable logging, and a not protected area adjacent to the park. Forest was the dominant land-cover type over the entire study period. We detected a gradient in land-cover continuity from the core zone (81 % continuity) to the inland buffer zone (74 %) and the area outside the park (66 %). Northern hardwood was the dominating forest type in all time points with high continuity (76 %). In contrast, pine forests show a more dynamic pattern with more than 50 % of the initial forests switching to non-forest or early succession forest types by 1928. More than half of the study area was considered as “natural virgin” (no changes in land-cover and forest community type) with a higher portion within the park than in the adjacent area. In contrast, areas with low naturalness are more abundant outside the park. Our study demonstrates the value of integrating historical information into naturalness assessments and the results provide useful information for future park management. More broadly speaking, our study advances research on the effectiveness of protected areas, by going beyond simple measures of averted deforestation, and introducing approaches to directly measure naturalness.

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.

The record of forest invasion by castern hemlock (Tsuga canadensis) during the course of Holocene migration provides useful information about invasion processes in temperate forest, a system that has been invaded by few exotic species. We used fossil pollen preserved in small forest hollows, which record forest composition on the scale of 1-3 ha, to study hemlock invasion of forests in the Sylvania Wilderness in the upper peninsula of Michigan, where there is now a mosaic of 3-30 ha stands dominated either by hemlock or by sugar maple (Acer saccharum) and basswood (Tilia americana). Fossil pollen was interpreted by comparison with 66 surface samples from small hollows in Michigan and Wisconsin, using three different statistical methods: pollen ratios, a dissimilarity index, and canonical variates analysis (CVA) ordination. We found that four hemlock stands along a 10-km transect across Sylvania originated as patches of white pine (Pinus strobus) forest that were invaded by hemlock ∼ 3000 yr ago (calibrated 14C dating) when hemlock expanded its range in northern Michigan. Invasion occurred at about the same time (within 800 yr) at all sites but was not associated with disturbance at any site. Over the next several thousand years hemlock coexisted with white pine, but eventually, at a time that differs from site to site, hemlock became dominant, and white pine disappeared from all but one of the four stands. These changes were apparently driven by climate changes over the last 4000 yr that caused the water table to rise (Brugam and Johnson 1997). The history of four nearby maple stands is more variable and less well understood. Unlike the hemlock stands, three of the four maple patches were not dominated by pine at the time of hemlock invasion, but instead had abundant oak (Quercus) and/or maple. Two of these stands were not invaded by hemlock, and the third, if invaded at all, was invaded for a few centuries by low densities of hemlock trees. Thus invasion by hemlock was sensitive to the species composition of the resident forest. Sugar maple and basswood increased in these stands, and by 2000 to 800 yr ago, depending on site, they resembled modern maple stands. The fourth patch was invaded by hemlock, but it was converted to a maple stand 1000-500 yr ago. A wood layer in the sediment is evidence that a catastrophic windstorm may have been responsible.

The effect of delaying female mating on population growth in codling moth ( Cydia pomonella (L.)) was found to act on a physiological time (degree-day) basis and was predictable using a simple quadratic equation. When combined with previous work on degree-day based mortality, we were able to evaluate how the magnitude of population reduction and survival varied between sites, years, and generations at locations in California, Michigan, Pennsylvania and Washington states. In general, reductions in population growth associated with females mating 1–3 days after emergence were greater in warmer areas and during warmer times of the year. In any given year and location, the temperature profiles during peak flight were crucial in determining the population reductions, but over an 11-year period, the average seasonal temperature profile was more important. During the overwintering generation, conditions were relatively mild in all locations and only minor differences were observed in population growth rates between locations. Populations experiencing 1–3 days delay in female mating were reduced 8, 19 and 32 % compared to populations experiencing no delay, respectively. During the first summer generation, population reductions doubled compared to those seen in the overwintering generation. During the second summer flight, reductions in population growth rate at the three cooler locations decreased, while they increased in the warmer California location. Overall, the results show delayed mating can help understand how population growth is related to environmental conditions experienced naturally by insect populations and will help guide studies of the mechanisms of mating disruption, a technique used for pest suppression in agricultural and forest systems.