Wayne State University

Greater Yellowstone Ecosystem

Much of my recent and current research has been located in the Rocky Mountains of Colorado and Wyoming, particularly in and around Yellowstone National Park. The 1988 fires in Yellowstone National Park created a very complex, fine-grained mosaic of lodgepole pine seedling densities across the burned landscape.  Several investigators have speculated that this "footprint" of the 1988 fires will persist until a similar disturbance again occurs, but few studies have actually examined the length of its persistence.  I studied the portion of the Yellowstone landscape left unburned by the 1988 fires to estimate the long-term effects of wildfires on stand structural heterogeneity, how that postfire heterogeneity might change with successional time, and to determine the rates and mechanisms of these changes.  Analyses of age distributions and stand reconstructions using dendrochronology suggested the effects of large wildfires shape the structure of this landscape for almost two centuries after the disturbance.  However, stand structural variability decreases over time because initially dissimilar stand structures develop though multiple mechanisms that act to compress the initial variability towards a common stand structure.  These changes in structural variability have direct influences on changes in landscape pattern, causing the landscape to become more coarse-grained as initially dissimilar stands coalesce into larger patches.  Thus large natural disturbances such as the 1988 Yellowstone fires may leave a structural imprint on the landscape, but the initial heterogeneity will decrease as succession occurs. This work suggests that the structure and productivity of very dissimilar post-fire lodgepole pine stands converges within the fire interval on this landscape, and that very broad variability in natural lodgepole pine forest densities exists irrespective of past forest management or fire suppression – an issue under great debate regarding fire hazard and fuels management in western forests. This work also highlights the natural occurrence of uneven-aged lodgepole pine stands and lends insight into potential silvicultural alternatives in these forests.

1 Year After Fire	20 Years After Fire	100 Years After Fire

My initial work on stand structure has been carried further to examine how global change may affect carbon cycling at stand- and landscape scales. Understanding the how climate, disturbances, and stand structure affect carbon dynamics remains an important challenge in ecology, particularly as the frequency and severity of disturbances increases with climate change.

Wilcox fire, Grand Teton NP, 2000	Beetle Kill in Grand Teton NP

Landscape heterogeneity in stand structure is linked to variability in carbon storage, and climate change may therefore drastically affect the carbon balance of landscapes and the globe by affecting the disturbance regimes that shape stand structure across landscapes. In Yellowstone, we asked how climate-mediated changes in fire regimes alter the distribution of carbon budgets and thus the behavior of the entire Yellowstone landscape as a net sink or source of carbon in the global carbon cycle. In particular, we focused on net ecosystem production (NEP) – the difference between net primary production and heterotrophic respiration – and how it varies with stand structure and succession. We used replicated chronosequences to measure how annual net carbon storage (NEP) varies with age and density built new allometric equations to predict tree biomass in the region, and extrapolated stocks and fluxes to the landscape.

Carbon storage following the 1988 fires	Hypothesized carbon storage following beetle outbreaks

Current work: We are currently in the midst of a study funded by the Department of Energy’s National Institute for Climate Change Research that expands the carbon/disturbance research to include insect outbreaks. The Greater Yellowstone Ecosystem and most of the Rocky Mountain West is experiencing an extensive and intensive insect outbreak, such that insects including the mountain pine beetle (MPB) are an important driver of carbon dynamics and may determine whether western landscapes are carbon sinks or sources. The overall objective of this study is therefore to understand how MPB outbreaks affect forest carbon storage at stand and landscape scales under multiple climate scenarios.

Colorado Front Range

My research focus includes applied as well as basic research that may contribute to management and conservation efforts. Much of my work is couched in conservation of biodiversity and investigates the persistence of threatened species and ecosystems across landscapes. Trembling aspen is one of the only deciduous forest types in the US Rocky Mountains, and is therefore a valued species for its contribution to biodiversity, wildlife habitat, and aesthetics.  Several investigators have documented a general decline and senecence of aspen stands across the West due to factors such as climate fluctuations, fire suppression and increased elk browse. We examined aspen stands on the northern Colorado Front Range to assess the current condition and to predict long-term trends in aspen forests across this heavily managed landscape. We identified six types of trends in aspen, distinguished mainly by the relative dominance and age distribution of aspen and co-existing conifers where applicable. Only 35% of stands exhibited age distributions that suggested a self-replacing stand, but only 24% of stands were declining. Because only 24% of aspen stands showed evidence of a true "decline", and many aspen stands in the region may have regenerated due to human activities, such a result suggests that a decrease from the current amount of aspen area may still fall within the historic range of variability of aspen coverage. This research suggests that factors leading to aspen decline such as fire exclusion, grazing, and ungulate browsing are evident within very specific ecological contexts, and their relative influences in shaping western aspen forests demand a broad-scale approach in assessing aspen decline that incorporates differences in regional and local climate.

Declining Aspen in Colorado	Lone Aspen in Colorado	Postfire Aspen in Colorado

Current work: Funded by the US Forest Service and in collaboration with John Bradford, USFS, we are initiating a new comparative study in northern Minnesota and the Colorado Front Range to examine the correlation between aspen mortality and drought. Many aspen stands throughout the southern Rocky Mountains and the Lake States not previously observed to be “declining” have experienced rather sudden, extensive canopy tree mortality over the last decade that corresponds to a relatively dry period over the last two decades. If drought causes aspen mortality, it likely reduces aspen vigor and growth, which means that drought may be adversely affecting many more aspen stands than previously realized. Understanding the relationship between drought and aspen mortality is especially important because future climatic conditions are expected to include greater frequency and severity of drought events. Our overall goal is to understand stand-level responses of aspen forests, including growth decline and mortality, to weather fluctuations, particularly drought, using a multi-scale approach that will examine differences in forest responses between regions as well as the importance of site conditions within each region.

Northern Lower Michigan

Kirtland's warbler is a federally endangered songbird that nests under young jack pine only in northern Lower Michigan.  The warbler nests in a given stand only for as long as there are lower live branches available to shelter the nest, such that it nests only in dense stands interpersed with small openings during a narrow window of duration of stand age.  Because jack pine regenerates over large areas only after fire, fire suppression has limited the amount of young jack pine within the warbler breeding range, and plantations are now the primary method for providing suitable habitat for the warbler.  I used a broad-scale, “top-down”, regionalization approach to classifying these ecosystems in order to understand and predict the timing and duration of use of jack pine forests by the warbler, including the importance and spatial pattern of wildfires in shaping this forest type across the breeding range, and the impact of converting natural jack pine forests to plantations. Such a description and classification of landscape ecosystems provides a useful ecological framework for conservation and management of Kirtland's warbler.

Kirtland's Warbler	Warbler's Population Number

Current work: We are working on an unfunded project to examine how well Kirtland’s warbler management fits into the historical range of variability of young jack pine forests in Michigan’s northern Lower Peninsula. Never an abundant bird, the warbler’s population today numbers approximately 1800 breeding pairs as a result of highly successful, extensive jack pine plantations placed all across the breeding range specifically for this purpose. We are using historical records of forest vegetation and reconstructed fire regimes to estimate the pre-settlement coverage of young jack pine stands for comparison to current coverage to determine the appropriateness of the current levels of warbler management.

Southeastern Lower Michigan

Though largely urban, southeastern Michigan offers many opportunities for forest and landscape ecology research. In particular, my work is addressing the ecological impacts of the emerald ash borer (EAB) on forests in the region. In an era where rates of ecological change are unprecedented, understanding the effects of introduced species is critical for predicting their consequences for native biodiversity. Identified only in 2002, the emerald ash borer is a destructive non-native insect that kills > 85% of healthy ash trees > 2.5 cm in diameter within 3-5 years of infestation, leaving seedlings and saplings unaffected. EAB has spread from its introduction in the Detroit area to Ohio, Indiana, Ontario, Maryland, and Virginia.

EAB locations	EAB Galleries	Dead Ash

Despite aggressive quarantine and eradication efforts, extensive tree mortality suggests that EAB impact on North American ash species may resemble that of chestnut blight and Dutch elm disease. Ecological research on this exotic insect has been limited to monitoring of mortality and dispersal modeling, but few data exist that describe the regenerative capacity of ash following EAB outbreaks. The overall objective of this research is to predict the future ability of ash trees to replace themselves and future changes in plant and animal composition at the forest floor where EAB-induced ash mortality is or will be extensive.