Ecology and Recovery of Eastern Old-growth Forests Andrew M. Barton & William S. Keeton, editors Annotated Table of Contents
Chapter 1. Introduction: Ecological and Historical Context Andrew M. Barton • Defining old growth is a “wicked” challenge. We take a permissive view, emphasizing the importance of old forests, relatively undisturbed by people, and allowing chapters authors to delineate old growth based on their ecosystems. • Old-growth forests are highly valued because they harbor biodiversity, provide services to humanity, and, according to many, have a right to protection. • Illustrated by two examples, extant old-growth forests have changed constantly over the past 20,000 years as a result of natural environmental changes. • Old-growth conservation and science arose as a response to the dramatic alteration of forests, changing social values, political action, and new environmental threats. • The mission of this book is to disseminate a diverse sample of cutting-edge, oldgrowth research pursued over the past two decades, which provides a foundation for the conservation of these important ecosystems. Chapter 2. Old-Growth and Mature Remnant Floodplain Forests of the Southeastern United States Loretta L. Battaglia and William H. Conner • Less than 40% of the once vast bottomland hardwood forest (BLH) ecosystem in the southeastern US remains due to conversion to agriculture and urban expansion, most of this as second and third-growth.
• The precious few old-growth and mature forest examples differ markedly from their young counterparts in that they harbor high species richness and structural diversity. • These old-growth tracts are valuable references for ongoing restoration efforts, but they are often embedded in a highly modified landscape and vulnerable to land use changes. • We identify four representative sites that span the historic distribution of BLH: Congaree Swamp National Park in central SC, Four Holes Swamp in coastal SC, Jean Lafitte National Historical Park and Preserve in coastal LA, and the Cache River Natural Area in southern IL. • For each of these, we summarize the ecological attributes, compare them with younger forests, and discuss threats, management strategies, and opportunities for bottomland hardwood forest.
Chapter 3. Fire-Maintained Pine Savannas and Woodlands of the Southeastern United States Coastal Plain Robert K. Peet, William J. Platt, and Jennifer K. Costanza • Old-growth concepts for pine savannas and woodlands of the southeastern US are based on sites with minimally-disturbed populations of old trees and ground-layer vegetation, and fire regimes that replicate ecological and evolutionary conditions present historically. • Highly uneven-aged old-growth pine populations persist over time as stands containing dense patches of recruits interspersed among more randomly dispersed large trees as much as several centuries old. Stands are maintained in demographic non-equilibria by recurring tropical cyclones and lightning strikes, and are blocked from transition to closed-canopy forests by frequent fires that also maintain conditions conducive for recruitment of pines into open patches. • Old-growth ground-layer vegetation includes grasses as aspect dominants, as well as a high diversity of shrubs, lianas, and especially forbs, many endemic to pine savannas and most of which persist under conditions of frequent, lightning-season fires via underground structures and which respond post-fire with regrowth and flowering. • Pines and some ground-layer savanna plants generate feedbacks on fuels, altering characteristics of fires. The resulting plant – fire “coevolution” involves iterative changes in characteristics of plants and fires, producing plant communities that are
highly integrated with respect to fire and similar in function to savannas worldwide that occur on impoverished soils in relatively constant climates. • In the current period of increasingly small fragments of natural landscape, human exploitation, and global change, maintenance of high-biodiversity, fiery ecosystems with old-growth attributes will require active management using prescribed fires that mimic the natural, lightning-season fires and ecological conditions under which the savanna species evolved.
Chapter 4. Old-Growth Forests in the Southern Appalachians: Dynamics and Conservation Frameworks Peter S. White, Julie P. Tuttle, and Beverly S. Collins • More than 100,000 ha of old-growth forests remain in the high mountain region of the Southern Appalachians. • These forests have been shaped – and will continue to be shaped – by direct and indirect human influences, natural disturbances, and fire, which has both natural and human components. • Old-growth forests of Great Smoky Mountains National Park from the 1930s and 1990s illustrate the complexity of historic and ongoing disturbances. • Canopy age structure (“old-growth” in the narrow sense) and degree of human influence (“naturalness”) are traditional attributes of old-growth definitions. • Adding a third attribute, forest continuity (ecosystem age, regardless of canopy age structure), leads to an inclusive definition of “old-growth” and calls for efforts to complete the inventory of old-growth forests in the Southern Appalachians. Chapter 5. Topography and Vegetation Patterns in an Old-Growth Appalachian Forest: Lucy Braun, You Were Right! Julia I. Chapman and Ryan W. McEwan • The importance of environmental gradients in structuring ecological communities is well established in ecology, but novel analysis techniques based on evolutionary relatedness and functional traits are providing new insight into how vegetation patterns are connected to environmental factors. • As noted by E. Lucy Braun, environmental filters act over the long-term to segregate species into community types. These patterns are most easily detected in systems that are relatively free of widespread anthropogenic disturbance, such as
old-growth forests, where species have had sufficient time to sort across abiotic gradients. • In this chapter, we present new analyses of tree communities in an old-growth Appalachian forest using phylogenetic and functional diversity indices. Our key finding is that topography is an important driver of community assembly among tree species at this site, and has remained important over a period of 30 years despite a slow, ongoing shift in species dominance from oak to maple. Low functional and phylogenetic diversity were seen in high elevation, south-facing areas, which indicates an environmental filtering effect where mature communities contain species with similar adaptations for surviving in dry, nutrient-poor conditions. • The mean values of the functional traits studied (including wood density, specific leaf area, maximum height, and seed mass), which are related to the dominant species in the sampled communities, all changed significantly within the midstory (trees 2.5–25 cm diameter) between 1979 and 2010. These long-term shifts in overall mean trait values reflect the ongoing recruitment of maple-dominated juvenile tree assemblages that differ in composition from the more varied mature overstory. These changes could have important implications for various ecosystem functions, such as nutrient cycling and carbon storage. Chapter 6. Old-Growth Disturbance Dynamics and Associated Ecological Silviculture for Forests in Northeastern North America Anthony W. D’Amato, Patricia Raymond, and Shawn Fraver • Studies of old-growth remnants have increased our knowledge of natural disturbance dynamics considerably over the past several decades • Natural dynamics of northeastern forests are dominated by frequent gap-scale events associated with wind, insects, and disease; however, infrequent, intermediate-scale disturbances play a disproportionately important role in affecting old-growth structure and composition • Ecological silvicultural systems based on these prevailing dynamics are largely centered around two-aged and uneven-aged systems, namely irregular shelterwoods and hybrid approaches that blend single-tree and group selection
Chapter 7. Historical Patterns and Contemporary Processes in Northern Lake States Old-Growth Landscapes David J. Mladenoff and Jodi A. Forrester
• Our understanding of the regional forest composition of the 1800s has expanded significantly through the combination of historical records with current technology. This has led to a deeper appreciation of what our remaining old-growth represents and an understanding of the processes and dynamics of old and natural forest systems, from the landscape to stand scales • Broad-scale spatial research helped to fill in our understanding of the high variability of old-growth composition due to environment and disturbance. The visualizations revealed the magnitude of change on the landscape, the low level of recovery of both forest structure and composition, and the potential for aboveground live biomass accumulation and carbon storage • Numerous comparative field studies have focused on describing the structure and function of old-growth hemlock-hardwood forests and compared these with young stands, examining forest composition, biomass, productivity, nutrient cycling, understory plant diversity, forest birds, and mammals. • By far the greater number of these studies pointed to variably-sized gaps and downed large woody debris as key to both the spatial variability in ecosystem processes and quantity of diverse species habitat. Chapter 8. Is Management or Conservation of Old Growth Possible in North American Boreal Forests? Daniel Kneeshaw, Philip J. Burton, Louis De Grandpré, Sylvie Gauthier, and Yan Boulanger • Old-growth boreal forests are dynamic and develop under the constraint of largescale fires and insect outbreaks • Their proportion changes across the boreal region, from being the abundant dominant forest type in maritime regions to occurring as rare small forest patches in continental regions where fire return intervals are short • Widespread commercial logging, in conjunction with natural disturbance regimes, creates distinct conservation, management and restoration challenges across the boreal forest • Multiple solutions, including stand-level approaches and long-term landscape-level goals, are needed to ensure the maintenance of boreal old-growth Chapter 9. Forest-Stream Interactions in Eastern Old-Growth Forests Dana R. Warren, William S. Keeton, Heather A. Bechtold, and Clifford E. Kraft • Riparian forests are changing dynamically in eastern landscapes as secondary stands continue to recover and redevelop towards structurally complex latesuccessional conditions.
• Important forest stream-interactions, such as large woody debris inputs, controls on light availability and related in-stream autotrophic production, structural influences on stream channel geomorphology, and in-stream nutrient processing are likely to change with forest stand development. • Late-successional and old-growth riparian forests have pronounced effects on stream ecosystems, resulting in exceptionally high large woody debris volumes, higher densities of debris dams, greater channel roughness and possibly flood resilience, spatially complex light environments and food webs, and greater rates of in-stream nutrient spiraling and retention. • Careful and judicious management for, and/or conservation, of structurally complex riparian forests will yield high quality stream habitats and stream ecosystem functions that are currently under-represented on eastern forest landscapes. Chapter 10. Belowground Ecology and Dynamics in Eastern Old-Growth Forests Timothy J. Fahey ● The belowground dynamics of eastern old-growth forests differ in some respects from younger forests especially as a result of larger trees and canopy gaps and greater pedodiversity (variability of soil morphology and other properties). ● Large canopy gaps sometimes can result in the formation of root gap and together with higher soil temperature and moisture could lead to nutrient losses by leaching (Figure 10-1). ● The large pits and mounds resulting from windthrow of big trees causes soil disturbance (i.e. “pedoturbation” - the mixing of soil layers) and local resetting of soil formation processes (Figure 10-2). Based on the long persistence of such microtopography, a cumulative increase in pedodiversity probably occurs in oldgrowth forest landscapes. ● There is little evidence demonstrating systematic differences between mature and old-growth forests in their fine root and mycorrhizal systems. Other soil features probably override disturbance history as a driving force behind such differences. ● Although buried wood can accumulate in some cold forests, the amounts measured for eastern deciduous forests are small because of rapid and complete wood decay. Moreover, although mycorrhizae are commonly found in woody debris, it is a relatively minor component of the substrate for fine root growth in these forests. ● Soil-dwelling plethodontid salamanders could depend on eastern old-growth forests as climate change refugia.
● Exotic earthworms have invaded some eastern old-growth forests with profound consequences for belowground processes because of their litter feeding and soilmixing activity. However, to date old-growth forests may have experienced less invasion than second-growth forests primarily because of limitations on dispersal vectors. Chapter 11. Biological Diversity in Eastern Old Growth Gregory G. McGee • Eastern old-growth forests are characterized structurally as having high occupancy of canopy and subcanopy space by live trees, high live basal area (median across select forest types ranging from 30-45 m2 ha-1), and many large live trees (30-100 trees ha-1 larger than 50 cm dbh). • Continuous mortality by scattered, individual trees leads to small average canopy gap sizes, and a high volume (medians range from ~40-110 m3 ha-1) of downed coarse woody debris (CWD) and basal area of standing CWD (2.0-8.5 m2 ha-1). • ‘Keystone structures’ such as large live trees and CWD, which are more abundant in old-growth forests than in young or managed forests, support diverse communities of fungi, lichens, bryophytes and invertebrates. • Substantial knowledge gaps exist in understanding organismal diversity in eastern old growth, compared to other northern temperate forest regions. • Given the demonstrable linkages between organismal diversity and the presence/abundance of keystone structures in northern temperate forests, biodiversity can likely be increased and sustained within managed forest landscapes by applying silvicultural practices that enhance structural heterogeneity. • Still, some evidence exists to indicate old-growth conditions, per se, (i.e., extended periods without disturbance) are as important as structural habitat availability for some taxa that are dispersal-limited or have low tolerance for variability in microenvironmental conditions. Chapter 12. Eastern Old-Growth Forests under Threat: Changing Dynamics due to Invasive Organisms John S. Gunn and David A. Orwig • Old-growth forests, like most temperate forests in eastern North America, are under increasing threats from global change. Threats from invasive organisms, in particular, are unlike anything experienced in millennia. These threats are
profoundly changing the remaining old-growth forests and pose serious challenges to redeveloping or restoring old-growth in the future. • The continued fragmentation of late-successional and old-growth forest communities can facilitate the movement of non-native invasive plants, pests, and pathogens deeper into forest patches. • Non-native invasive plant, pest, and pathogens pose a threat to the persistence and recruitment of old-growth forests through direct mortality, the suppression of regeneration of native species, alteration of forest structure, delay of forest succession, and reduced fitness and growth of native species. • These novel pressures are likely to increase in a climate change context where conditions become more favorable for invading pests and pathogens. Additionally, the potential for more frequent and intense natural disturbances can increase the susceptibility of old-growth stands to invasive pests and pathogens. • Efforts to minimize the potential damage of invasive plants, pests, and pathogens to old growth stands should focus on the prevention of establishment rather than costly and largely ineffective control measures. Chapter 13. Silviculture for Eastern Old Growth in the Context of Global Change William S. Keeton, Craig G. Lorimer, Brian J. Palik, and Frédérik Doyon • Silvicultural management for structural complexity and old-growth characteristics in secondary forests is no longer a theoretical proposition. It is now a well-tested approach and increasingly applied in a variety of operational settings. • Old-growth silviculture yields a variety of co-benefits, including timber revenue, habitat for under-represented late-successional biodiversity, carbon storage, and riparian functionality. As such it can be integrated with holistic forest management providing a broad array of ecosystem goods and services. • A variety of novel stressors, including climate change and invasive pests and pathogens, pose serious challenges to old-growth silviculture. • There is no strict code or “one-size-fits-all” approach for old-growth silviculture. Rather, managers can target a range of old-growth characteristics for inclusion within working forests. • Old-growth silviculture represents an adaptive forest management strategy. It will help maintain resilience on managed forest landscapes. Chapter 14. Source or Sink? Carbon Dynamics in Eastern Old-Growth Forests and Their Role in Climate Change Mitigation
William S. Keeton • Old-growth forests contribute to climate change mitigation by storing very large amounts of carbon in living and dead biomass. • There is considerable debate surrounding long-term carbon dynamics in latesuccessional forests. Some studies suggest a capacity for net positive carbon uptake for longer time periods than previously hypothesized, while others maintain that sink capacity declines to zero after the first two centuries of stand development. Multiple biomass accumulation pathways are likely in late-successional eastern forests. • Natural disturbances maintain positive sink capacity in late-successional landscapes and transfer carbon to dead wood pools, which add to total ecosystem carbon storage. • Late-successional landscapes influenced by periodic partial disturbances often do not demonstrate equilibrium or steady-state biomass dynamics. • Carbon dynamics in old-growth ecosystems will shift with global climate change. • Management for old-growth characteristics in secondary forests can enhance the carbon sink capacity of eastern landscapes. Chapter 15. Conclusion: Past, Present, and Future of Old-Growth Forests in the East William S. Keeton and Andrew M. Barton • The romanticism of “old-growth is no less marvelous seen through the lens of contemporary ecological understanding, which stresses the dynamics and varied nature of late-successional ecosystems. • Old-growth is best seen as a condition embedded with complex primary forest systems. Rather than having a single set of archetypical characteristics, old-growth spans a range of possibilities depending on forest type, site conditions, and disturbance histories. • New discoveries of old-growth tracts continue to expand our opportunities to view and learn about late-successional forests. • A complex interplay of climate, natural disturbance regimes, and functional traits of tree species explains part of the tremendous differences in old-growth forests across eastern North America. • The heavy imprint of humans on old-growth forests contributes to an even more compelling case for their importance, and ecologists have been striving to put new ideas to the test for recovering extant and creating new old growth for the future.
• Old-growth eastern forests have a place on the future landscape. They add adaptive capacity and resilience to ecosystems buffeted by global change. But baselines for old-growth dynamics, structure, and composition will shift as environmental boundary conditions change.