The Historical Ecology Handbook

A Restorationist's Guide to Reference Ecosystems

Dave Egan, Evelyn A. Howell, Dave Egan, Evelyn A. Howell

• Publisher: Island Press
• Year: 2005
• Print ISBN: 9781597260336, 9781559637459
• eBook ISBN: 9781610913348
• Subtopic: Ecology

The Historical Ecology Handbook makes essential connections between past and future ecosystems, bringing together leading experts to offer a much-needed introduction to the field of historical ecology and its practical application by on-the-ground restorationists.

Chapters present individual techniques focusing on both culturally derived evidence and biological records, with each chapter offering essential background, tools, and resources needed for using the technique in a restoration effort. The book ends with four in-depth case studies that demonstrate how various combinations of techniques have been used in restoration projects.

The Historical Ecology Handbook is a unique and groundbreaking guide to determining historic reference conditions of a landscape. It offers an invaluable compendium of tools and techniques, and will be essential reading for anyone working in the field of ecological restoration.

II

Biological Evidence

OBSERVATION is one of the cornerstones of any scientific endeavor, so it seems appropriate that the biological evidence section begins with a chapter about how to infer the history of a wooded site through careful inspection and attention to detail. P. L. Marks and Sana Gardescu are plant ecologists who see history in the way a tree has formed, in dead trees and logs, and in the presence or absence of understory vegetation. They “read the landscape.” The method of inferring the history of a forest from observational field evidence that they describe in chapter 7, while qualitative, is, nevertheless, a vital first step in many restoration projects. The information from such work can also be used effectively to initiate and support more detailed, quantitative studies.

Dendrochronology or tree-ring dating is arguably one of the most widely recognized and versatile techniques for studying past environmental conditions. Working in the lineage of A. E. Douglas, the founder of modern dendrochronology, Kurt Kipfmueller and Thomas Swetnam (chapter 8) discuss the principles, practice, applications, and limitations of their science. As they explain, there is more to this work than simply counting tree rings.

Owen Davis describes another versatile technique—the analysis of pollen and related microfossils—in chapter 9. Like dendrochronology, palynology is a powerful means of studying past ecosystems, providing evidence over long periods of time and at a variety of scales. In addition to describing the basics of palynological investigation, Davis provides several examples of how palynology has been used to reconstruct historic vegetation.

The study of packrat middens is a relatively new way of learning about past environments in arid regions and one that complements other studies, such as palynology and dendrochronology. In chapter 10, David Rhode provides an overview of the work being done in that field, the strengths and weaknesses of the technique, and an outline of midden collection and analysis methods.

Historic animal assemblages is the subject of chapter 11, in which Michael Morrison wrestles with the problem of how to find good historical data about beings that are much more mobile than plants. His approach is multifaceted and includes discussions of the work done by zooarchaeologists and paleontologists in addition to advice about how to use museum collections and databases, literature, and relict fauna to determine historic animal assemblages. He also provides the reader with valuable guidelines for working with incomplete data sets.

In chapter 12, Stanley Trimble provides a myriad of documentary and database sources for the restorationist who needs historic information about factors such as soils, geomorphology, and hydrology.

Finally, in chapter 13, Glen Fredlund discusses another kind of microfossil—opal phytoliths, the “jewels of the plant world”—and its use in reconstructing historic ecosystems, especially those associated with grasslands. Like several other contributors, he is quick to point out the limitations of the approach under discussion, which is, nevertheless quite powerful when properly applied.

7

Inferring Forest Stand History from Observational Field Evidence

P. L. Marks and Sana Gardescu

There are many reasons for wanting to know the history of a forest. For a restoration ecologist, learning how a current forest stand—its vegetation, structure, and species composition—came into being is a fundamental issue. With that knowledge and a familiarity with the local flora, a restorationist can begin to plan how to use environmental conditions, successional pathways, disturbance, or plantings to return a forest to a historic or other desired state. Awareness of a site’s history is also important for anyone interested in understanding the relationship between vegetation and environment, since variations in stand history can lead to spurious correlations and misinterpretations of the effects of current conditions. Information on species-site relationships is fundamental both for basic ecology and for restoration efforts (Aber 1987), while retrospective studies can often provide important insights into ecological processes (Foster, Orwig, and McLachlan 1996).

This chapter focuses on ways that site history can be inferred from evidence that can be directly observed from a careful search through a piece of forest. In the following section of this chapter, we describe the kinds of field evidence that an experienced naturalist might use. In the subsequent section, we provide examples that demonstrate how the various types of field observations can be used to differentiate forest stands with different histories, such as old-growth forest vs. second-growth logged stands, or secondary post-agricultural forests vs. primary forest. We use the term secondary forest for stands that developed on land that was once cleared for farming, in contrast to primary forests, which were never cleared for agriculture but are not necessarily undisturbed old growth. Little old-growth forest is left in the United States because most forest stands have been logged or cleared for farming or urbanization. Since logged stands are also commonly referred to as “secondary” forest, to avoid confusion we will use post-agricultural for forest stands that developed on former farm fields.

Observations of Field Evidence

There are a variety of field clues that, if properly interpreted, reveal significant aspects of a forest’s history (table 7.1). These include features of the trees and understory plants in the stand, microtopography, and the stand edges. Because of their longevity, trees preserve a record of previous growing conditions, both while they are living and, in many cases, long after they die. How far back in time one can extrapolate depends on the type of evidence as well as the species and climate, but most field observations reflect primarily the most recent hundred years—or in the case of a young post-agricultural stand, a few to several decades. Often the signs are indistinct, or have more than one possible interpretation, so it is important to observe more than one kind of feature and, where possible, combine field evidence with other types of historical information.

Stand Edges

Where a forest stand of interest is surrounded by, or adjacent to, other forest, the shape and edges of the stand can often be revealing. An abrupt shift in stand structure or species composition that does not correspond to changes in environment, such as differences in drainage or slope, suggests that the history of the stand differs from that of the surrounding forest. Straight boundaries or rectilinear stands found within continuous forest usually indicate human activity rather than natural disturbance—one side or the other, or both, may have been farmed or logged (Russell 1997). Former agricultural field edges are sometimes visible as wire fencing or stone walls within what is now forest. Evidence that a former edge, now embedded in forest, was once adjacent to an open field can be seen in the asymmetric form of the trees along the old edge (figure 7.1).

Table 7.1. Types of observations that can be used to infer forest history

Features	Examples	Interpretations
Stand edges	straight (rectilinear) discontinuities	farmed or logged on one side or both
	line of low-branched trees in forest	former hedgerow between fields
Stand composition	old hawthorns and apple trees	former pasture
	maples (fire-sensitive) absent	burned
Tree form	branchy, spreading, or “wolf” trees	former field or savanna
Dead or damaged trees	abundant cut stumps	logged
	tip-ups	windthrow
	fire scars	burned
Understory plants	weedy species present	former old field or pasture
	sparse understory vegetation	possible grazing or browsing
Microtopography	windthrow pits and mounds	never plowed

Property boundaries (frequently indicated by posted signs) within continuous forest are also important to note because the stands on either side are likely to have different management histories. Current or former landowners may have helpful information about a stand’s history and past management (see chapter 4). Former fields and hedgerows, clear-cuts, and large natural-disturbance openings are often evident in old aerial photographs (see chapter 5). Such visual information can be useful for determining the boundaries of the current stand.

Stand Structure and Composition

The forest trees within a stand—their forms, sizes, and species composition—reveal much about its history. Trees develop specific shapes depending on whether they grow in the interior of a forest, along an edge, or in the open (Egler 1977; Oliver and Larson 1996). Low, spreading branches on trees that are now surrounded by forest are diagnostic of stands that originated on abandoned farm fields, large forest clearings, or former savannas. However, branchy, open-grown trees can also be found in primary forest, on soils where a dense canopy does not develop, such as oak woodlands on dry ridges, so it is important to be familiar with the local natural variation in forest types. Open-grown forms are not seen if the regenerating saplings or residual stems were at high density, which is normally the case in stands that developed after windthrow or logging.

Figure 7.1. A well-defined woodland edge (above the arrow) between two stands of different ages. The younger, post-agricultural forest is to the left, evident in the profusion of spreading branches on the left-hand side of the trees along the former open edge.

Stand size and age structure can be a useful diagnostic tool. Large-diameter trees are characteristic of old-growth stands, although not all old forests have large trees, depending on site conditions (Oliver and Larson 1996). Uniformity in diameter of the canopy trees often indicates that the stand initiated after a large disturbance, such as logging or a windstorm. Alternatively, the absence of one or more size classes from a full range of tree diameters suggests a failure in tree establishment for a period of time, possibly due to fires or grazing.

There are several caveats to using stand structure to infer history. One needs to know what the normal structure is for that forest type in order to recognize departures, which can be subtle (Veblen 1992). In some cases it may be necessary to sample the stand to determine the size distribution and composition (Bonham 1989). Since it is the age structure that shows the pattern of stand development, and because stem diameters and tree heights are frequently not reliable indicators of relative ages (Cooper 1960; Veblen 1992; Oliver and Larson 1996), it is better to age the trees using annual tree rings whenever possible (see chapter 8). Even so, age structure can sometimes give a false impression. For instance, an empty age class can be due to high sapling mortality rather than a period of no seedling establishment (Johnson, Miyanishi, and Kleb 1994).

Tree species composition is often a good indicator of important aspects of a stand’s past. Knowledge of the natural variations in forest type within the local landscape is key, because departures from expectation are a clue that something has altered the pattern. For instance, a stand of red maple (Acer rubrum) and white ash (Fraxinus americana) in a region where nearby forests on similar upland soils are mixtures of American beech (Fagus grandifolia) and sugar maple (Acer saccharum) is likely to have had a different history. In central New York, dominance by red maple and white ash is indicative of post-agricultural forest (Nyland, Zipperer, and Hill 1986; Mohler 1991). Certain species are associated with particular site histories, for example, jack pine (Pinus banksiana) with fire, or apple (Malus spp.) and hawthorn (Crataegus spp.) with pastures. Others, such as aspen (Populus spp.) and birch (Betula spp.), can be found in a variety of clearings, including old fields, clear-cuts, and stands opened up by fire or wind. The absence of a species can also be informative. For example, fire-sensitive species such as eastern hemlock (Tsuga canadensis) are missing in forests that have burned, and beech trees are not found in the canopy of young post-agricultural stands. The associations between particular indicator species, habitat, and site history vary across regions, so it is important to know the local vegetation. For example, tulip poplar (Liriodendron tulipifera), a mesophytic forest species, is not an old-field invader toward the northern end of its range in New York but is common in many post-agricultural old-field stands in some regions farther south.

Dead and Damaged Trees

Another stand feature that can reflect forest history is the presence and abundance of dead timber—standing dead trunks, stumps, and downed logs. Dead trees can provide useful information, especially if they are large, numerous, or of a different species or growth form than the current live canopy trees. For example, large, branchy, dead white pines (Pinus strobus) standing in a forest now overgrown by hardwoods are often diagno...

Table of contents

• About Island Press
• About the Society for Ecological Restoration International
• SOCIETY FOR ECOLOGICAL RESTORATION INTERNATIONAL
• Title Page
• Copyright Page
• Table of Contents
• Table of Figures
• Acknowledgments
• Foreword
• Preface to the 2005 Edition
• Introduction
• I - Cultural Evidence
• II - Biological Evidence
• III - Synthesis
• About the Contributors
• Index
• Island Press Board of Directors