Forgotten Grasslands of the South: Natural History and Conservation

By Reed F. Noss and Edward O. Wilson

Forgotten Grasslands of the South is a literary and scientific case study of some of the biologically richest and most endangered ecosystems in North America. Eminent ecologist Reed Noss tells the story of how southern grasslands arose and persisted over time and addresses questions that are fundamental for conserving these vital yet poorly understood ecosystems.

The author examines:

• the natural history of southern grasslands
• their origin and history (geologic, vegetation, and human)
• biological hotspots and endangered ecosystems
• physical determinants of grassland distribution, including ecology, soils, landform, and hydrology fire, herbivores, and ecological interactions.

The final chapter presents a general conservation strategy for southern grasslands, including prioritization, protection, restoration, and management. Also included are examples of ongoing restoration projects, along with a prognosis for the future.

In addition to offering fascinating new information about these little-studied ecosystems, Noss demonstrates how natural history is central to the practice of conservation. Natural history has been on a declining trajectory for decades, as theory and experimentation have dominated the field of ecology. Ecologists are coming to realize that these divergent approaches are in fact complementary, and that pursuing them together can bring greater knowledge and understanding of how the natural world works and how we can best conserve it.

Forgotten Grasslands of the South explores the overarching importance of ecological processes in maintaining healthy ecosystems, and is the first book of its kind to apply natural history, in a modern, comprehensive sense, to the conservation of biodiversity across a broad region. It sets a new standard for scientific literature and is essential reading not only for those who study and work to conserve the grasslands of the South but also for everyone who is fascinated by the natural world.

• Language: English
• Publisher: Island Press
• Release date: Dec 3, 2012
• ISBN: 9781610912259

Book preview

Stowe.

CHAPTER 1

Natural History of a Forgotten American Grassland

We left the magnificent savanna and its delightful groves, passing through a level, open, airy pine forest, the stately trees scatteringly planted by nature, arising straight and erect from the green carpet, embellished with various grasses and flowering plants.

William Bartram (1774, near present-day Gainesville, Florida)

Taking a break from after-dinner email, I stroll into the family room, glass of cabernet in hand, to find my family watching the Discovery Channel on TV. I almost never watch television, so I do not know what to expect when I encounter one of these strange machines. This time I see a view from a low-flying aircraft of a beautiful green prairie landscape somewhere in the Great Plains of North America. The low undulating hills and soft, waving grass roll into the distant horizon. It is an inviting and comforting sight, a verdant scene once common in the center of our continent but now hard to find due to conversion of millions of acres of prairie to agriculture. The narrator, a well-known actress who, my daughter informs me, has battled aliens in movies, repeats a well-worn refrain: Grasslands occur where there is too much rain for desert, but not enough rain to support forest.

I hurry back to my computer to capture that quote, which can be found in various forms in countless textbooks. In a 1991 book series on ecosystems of the world, R.T. Coupland states that grasslands occur along a climatic gradient between desert and forest. A textbook of biogeography by Mark Lomolino and coauthors declares that temperate grasslands are situated both geographically and climatically between the deserts and the temperate forests (fig. 1.1). These statements epitomize the paradox of grasslands in the rainy southeastern United States: few people, even ecologists, know they exist or expect them to be here. The South has more than enough rain to support forest. Whether a particular landscape in the South supports forest or grassland depends on factors other than precipitation—especially fire—but also soils, herbivores, and other influences. Ecologists describe this phenomenon as alternative stable states. Grassland was a common or dominant alternative state across much of the South, but that fact has been largely forgotten.

When educated people in North America hear the terms grassland or prairie, most of them visualize the Great Plains—the scene I saw on television. Here, grassland dominated a vast region or biome. Grassland is the largest of the four major biomes on earth and the largest in North America, covering some 300 million hectares (ca. 750 million acres) before European settlement. (Note: I use English units in this book for the benefit of the general reader, but provide conversions from metric to English, as appropriate, where metric units are used in original sources.) The grassland biome (including savannas, which are grasslands with scattered trees) covers more than 40 percent of the land surface of the earth and is inhabited by more people than any other biome.

Mean Annual Precipitation (cm)

Figure 1.1. A climograph showing biome-scale relationships between climate and vegetation. Grassland/savanna is shaded. Grasslands in the southeastern United States do not follow this pattern of being intermediate between desert and forest. Adapted from Lomolino et al. (2006) after Whittaker (1975).

The climate of the South (fig. 1.2) varies greatly with latitude, longitude, and elevation, but none of it matches the traditional description of the grassland biome. Whereas most of the grassland biome of North America receives well under forty inches of rain per year, the South gets about forty-eight to eighty inches. The climate, except at high elevations, is humid-temperate to warm-temperate from the Ohio Valley south to approximately the northern Florida Peninsula and Gulf of Mexico. Florida has a steep climatic gradient, with average temperature increasing rapidly with decreasing latitude. Northern Florida experiences regular freezes in winter; freezes decline sharply in frequency southward. South Florida is protected by the Gulf Stream, which originates as warm water from the tropical North Atlantic. Many biogeographic classifications designate south Florida as tropical, consistent with the dominance of south Florida (especially the Keys) by Antillean species. The climatic and physiographic diversity of the South partially explains the high species richness found in southern grasslands, but there is much more to it than that, as this book will explore.

Figure 1.2. The study area, defined to encompass a variety of grasslands with southern (and often western) affinities. This entire region of the southeastern United States is referred to as the South in this book. Southeast and southeastern are used, where applicable, for the region east of the Mississippi River and to contrast this region with the southwestern and south-central United States.

NATURAL HISTORY FOR CONSERVATION

This book is about grasslands of the South, but it explores a bigger topic: how knowledge and practice of natural history are essential to the conservation of biological diversity. The logic is straightforward: to conserve wild living things and their habitats, we must know them and understand how they live and interact. Recognizing a species by name is essential to learning more; hence, it is deplorable that training in taxonomy is plummeting. Consider this example: Antje Ahrends and coauthors, in a paper called Conservation and the botanist effect, show through a study of plant records from Tanzania that botanists with proper training in plant identification record more species (20 more species per 250 specimens) and more endemics (narrowly distributed species) and other taxa of conservation concern than botanists with inferior taxonomic skills. Poor training in natural history inevitably leads to second-rate conservation.

Natural history in the broad sense is not just identifying and naming things; it incorporates and intertwines biogeography, ecology, evolutionary biology, anatomy, physiology, taxonomy, systematics, paleontology, environmental history, geography, anthropology, archaeology, and other subjects, but with a focus on whole organisms and communities. What distinguishes natural history from most of current academic science is not just its acceptance of observation as a complement to experimentation, its rejection of extreme reductionism and hyperspecialization, or that much of it must be learned outdoors. More essentially, natural history insists on intimate familiarity with some aspect of biological diversity. A naturalist can be a generalist (familiar with many groups of organisms or types of ecosystems) or a specialist (highly knowledgeable about one or a few groups or places)—we need both. Perhaps the ideal naturalist has broad knowledge complemented by specialized expertise on a particular taxonomic group or subject. The great ant biologist, all-round naturalist, and living legend Ed Wilson comes to mind, as does the generalist Charles Darwin with his special interest in barnacles, orchids, and earthworms, among other groups.

A modern tragedy is that we are losing naturalists as the old ones die off or retire and few new recruits are trained or hired. Schools and universities are eliminating field trips and field-based courses. At the same time—and the two trends are connected—major conservation organizations have shifted away from natural history and even from protecting biodiversity as a primary goal. Instead, they have moved into the vaguely defined territory of ecosystem services, where nature is valued for its functional and economic services to human society, not for its beauty, fascinating peculiarities, or inherent dignity. This trend worries me, because a society that values nature only for its blunt utilitarian worth is not likely to care much about the extinction of species or the loss and degradation of natural communities that offer no tangible services. As extinction rates increase, so does the urgency of restoring natural history to its rightful place in science and conservation—at least on a par with concern for ecosystem services. Biodiversity and ecosystem services are complementary and should not be placed in competition with each other on the conservation agenda.

Beyond its importance for conservation, natural history provides a way for people to feel at home. Nothing alarms me more than someone who has no clue about what watershed she lives in and cannot name even five or ten species of plants and animals in her neighborhood. Such lack of awareness signals a pathological disconnection from nature. We need to know our nonhuman neighbors and come to see them as friends. Learning about the geologic history, flora, and fauna of the place we live in helps us feel that we belong here, regardless of our socioeconomic status, race, ethnicity, or whether or not we were born and raised in this place. Natural history is democratic—anyone can practice it—and it opens up limitless opportunities for joyful experiences. These experiences then circle back to conservation. We become more eager to save plants, animals, and places when they are familiar rather than strangers.

This book is a journey driven by curiosity, which is what being a naturalist is all about. From my first exposure to southern grasslands, I wondered why these places are so scarce in trees, whereas often adjacent to them are dense forests or swamps. As a beginning graduate student I learned that the pine savannas I viewed on field trips to Florida were the prevailing vegetation type of the Coastal Plain until quite recently. I did not yet know that the mixed hardwood forests I saw through the car windows as a child during family trips to Florida, forests which now dominate much of the undeveloped parts of the region, are for the most part artifacts of fire exclusion or former agriculture. Many trained ecologists do not know this.

Years later, while researching the status of endangered ecosystems across the United States, I discovered that grasslands are, in general, the most imperiled of all terrestrial ecosystems in the country. This is especially true when endangerment is measured as extent of decline since European settlement, but is also often true in terms of present and future threat. Some of these grassland ecosystems dominated entire physiographic regions, such as the Coastal Plain, Great Plains, and Palouse, whereas others, such as in the Appalachians, Midwest, and Northeast, occurred as relatively small patches in a matrix of dissimilar vegetation, usually forest. Learning about the plight of grasslands, I pledged to do what I could to protect them and help them recover their former glory. Such is the moral responsibility of a naturalist.

GRASSLANDS IN THE SOUTH?

I regularly meet professional ecologists, including some southerners, who give me a puzzled look when I mention that I am writing a book on southern grasslands. The lack of awareness of native grasslands in the South represents a case of collective amnesia. A few human generations ago, grasslands were abundant across much of the South; today they are rare. Driving through the region today, one mostly sees agricultural fields, pine plantations, dense and mostly young hardwood forests and swamps, and, increasingly, urban sprawl. One has to know where to go to find remnant southern grasslands. If you find one, you might be surprised—a few still cover tens of thousands of acres.

I am fortunate to live in Florida where, amazingly, given the obscenely large human population (approximately 20 million in 2012) and ravenous development pressure, more native grassland remains than in any other southeastern state. This fact was documented in a 1993 book chapter by Hal DeSelm and Nora Murdock on grass-dominated ecosystems in the South. Yet, we have lost much of our grassland in Florida, as elsewhere. Using General Land Office Survey records, Karen Stephenson calculated nearly 2 million acres of prairies and 40,000 acres of savanna (not including pine savannas and woodlands) in the Florida Peninsula during the nineteenth century. The largest area of grassland was in south-central Florida—the marvelous Florida dry prairie (plate 7). Exquisite historical accounts of the dry prairie were collected by botanist Edwin Bridges and published in 2006. Historic Florida grasslands have been largely converted to agriculture and other human land uses; still, around 10 percent of their pre-European distribution remains, plus considerable acreage in longleaf and other pine savannas and woodlands.

In spite of studies documenting extensive historic grasslands in the South, many authors flatly deny the existence of prairies and other grasslands east of the Great Plains. For example, Rick Cech and Guy Tudor, in their otherwise excellent book, Butterflies of the East Coast, claim that there are no true prairies in the East today and that even the Florida dry prairie is technically neither a prairie nor a grassland. Other authors acknowledge the existence of grasslands in the South, but claim they were all created by Native American use of fire or sprang up on abandoned agricultural land. Such opinions are misinformed. The authenticity and antiquity of southern grasslands are vividly demonstrated by the enormous number of species (species richness) and narrowly distributed species (endemism) of grassland plants and several animal groups in these communities. A simple juxtaposition makes the case: table 1.1 shows species numbers within five classic prairie plant genera of the Prairie region (the Great Plains and Midwest) compared with the South. The South beats the Prairie region hands down.

Table 1.1. Which is the hotspot of grassland biodiversity? For five classic plant genera characteristic of the Prairie Region, species richness is greater in the South.

Source: Alan Weakley, University of North Carolina Herbarium (personal communication).

The poor awareness of southern grasslands is partly a problem of perception and terminology. Although many grasslands are easily recognizable to ecologists and laypeople alike, there is little consensus about what to include in the category of grassland. I favor a broad and straightforward definition, for example from Cecil Frost: A grassland is any community in which the grass layer, with its associated forbs is the dominant layer in terms of either total cover or biomass or both. This definition encompasses some communities that are not conventionally considered grasslands. For instance, many ecologists know that the Coastal Plain was once dominated by longleaf pine (Pinus palustris) communities, but in common parlance these are forests, not grasslands. In the National Vegetation Classification, these communities are considered woodlands or sparse woodlands (fig. 1.3). Ecologists, foresters, and others who conduct research or management in longleaf pine ecosystems increasingly recognize their true character: grasslands with varying densities of trees (fig. 1.4). A 2009 paper by plant ecologist Susan Carr and colleagues uses the term pyrogenic grasslands in reference to pine savannas and dry prairies in Florida, which depend on frequent fires promoted by their flammable native plants.

Figure 1.3. General categories of the Standardized National Vegetation Classification System. Longleaf pine ecosystems fall into the Woodland and Sparse Woodland categories, whereas other grasslands covered in this book fall into the Herbaceous category, with some glades and outcrops falling into the Sparsely Vegetated/Non-Vascular category. Adapted from The Nature Conservancy (1994).

Figure 1.4. Is this a grassland? This virgin longleaf pine-wiregrass community on the Wade Tract near Thomasville, Georgia, might be called a forest or a woodland. The vast majority of the species here, however, reside in the grass-dominated groundcover, and this is where most of the key ecological processes operate.

Under natural, frequently burned conditions, canopy cover in most longleaf pine communities rarely exceeds 60 percent, which permits a grassy ground-cover to flourish (plate 27). Consistent with my inclusive definition, Coupland defines vegetation types with scattered trees and shrubs as grasslands, the decisive criterion being the dominance of grasses in the groundcover: "In some instances shrubs or trees emerge above the canopy as scattered individuals to form savannas…. An ecosystem may be designated as grassland when the canopy of grasses is continuous or nearly