Chapter II - The Savanna

World Wide

The term savanna comes from an Amerindian word which was used in a 1535 publication by Oviedo y Valdes to describe "land which is without trees but with much grass either tall or short." In the late nineteenth century the definition was widened to include grassland with trees. Savanna as a descriptive term used by scientists refers to vegetation, climate, and land use. It describes vegetation as characterized by a continuous graminoid stratum, more or less interrupted by trees or shrubs. The grassy ground plane could be up to approximately 6 feet high forming a 25-100% cover while the interrupting trees and shrubs would be approximately 6-40 feet high forming a 10-25% cover. While this definition is applied to tropical savannas, definitions offered later in this thesis referring to the oak savannas of the Midwestern United States allow for a denser tree canopy. The tree spacing in a savanna should be at least greater than the diameter of the individual canopies (Cole 4-12).

The distribution and origins of savannas can be hard to define. Differing views can result from looking at influencing factors such as climate, soils, fires, animals, humans, and various combinations of these (Cole v,16). The worldwide distribution of the savanna originates in the tertiary period, tens of millions of years ago, when rising mountain ranges interrupted the worldwide precipitation patterns, causing the vast continental forests to recede, leaving in their wake the savannas, deserts and grasslands that persist today (Wagner 12). In various forms savannas cover 8,391,600 square miles and make up about half the grasslands of the world. Occurring on all continents but Antarctica, savannas tend to develop in subtropical regions, primarily in continental interiors, and/or on open plains. Soil water content and fluctuation, wind and evaporation, wide temperature fluctuation, and seasonality of precipitation all play a role in their formation (Risser et al. 3). Savanna landscapes can also be caused by human intervention rather than natural factors. For instance, landscapes classified as savannas in Asia are thought to be derived from centuries of cutting, burning, grazing, and cultivating the former deciduous forest (Cole 6). If that is the case it may perhaps be appropriate to classify much of the modern cultural landscape as savanna.

Cole describes the plant species of savannas as having morphological features and physiological responses that are mainly influenced by drought and, to a lesser extent, fires. While these conditions are discussed in relation to tropical savannas, it may be reasonable to relate them to temperate savanna species as well. For instance, in some tropical savanna trees, contorted trunk and stem growth, caused by the death of apical meristems and the thick corky bark, are a response to seasonal drought and, to a lesser extent, fire. Such growth patterns can be seen in the contorted limbs of blackjack oaks and post oaks, both members of the former southeastern North American savannas. Other characteristics such as the ability to resprout from rootstocks can be seen in both African and North American species. The majority of native warm season grasses, which are the most abundant species of any savanna, generally grow in a tussock form and usually have seasonal aerial shoots and protected apical buds (Cole 6-9). They can be highly fire adapted as in the genera of the Andropogonea family of grasses, particularly Andropogon (Komarek, Fire Ecology 212).

Many people can identify the visual aspects of the tropical savanna due to the imagery of popular sources such as the 1970s television show "Wild Kingdom," or any book about African animals. The strongest visual characteristics that emerge from such imagery might be the expansive horizons, the grass covered plains, and the widely spaced trees, sometimes with a very distinct and high browse line.
 

The Eastern North American Savanna

The popular imagery of African savannas is not, however, entirely transferable to eastern North America. In some geography texts, the savanna is not even included as a biome type in North America. For instance, Muller's Biogeography mentions only steppe and forest as North American biomes (214). However "savanna" is used by others to describe vegetation community types where prairie or steppe grades into forest. Because there is no clear definition within this transitional zone, many variations in definition can occur. The range in percentage of canopy cover in the Midwest oak savanna is viewed differently by different observers. While John T. Curtis defines canopy cover as at least one tree per acre but less than 50% canopy cover (330), some observers include stands with up to 80% cover (Nuzzo 9). Generally these savanna canopies are oak dominated, with or without a shrub layer; with an herbaceous, predominantly grassy ground layer of both prairie and forest species; and having the appearance of an open or scrub savanna. It is also considered a fire dependent community, or in the absence of fire, drought dependent (Nuzzo 9-10).

Within North America there are many savanna or savanna-like grassland landscapes. It may be appropriate here to refer to savannas not only as woodland but also as grassland, since grasslands can be defined as biological communities with few trees or shrubs, dominated by grasses with mixed herbaceous vegetation (Risser et al. 2). The term prairie is reserved for grasslands which are maintained by "natural" forces (Joern and Keeler 15). It is used not only to describe grasslands of the central United States, but also their counterparts of similar physiognomic and floristic composition in the East. It is sometimes replaced by the term barren, especially in Tennessee and Kentucky (Deselm and Murdock 89).

Savannas or savanna-like landscapes can be found across the United States, usually as ecotones or edge environments between grassland and forest. Some of these are the oak savannas of the Midwest, the chaparrals of California, and the park lands of the Rocky Mountains. Southeastern grassland communities, shown in Figure 2.1, which should be recognized in a discussion of the modern Piedmont savanna include the Black Belt and Jackson prairies of Alabama and Mississippi; the various savannas and flatwoods of the Atlantic Coastal Plain; the coastal prairies of the Gulf Coastal Plain; the various glades and barrens occurring in most southeastern states associated with limestones, hardpans, shales, and other non-Coastal Plain soil conditions; and the balds found scattered up and down the eastern uplands (90-92). If not cultivated, planted for timber, or developed, some remnants of these grassland communities have persisted where adequate precipitation normally causes forest succession.

Figure 2.1 Map of southeastern grasslands also showing Piedmont physiographic region. Dots represent small grassland areas; 1, Kentucky Barrens; 2, Grand Prairie; 3, Coastal Prairie; 4, Jackson Prairie; 5, Black Belt Prairie; 6, St. John's and Kissimmee River Prairies; 7, Dry Prairies west of Lake Okeechobee (Deselm and Murdock 88).

It should be mentioned that Radford includes the tall grass prairie among the categories of flora provinces within the Piedmont. It is included in reference to granite outcrops, gabbro depressions, secondary fields, and serpentine barrens (13, 28). Remnant evidence and historical description of the "Piedmont Prairie" of North Carolina and South Carolina and other presettlement Piedmont landscapes suggest that these landscapes would also have related to the prairie floral province.

The distribution of the more eastern and central United States savanna and prairie landscapes can be traced to the climatic changes of the last ice age. Around 6000 years ago the climate was more arid with more frequent fire and drought, allowing more western prairie landscapes to invade further east. This was followed up to now by a wetter period that allowed only patchy remnants of tallgrass prairie, some mentioned earlier, to persist among the eastern forests (Horan 18). Even in New England, savanna landscapes persisted into the era of European exploration. In 1542, Verrazano visited Narragansett Bay (in what is now Rhode Island) and found extensive open areas and forests that could be traversed easily "even by a large army"(Cronon 25).

Though it has not been studied, the extent of the range of the post oak and blackjack oak in the eastern deciduous forest, might reflect the former range of savanna landscapes in the eastern deciduous forest, because of their fire tolerance, shade intolerance, and slow growth. Both have a similar range from in or near southern New England, across the South to the prairie border (Duncan and Duncan 277, 282; Little 397,409; Miller 100-102,164).

Mechanisms that kept the presettlement tall grass prairie and savannas of the Midwest and East from becoming dense forests included factors mentioned earlier in this chapter such as seasonal drought, frequent fires, grazing, and occasionally special soil conditions. Across the climatic moisture gradient from east to west, depending on local conditions, vegetation structure would vary from low, stunted and dispersed to taller and more evenly distributed. These and other ecological characteristics will be explored more thoroughly in Chapter V.

Perhaps the aesthetic qualities of the vanished eastern North America savanna landscapes is best understood through the eyes of those who saw it as an intact landscape. The aesthetic qualities of a Wisconsin savanna were described by J. W. Hoyt in 1860.

Grouped here and there, like so many old orchards, on the summit of a gentle swell of land or on the border of marsh, prairie, or lake, there is nothing in the whole catalogue of American sylva that equals these Burr Oaks for their charming, homestead-like expressions they give to the landscape (Gobster 65).

William Bartram in the late 1700s was always eloquent in his descriptions of the presettlement southeastern landscape. Here he describes an area west of the Oconee river in the Georgia Piedmont and an area west of the Chattahoochee river in the Alabama Piedmont.

...a pleasant territory, presenting varying scenes of gentle swelling hills and levels, affording sublime forests, contrasted by expansive illumined green fields, native meadows and Cane breaks...(307) ...the ascents produce grand high forests, and the plains present to view a delightful varied landscape, consisting of extensive grassy fields, detached groves of high forest trees, and clumps of lower trees, evergreen shrubs and herbage; green knolls with serpentine, wavy glittering brooks coursing through green plains; and dark promontories, or obtuse projections of the side long acclivities, alternately advancing or receding on the verge of the illumined native fields, to the utmost extent of sight. (316)

Perhaps the most compelling description of a savanna landscape was written in the 1840s by James Fenimore Cooper, describing the setting for the opening of the novel Oak Openings, in the then "unpeopled forests of Michigan" in 1812:

The region was, in one sense, wild, though it offered a picture that was not without some of the strongest and most pleasing features of civilization. The country was what is termed "rolling", from some fancied resemblance to the surface of the ocean, when it is just undulating with a long "ground swell." Although wooded, it was not as the American forest is wont to grow, with tall straight trees towering towards the light, but with intervals between the low oaks that were scattered profusely over the view, and with much of that air of negligence that one is apt to see in grounds, where art is made to assume the character of nature. The trees, with very few exceptions, were what is called the "burr oak," a small variety of a very extensive genus; and the spaces between them, always irregular, and often of singular beauty, have obtained the name of "openings;" the two terms combined giving their appellation to this particular species of native forest, under the name of "Oak Openings."

These woods, so peculiar to certain districts of the country, are not altogether without some variety, though possessing a general character of sameness. The trees were of very uniform size, being little taller than pear trees, which they resemble a good deal in form; and having trunks that rarely attain two feet in diameter. the variety is produced by their distribution. In places they stand with a regularity resembling that of an orchard; then, again, they are more scattered and less formal, while wide breadths of the land are occasionally seen in which they stand in copses, with vacant spaces, that bear no small affinity to artificial lawns, being covered with verdure. The grasses are supposed to be owing to the fires lighted periodically by the Indians in order to clear their hunting-grounds.

Toward one of these grassy glades, which was spread on an almost imperceptible acclivity, and which might have contained some fifty or sixty acres of land, the reader is now requested to turn his eyes. (10-11)

The general disappearance of the eastern North American savannas is a result of human activity. For eons they were maintained by meteorological and geological conditions, and more recently by human influence. When human influence changed from the use of burning to the practice of fire suppression, open landscapes quickly reverted to thickets, then forests. For instance on Cape Cod, Massachusetts in the early 1600s William Wood described a place the pilgrims had arrived to find as grassland, which was now covered with "much underwood" since the Indians (and their burning) had vanished due to the plague 14 years earlier. Because it had not been burned, parts of Cape Cod had become "unuseful and troublesome to travel through, insomuch that it is called ragged plain because it tears and rents the clothes of them that pass"(Cronon 90). Much later, as European settlers reached the Midwest, oak savannas disappeared within 20 to 40 years of settlement as a result of fire cessation (Nuzzo 11). Nuzzo points out that the extensive fire breaks caused by plowing and grazing of grasslands and construction of roads and rails ended widespread burning, causing the demise of fire dependent communities in the Midwest. Some savanna remnants, however, have persisted where special conditions prevail. For example, of the approximately .02 percent of the original Midwest oak savannas remaining, the vast majority have very droughty conditions. Grazing has also helped preserve some savannas, along with some controlled burning and accidental fires caused by coal powered trains (Nuzzo 11). Some southeastern remnants, surviving due to such conditions, will be presented later in studying the ecological and aesthetic makeup of the Piedmont savanna.

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