protect crops, livestock, residents, and homesites; clean the air; protect water quality ... conservation practices, trees can contribute to a more sustainable farm ... Texas. In the northern portions of the region, temperatures in January can ..... to resource management agencies and their staffs, schools, FFA and 4-H programs,.
15. Conservation Forestry for Sustainable Great Plains Ecosystems Gerald F. Bratton U.S. Department ofAgriculture Peter R. Schaefer South Dakota State University James R. Brandle University ofNebraska--Lincoln
Two hundred years ago, the American Great Plains was a region dominated by grassland yet enriched by patches of woody vegetation, a region of harsh climatic extremes characterized by spring flooding and summer drought, and a region devastated by wildfIre yet renewed by regrowth. Forests moved onto the Plains during periods of abundant moisture only to be pushed back by drought and wildfIre. With the advent of agricultural development, the nature of vegetation has changed. WildfIre, floods, and roaming buffalo herds found little tolerance among a society whose existence was, and continues to be, dependent upon the successful husbandry of crops and livestock. With development came dams, suppression of wildfIre, extensive areas of cropland, and replacement of roaming buffalo herds with intensive grazing systems dominated by cattle. A system with great diversity became one of monocultures. Today the Great Plains ecosystem is very different than it was 200 years ago. The Plains are intensively managed and designed to provide an abundance of food and fIber. It is in this managed ecosystem that conservation forestry has a vital role to play. Woodlands and trees are some of the most valuable, least recognized, and vastly underestimated resources available in the region. Occupying less than 5 percent of the land area, woodlands provide a variety of wood products and enhance economic and environmental sustainability. Trees protect soil from erosion; control blowing snow; protect crops, livestock, residents, and homesites; clean the air; protect water quality and quantity; add economic and biological diversity; provide critical habitat for migratory and local wildlife; and improve aesthetic values. Trees diversify farm income by providing fuel wood; specialty crops such as Christmas trees, nuts, and fruits; and traditional products like posts, lumber, and veneer. Although trees are not presently
Stanley R. Johnson and Aziz Bouzaher (ed.), Conservation of Great Plains Ecosystems. 211-227. © 1995 Kluwer Academic Publishers.
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considered a major component of traditional agriculture, when combined with various conservation practices, trees can contribute to a more sustainable farm operation. For example, field windbreaks reduce residue requirements under minimum tillage systems. Consequently, low residue crops such as soybeans may be added to the rotation without significantly increasing the danger of wind erosion. By using several conservation practices, the producer gains the flexibility to choose the best management practices for a variety of crops.
Environmental Variability: Climate The Great Plains is a region of climatic extremes and vegetation contrasts. Average temperatures range from below 4°C in the Canadian Prairies to above 21°C in southern Texas. In the northern portions of the region, temperatures in January can easily reach -40°c. By contrast, in southwestern Texas, temperatures often exceed 40°C in July or August. Overall, there is a gradual gradient from warm to cool from the eastern border of the region to the base of the Rocky Mountains (NOAA 1983; USDA 1935). However, of greater significance to the woody plants are the rapid changes in temperature that can sometimes fluctuate over 27°C within a 12-hour period. Precipitation shows a similar pattern. The driest areas are in southwestern Texas where precipitation averages 250 millimeters per year. In contrast, rainfall in southeastern Texas may exceed 1,000 millimeters annually. Across the midsection of the region from central Iowa to eastern Colorado, annual precipitation decreases from 830 millimeters to 300 millimeters. Along the Canadian border, northern Minnesota receives approximately 520 millimeters while northwestern North Dakota receives less than 400 millimeters (NOAA 1983; USDA 1935). In the southwest, the combination of high temperature and low precipitation results in high levels of evaporation, which severely limits tree growth. More important than precipitation averages are precipitation extremes. Most of the Great Plains is subjected to periodic droughts of varying lengths. For example, tree ring data from archaeological sites in Ash Hollow, Nebraska, indicate that over the last 700 years there have been a total of 21 drought periods of five years or more, the longest of which lasted 38 years (Weakly 1943). Obviously, these types of droughts have a major impact on the distribution and survival of woody vegetation. Present concerns about global climate change are relevant to discussion of woodland resources. Most general circulation models project that the North American Great Plains will become warmer and drier as atmospheric carbon dioxide increases (IPCC 1990). By the year 2030, temperatures in the central part of the region are projected to be 2° to 4°C higher, with winter precipitation increasing 0 to 15 percent and summer
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precipitation decreasing 10 to 15 percent. Soil moisture in summer is projected to be 15 to 20 percent lower than current averages. If correct, these changes would have dire consequences for plant growth in a semiarid environment.
History of Tree Planting The Great Plains has a history of tree planting, beginning with the earliest settlers. Both state and federal laws encouraged tree planting. The Timber Culture Act of 1873 encouraged settlement of the region and led to more than 10 million acres of tree claims but resulted in only limited tree planting success. Repealed in 1891, the Timber Culture Act was replaced by the Kincaid Act in 1904, the Clark-McNary program in 1924, and subsequently the Prairie States Forestry Project in the 1930s. During this latter effort, nearly 212 million trees were planted in more than 18,000 miles of multirow windbreaks (Droze 1977). A 1954 survey of these windbreaks by Read (1958) indicated that only 42 percent were in good condition and 27 percent were in poor condition or had been removed. A 1975 report by the General Accounting Office (1975) indicated that in Kansas, Nebraska, and Oklahoma, removal rates exceeded 10 percent per year, primarily because of installation of center-pivot irrigation systems. A 1980 survey by the U.S. Department of Agriculture, Soil Conservation Service, was more optimistic, indicating that windbreak plantings in Kansas, Nebraska, North Dakota, Oklahoma, and South Dakota exceeded removals by 1.8 percent (USDA 1980). Unfortunately, the optimism was short lived. From 1982 to 1987, the Great Plains region lost 24,149 windbreaks (approximately 3.2 percent). The most recent efforts to encourage tree planting were under the Conservation Reserve Program. But in the Great Plains, less than 5 percent of the eligible acres were planted to trees; the rest were planted to grass (Deneke and Bratton 1989). This is particularly unfortunate since a survey by the Forestry Committee of the Great Plains Agricultural Council indicated that grass was chosen because it could easily be removed upon expiration of the lO-year contracts (Bratton 1987).
Description of Woodland Resources The Great Plains region consists of a variety of intermixed vegetation types. This complicated mix of forest and grass vegetation existed in relative equilibrium until the introduction of contemporary agricultural systems and is best understood when divided into three subunits: a western transition zone, the interior grasslands, and an eastern transition zone (Figure 15.1).
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A Western transition zone B Interior grasslands C Eastern transition zone
Figure 15.1. Major woodland zones in the Great Plains
Eastern and Western Transition Zones Along the east and west boundaries, different woodland, grassland, and cropland systems intermingle in intricate landscape. Woodlands within these zones are composed of riparian forests, woody draws, and savannas, as well as orchards and plantations. The eastern edge of the Great Plains lies along the western extent of three eastern forest types: the northern hardwood forest, the central hardwood forest, and the southern pine region. These woodlands flourish on sites that are too steep, frequently flooded, or otherwise unacceptable for agriculture, but which may be extremely profitable for timber production. As a result, many acres of high-quality timber stands extend like fingers into the Great Plains grasslands. The western edge of the Great Plains abuts the ponderosa pine and pinyon-juniper woodlands of the Rocky Mountains. These western transition woodlands lie in the rain shadow of the Rocky Mountains, are relatively dry, and are generally less productive in traditional forest products. These woodlands are of immense beauty and provide valuable homesites, watershed protection, wildlife habitat, livestock grazing, and recreational use.
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Interior Grasslands
The grassland ecosystems of the interior Great Plains were historically maintained by drought and ftre. Once nearly free of trees except for narrow belts of riparian woodland or isolated woody islands, the grasslands existed because of protection afforded by wet sites or topography (Wells 1965; see also Figure 15.2). They are now fragmented and altered by farming and intensive grazing. Now that wildftre is controlled, trees are commonplace. Some are present as a result of tree planting efforts of prairie residents. Others are native or have naturalized and exist as riparian woodlands or woody draws. Many are spreading into adjacent grassland areas.
Native Woodland Resources
While there are more than 20 million acres of native woodland in the Great Plains, they represent less than 1 percent of the total land area of the region. Comprehensive inventories of all the states in the region are incomplete. Several states have no detailed inventory, while others have inventories of only major forested areas. State foresters report that while there is a desperate need for in-depth woodland inventories to assist with proper resource planning and management, funds for complete inventories are meager. For sake of simplicity, both transition zones and interior woodland resource data are combined and categorized into two major groups: native woodland resources (Table 15.1) and planted woodland resources (Table 15.2). The native woodland resources will be further delineated into commercial and noncommercial forestland where individual state inventories allow. The wooded riparian areas are of special importance for several reasons: • Improving water quality by buffering runoff from adjacent lands • Stabilizing stream banks • Shading streams to maintain cooler temperatures for quality fisheries • Storing water and helping to reduce flood severity • Providing wildlife habitat and recreation areas • Supporting productive forests for the economic development of forest products • Increasing biodiversity and stability in agricultural ecosystems The health and vigor of many native woodland resources are declining. Natural resource practitioners report that expanded farming practices, uncontrolled grazing, and indiscriminate logging have seriously depleted and degraded much of the resource, which result in accelerated stream bank erosion, increased cropland erosion, less wildlife habitat, lower quality forest products, increased water pollution, and a generally less attractive environment.
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Source: Adapted from Wells 1965.
Figure 15.2. Nonriparian woodlands in the Great Plains A
Montana, eastern Wyoming, and western Dakotas. Woodland: Pinus ponderosa, Juniperus scopulorum.
B
Pembina escarpment and Turtle Hills, North Dakota; and Erskine and Big Stone Moraines, Minnesota. Woodland: Populus tremuloides, Quercus macrocarpa.
C
Pine Ridge escarpment, South Dakota, Nebraska, and Wyoming. Vegetation similar to A.
D
Niobrara escarpments, Nebraska. Woodland: P. ponderosa, J. scopulorum, 1. virginiana, Q. marocarpa.
E
Sand Hills area, Nebraska. Woodland: isolated stands of P. ponderosa, 1. virginiana, Celtis occidentalis.
F
Western Kansas. Woodland: isolated stands of J. virginiana.
G
Wildcat Hills, Nebraska. Vegetation similar to A.
H
Cedar Point, Colorado. Woodland: P. ponderosa, 1. scopulorum.
J
Black Mesa-Mesa de Maya area, Oklahoma, New Mexico, and Colorado. Woodland: Pinus edulis, P. ponderosa, Juniperus monosperma, J. scopulorum, Quercus undulata.
K
Canadian escarpment, New Mexico. Vegetation similar to J.
L
Llano Estacodo, New Mexico and Texas. Woodland: on northwest, P. edulis, J. monosperma, Q. undulata; on east (break of the Plains), Juniperus pinchotii, Quercus mohriana.
M
Callahan Divide, Texas. Woodland: Quercus virginiana, Q. shumardii, Q. mohriana, Juniperus ashei, 1. pinchotii.
N
Edwards Plateau, Texas. Woodland: Similar to M.
o
Oklahoma and eastern Kansas. Woodland: Quercus stellata, Q. marilandica, Q. muehlenhergii, Q. shumardii,1. virginiana.
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Table 15.1. Native woodland resources in the Great Plains State
Commercial
Noncommercial
Total
Nonforest
percent
1,000 acres Colorado Iowa Kansas Minnesotaa Missouria Montanaa Nebraska New Mexico a North Dakota Oklahomaa South Dakota Texas a Wyominga Total
2,050 1,207 660 2,532
522 150 196 742
537
108
343 9,400
148 900
Forest
13,667 33,766 50,979 18,509 17,008 98,003 48,333 50,445 43,821 40,715 47,149 19,228 16,074
13 2,572 1,358 856 3,275 718 5 491 10,300 714 51
