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United States Southwest

Marlin Johnson

Description and Administration
 

Southwestern United States forests and woodlands have developed largely along lines of local climates defined by elevational zones.  At the lower elevations and precipitation levels, there are several woodlands.  The principal ones are pinyon-juniper (Pinus edulis-Juniperus spp.), riparian, and Madrean oak (Quercus spp.) woodlands (Burns 1983).
 

As elevation increases[F1]  to about 1800 to 2400 meters, ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) becomes predominant and often occurs as a single species over large areas, especially on the Colorado Plateau of Arizona, New Mexico, Colorado and Utah.  The orange, platy bark and stately form of the ponderosa pine is often photographed, written about and admired for its beauty.  Forests dominated by ponderosa pine comprise about two-thirds of the forest lands in Arizona and New Mexico.
 

Moving up in elevation from the ponderosa pine zone, we find a mixed conifer zone up to about 3,000 meters that, at its lower elevations is comprised largely of ponderosa pine and Douglas-fir (Pseudotsuga menziesii var. glauca).  As elevation increases, these two species decrease in number and white fir ((Abies concolor), Englemann spruce (Picea engelmannii), quaking aspen (Populus tremuloides), and corkbark fir (Abies lasiocrpa var. arizonica) take over.  Quaking aspen often occurs in pure stands, adding an element of diversity and beauty with its white trunks and golden fall color.  Aspen is usually a seral forest type that is replaced by conifers as it ages. At the highest elevations, we find forests of Englemann spruce and corkbark fir.  
 

Woolsey (1911) and also Lang and Stewart (1910) gave us the first quantified forest inventories for the region.  Neither  inventory was Southwest-wide, and thus, do not give us a picture of conditions on a same-area, statistically sound basis.  Nevertheless, these inventories covered several areas and included a large number of plots, so providing the best quantified picture available today of early 20th-century conditions.  In ponderosa pine these inventories show about 50 trees per hectare, in contrast to inventories in the 1990’s which show about 350 trees per hectare greater than 12 centametres in diameter at breast height.  These inventories, early photographs, and early descriptions, and studies based on stumps and other evidences all tell the same basic story of open forests in the Southwest before 1910 (Covington, and Moore, 1994a).
 

Approximately one-fourth of the land, or 14.5 million hectares in the Southwest is forested.  Of the forest land, about 3.7 million hectares, or one-third, is timberland; the rest is woodland.  Nearly one-half of all forest land is in national forests, with less than 10 percent in other public ownerships and about 40 percent in private ownerships.  Approximately one-half of the private forest land, or 3.2 million hectares, is on Indian trust lands managed by Native American tribes.
 

History and Function
 

Before European settlement, fires burned frequently (2 to 10 years) at low intensities at lower elevations and less frequently but with moderate intensities at higher elevations (Swetnam and Baisan, 1996).  Lightning, which is common in the Southwest, was the main source of ignitions prior to the main period of European-American settlement.  Native Americans contributed to fire frequencies because of escaped domestic fires and intentional burning, although burning by Native Americans has not been documented in the Southwest to the degree that it has in the Northern Rockies (Swetnam and Baisan, 1996).
 

Changes since 1880
 

A reduction in ecosystem fire had occurred by the 1880's, coinciding with the arrival of  many [F2] European settlers and substantial increases in livestock grazing levels.  By 1890, cattle numberd about 1.5 million head in Arizona and New Mexico (Baker et al, 1988).  [F3] Grazing by domestic livestock removed grasses that had previously carried cool ground fires.  This coincided with a few good moisture years in the first few decades of the 20th century, which led to dense regeneration and forests with far more trees than before. 
 

Other factors contributed to reduced fine fuels and, therefore, the reduction of fire frequency as the 19th century ended and the 20th began (Pyne, 1996).  Loggers began removing mature trees.  Bark beetles, fungi, and dwarf mistletoe infested the thickets that, in the absence of grass and fire, sprang up profusely. Droughts further reduced grasses.  Roads built by settlers, fixed landownership patterns, reservation of public lands, and establishment of professional firefighting also contributed  to a dramatic reduction in low-intensity fires.  Through [F6]time, this encouraged increased forest density and fuel arrays that today promote intense fires.
 

Most of these changes occurred at lower elevations in the pinyon-juniper, ponderosa pine and lower mixed-conifer forests.  Fewer fire cycles have been missed in the higher elevation mixed-conifer and spruce-fir belts, but nevertheless change is occurring there too.
 

Current issues facing land managers and land owners
 

There is growing concern among natural resource professionals that disruption of natural fire regimes, increase in tree numbers, and increases in landscape homogeneity are a far greater threat to biological diversity and ecosystem sustainability than is generally realized (Caraher et al, 1992; Kaufmann et al. 1992; Everett et al.1993; Mutch et al. 1993; Covington et al, 1994; Covington and Moore 1994b; Pyne, 1996). Pyne states: “These fuel loads are an environmental debt, like toxic dumps.  They will take decades of determined action to clean up, and then only if society has the resolve and the money.”
Unless concerted actions are taken to reverse ongoing ecosystem degradation, sustainability of native woodlands and forest ecosystems is uncertain.
 

As Southwest forests grow more dense, the nature of forest fires has changed.  Fires now burn less frequently, but are high-intensity, stand-replacing fires (Hessburg et al, 1993, Covington and Moore 1994a).  Firefighters have noted conditions in recent years that cause grave concern about their safety and their ability to control fires.  While crown fires in ponderosa pine forests were almost unheard of earlier last century (Cooper, 1960), today they are commonplace.  Crown fires increased from 4,000 hectares per year in the 1940's (Pyne, 1996) to sometimes over100,000 hectares since 2000 (Forest Service Data), despite a massive commitment to high-technology firefighting. Society spends considerable resources (sometimes in vain) to stop these fires before they destroy not only natural resources but human developments as well.
 

Management and Policy
 

A variety of activities will need to be applied by landowners and on-the-ground managers in concert to restore Southwestern forests.  Included are prescribed fire, thinning, and harvests to mimic natural disturbances.  Wildfire inevitably will still occur, and while some of it may be positive for the forests, much of it will be destructive.  Therefore, post-fire rehabilitation and reforestation will also be needed.  
 

Tribal and private lands in many cases have been managed more actively than national forest lands.  Thus, current overcrowding in forest stands is generally more prominent on the national forests than on other ownerships.  The Forest Service is moving toward additional treatments but only has been somewhat successful, removing around 5 percent of net new growth in recent years.  Establishment of regional or national policies requiring  use of any one or a certain combination of treatments should be avoided in order to get decisions based on the conditions in a landscape, and on individual sites within that landscape.  Southwest forests can be managed sustainabily for long-term land health and for key resources such as wildlife, water, recreation, and carbon sequestration but will initially require significant investments in removal of excess trees, especially the high numbers of smaller trees established since about 1900. (Johnson et al, 1996).
 

 Literature Cited
 
Baker R.D., Maxwell, R.S., Treat, V.H., Dethloff, H.C. 1988. Timeless heritage: a history of the Forest Service in the Southwest. US Forest Service, FS-409. 208 p.
 
Burns, R. M. (Tech. Compiler).1983. Silvicultural Systems for the Major Forest Types of the United States. Agriculture Hdbk No. 445. Washington, DC: United States Department of Agriculture, Forest Service. 191 p.
 
Caraher, D.L., J. Henshaw, F. Hall, F. Hall, WH Knapp, BP McCammon, J. Nesbitt, RJ Pederson, I. Ragenovitch, and C. Tiez. 1992. Restoring ecosystems in the Blue Mountains- a report to the Regional Forester and the Forest Supervisors of the Blue Mountain Forests.  USDA Forest Service, Pacific Northwest Region.  Portland, OR. 15 p.
 
Cooper. C. F.1960. Changes in vegetation, structure and growth of southwestern pine forests since white settlement. Ecological Monographs. 30:129-164.
 
Covington, W. W., R.L. Everett, R. Steele, L.L. Irwin, T.A. Daer, Auclair, and N.D. Allan, 1994. Historical and Anticipated Changes in Forest Ecosystems of the Inland West of the United States. In: pp. 13-63. Sampson R.N. and D. Adams (Eds.). Assessing Forest Ecosystem Health in the Inland West. The Hayworth Press, Inc., New York,1994.
 
Covington, W.W. and M.M. Moore. 1994a. Postsettlement changes in natural fire regimes and forest structure: ecological restoration of old-growth ponderosa pine forests. In: pp. 153-181. Sampson, R.N. and D. Adams (Eds.) Assessing forest Ecosystem Health in the Inland West. The Haworth Press, Inc. New York, 1994.
 
Covington, W. W. and M. M. Moore. 1994b. Southwest ponderosa pine forest structure and resource condition changes since Euro-American settlement. Journal of Forestry. 92:39-47.
 
Everett, R.L., P.F. Hessburg, M.E. Jensen and B.T. Bormann.  1993. Eastside forest ecosystem health assessment, Volume I, Executive Summary. USDA Forest Service, Pacific Northwest Research Station. 57 p.
 
Hessburg, P.F., R.G. Mitchell and G.M. Flip. 1993. Historical and current roles of insects and pathogens in eastern Oregon and Washington forest landscapes. In: pp. 485-536. Hessburg, P.F. (Comp.) Eastside forest ecosystem health assessment-Volume III: Assessment. USDA Forest Service, Pacific Northeast Research Station.
 
Johnson, M.A., J. Barbour, J.Bliss, S.L. Chiang, D. Green, D. Toweill, S. Willits, and M. Znerold. 1996.  Ecosystem Management and the Use of Natural Resources. In Toward a scientific and social framework for ecologically based stewardship of federal lands and waters. Proceedings of ecological stewardship workshop, Tucson, Az. Dec. 4-14, 1995.

Kaufmann, M.R., W.H. Moir and W.W. Covington. 1992. Old-growth forests: what do we know about their ecology and management in the Southwest and Rocky Mountain Region? In: Kaufmann, M.R.; Moir, W.H.; Bassett, R.L. (Tech. Coords.). Old-growth forest in the Southwest and Rocky Mountain Regions:proceedings of a workshop. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station. General Technical Report RM-213. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 1-11.
 
Kaufmann, M. R., W. H. Moir, and W. W. Covington.  1992.  Old-growth forests:  what do we know about their ecology and management in the Southwest and Rocky Mountain Regions?  USDA Forest Service, Rocky Mtn. For. and Range Exp. Sta. Gen. Tech. Rep. RM-213.  pp. 1-11. 
 
Lang, D.M., and S.S. Stewart. 1910. Reconnaissance of the Kaibab National Forest. USDA For. Serv. Unpubl. rep.
 
Mutch, R.W., S.F. Arno, J.K. Brown K.; Carlson, Clinton E.; Ottmar, Roger D.; Peterson, Janice L. 1993. Forest health in the Blue Mountains: a management strategy for fire-adapted ecosystems. USDA Forest Service, Pacific Northwest Research Station. General Technical Report PNW-GTR-310. 14 p.
 
Pyne, Stephen J. 1996. Nouvelle Southwest.  In: pp. 9-16. Conference on Adaptive Ecosystem Restoration and Management: Restoration of Cordilleran Conifer Landscapes of North America.  General Technical Report RM-GTR-278.
 
Swetnam, Thomas W. and C.H. Baisan, 1996. Historical Fire Regime Patterns in the Southwestern United States Since AD 1700. In: Proceedings of the Second La Mesa Fire Symposium. USDA Forest Service General Technical Report RM-GTR-286:11-46.
 
Woolsey, T.S. Jr. 1911. Western yellow pine in Arizona and New Mexico. USDA For. Serv. Bull. 101.