Our Livint; Rc.s(yiirrc\ — TcnrslridI EciiSYsrcins 



223 



Table. Increase In the number of vvildfues and area 

 burned on sagebrush sleppe in Idaho (dala from the 

 Bureau of Land Manasenient. Idaho State Office. Boise) 



Western Juniper Woodlands 



Juniper woodlands occupy 17 million ha (42 

 million acies) in the Intermountain region (West 

 1988). Juniper species common to this legion 

 are western juniper Uimipcnis ovcidentalis). 

 Utah juniper U- osteospenmi), single-seeded 

 juniper {J. moiwsperma). and Rocky Mountain 

 juniper (J. scopiiloniiu). Presettlement juniper 

 wiH>dlands were usually savanna-like or con- 

 fined to rocky outcrops not typically susceptible 

 to fire (Nichol 1937). 



Juniper woodlands began increasing in both 

 density and distribution in the late 1800's (R.F. 

 Miller. Eastern Oregon Agricultural Research 

 Center, unpublished data; Fig. 2) because of 

 climate, grazing, and lack of fire (Miller and 

 Waigand 1994). Warm and wet climate condi- 

 tions then were ideal for juniper and grass seed 

 production. Fire frequency had decreased 

 because the grazing of domestic livestock had 

 greatly reduced the grasses and shrubs that pro- 

 vided fuel, and relocation of Native Americans 

 eliminated an important source of ignition. 

 Continued grazing and 50 years of attempted 

 fire exclusion have allowed juniper expansion 

 to go unchecked. 



Ponderosa Pine Forest 



Decreases in fire frequency are also serious- 

 ly affecting ponderosa pine (Piniis ponderosa) 

 forests, a common component on about 16 mil- 

 lion ha (40 million acres) in the western United 

 States. Historically, the ponderosa pine ecosys- 

 tem had frequent, low-intensity, surface fires 

 that peipetuated park-like stands with grassy 

 undergrowth (Banett 1980). For six decades, 

 humans attempted to exclude fire on these sites 

 (OTA 1993). Fifty years ago. Weaver (1943) 

 stated that complete prevention of forest fires in 

 the ponderosa pine region had undesirable eco- 

 logical effects and that already-deplorable con- 

 ditions were becoming increasingly serious. 

 Today, many ponderosa pine forests are over- 

 stocked, plagued by epidemics of insects and 

 diseases, and subject to severe stand-destroying 

 fires (Mutch et al. 1993). 



Lodgepole Pine Forest 



Like ponderosa pine forests, lodgepole pine 

 iPiniis contorta) forests are experiencing a 



change in structure, distribution, and functi(Mi- 

 ing of natural processes because of fire exclu- 

 sion and increases in disease. Wildfire may be 

 the most important factor responsible for estab- 

 lishment of existing stands (Wellner 1970). 

 Historical stand-age distributions in lodgepole 

 pine forests indicated an abuntlance of younger 

 age classes resulting from periodic fires. Fire 

 exclusion, by precluding the initiation of new 

 stands, is responsible for a marked change in dis- 

 tribution of age classes in these forests (Fig. 3). 

 Dwarf mistletoe {Arceiiihohiinn ciiiwri- 

 caniiiu}. the primary disease of lodgepole pine, 

 also has a profound effect on forest structure 

 and function, although it occurs slowly. Data 

 show that chronic increases of dwarf mistletoe 

 are partly due to the exclusion of fire 

 (Zimmerman and Laven 1984) because fire is 

 the natural control of dwarf mistletoe and has 

 played a major role in the distribution and abun- 

 dance of current populatiiins and infection 

 intensities (Alexander and Hawksworth 1975). 

 As the frequency and extent of fire have 

 decreased in lodgepole pine stands over the last 

 200 years, dwarf mistletoe infection intensity 

 and distribution are clearly increasing 

 (Zimmerman and Laven 1984). 



Southern Pinelands 



In contrast to the juniper, ponderosa pine, 

 and lodgepole pine communities, fire frequen- 

 cies have not drastically decreased in the 78 

 million ha (193 million acres) of southern 

 pinelands. These pinelands are composed of 

 diverse plant communities associated with long- 

 leaf (Finns pciliistris), slash {P. elliotti). loblolly 

 {P. taeda), and shoilleaf pines {P. echinata). Fire 

 has continued on an altered basis as an ecologi- 

 cal process in much of the southern pinelands; 

 historically, fire burned 10%-30% of the forest 

 annually (Wright and Bailey 1982); the .south- 

 ern culture never effectively excluded fire from 

 its pinelands (Pyne 1982), although human- 

 ignited fires have partially replaced natural 

 fires. Consequently, the amount of fire has been 

 reduced and the season of burns has changed 

 from predominately growing-season to dor- 

 mant-season (fall or winter) fires (Robbins and 

 Myers 1992). Altering the burning season and 

 frequency has significantly affected southern 

 pineland community structure, composition, 

 and biological diversity (Fig. 4). 



Implications 



The role of fire becomes more complex as it 

 interacts with land management. Maintaining 

 interactions between disturbance processes and 

 ecosystem functions is emphasized in ecosys- 

 tem management. It is vital for mangers to 



1800 1850 1900 1950 2000 



Fig. 2. Cumulative estabhshment 

 of western juniper on Steens 

 Mountain. Oregon (adapted from 

 R.F. Miller. Eastern Oregon 

 Agricultural Research Center, 

 unpublished data). 



100 150 200 250 300 

 Stand age (years) 



Fig. 3. Historical and actual age- 

 class distnbutions of lodgepole 

 pine forest. 



■ Hardwoods ■ Vines ■ Shrubs 

 ■ Forbs ■Grasses 



Santee fire plots. South Carolina 



Fig. 4. Understor>' plant crown 

 coverage after 30 years of burning 

 (Waldropetal. 1987). 



