Tcmsinal Eahswsteius — Our Livnii^ Rtsnurcc.s 



Altered Fire 

 Regimes 

 Within Fire- 

 adapted 

 Ecosystems 



by 



Gardner W. Ferry 



Robert G. Clark 



Roy E. Montgomery 



Bureau of iMud Management 



Robert W. Mutch 

 U.S. Forest Service 



Willard P. Leenhoiits 



U.S. Fish and Wildlife Service 



G. Thomas Zimmerman 



National Park Service 



Fires ignited by people or through natural 

 causes have interacted over evolutionary 

 time with ecosystems, exerting a significant 

 intluence on numerous ecosystem functions 

 (Pyne 1982). Fire recycles nutrients, reduces 

 biomass. inlluences insect and disease popula- 

 tions, and is the principal change agent affecting 

 vegetative structure, composition, and biologi- 

 cal diversity. As humans alter fire frequency and 

 intensity, many plant and animal communities 

 are experiencing a loss of species diversity, site 

 degradation, and increases in the size and sever- 

 ity of wildfires. This article examines the role 

 fire plays in the ecological process around 

 which most North American ecosystems 

 evolved. 



The five plant communities selected for 

 study were the sagebrush steppe, juniper wood- 

 lands, ponderosa pine forest, lodgepole pine 

 forest, and the southern pineland (Fig. I ). Status 

 and trends of altered fire regimes in fire-adapt- 

 ed ecosystems highlight the role that fire plays 



in wildland stewardship. Fire regimes are con- 

 sidered as the total pattern of tires over time that 

 is characteristic of a region or ecosystem 

 (Kilgore and Heinselman 1990). 



Sagebrush-grass Plant 

 Communities 



Greater frequency of fire has seriously 

 affected the sagebrush steppe during the last 50 

 years (Table). One such community, the semi- 

 arid intermounlain sagebrush (Artemisia 

 species) steppe, encompasses about 45 million 

 ha (112 million acres). After repeated fires, non- 

 native European annual grasses such as cheat- 

 grass (Bromiis tectonim) and medusahead 

 [Tacniatherum capiit-mediisae) now dominate 

 the sagebrush steppe (West and Hassan 1985). It 

 is unclear whether cheatgrass invasion, heavy 

 grazing pressure, or shorter fire return intervals 

 initiated the replacement of perennial grasses 

 and shrubs by the non-native annual grasses. It 

 is clear, however, that wildfires aid in replacing 

 native grasses with cheatgrass, as well as caus- 

 ing the loss of the native shrub component 

 (Whisenant 1990). Inventories show that cheat- 

 grass is dominant on about 6.8 million ha (17 

 million acres) of the sagebrush steppe and that 

 it could expand into an additional 25 million ha 

 (62 million acres) in the sagebrush steppe and 

 the Great Basin sagebrush type (Reliant and 

 Hall 1994). 



Juniper woodlands 



I Lodgepole pine 



Fig. 1. Range of: a — sagebru.sti 

 steppe; b — juniper woodiands; 

 c — ponderosa pine; d — iodge- 

 pole pine; and e — soutfiem 

 pineland communities in ttie 

 United States. 



I Ponderosa pine 



