|Miller, Richard - OREGON STATE UNIV|
Submitted to: Eastern Oregon Agricultural Research Center
Publication Type: Experiment Station
Publication Acceptance Date: February 1, 2004
Publication Date: June 12, 2004
Citation: Bates, J.D., Svejcar, A.J., Miller, R. 2004. Forage production in a cut juniper woodland. Eastern Oregon Agricultural Research Center. Range Field Day Report 2004: Current Forage and Livestock Production Research. Special Report 1052. p. 24-31. Interpretive Summary: The rapid expansion of western juniper into neighboring plant communities during the past 130 years has caused considerable concern because reduced forage production. One objective of removing western juniper is to restore grassland productivity. In this study we evaluated grassland production for 12 years following removal of western juniper by cutting with chainsaws. Trees were cut in the summer of 1991. Forage production increased by over 2000% from 40 lb/acre to almost 1000 lb/acre by the 5th year (1996) after cutting. Between 1996 and 2003, forage production has averaged about 1000 lb/acre a year. The composition of the understory has been dominated by native perennial bunchgrasses. By 2003, 90% of forage production was composed of these bunchgrass species, the balance consisting in order of importance, perennial forbs, non-native annual grasses, native bluegrass, and native annual forbs. The cutting of juniper restored forage production in this plant community reducing the number of acres required to feed a cow and calf for a month from 33 to 3 acres. By increasing the forage base management flexibility is improved and options for management are increased, which has important economic and ecological benefits. By increasing the forage base in one are permits other juniper-dominated areas to be treated with proper post-treatment grazing rest. Increasing the forage base in upland plant communities can reduce grazing pressure in riparian communities.
Technical Abstract: Western juniper expansion into the sagebrush steppe diminishes forage production, reduces plant and wildlife diversity, and negatively impacts hydrologic function. One goal of removing invading juniper woodlands is to restore herbaceous productivity. This study assessed forage production and plant successional dynamics for twelve years following juniper cutting. Biomass, cover, and density of understory species were compared between cut (CUT) and uncut woodland (WOODLAND). We also compared production and composition among three zones in the CUT treatment; old canopy, under juniper debris, and interspace. Total biomass, cover, and density increased in the CUT treatment over time and were greater in the CUT when compared to the WOODLAND. Biomass increased from 322 lb/acre in 1993 to 966 lb/acre in 2003 in the CUT treatment. Biomass was 10 times greater in the CUT versus WOODLAND. Densities of perennial grasses have remained stable at 10 plants/yd2 since 1997. Herbaceous biomass and cover did not change between 1997 and 2003 indicating that by the 6th year after cutting, remaining open areas had been occupied. Vegetation response in the CUT depended on zonal location. Cheatgrass dominated debris and canopy zones between the 5th and 10th year post-cutting. However, by 2003 perennial grass biomass was 2 times greater than annual grass in these zones. In interspace zones perennial grasses were the dominant functional group with higher cover and biomass than other functional groups. Retaining juniper debris on this site did not benefit establishment and growth of perennial grasses compared to interspace and canopy zones. Juniper cutting successfully restored forage production in this plant community reducing the number of acres required per AUM from 33 to 3. For livestock operations, increasing the forage base improves management flexibility and expands available management options, which has both economic and ecological benefits. Increasing the forage base permits other juniper-dominated areas to be treated with proper post-treatment rest. Increasing the forage base in upland plant communities may also lessen grazing pressure in riparian communities.