Submitted to: Eastern Oregon Agricultural Research Center
Publication Type: Experiment Station
Publication Acceptance Date: 1/15/1998
Publication Date: N/A
Citation: MILLER,R.F., SVEJCAR,A.J., ROSE,J., WOODLAND SUCCESSION: STRUCTURE, COMPOSITION, AND THRESHOLDS, EASTERN OREGON AGRICULTURAL RESEARCH CENTER, 1998, SPECIAL REPORT 991 Interpretive Summary: Western juniper has been aggressively expanding into sagebrush plant communities for the past 120 years. There are nearly 8 million acres of rangeland currently influenced by western juniper and 90% of the acreage has been invaded within the last 100 years. On some sites the invasion of juniper can greatly reduce the shrub and grass species. thereby negatively influencing forage production and wildlife habitat. We studied 108 individual juniper sites in southeastern Oregon and northeastern California. We separated the sites into six different community types which ranged from shallow soil low sagebrush to deep soil aspen. We were able to define distinct phases of juniper invasion regardless of community type. The effects of invasion on the individual species was dependent on community type. The results of this study will help managers: 1) determine the stage of juniper invasion on individual sites, and 2) prioritize sites for juniper control efforts, and 3) predict the response of individual sites to juniper control efforts.
Technical Abstract: The effects of developing woodlands on community structure and composition were evaluated across several community types. Differences in stand structure of closed woodlands were also evaluated for these community types. Community types ranged from low sagebrush communities occupying shallow, heavy-clay soils to clay loam mountain big sagebrush communities to deep loamy soil occupied by aspen. Juniper woodlands at stand closure ranged from 21- to 90-percent cover and from 64 to 1731 full size trees/ha across these community types. Sagebrush declined across all mountain big sagebrush community types as juniper increased. Herbaceous cover and diversity significantly declined on Thurber needlegrass community types occupying southerly aspects. However, herbaceous cover and diversity did not appear to decline in Idaho fescue communities occupying northerly aspects.