|Miller, Richard - OREGON STATE UNIV|
Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 11, 2001
Publication Date: July 20, 2002
Citation: BATES,J.D., SVEJCAR,A.J., MILLER,R.F., EFFECTS OF JUNIPER CUTTING ON NITROGEN MINERALIZATION, JOURNAL OF ARID ENVIRONMENTS 2002, 51:221-234. Interpretive Summary: Western juniper is a woody rangeland species that has dramatically increased in acreage during the past 100 years, and currently dominates nearly 8 million acres in the northwestern U.S. The increase has been attributed to climatic patterns, overgrazing during the early part of the century, and/or reduced fire frequencies. Livestock producers and federal land managers have observed improved forage production with juniper removal, but few studies have documented the effects of western juniper cutting on either forage production or site nitrogen status. We found that cutting western juniper increased forage production by a factor of 9 and forage nitrogen by a factor of 10 by the second year after cutting. There was no evidence that juniper cutting resulted in nitrogen losses from the site. Nitrogen loss after cutting is a concern in some forested ecosystems. Thus, on western juniper dominated sites, cutting is a viable option for restoring forage that can then be used to sustain livestock and wildlife production.
Technical Abstract: Western juniper (Juniperus occidentalis spp. occidentalis Hook.) woodlands have rapidly spread into the sagebrush steppe of the northern Great Basin the past 100 years. The influence of juniper on soil N dynamics in cut and uncut woodlands was investigated. Eight 1-ha blocks were established in a juniper woodland. In half of each block all trees were cut with cut trees left on site. Sampling on cut plots was stratified to include intercanopy and debris zones. Debris zones were defined as sites under cut trees which had not previously received inputs of juniper litter. In the uncut treatment, intercanopy and canopy zones were sampled. Sampling was conducted for a 2 year period post-cutting. The first sample year was a moderately dry year and the second sample year was a very wet year. Measured parameters included KC1 extractable N (NH+4-N and NO-3-N), nitrification, N mineralization (using buried bag technique), volumetric soil moisture, total soil C and N, and herbaceous biomass. In the dry year, soil moisture, KC1 extractable N, and N mineralization were higher in the cut intercanopy zones vs. the other locations. In the wet year, KC1 extractable N and N mineralization did not differ among the zones. The effect of year, dry vs. wet, overwhelmed the effect of juniper removal. The initial effect of juniper cutting was an increase in KC1 extractable N, but by the second year post-treatment differences for the N variables measured were not apparent. In the dry year there was a higher potential for N loss from soils as a result of the buildup of KC1 extractable N. The methods used to assess extractable N and N mineralization indicate that most of the extractable N in soils was taken up by soil micro-organisms and not lost via leaching or denitrification. Soils beneath downed trees had lower nitrification and N mineralization rates compared to the intercanopy. In the uncut woodland, N mineralization and nitrification rates and KC1 extractable NO-3 levels in intercanopy soils were greater or equal to rates and levels in the canopy zone. There was not a fertility island effect in canopy influenced soils for available N in the uncut juniper woodland.