| MichaeL G. "Sherm" Karl and Paul S. Doescher |
| Authors are rangeland management specialist-ecologist, Interior Columbia Basin Ecosystem Management Project, USDA-Forest Service, Walla Walla, Wash. 99362; and professor, Department of Rangeland Resources, Oregon State University, Corvallis, Ore. 97331. At the time of the research, the senior author was graduate research assistant, Department of Rangeland Resources, Oregon State University, Corvallis, Ore. |
Abstract |
| Mismanagement of livestock can result in herbivory on Pinus seedlings with potential for growth loss. From 1986 to 1990 on a conifer plantation in the Mixed-Conifer Zone of southwestern Oregon we measured the aboveground growth of ponderosa pine (Pinus ponderosa Douglas ex Lawson & C. Lawson var. ponderosa) seedlings that had sustained (1) removal of terminal stem or bud tissue by cattle, and (2) no removal (control). In 1990 (year 5 of the plantation), cumulative, absolute height and stem volume on seedlings that sustained terminal tissue removal were similar to control seedlings. In 1988, relative height growth was comparable between control seedlings and seedlings sustaining tissue removal in May 1987. In contrast, 1988 relative height growth was 22% (P < 0.05) for seedlings sustaining tissue removal in August 1987, compared with control seedlings. Relative stem volume growth in 1988 ranged from 21 to 26% (P < 0.05) for seedlings sustaining tissue removal in (1) August 1987, (2) April or May 1988, and (3) 1987 and 1988, compared with control seedlings. Reduced relative growth was short-term. Relative growth rates for seedlings sustaining tissue removal were comparable to control by the first or second year after removal. Seedlings sustaining tissue removal before winter bud set (April and May) were more likely to recover by the first year than seedlings sustaining tissue removal after winter bud set (August). We propose that if silviculturists prescribe cattle grazing early in the growing season and terminal tissue is removed at that time, they can still achieve understory vegetation control and enhanced soil water availability without jeopardizing long-term aboveground growth of ponderosa pine. The lack of spatial replication of treatments (terminal tissue removal dates) limits spatial extrapolation of our findings. The credibility of our findings should be tested with additional research on the growth response of ponderosa pine seedlings subsequent to actual livestock herbivory, conducted with spatially replicated treatments. |
| Key Words: forest grazing, Pinus ponderosa, conifer seedling growth, relative growth rate, height growth, stem volume growth |