There is concern over the decline of aspen and the lack of successful regeneration due to overgrazing by both cattle and wildlife. Any increase of aspen or its long-term persistence in the landscape is dependent on the continuous recruitment of aspen suckers. I conducted two studies on Lassen National Forest, California, USA, to aid development of livestock grazing strategies to restore aspen stands with excessive livestock browsing. The aim of the first study was to evaluate how individual aspen suckers respond to intensity and season of browsing. Thirty-three combinations of intensity and season of brows on aspen were implemented. Greatest growth was on suckers with no terminal leader browse and < 25% biomass removed from branches. Lowest growth occurred when 90% of terminal leader length and 50% of branch biomass was removed. Growth was most negatively affected by browse on terminal leaders and when browsing occurred mid-season only or both early and mid-season. Occurrence of conifers in the overstory significantly reduced sucker growth.
The second study was designed to examine cattle preference for aspen habitat. I evaluated seasonal dynamics of forage biomass, quality, and utilization of vegetation types found within aspen-meadow complexes. Utilization varied among vegetation types and season, with aspen regeneration receiving up to 100% use in late season. Aspen regeneration had higher forage quality compared to aspen understory and meadow vegetation regardless of season or year. Principal utilization during early season occurred in the meadow and aspen understory. Mid-season decreases in meadow and aspen understory forage quantity and quality coincided with a marked increase in aspen regeneration utilization. Forage quality and biomass were at the lowest levels by late season in all three vegetation types. Seasonal utilization of vegetation by cattle is a function of forage quantity, biomass, and cow nutrient demand. Browse on aspen regeneration terminal leaders during mid-season over consecutive years, and repeated browse during a single growing season should be avoided. Managers can use early season grazing to reduce aspen browsing, set stocking rates so that herbaceous forage quantity is not limiting, and provide supplements to insure that limiting nutrients are available to cattle.
|Advisor:||Tate, Kenneth W.|
|Commitee:||Barbour, Michael, Bartos, Dale L., George, Melvin|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 71/10, Dissertation Abstracts International|
|Subjects:||Ecology, Conservation, Natural Resource Management, Range management|
|Keywords:||Aspen, Grazing, Management, Populus tremuloides, Restoration|
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