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For herbivores, nutrient intake is limited by the relatively low nutritional quality of plants and high concentrations of potentially toxic defensive compounds (plant secondary metabolites, PSMs) produced by many plants. In response to phytochemical challenges, some herbivores selectively forage on plants with higher nutrient and lower PSM concentrations relative to other plants. Pygmy rabbits (Brachylagus idahoensis) are dietary specialists that feed on sagebrush (Artemisia spp.) and forage on specific plants more than others within a foraging patch. We predicted that the plants with evidence of heavy foraging (browsed plants) would be of higher dietary quality than plants that were not browsed (unbrowsed). We used model selection to determine which phytochemical variables best explained the difference between browsed and unbrowsed plants. Higher crude protein increased the odds that plants would be browsed by pygmy rabbits and the opposite was the case for certain PSMs. Additionally, because pygmy rabbits can occupy foraging patches (burrows) for consecutive years, their browsing may influence the nutritional and PSM constituents of plants at the burrows. In a post hoc analysis, we did not find a significant relationship between phytochemical concentrations, browse status and burrow occupancy length. We concluded that pygmy rabbits use nutritional and chemical cues while making foraging decisions.

Five foliar constituents were measured seasonally from the three subspecies of big sagebrush in Montana. Monoterpene, crude terpenoid, and crude fat levels were lowest in the spring, increased through the summer with maximum quantities at flowering or in the fall and winter months thereafter. Crude protein and total nonstructural carbohydrates were at highest concentrations in the spring, decreased in the summer, and rose again in the fall. Sagebrush foliage consists of an external and internal component. The external material is glandular secondary metabolic products, primarily terpenoids, and cuticular waxes. The internal constituents are cell-wall polymers, protein, nonstructural carbohydrates, and lipids. A S-mhmte chloroform extraction of fresh whole leaves removed the external material (crude terpenoids) with minimal affect on the internal components. Steam distillation extracted the epidermal terpenoids and the internal nonstructural carbohydrates leaving the cuticular waxes and protein in the dry matter residue. Plants are capable of biosynthesizing a tremendous number of chemicals that have potential uses as food, fiber, fuels, and chemicals (Buchanan et al. 1978 a,b). Many of these resources, however, have been unutilized because of high costs, inadequate technology and limited knowledge of chemical composition. The rising cost of fossil fuels, particularly oil, has stimulated an interest in the chemicals and biomaterials that can bederived from plants. In the United States and Mexico research is being directed toward both native and introduced species that have evolved and adapted to the harsh semiarid and arid environments (Campos-Lopez and Roman-Alemany 1980, Johnson and Hinman 1980), where inadequate water supplies have limited agricultural development. On these drier sites, new crops could be established without affecting current food and fiber production. Big sagebrush (Artemisia tridentata) is an abundant shrub on semiarid rangelands with considerable economic and biological impact (Gifford et al. 1979). Its distribution and population densities have increased during the last century due to overgrazing of the associated grasses, fire control, and the shrubs' inherent resistance to herbivores (Morris et al. 1976, Younget al. 1979). Improvement of sagebrush-grasslands for livestock production is a desirable management practice and requires the eradication of sagebrush. This can be accomplished by a variety of techniques with variable costs and returns (Nielsen 1979). Harvesting the shrubs for their biomaterials might be a feasible alternative to destroying them and could provide some management flexibility for sagebrushgrasslands. Sagebrush biomass has two distinct components, wood and foliage. The stems and branches are primarily cell-wall polysaccharides held together with lignin and chemically similar to the wood of other angiosperms (Shafizadeh and Buckwa 1970). The foliage The authors are research associate professor, graduate student, and professor, Wood Chemistrv Laboratorv. Deoartment of Ch...

Water and solvent extracts from the aerial tissues ofCentaurea maculosa, spotted knapweed, inhibited the root growth of lettuce. Column chromatography and lettuce bioassay of a chloroform extract led to the isolation of cnicin, a sesquiterpene lactone. Pure cnicin was bioassayed at 0, 1, 2, 4, 6, 8, and 10 mg/5 ml water with lettuce, created wheatgrass, bluebunch wheatgrass, rough fescue, western larch, lodgepole pine, and spotted knapweed. Germination was inhibited at one or more concentrations for all species except lodgepole pine and spotted knapweed. Growth, particularly of the roots, was retarded between 1 and 4 mg of cnicin. Lettuce, bluebunch wheatgrass, and spotted knapweed were inhibited significantly at all concentrations tested.

Samples of current year's growth of leaves and stems were collected in February 1983 from basin big sagebrush (Artemisia tridcntotoNuit.-), Wyoming big sagebrush (A. t. wyomingensis Beetle and Young), mountain big sagebrush (A.t. vaseyana [Rydb.] Rectle), and black sagebrush (A. nova Nels.) on a mule deer (Odocoikushemionushemionu) winter range near Cardiner, Montana. Samples were from both lightly and heavily used plants (form classes) within each taxon. Crude terpenoids were separated into 3 groups: beadspace vapors, volatile, and nonvolatile crude terpenoids. Compounds in each group are thought to stimulate the sensory organs of mule deer. Individual compounds were identified and quantified for comparison with preference ranks among taxa and between utilixation form classes. Seven compounds were selected by discrhnlnant analysis as indicators among the 4 taxa, with methacrolein+ethanol, p-cymene, and the smquiterpene lactones the most probable preference determinants. Seven other compounds were found useful for separating plants within taxa into form classes. Chemical differences between the 2 form classes, however, were less distinguishable than were those among the 4 taxa.

Sixteen days after a September wildfire, ethanol and water were measured in phloem and sapwood at breast height and the base of Pinus ponderosa Dougl. ex P. & C. Laws. with zero (control), moderate, heavy, and severe crown scorch. The quantity of ethanol increased with each level of injury, resulting in trees with severe scorch containing 15 and 53 times more phloem and sapwood ethanol, respectively, than controls. Ethanol concentrations in the sapwood and adjacent phloem were related, probably as a result of diffusion. Upward movement in xylem sap was most likely responsible for the relationship between sapwood ethanol concentrations at breast height and the stem base. As trees recovered from their heat injuries, the ethanol concentrations declined. In contrast, ethanol accumulated in dead trees that lost their entire crowns in the fire. Various bark and xylophagous beetles landed in greater numbers on fire-damaged trees than on controls the following spring and summer, suggesting that ethanol was being released to the atmosphere and influencing beetle behavior. Beetle landing was more strongly related to sapwood ethanol concentrations the previous September than in May. Sapwood ethanol measured 16 days after the fire was the best predictor of second-year mortality for trees with heavy and severe crown scorch.

Ethyl acetate extracts from heartwood of seven western conifer trees and individual volatile compounds in the extracts were tested for antimicrobial activity against Phytophthora ramorum. Extracts from incense and western redcedar exhibited the strongest activity, followed by yellow-cedar, western juniper, and Port-Orford-cedar with moderate activity, and no activity for Douglas-fir and redwood extracts. Chemical composition of the extracts varied both qualitatively and quantitatively among the species with a total of 37 compounds identified by mass spectrometry. Of the 13 individual heartwood compounds bioassayed, three showed strong activity with a Log(10) EC(50) less than or equal to 1.0 ppm (hinokitiol, thymoquinone, and nootkatin), three expressed moderate activity ranging from 1.0-2.0 ppm (nootkatol, carvacrol, and valencene-11,12-diol), four compounds had weak activity at 2.0-3.0 ppm [alpha-terpineol, valencene-13-ol, (+)-beta-cedrene, (-)-thujopsene], and three had no activity [(+)-cedrol, delta-cadinene, and methyl carvacrol]. All of the most active compounds contained a free hydroxyl group, except thymoquinone. The importance of a free hydroxyl was demonstrated by the tremendous difference in activity between carvacrol (Log(10) EC(50) 1.81 +/- 0.08 ppm) and methyl carvacrol (Log(10) EC(50) >3.0 ppm). A field trial in California, showed that heartwood chips from redcedar placed on the forest floor for 4 months under Umbellularia californica (California bay laurel) with symptoms of P. ramorum leaf blight significantly limited the accumulation of P. ramorum DNA in the litter layer, compared with heartwood chips from redwood.