@article {50567, title = {Loss of phenolic compounds from leaf litter of creosotebush [Larrea tridentata (Sess. \& Moc. ex DC.) Cov] and tarbush (Flourensia cernua DC.)}, journal = {Journal of Arid Environments}, volume = {61}, number = {1}, year = {2005}, month = {April 1, 2005}, pages = {79-91}, abstract = {We examined loss of organic matter and phenolics from leaf litter of two shrubs that are invasive in the Chihuahuan Desert. Fiberglass bags (1-mm mesh) containing creosotebush [The objective of this paper is to provide insights into exotic and native invasive species dynamics using a conceptual model developed from the long history of research on native woody plant invasion into perennial grasslands. We first describe our new conceptual model that focuses on landscape characteristics (spatial configuration and connectivity) interacting with environmental drivers and biotic processes across multiple scales. We then provide support for the model using a long-term dataset from southern New Mexico. Finally, we discuss new insights this model has to offer for understanding, predicting, and managing exotic invasive species dynamics. (Sess. \& Moc. ex DC.) Cov.] or tarbush (Flourensia cernua DC.) leaf litter were placed below shrubs in two positions (soil surface and 5 cm belowground) and removed at several intervals up to 90 days during winter (creosotebush and tarbush) and spring (creosotebush). Over the 90-day sampling interval, organic matter loss from creosotebush and tarbush during the winter sampling period was low for both surface and buried litter, ranging from 1.7-5.2\%. Losses of organic matter from creosotebush litter during the spring were much greater (75.1 and 33.5\% for buried and surface samples, respectively). Total phenolic losses after 90 days were 1.6, 4.8, 21.6, 13.5, 87.1, and 43.5\% for winter buried creosotebush, winter surface creosotebush, winter buried tarbush, winter surface tarbush, spring buried creosotebush, and spring surface creosotebush litter, respectively, while losses of condensed tannins for the same samples were 45.8, 56.1, -34.0, -41.8, 91.1, and 67.4\%. Nordihydroguaiaretic acid loss from creosotebush litter was 25.4, 18.3, 95.2, and 66.7\% for winter buried, winter surface, spring buried, and spring surface samples, respectively, over the 90-day interval. Losses of organic matter and phenolics were generally greater in buried vs. surface and spring vs. winter samples, and losses typically occurred during the last 30-45 days. http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WH9-4DGW3YW-3-C\&_cdi=6845\&_user=1496926\&_orig=browse\&_coverDate=04\%2F01\%2F2005\&_sk=999389998\&view=c\&wchp=dGLbVlb-zSkzV\&md5=f5a61c1ff74b379cac3f662abc4550b3\&ie=/sdarticle.pdf}, keywords = {creosotebush, Flourensia cernua DC., Larrea tridentata, leaf litter, loss, organic matter, phenolics, tarbush}, url = {/files/bibliography/05-024.pdf}, author = {P.W. Hyder and E.L. Fredrickson and Richard E. Estell and M.E. Lucero and M.D. Remmenga} } @article {50788, title = {A digital photographic technique for assessing forage utilization}, journal = {Journal of Range Management}, volume = {56}, number = {2}, year = {2003}, month = {March 1, 2003}, pages = {140-145}, abstract = {Changes in forage utilization have been difficult to measure nondestructively without some level of subjectivity. This subjectivity, combined with a lack of reproducibility of visual estimates, has made forage utilization measurement techniques a topic of considerable discussion. The objective of this study was to develop and test the accuracy and repeatability of an objective, computer-based technique for measuring changes in plant biomass. Digital photographs of target plants acquired before and after partial defoliation were analyzed using readily available image analysis software. Resulting data were used to develop a simple linear random coefficient model (RC) for estimation of plant biomass removed based on the area of the plant in the photo. Sample collection took approximately 20 minutes/plant for alfalfa (Medicago sativa L.). Analysis of images took another 60 to 90 minutes. Regression analysis gave an R2 of 0.969 for predicted vs. observed plant weights. Testing this model using 10 alfalfa plants yielded weight estimates of defoliated plants accurate to within +/- 8.5\%. The advantage of the RC model is its ability to use easily obtained coefficients from simple linear regression models developed from each plant in a way that accounts for the lack of independence between samples within an individual plant. The technique described here offers an objective and accurate method for measuring changes in plant biomass with possible applications in ecology, botany, and range science. In particular, application of this technique for estimating forage utilization may improve accuracy of estimates and, thereby, improve range management practices.}, url = {/files/bibliography/03-015.pdf}, author = {P.W. Hyder and E.L. Fredrickson and M.D. Remmenga and Richard E. Estell and Pieper, Rex D. and D.M. Anderson} } @conference {50894, title = {Changes in phenolic compounds and organic matter in leaf litter from creosotebush [Larrea tridentata (Sess. \& Moc. ex Dc.) Cov.] and tarbush (Flourensia cernua dc.)}, booktitle = {55th Annual Meeting, Society for Range Management}, year = {2002}, month = {February 13-19, }, pages = {13}, address = {Kansas City, MO}, abstract = {Creosotebush and tarbush leaf litter contain phenolic compounds that may interact allelopathically with surrounding plants and soil biota. Our objective was to measure decline in phenolic concentrations with time. We placed fiberglass bags (1mm mesh) of litter beneath creosotebush and tarbush canopies. One set (two bags) was placed on the soil surface and one set was buried at 5 cm. Bags (six replicates, two duplicates) were collected at 0, 1, 3, 5, 7, 11, 15, 22, 30, 45, 60 and 90 days. Sets 1 and 2 (winter creosotebush and tarbush, respectively) were placed from February to April. Set 3, spring creosotebush, was placed from April to July. Set 1 lost organic matter at the rate of 0.000525 and 0.00406 mg/day; total phenolics, 0.209 and 0.111 mg/day; and, condensed tannins, 0.579 and 0.385 mg/day for surface and buried, respectively. Set 2 lost organic matter (0.00255 and 0.00392 mg/day) and total phenolics (0.449 and 0.517 mg/day) while concentrations of condensed tannins increased (0.0593 and 0.0929 mg/day) for surface and buried samples, respectively. Set 3 lost total phenolics (0.0470 and 0.151), nordihydroguaiaretic acid (0.165 and 0.210), condensed tannins (0.0863 and 0.0891), and organic matter (0.0247 and 0.0570 mg/day) for surface and buried, respectively. Percent organic matter loss was 1.99\% and 3.23\% for winter creosote, surface and buried samples, respectively; 2.31\% surface and 2.49\% buried for tarbush; and, 34.10\% and 75.27\% for surface and buried spring creosote, respectively. We demonstrated that concentrations of phenolic compounds decline in both surface and buried leaf litter.}, author = {P.W. Hyder and E.L. Fredrickson and Richard E. Estell and Kris Havstad and G.B. Donart} } @article {50895, title = {Distribution and concentration of total phenolics, condensed tannins, and nordihydroguaiaretic acid (NDGA) in creosotebush (Larrea tridentata)}, journal = {Biochemical Systematics and Ecology}, volume = {30}, number = {10}, year = {2002}, month = {November 1, 2002}, pages = {905-912}, abstract = {Shrubs have been replacing arid grasslands over large parts of the American southwest for most of the last century. Multiple mechanisms have been proposed to explain this vegetation shift. One hypothesis invokes allelopathy as a mechanism for maintenance of shrub dominance in former arid grasslands. This paper focuses on the presence and distribution of compounds with allelopathic and/or phytotoxic potential found within creosotebush [Larrea tridentata (Sess. \& Moc. ex DC.) Cov. Total phenolics, condensed tannins and nordihydroguaiaretic acid (NDGA) were measured in nine categories of tissue within creosotebush. Total phenolic and condensed tannin concentrations were determined using colorimetric methods while NDGA content was determined with high performance liquid chromatography (HPLC). Total phenolics were present throughout the plant with highest concentrations in leaves (36.2 mg/g), green stems (40.8 mg/g) and roots (mean for all root categories = 28.6 mg/g). Condensed tannins were found in all tissues except larger woody stems (5 to 12mm in diameter) with highest concentrations in flowers (1.7 mg/g), seeds (1.1 mg/g), and roots less than 5mm in diameter (1.1 mg/g). Flowers, leaves, green stems and small woody stems (<5mm in diameter) all contained NDGA with highest concentrations in leaves (38.3 mg/g) and green stems (32.5 mg/g). The distribution and nature of secondary compounds are variable among various locations within the plant. Moreover, secondary compounds are present in locations and concentrations that suggest they could have a role in allelopathic and/or phytotoxic interactions with surrounding organisms.}, url = {/files/bibliography/02-044.pdf}, author = {P.W. Hyder and E.L. Fredrickson and Richard E. Estell and M.R. Tellez and Gibbens, Robert P.} } @article {50896, title = {Transport of phenolic compounds from leaf surface of creosotebush and tarbush to soil surface by precipitation}, journal = {Journal of Chemical Ecology}, volume = {28}, number = {12}, year = {2002}, month = {December 1, 2002}, pages = {2469-2476}, abstract = {During the last 100 years, many desert grasslands have been replaced by shrublands. One possible mechanism by which shrubs outcompete grasses is through the release of compounds that interfere with neighboring plants. Our objective was to examine the movement of secondary compounds from the leaf surface of creosotebush and tarbush to surrounding soil surfaces via precipitation. Units consisting of a funnel and bottle were used to collect stemflow, throughfall, and interspace precipitation samples from 20 creosotebush (two morphotypes) and 10 tarbush plants during three summer rainfall events in 1998. Precipitation samples were analyzed for total phenolics (both species) and nordihydroguaiaretic acid (creosotebush only). Phenolics were detected in throughfall and stemflow of both species with stemflow containing greater concentrations than throughfall (0.088 and 0.086 mg/ml for stemflow and 0.022 and 0.014 mg/ml for throughfall in creosotebush morphotypes "U" and "V," respectively; 0.044 and 0.006 mg/ml for tarbush stemflow and throughfall, respectively). Nordihydroguaiaretic acid was not found in any precipitation collections. Our results show that phenolic compounds produced by creosotebush and tarbush can be transported to the soil surface by precipitation, but whether concentrations are ecologically significant is uncertain. Secondly, nordihydroguaiaretic acid was not present in the runoff from creosotebush.}, url = {http://www.springerlink.com/content/t630375412426743/fulltext.pdf}, author = {P.W. Hyder and E.L. Fredrickson and Richard E. Estell and M.E. Lucero} } @conference {51229, title = {Computerized technique for the assessment of plant utilization by herbivores}, booktitle = {Society for Range Management Meeting}, volume = {51}, year = {1998}, month = {1998}, pages = {Abstract 34}, abstract = {A digital-photographic method was developed to determine degree of plant herbivores. Forty alfalfa plants were used to develop predictive regressions was photographed from two angles, 0 and 90, for baseline values of area. Samples approximating volumes typical of sheep bites were then removed from each plant. After each sample was removed the plant was again photographed from both angles. This was repeated until the entire aboveground portion of the plant was removed. Two methods were used for sampling; (1) removing leaves and stems simultaneously, (2) removing leaves only. The resulting photographs were digitized and loaded into a graphics program that allowed pixel area to be determined. A random coefficient model was used to calculate the relationship between sample mass and pixel area. Analyses were performed on 0{\textdegree}, 90{\textdegree} and both angles combined. The combination of the two proved to be the best predictor of mass removal. The confidence interval widened as the proportion of material removed increased. Although accuracy and precision was appropriate for some applications, several planned modifications should increase accuracy and ease of the method.}, author = {P.W. Hyder and E.L. Fredrickson and Richard E. Estell and Kris Havstad and M.D. Remmenga} }