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Displaying 23,131 - 23,140 of 65,208 PublicationsFUEL CONDITIONS ASSOCIATED WITH NATIVE AND EXOTIC GRASSES IN A SUBTROPICAL DRY FOREST IN PUERTO RICO
Exotic grasses capable of increasing frequency and intensity of anthropogenic fire have invaded subtropical and tropical dry forests worldwide. Since many dry forest trees are susceptible to fire, this can result in decline of native species and loss of forest cover. While the contribution of exotic grasses to altered fire regimes has been well documented, the role of native grasses in contributing to fuel loads in dry forest has received little attention. We assessed differences in fuel conditions among native and exotic grasses within a subtropical dry forest preserve in Puerto Rico. We...AuthorsSkip Van Bloem, Jarrod M. Thaxton, Stefanie WhitmireKeywordsSourceFire EcologyYear2012- We evaluated how governmental forest regulation in Costa Rica, Guatemala, and Nicaragua has succeeded or failed in fostering changes in forest owner and user behavior that enhance the sustainability of tropical forest management. As expected, sufficient resources and capacity for forest policy implementation are crucial for attaining governmental forest policy objectives, but innovative arrangements for promoting, enforcing, and verifying policy compliance can compensate for limited regulatory resources and processes. The findings also indicate that: the level of governmental commitment to...AuthorsKathleen McGinley, Frederick W. CubbageKeywordsSourceJournal of Sustainable ForestryYear2012
- Current mortality in lodgepole pine caused by mountain pine beetle (MPB) throughout much of western North America has resulted in concern about future forest structure. To better understand the long-term effects of the current mortality, and how it might differ depending on forest species composition, we measured forest vegetation and woody fuel accumulations in forest affected by a MPB outbreak in the late 1970s and early 1980s and compared conditions to 1980s USDA Forest Service data to quantify changes in the approximately 30 years following tree mortality. Stands were classified into...AuthorsKristen A. Pelz, Frederick W. SmithKeywordsSourceForest Ecology and Management. 280: 93-102.Year2012
- We compared soil properties beneath naturally-occurring patches of Lycium ruthenicum Murray (fam. Solanaceae) to evaluate the shrub’s potential to improve the fertility of saline soils. Soil pH, total nitrogen and carbon and extractable potassium, magnesium and phosphorus were respectively significantly higher in the A and B horizons of Lycium shrub patches compared to adjacent unvegetated soils. The influence of Lycium on these soil properties increased with shrub density. Total soil N and extractable Mg and K concentrations were 1.8, 2.6- and 6.6-fold higher under dense Lycium shrub...AuthorsGholam Ali Jalali, Hossein Akbarian, Charles C. Rhoades, Hamed YousefzadehSourcePolish Journal of Ecology. 60(4): 845-850.Year2012
- Accurately simulating gross primary productivity (GPP) in terrestrial ecosystem models is critical because errors in simulated GPP propagate through the model to introduce additional errors in simulated biomass and other fluxes. We evaluated simulated, daily average GPP from 26 models against estimated GPP at 39 eddy covariance flux tower sites across the United States and Canada. None of the models in this study match estimated GPP within observed uncertainty. On average, models overestimate GPP in winter, spring, and fall, and underestimate GPP in summer. Models overpredicted GPP under...AuthorsKevin Schaefer, Christopher R. Schwalm, Chris Williams, M. Altaf Arain, Alan Barr, Jing M. Chen, Kenneth J. Davis, Dimitre Dimitrov, Timothy W. Hilton, David Hollinger, Elyn Humphreys, Benjamin Poulter, Brett M. Raczka, Andrew D. Richardson, Alok Sahoo, Peter Thornton, Rodrigo Vargas, Hans Verbeeck, Ryan Anderson, Ian Baker, T. Andrew Black, Paul Bolstad, Jiquan Chen, Peter S. Curtis, Ankur R. Desai, Michael Dietze, Danilo Dragoni, Christopher Gough, Robert F. Grant, Lianhong Gu, Atul Jain, Chris Kucharik, Beverly Law, Shuguang Liu, Erandathie Lokipitiya, Hank A. Margolis, Roser Matamala, J. Harry McCaughey, Russ Monson, J. William Munger, Walter Oechel, Changhui Peng, David T. Price, Dan Ricciuto, William J. Riley, Nigel Roulet, Hanqin Tian, Christina Tonitto, Margaret Torn, Ensheng Weng, Xiaolu ZhouKeywordsSourceJournal of Geophysical Research. 117(G3): 15 pp.Year2012
- Snowshoe hares (Lepus americanus) are a primary prey species for Canada lynx (Lynx canadensis) in western North America. Lynx management plans require knowledge of potential prey distribution and abundance in the western United States. Whether even-aged regenerating forests or multi-storied forests contain more snowshoe hares is currently unknown. During 2006-2008, we estimated snowshoe hare density in 3 classes of 30-70-year-old lodgepole pine (Pinus contorta) and 4 classes of late seral multi-storied forest with a spruce (Picea engelmannii)-fir (Abies lasiocarpa) component in the...AuthorsNathan D. Berg, Eric M. Gese, John R. Squires, Lise M. AubrySourceJournal of Wildlife Management. 76(7): 1480-1488.Year2012
- Family forestry is characterized by heterogeneity in ownership structure, owners’ objectives, and management practices. Differences among forest landowners by age and occupation have been regularly documented, but other social dimensions, such as race and gender, have received considerably less attention. We conducted exploratory research on racial and gender differences among forest landowners in two Alabama counties via a mail survey in order to identify promising areas for future research and forestry outreach. We found that gender and race influence land holding practices, management...AuthorsJohn Schelhas, Yaoqui Zhang, Robert Zabawa, Bin ZhengSourceInternational Journal of Social ForestryYear2012
- As wind energy production drives the manufacturing of wind turbine blades, the utilization of glass and carbon fiber composites as a material of choice continuously increases. Consequently, the needs for accurate structural design and material qualification and certification as well as the needs for aging predictions further underline the need for accurate constitutive characterization of composites. In the present paper we describe an outline of a recently developed methodology that utilizes mutliaxial robotically controlled testing combined with design optimization for the automated...AuthorsJohn Michopoulos, Athanasios Iliopoulos, John C. HermansonSourceIn: Materials Challenges in Alternative and Renewable Energy II: Ceramic Transactions (eds G. Wicks, J. Simon, R. Zidan, R. Brigmon, G. Fischman, S. Arepalli, A. Norris and M. McCluer), John Wiley & Sons, Inc., Hoboken, NJ, USA. 14 p.Year2012
- This paper is describing the preliminary results of an effort to validate a methodology developed for composite material constitutive characterization. This methodology involves using massive amounts of data produced from multiaxially tested coupons via a 6-DoF robotic system called NRL66.3 developed at the Naval Research Laboratory. The testing is followed by the employment of energy based design optimization principles to solve the inverse problem that determines the unknown parameters of the constitutive model under consideration. In order to validate identified constitutive models,...AuthorsJohn G. Michopoulos, Athanasios lliopoulos, John C. Hermanson, Adrian C. Orifici, Rodney S. ThomsonKeywordsSourceIn: Proceedings of the ASME 2012 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference, August 12-15, 2012, Chicago, IL, IDETC/CIE 2012; 10 p.Year2012
- This paper describes a data reduction methodology for eliminating the systematic aberrations introduced by the unwanted behavior of a multiaxial testing machine, into the massive amounts of experimental data collected from testing of composite material coupons. The machine in reference is a custom made 6-DoF system called NRL66.3 and developed at the NAval Research Laboratory, that consists of multiple sets of hexapod configurations essentially forming a recursive synthesis of multiple parallel mechanisms. Hexapod linkages, the grips, and other deformable parts of the machine absorb...AuthorsAthanasios lliopoulos, John G. Michopoulos, John C. HermansonKeywordsSourceProceedings of the ASME 2012 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference, August 12-15, 2012, Chicago, IL, IDETC/CIE 2012, DETC2012-71119; 2012; 11 p.Year2012