College of Agriculture & Natural Resources
Permanent URI for this communityhttp://hdl.handle.net/1903/1598
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
Browse
3 results
Search Results
Item Modeling Nitrogen, Phosphorus and Water Dynamics in Greenhouse and Nursery Production Systems(2011) Majsztrik, John Christopher; Lea-Cox, John D.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Nutrient and sediment runoff from the six states and Washington, DC that form the Chesapeake Bay watershed is a major cause of environmental degradation in the Bay and its tributaries. Agriculture contributes a substantial portion of these non-point source loads that reach the Bay from its tributaries. Research in this area has traditionally focused on agronomic farm contributions, with limited research on the nursery and greenhouse industry. This research presents the first known attempt to model operation-specific information, validated by published research data, where multiple variables are assessed simultaneously. This research provides growers and researchers with a tool to assess and understand the cultural and environmental impact of current practices, and predict the impact of improving those practices. Separate models were developed for greenhouse, container-nursery and field-nursery operations, since specific production variables and management practices vary. Each model allows for simple entry of production input variables, which interface with the Stella modeling layer. Each model was first calibrated with one published research study, and subsequently validated with another peer-reviewed study, with multiple independent runs for each model. Validation results for all three models showed consistent agreement between model outputs and published results, increasing confidence that models accurately process all input data. Verified models were then used to run a number of what-if scenarios, based upon a database of production practices that was gathered from 48 nursery and greenhouse operations in Maryland. This database provided a detailed analysis of current practices in Maryland, and adds significantly to our understanding of various operational practices in these horticultural industries. Results of the what-if scenarios highlighted model sensitivities and provided answers to hypotheses developed from the analysis of the management database. Some model functions, such as denitrification, would greatly benefit from additional research and further model modification. Models were designed to be easily adapted to local conditions for use throughout the U.S. and potentially other parts of the world.Item Stated Preference Methods and Models: Analyzing Recreational Angling in New England Groundfisheries(2011) Jarvis, Sonia; McConnell, Kenneth E; Agricultural and Resource Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Policy analysis of nonmarket goods requires accurate knowledge about the behavior of economic agents. This dissertation explores several facets of behavior models in recreational angling for three New England groundfish species. Stated preference methods are used frequently for nonmarket applications because data are scarce, but survey design can affect the results of behavior models via changes in respondents' cognitive processes. Methodological biases due to task complexity, measured by survey length, number of alternatives, and the degree of information overlap are observed in discrete choice experiment questionnaires, evidenced by differences in estimated model parameters and error variances. Additionally, ignoring task complexity increases mean marginal willingness-to-pay estimates. Information processing and decision heuristics should be considered in survey design and accounted for in estimated models. Empirical specifications for utility models of recreational angling are also explored because numerous variants are employed in analyzing stated preference data. Inclusion of responses from different survey subpopulations affect estimated utility function parameters and mean marginal willingness-to-pay values. Utility models that are nonlinear in catch are as statistically robust as their linear counterparts but allow for diminishing marginal utility in fish, which is more consistent with recreational angling behavior. Failure to account for sources of heterogeneity such as angler avidity, species familiarity, and demographic information affect behavioral interpretations considerably. Recreational fisheries are commonly managed using bag (creel) and minimum size restrictions. Many surveys include regulations as attributes in choice experiments, but models of angler behavior should not contain regulatory variables explicitly because they rarely factor into angler participation decisions directly. Because catch is random, regulations affect angler decisions indirectly by changing the underlying distributions for keep and release. A framework for understanding the effect of regulations on angler behavior given the stochastic nature of catch is developed. Short-run and long-run fishery implications are evaluated using a bioeconomic simulation.Item Ecological Values and Ecosystem Services of Natural Forests: A Study of Prince William Forest Park, Virginia(2010) Dawson, Allen; Sullivan, Joseph; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Abstract The Urban Forest Effects (UFORE) model developed by the USDA Forest Service quantifies the ecological benefits of urban forests. UFORE has been used to analyze many urban areas, including National Park land in Washington, D.C., but has not been applied to natural forests. We conducted a UFORE analysis of Prince William Forest Park for species composition and individual tree characteristics including tree height, DBH, canopy architecture, and general tree health, collecting data during the 2007 field season. The results show that the park contains over 6,287,000 trees and these trees store 394,000 tons of carbon with an annual net sequestration rate of 12,300 tons. This forest also abates 414 tons of air pollution annually. These results quantify and affirm to policymakers and the public the value and ecological importance of the forests managed by the National Park Service surrounding metropolitan Washington, D.C.