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Dissertation Defenses

Doctoral students who have an upcoming dissertation oral defense are posted here. So why not take this opportunity to learn about the research that our graduate students are doing!

Dissertation Defense for Jose Lopez


Department Contact Email: gutloja@gmail.com

Defense Title: Ecohydrology of aspen and eucalyptus plantations

Defense Date and Time: 07/26/18 12:00 pm

Defense Location: Morse Hall 201

Defense Advisor: Heidi Asbjornsen

Defense Abstract: Forecast scenarios predict an increase in the demand of alternative sources of energy during the coming decades, such as woody biomass crops (WBC). WBC have the potential to become a major challenge for the next generation of researchers, policymakers and land managers. However, the current rationale for promoting plant-based over petroleum-based energy sources emphasizes the benefits of reduced carbon dioxide and other emissions, while giving less attention to potential impacts to water resources.
The goal of my research was to assess potential ecohydrological impacts associated with the production of biomass for bioenergy from aspen (Populus tremuloides Mich.) in Wisconsin, USA, and eucalyptus (Eucalyptus grandis) plantations in Entre Rios, Argentina. My study was part of a larger project that examined the impacts, barriers and opportunities related to bioenergy production across the Americas (USA, Mexico, Brazil, Argentina).
We selected plantation ages within the most common rotation cycles for each species. In Wisconsin, we studied three sites, a 10 and a 24-year-old (YO) plantations and a reference 34-year-old mature forest. In Argentina, two 1-year-old plantations, one at high and one at regular density, a 4-year-old, a 10-year-old plantation, and a reference grassland. This was a unique study to determine annual water use based on a combination of tree-level measurements of water use using sap flow sensors, and deterministic models of potential evapotranspiration.
We validated two sap flow methods (heat dissipation and heat ratio), and validated a third method (maximum heat ratio) capable of measuring high flow rates. In aspen plantations, water use at the site level generally increased with age, even when site density decreased over time (from approx. 6500 to 1900 from 10 to 34 YO). We observed that young plantations (10 YO) used 80% of the annual water early in the growing season, compared to a 45% for the same period in the Mid-aged and Mature plantations. Our simulated total water use rates under two scenarios, a forty-year and four ten-year rotations, indicates that multiple short rotations result in approx. 70% less water use than a single forty-year rotation.
On eucalyptus plantations, when the density remained constant, site-level water use decreased with plantation age, reaching maximum water use rates at around 4 YO (~6 mm) and declining afterwards for the remainder of the typical 15-year rotation cycles (2 mm in 10 YO plantations). In experimental one-YO plantations with double tree density, site water use increased approx. 50%. Finally, in both plantations we observed that reference evapotranspiration, estimated with the Penman-Monteith equation, was a poor predictor of water use in young plantations.


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