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Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Includes bibliographical references. / by William A. Vagt. / M.S.

Invasive species introductions, namely the chestnut blight fungus (Cryphonectria parasitica) and hemlock woolly adelgid (Adelges tsugae), have permanently altered the overstory canopy of Appalachian forests by causing the dramatic die-offs of two ecologically significant tree species, American chestnut (Castanea dentata) and eastern hemlock (Tsuga canadensis). These canopy dominants once had significant roles in regulating understory communities. The loss of these trees, along with fire suppression, has driven two common evergreen shrubs, rosebay rhododendron (Rhododendron maximum) and mountain laurel (Kalmia latifolia), to expand and proliferate in areas where they were once restricted. These two common shrubs are recognized agents of change in Appalachian forests because of their abilities to modify soil seed banks, regulate light, and alter the local soil chemistry. This study documented evergreen shrub expansion across the Coweeta Creek basin over the past 36 years analyzing changes in winter greenness using harmonized multi-decadal archives of Landsat imagery. We found the greatest change in winter greenness in relatively dry areas: higher elevations (1275–1300 m), steeper slopes (33°–35°), southward aspects, and far from streams (600–800 m). Historical field data collected in three unmanaged watersheds at Coweeta showed a simultaneous decrease in T. canadensis and increase in R. maximum. We also documented the decline of a xerophytic canopy tree species, pitch pine (Pinus rigida), and an associate understory shrub, K. latifolia. Our analysis of the influence of terrain variables on evergreen shrub expansion allowed us to determine which of the two species was expanding in various locations with reasonable certainty. This study provides spatially explicit data on the expansion of two evergreen shrub species at the Coweeta Hydrologic Laboratory that could be used to pinpoint areas for future management interventions. / Master of Science / Forests in the eastern United States have changed substantially in response to the introduction of highly competitive invasive species. Some overstory tree species have been virtually eliminated from their functional role in regulating understory vegetation in many southern Appalachian ecosystems. Die-offs of these trees have allowed understory evergreen shrubs to expand into areas where they were once restricted. Shrubs that have expanded in response to overstory tree die-offs can alter the ecology of forests for the foreseeable future. Our work leveraged multi-decadal archives of wintertime satellite imagery to document the spread of understory evergreen shrubs in a watershed located in western North Carolina. We investigated the relationship of this spread to local environmental characteristics like elevation, steepness (slope), slope direction (north, south, east, west), and distance-from-stream. The greatest changes in evergreen vegetation were documented on terrain at relatively high elevations, locations farther from streams, on southerly aspects, and on relatively steep terrain. We included historical field data collected during the same time period that showed a simultaneous increase in two understory evergreen shrub species after the die-off of ecologically significant overstory tree species. This information will help forest managers by describing areas where substantial spread has occurred and potentially use this information to inform future management action.

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Groundwater response to climate variability and land cover change is important for sustainable management of water resources in the Southwest US. Global Climate Models (GCM) project that the region will dry in the 21st century and the transition to a more arid climate may be under way. In semiarid Basin and Range systems, this impact is likely to be most pronounced in Mountain System Recharge (MSR), a process which constitutes a significant component of recharge in these basins. Despite the importance of MSR the physical processes that control MSR, and hence the climate change impacts, have not been fully investigated because of the complexity of recharge processes in mountainous catchments and limited observations. In this study, methodologies were developed to provide process-based understanding of MSR based on empirical and data-driven approaches. For the empirical approach, a hydrologically-based seasonal ratio the Normalized Seasonal Wetness Index (NSWI) was developed. It incorporates seasonal precipitation variability and temperature regimes to seasonal MSR estimation using existing empirical equations. Stable isotopic data was used to verify recharge partitioning. Using the NSWI and statistically downscaled monthly GCM precipitation and temperature data, climate change impacts on seasonal MSR are evaluated. Second, a novel data-based approach was developed to quantify mountain block recharge based on the catchment storage-discharge (S-Q) relationships and informed by isotopic data. Development of S-Q relationships across the Sabino Creek catchment, Arizona, allowed understanding of MBR dynamics across scale.Two ArcGIS desktop applications were developed for ArcGIS 9.2 to enhance recharge and evapotranspiration (ET) estimation: Arc-Recharge and RIPGIS-NET. Arc-Recharge was developed to quantify and distribute recharge along MODFLOW cells using spatially explicit precipitation data and a digital elevation model. RIPGIS-NET was developed to provide parameters for the RIP-ET package and to visualize MODFLOW results. RIP-ET is an improved MODFLOW ET module for simulating ET. RIPGIS-NET improves alluvial recharge estimation by providing spatially explicit riparian ET estimates. Using such tools and the above methods improves recharge and ET estimation in groundwater models by incorporating temporally and spatially explicit data and hence the assessment of climate variability and land cover change on groundwater resources can be improved.

I described recreational use in mountain sheep (Ovis canadensis mexicana) habitat in the Pusch Ridge Wilderness (PRW), Tucson, Arizona. I also examined human attitudes held by PRW recreationists and homeowners within 1 mile (1.6 km) of PRW boundary towards several mountain sheep management options. I used geographic information system modeling and social science survey methodology. Recreational use along two trails that traverse mountain sheep habitat was frequent (66 individuals/day use Pima Canyon trail, 26 individuals/day use Romero Canyon trail) and primarily limited to the lower 3 miles (4.8 km) of the trails. Compliance with existing dog leash regulations is low (41.8% on Pima Canyon trail, 62.8% on Romero Canyon trail). Recreationists and homeowners within 1 mile (1.6 km) of PRW support the elimination of dogs within PRW and support planned burns of PRW to improve mountain sheep habitat. Recreationists and homeowners also support closing all or parts of PRW to protect the long term viability (>100 years) of the sheep population. Homeowners within 1 mile (1.6 km) of PRW primarily enjoy passive recreational use of PRW (i.e, viewing the wilderness).

Approved for public release, distribution is unlimited / Vertically propagating waves (VPWs) generated by prominent mountain ridges are a severe hazard to military aircraft operations. Properly forecasting the initiation and duration of such a phenomenon is critical, yet quite often missed by turbulence forecasters. A primary reason for poor forecast skill is vague VPW forecasting guidelines at the Air Force operational centers, focusing a majority of attention on the less severe, more common trapped lee wave response. The United States Air Forces in Europe Operational Weather Squadron (USAFE OWS) has requested a tool to aid in improving forecast ability of VPW events. Satellite analysis from October 2003 through March 2004 indicated an occurrence of six major VPW events to the lee of the Alps. Actual verification of turbulence in each VPW was unavailable due to the minimal pilot report (PIREP) database kept for military flights over Europe, therefore, a subjective assessment of turbulent conditions was determined depending on the resulting cloud signature. Using NCEP GFS model analysis and upstream upper air soundings during these events, an average synoptic condition and critical weather parameters were created. These developed tools were then tested from October 2004 through March 2005 to prove their reliability. In a limited data set these tools identified all VPW events, with only a 25% false alarm rate. This is compared to a 6% forecast ability with 0% false alarm rate determined during the 2003-2004 winter season by USAFE OWS forecasters. These new rules should be valuable in that they will provide a much needed capability for synoptic scale turbulence forecasters to better determine hazardous aviation conditions associated with VPWs. / Captain, United States Air Force