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Effects of woody vegetation on shallow soil moisture at a semiarid montane catchment




Traff, Devin, author
Niemann, Jeffrey D., advisor
Green, Timothy R., committee member
Butters, Greg, committee member

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Soil moisture plays an integral role in many ecohydrologic processes and applications, particularly in semiarid environments. While interactions between vegetation and soil moisture at greater depths are relatively well understood, less is known about soil moisture at depths of 5 cm or less. In this study we investigate the impact of woody vegetation on shallow soil moisture dynamics for forested and shrubland ecosystems in a semiarid montane catchment. Instrumentation was installed on a forested north-facing hillslope (NFS) and a south-facing hillslope (SFS) vegetated primarily by shrubs at three types of locations: open or intercanopy, under mountain mahogany (Cercocarpus montanus) shrubs, and under ponderosa pine (Pinus ponderosa) trees. Rain gauges and pyranometers were installed to assess the impact of interception and shading, while time-domain reflectometry (TDR) probes were inserted into the top 5 cm of the soil to monitor hourly soil moisture. The observations suggest that interception reduces throughfall to about 25-50% of rainfall under the mountain mahogany and ponderosa pines. Shading is important for all locations on the NFS (PET ~ 20% of the SFS open location), but less shading occurs under the SFS mountain mahogany (PET ~ 40% of the SFS open location). Shallow soil under all vegetation types is typically wetter than at the SFS open location for dry conditions and drier than the SFS open location for wet conditions. Average shallow soil moisture is higher under all vegetation types than in the open, suggesting that the shading effect is stronger than the interception effect for the conditions studied.


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