Date of Award
Master of Science (MS)
Civil and Environmental Engineering
Land Management, Prescribed Fire, Sagebrush-steppe ecosystem, Soil Hydrological Properites, Soil Water Repellency
Prescribed fire is an important tool for rangeland management in sage-steppe ecosystem, yet the long-term effects of this practice have not been well studied. Previous studies of fire-affected soil water repellency have identified the strength and persistence of SWR after burning in different types of forests but have not identified consistent timelines for post-fire recovery. This study explores the impacts of fire and plant community succession on SWR and infiltration properties to further inform rangeland managers regarding the long-term impacts of prescribed fire on SWR and infiltration properties in sagebrush-steppe ecosystems.
The objectives of this study were: 1) To explore the temporal effects of prescribed burning in a sagebrush-dominated landscape; 2) To investigate spatial variability of soil hydrologic properties with changes in plant cover (aspen, big mountain sage and low sage) and soil texture; 3) To determine relationships among soil organic fractions, soil hydrophobicity and infiltration properties.
Fieldwork was conducted in paired watersheds in the Northwest Watershed Research Center at Upper Sheep Creek (USC) and an unburned adjacent watershed Wood Gulch Creek (WGC), southwest of Boise, Idaho. These two watersheds are very similar in that they have three dominant vegetation cover communities: Low Sage, Big Mountain Sage and Aspen, similar elevation and topography. They differ in that USC is a long-term enclosure from cattle grazing and the site of a prescribed fire, while WGC watershed is open to cattle grazing and has not burned in recent history. Prior measurements of pre-burn and post-burn infiltration tests and Water Drop Penetration Time (WDPT) at USC were extended in this study. Several analysis methods were used to calculate hydraulic conductivity, sorptivity and Water Repellency Index (WRI). Additionally, ten replicate soil samples of 15 cm depth were cored from each transect and used to analyze the fraction of organic matter and the static water-soil contact angle.
The recent analyses showed that the severity and occurrence of surface soil water repellency was substantially reduced eight years after fire treatment within the area originally covered with big sage, where the fire intensity were greatest. Also, hydraulic conductivity significantly increased in each vegetation cover type over the eight-year period of study. The comparisons among soil hydrological properties shows that hydraulic conductivity is not directly related to SWR, and sorptivity is inversely related to WRI in a general sense. The spatial variability in conductivity is primarily controlled by soil texture, whereas sorptivity is affected by soil organic content and soil wettability. The frequency of SWR was least in Low Sage and greatest in Aspen, reflecting a significant difference in soil organic content. Measurements of static water contact angle and organic content analysis show a strong positive correlation, primarily for Aspen and Big Sage sites. However, many soil samples from Big Sage and Aspen sites had substantial organic matter yet were not hydrophobic. It is concluded that soil organic matter content is not well correlated to SWR at microsite scale but may applicable as general indicator of infiltration capacity or SWR at larger scale within similar soils and vegetation type. The increased infiltration capacity eight years after fire at USC Low Sage indicates a long-term benefit of prescribed fire for increased fodder production and runoff management in semiarid rangeland.
Cheng, Yang, "THE PRESCRIBED BURNING IMPACTS ON SOIL WATER REPELLENCY AND SOIL HYDROLOGICAL PROPERTIES IN SAGEBRUSH-STEPPE ECOSYSTEM" (2016). Dissertations - ALL. 540.