Summer evapotranspiration trends as related to time following logging of high elevation forest stands in Sierra Nevada

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Summer evapotranspiration trends as related to time following logging of high elevation forest stands in Sierra Nevada
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   Summer Evapotranspiration Trends as Related to TimeFollowing Logging of High Elevation Forest Standsin Sierra NevadaByRobert Ruhl ZiemerB.S. (University of California) 1959THESISSubmitted in partial satisfaction of the requirements for the degree ofMASTER OF SCIENCEinForestryin theGRADUATE DIVISIONof theUNIVERSITY OF CALIFORNIAApproved:Paul J. ZinkeRudy F. GrahPeter W. BirkelandCommittee in ChargeDeposited in the University Library 1963Date Librarian  iiTABLE OF CONTENTSPageINTRODUCTION . . . . . . . . . . . . . . . . . . . 1DESCRIPTION OF STUDY . . . . . . . . . . . . . . . 4Location . . . . . . . . . . . . . . . . . . 4Soils . . . . . . . . . . . . . . . . . . . . 4Precipitation . . . . . . . . . . . . . . . . 6Soil Moisture Sampling Sites . . . . . . . . . 6Selection Criteria . . . . . . . . . . . . . . 6Sampling Design . . . . . . . . . . . . . . . 6Soil Moisture Measurement . . . . . . . . . . . 11Neutron Soil Moisture Determination . . . . . 11Calculation of Soil Moisture . . . . . . . . . 14Correction for Summer Precipitation . . . . . 17Weighting of Area Sampled . . . . . . . . . . 18Correction to Comparable Periods of Measurement 19Comparability of 1960 and 1961 Depletion . . 21SeasonsRESULTS AND DISCUSSION . . . . . . . . . . . . . . 24Seasonal Trend of Soil Moisture Depletion . . . . 24Effect of Field Capacity . . . . . . . . . . . 32Effect of Soil Depth . . . . . . . . . . . . . 34Effect of Ground Cover . . . . . . . . . . . . 35Seasonal Soil Moisture Depletion in Logged . . 36OpeningsMaximum Soil Moisture Depletion . . . . . . . . 38Effect of Time Since Logging . . . . . . . . . 38Effect of Canopy Cover . . . . . . . . . . . . 42Soil Moisture Savings . . . . . . . . . . . . . 42Seasonal Trends . . . . . . . . . . . . . . . 46At Maximum Depletion . . . . . . . . . . . . . 46SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . 49LITERATURE CITED . . . . . . . . . . . . . . . . . . 57APPENDIX . . . . . . . . . . . . . . . . . . . . . . 57  iiiLIST OF FIGURESFigure Page1. Location of study area. 52. Location of soil moisture sampling points within a typical 10forest opening and a hypothetical profile of soil moisturecontent within that opening at maximum depletion.3. Correction of observed soil moisture in percent by volume 15for neutron loss to the atmosphere at the 6-inch soil depth.4. Accumulation of relative day length times 2 p.m. vapor 22pressure deficit index (  Dr x VPD 2 p.m.) from June 1 for1960 and 1961.5. Soil moisture in percent by volume at 0- to 42-inch soil 25depth in plot L-1a logged in 1959, for various datesthrough the summer moisture depletion season and into thefall moisture recharge season, 1960 and 1961.6. Plot L-1a, logged 1959. 267. Plot L-1b, logged 1959. 288. Plot L-3a, logged 1950. 299. Plot L-4a, logged 1946. 2910. Plot L-5a, logged 1923, 1949 and 1955. Note snowmelt 30pattern in southern edge of opening. Photo takenJune 7, 1961.11. Soil moisture depletion related to day length times vapor 33pressure deficit from the forested portion of plots ofvarious field capacities In inches per 4-foot soil depth,June to September, 1960 and 1961.12. Soil moisture depletion in logged openings of various ages 37within a field capacity range of 15.9 to 17.8 inches per4-foot soil.13. Soil moisture in percent by volume at 0- to 42-inch soil 40depth at maximum moisture depletion for logged openings ofvarious ages.14. Seasonal pattern of soil moisture savings (moisture loss 48from open minus moisture loss from forest), by Individualplots, logged in 1959, 1955, 1950, and 1948.15. Effect of age of logged openings upon water savings at 48maximum soil moisture depletion for two field capacityranges.  ivLIST OF TABLESTable Page1.Characteristics of soil moisture sampling sites. 72.Plot soil moisture adjusted for 1 H opening size, by 44year of logging, and time, 1960 - 1961.3.Soil moisture data by plot number, sampling point 58and soil depth.  vABSTRACTThe quantity of summer soil moisture loss from logged forestopenings was related to the length of time since the creation of theopening in a study made in the subalpine forest zone of the SierraNevada west-side near the Central Sierra Snow Laboratory, California,within the elevational range of 6,000 to 7,000 feet. Soil moisturedepletion was measured in logged forest openings which were created in1959, 1955, 1950, and 1948, and in the forest surrounding theseopenings. At the period of maximum soil moisture depletion, openings 1year old were found to have 6.9 inches more soil moisture per 4-footsoil than did the surrounding forest which is an expression of thequantity of moisture saved as a result of the logging operation. Inopenings 5 years old the savings has decreased to 2.9 inches, after 10years to 1.2 inches and after 12 years to 0.7 inches. A projection ofthe regression in-dicates that the moisture savings at maximumdepletion will reach zero 16 years after cutting. Soil moisturedepletion is traced through two summer depletion seasons and into thefall moisture recharge periods. The effect of soil field capacity soildepth, ground cover, and summer precipitation upon soil moisturedepletion trends also is discussed.
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