The Influence of Vegetation on Soil Thermal Regime at the San Dimas Lysimeters

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Abstract
Soil temperatures for four lysimeters (bare, grass, scrub oak, and pine) during a 7‐year period (1952–1959) were studied. Observed temperature data of each lysimeter was subjected to harmonic analysis reducing the temperature time curves to a series of Fourier coefficients and the following empirical equations: Tz = 62.70 + 18.53 exp (−0.1273z) sin (30t − 8.15 [3] −7.98z) °F. for the bare lysimeter Tz = 58.20 + 16.02 exp (−0.1240z) sin (30t − 16.17 [4] −7.22z) °F. for the scrub oak lysimeter Tz = 60.44 + 18.32 exp (−0.1167z) sin (30t − 15.48 [5] − 7.05z) °F. for the Coulter pine lysimeter Tz = 60.96 + 17.43 exp (−0.1179z) sin (30t − 16.15 [6] −7.19z) °F. for the grass lysimeter Presence of vegetation has altered the soil temperature regime by reducing mean annual soil temperature and temperature amplitudes. Vegetation has introduced patterns of time delay in the soil temperature profile characteristic of the vegetation cover and directly related to the soil moisture regime. When the lysimeters with vegetation cover are compared, the influence of vegetation is of varying magnitude as shown by marked differences in soil temperature regime and soil thermal properties.With exception of the top 6 inches of soil, observed data for the average annual cycle of temperature agrees well with calculated values using the theory of heat flow. The slight difference in average monthly temperatures are much smaller than the natural differences from year to year.
Funding Information
  • Pacific Southwest Forest
  • Range Experiment Station (51, A5fs-16565)

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