An empirical model for predicting diurnal air-temperature gradients from edge into old-growth Douglas-fir forest

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Edge — the boundary line between clearcut and adjacent old-growth forest — is one of the critical landscape elements in the highly fragmented forest landscapes of North America's Pacific Northwest. Ecological phenomena at edges may be better understood by examining the physical environments near the edge. To further this objective diurnal air temperature gradients were measured along 16 gradients from the edge into the interior old-growth Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] forest over the 1989 and 1990 growing seasons and analyzed effects of edge orientation (relation of edge-facing to the azimuth) and macroclimate (local weather conditions of the clearcut) on these gradients were also explored through regression analysis. The air temperature gradient was expressed with a simple exponential equation involving three intermediate variables of interest: air temperature in the interior forest (TEMPIF), difference in air temperature between the edge and inside the forest (Δ AT), and changing ratio of temperature along the gradient (SLOPE). Linear or nonlinear regression equations were developed to predict TEMPIF, Δ AT, and SLOPE. Correlation analysis always preceded regression analysis, in which the relationships between the regression parameters and independent variables representing edge orientation and macroclimate were further explored. A computer model developed from the final empirical relationships successfully predicted air temperature gradients, circumventing the need for time-consuming field measurements with expensive meteorological instruments, and generated new information about the influences of edge orientation and macroclimate on air temperatures. TEMPIF, ΔAT, and SLOPE were shown to be highly sensitive to the dependent variables. Although model application should be limited to edges created by recent (10- to 15-year-old) clearcuts adjoining old-growth Douglas-fir forest, the modeling approach could be applied to edges with different characteristics by modifying the relationships.

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Reference Code: A93CHE01IDUS

Full citation: Chen, J., J. F. Franklin, and T. A. Spies. 1993. An empirical model for predicting diurnal air-temperature gradients from edge into old-growth Douglas-fir forest. Ecological Modeling 67(1993): 179-198.

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