Table 1— Temperature measurements taken by study site, overstory, and surface condition 



Study site 



Lubrecht Coram Union Pass 



Measurement 



location Surface Air Soil Surface Air Soil Surface Air Soil 



Overstory treatment; 



Uncut X XX X XX x xx 



Clearcut x xx x xx x xx 



Shelterwood x — x — ___ 



Understory removal x — — — — — — — — 



Surface condition: 



Litter X— — x— — x xx 



Mineral soil x — — — — — — — — 



Burned x— — x— — x xx 



Chips ______ X XX 



Table 2 — Length of time following treatment that temperatures 

 were measured by study site 



Years following treatment 



Study site 1 2 3 4 5 6 7 



Lubrecht x x x 



Coram x x x x x x x 



Union Pass^ x 



^Temperatures were measured for only 1 year. 



Temperatures were measured using small, 0.064-inch 

 diameter, thermistor beads inserted in 0.094-inch diameter 

 by 0.5-inch long stainless steel tubing. Shielded 30-gauge 

 wire attached to the thermistor ran 6 to 10 ft to a junc- 

 tion box. Multiconductor cables (18-gauge) up to 2,500 ft 

 long were connected from the junction box to a recording 

 data acquisition system. Each data acquisition system 

 handled from 16 to 40 temperature sensors. Temperatures 

 were recorded hourly on a 12-month basis for varying 

 lengths of time (table 2). 



Net radiation was measured on all sites for some of the 

 treatments. Continuous monitoring of net radiation was 

 done for the clearcut and uncut treatments at Coram for 

 4 years and at Lubrecht for 3 years. Net radiation mea- 

 surements were also made over each of the surface treat- 

 ments at noon on a clear day at Lubrecht and Union Pass. 

 These data are used in the discussion to help explain how 

 treatments affect temperature. 



Analysis 



Analysis of research results involved: (1) evaluating ef- 

 fects of overstory removal treatment on surface, air, and 

 soil temperatures; and (2) evaluating effects of surface 

 condition, resulting from residue treatments on surface, 

 air, and soil temperatures. The discussion of results is 

 presented in that order. Because treatment effects are in- 

 fluenced by the elevation, terrain, and climatic character- 

 istics of the specific locations studied, results are also 

 generally presented separately for the three study sites. 

 As discussed earlier, the range of overstory treatments 

 and surface conditions, as well as temperature observa- 



tions, also varies by site. Consequently, between-site 

 comparisons are necessarily limited. 



To evaluate treatment effect on surface temperature, we 

 used two types of summaries: (1) monthly average max- 

 imum and minimum temperatures were calculated, and 

 (2) the occurrence of potentially lethal temperatures- 

 referred to as hot events and cold events— was tabulated. 

 Statistical tests (to be described later) determined treat- 

 ment differences for maximum and minimum temperature 

 by month for May through October. The percentage of 

 months, over the measurement period, that differences 

 were significant was then compared for the overstory 

 treatments and surface conditions. 



We calculated the number of hot events and cold events 

 based on surface temperatures, then used these to indicate 

 the hazard for seedling mortality. A hot event (HE) is 

 defined as 2 or more consecutive hours of temperatures 

 that are greater than 122 °F or 1 hour at 133 °F or 

 higher. A cold event (CE) is an occurrence of minimum 

 temperature of 23 °F or colder. These thresholds— 122, 

 133, and 23 °F— were picked to represent average lethal 

 levels for several tree species (Baker 1929; Hare 1961; 

 Levitt 1980). The HE's and CE's are summed over the 

 growing season, then used to calculate the percentage of 

 days that they occurred within the period. Neither the HE 

 nor the CE is intended to suggest that seedling mortality 

 will invariably result from these events, but they do repre- 

 sent a significant hazard to survival. We then compared 

 HE and CE data with measured seedling survival on the 

 study areas. 



To evaluate treatment effect on air temperatures, we 

 used daily maximum and minimum values and average day 

 and night temperatures. We used the day and night aver- 

 age temperatures because they influenced growth of tree 

 seedlings (Cleary and Waring 1969; Hellmers and others 

 1970). 



Because soil temperatures are much more stable than 

 surface or air temperatures, daily averages were used to 

 compare treatments at depths below 2 inches. Tempera- 

 tures in the humus layer (0.4 to 2.0 inches deep) are in- 

 cluded in the results as soil temperatures. Analysis of the 

 humus layer includes maximum and minimum tempera- 

 tures and HE's and CE's. Temperatures in the root zone 



5 



