Table 2 — Tree and soil temperatures (°C) in thinned and unthinned lodgepole pine stands obtained by infrared thermometer, 

 August 13, 1985, in northern Utah 



Stand condition 



Thinned Unthinned 



Characteristic Number^ Min. Max. Mean^ 



Sd Min. Max. 



Mean Sd 



Soil 50 16 58 30.8a 

 Tree north side 50 13 31 24.2a 

 Tree south side 50 15 45 26.6a 



10.5 14 45 

 3.8 17 30 

 5.6 17 33 



26.0b 6.8 

 23.5a 3.1 

 24.3b 3.8 



'Number of observations in each stand. 



'Means in rows followed by different letters significantly different (P<0.05). 







Table 3 — Numbers of mountain pine beetles caught August 21 to September 5, 1985, in Lindgren traps baited with mountain 

 pine beetle lure and placed in thinned and unthinned lodgepole pine stands in northern Utah 



Males 



Females 



Total 



Trap No. No. Percent 



No. Percent No. 



Percent 



Thinned 



0.0 

 25.0 

 10.5 



3 

 3 

 17 



100.0 

 75.0 

 89.5 



3 

 4 



19 



Total 



11.5 



23 



Unthinned 



88.5 



26 



5.2 



34 

 41 

 15 



18.1 

 19.5 

 18.8 



154 

 169 

 65 



81.9 

 80.5 

 81.2 



188 



210 

 80 



Total 



90 



18.8 



388 



81.2 



478 



94.8 



DISCUSSION 



Our discussion centers on the three areas outHned in 

 the Results section. 



Stand Characteristics 



The principal difference between the thinned and un- 

 thinned stands used in this microclimatic study was the 

 two measures of density. Basal area was 14.9 m^/ha and 

 numbers of trees 382.3/ha less in the thinned than in the 

 unthinned stand. The average diameters of trees in both 

 thinned and unthinned stands did not differ significantly. 

 The difference in density appears to be responsible for the 

 differences in microclimate in the two stands. 



Stand Microclimate 



Microclimatic observations showed consistent differ- 

 ences between the thinned and unthinned stands. Thin- 

 ning lodgepole pine stands results in increased light inten- 

 sity, wind movement, insolation, and temperature. These 

 factors, either separately or in various combinations, ap- 

 pear to affect MPB activity. The differences observed 

 between thinned and unthinned stands are sometimes 

 quite subtle. However, even minor changes in microcli- 

 mate could have profound effects on MPB. 



8 



