Beetle Response 



Beetle response to thinned and unthinned stands was 

 determined by using pheromone-baited traps in the gen- 

 eral vicinity of the microclimate study. Three Lindgren 

 funnel traps were hung in a thinned stand and three in 

 an adjacent unthinned stand. Traps were 100 m apart 

 within stands and 300 m apart between stands. Those 

 stands were approximately 1 km north of the stands 

 where microclimatic observations were made. There were 

 no beetle-infested trees in the two stands at the time of 

 trapping. The traps were baited with the standard MPB 

 lure (Phero Tech Inc.) consisting of ^ra^s -verbenol, exo- 

 brevicomin, and myrcene. Beetles were collected from the 

 traps weekly during a 3-week period, August 15 to 

 September 5, 1985, the summer before microclimate ob- 

 servations were made. Beetles were taken to a laboratory 

 where they were sexed and counted. 



Data Analysis 



Characteristics and temperatures of thinned and un- 

 thinned stands obtained during stand surveys were sub- 

 jected to analysis of variance to test for significant diflFer- 

 ences. Statistical analysis of data from the micrologger 

 was not possible because we had only enough equipment 

 to monitor microclimate of one tree in each of the two 

 stands. Therefore, we used a time series analysis system 

 software package for microcomputers to manipulate vari- 

 ous combinations of factors to show trends that exist be- 

 tween the thinned and unthinned stands, as well as 

 within the sampled tree. The raw data were plotted, and 

 a smoothing technique was used to reduce some of the 

 inherent variation. We accomplished this smoothing by 

 calculating a moving average of the raw data. These 

 smoothed curves were better able to show consistent 

 trends between similar factors than had previously been 

 observed. Because the version of the program used would 

 accept only 550 values, we used the hour averages to look 

 at the overall trends for the 23 days. More variance was 

 deleted from the curves when a larger time span (49 

 hours versus 5 hours) was used to obtain the smoothed 

 average. Next, to see if we were masking detail, we used 

 the 15-minute readings and plotted the 5 days that en- 

 compassed the peak flight period (Julian day 215). Fi- 

 nally, we plotted averaged smoothed data for the day that 

 peak flight occurred (midnight to midnight). 



RESULTS 



We looked at the results in terms of stand characteris- 

 tics, microclimate, and beetle response. 



Stand Characteristics 



Characteristics of the thinned stand in which microcli- 

 mate was observed were an average basal area of 22.1 

 mV ha, a density of 707.8 trees/ha, and an average diame- 

 ter of 20.2 cm. Dominant and codominant trees averaged 

 15.1 m in height, with live crown 52 percent of total 

 height. In contrast, the adjacent unthinned stand had a 



basal area of 37.0 m^/ha, a density of 1,090.1 trees/ha, and 

 an average diameter of 18.6 cm. Dominant and codomi- 

 nant trees averaged 15.1 m in height, with live crown 53 

 percent of total height (table 1). Of these stand character- 

 istics, only the stand density measures of basal area and 

 trees per hectare were significantly different between 

 stands (P <0.05). 



Stand Microclimate 



Temperature (23 Days) — Curves for a 23-day period 

 obtained via smoothing raw data appeared similar be- 

 tween the south and north sides of the sampled tree at 

 breast height in the thinned stand. The average tempera- 

 ture varied between 9 °C at the beginning of the 23 days 

 to a high of approximately 18 °C around August 5, 1986. 

 Both sets of curves show close correlation between the 

 surface and phloem temperatures. However, a slight 

 separation (0.5 °C) was noticed for the south side of the 

 tree. 



Similar traces were observed between the thinned and 

 unthinned stand. Subsurface temperatures reflect what 

 occurs on the bark surface but with slightly less magni- 

 tude. The phloem curve for the south side in the thinned 

 stand was consistently 1 to 2 °C higher than the phloem 

 curve in the unthinned stand (fig. 2A), while the surface 

 temperature on the south side in the thinned stand (fig. 

 2B) responded with a 1 to 3 °C greater difference from 

 that in the unthinned stand. 



Less difference was observed between the thinned and 

 unthinned stands when comparisons were made on the 

 north side of the sampled trees. Traces of the curves on 

 the north side were similar to those on the south side. 

 However, as expected, the south side was consistently 3 to 

 4 °C higher. On the north side, curves for the phloem 

 temp>erature mimicked the surface temperature, and a 

 difference of less than 0.5 °C between the thinned and 

 unthinned stand was observed. 



Temperature (5 Days) — Smoothing over a 5-day pe- 

 riod was done to express more detail for any one 24-hour 

 period. This information was partially masked when 

 smoothing was done for the full 23 days. Initially, we 

 looked at pairs of curves showing within-tree differences 

 at breast height in both treatments. Similar responses 

 were observed, and figure 3 shows the various combina- 

 tions. Over a 24-hour period, there is a reversal in domi- 

 nance of the two temperature curves. From early after- 

 noon through late evening, surface temperature is 

 warmer than phloem temperature, but for the rest of the 

 period it is just the opposite. These trends are consistent 

 from day to day over the 5 days. At the point of maximum 

 separation, there is <0.5 °C difference. We see much more 

 separation in the averaged temperature curves (fig. 4) 

 when we make comparisons between the same sample 

 points for the two treatments. This information is an 

 elaboration of the previous figure 2B. The thinned stand 

 always had the higher temperature. The difference 

 ranged from 2 to 3.5 °C, and the biggest difference 

 occurred during the hottest part of the day. 



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