25 



O 



Julian Days 



Figure 3 — Smoothed curves for a 5-day period 

 contrasting phloem and bark surface temperatures 

 on the south side of a lodgepole pine tree in a 

 thinned stand. 



Temperature (1 Day) — More details are shown when 

 smoothing is done over a 24-hour period. Three typical 

 curves (fig. 5) are shown for temperatures recorded on the 

 north side of the sample trees at breast height. First, we 

 see a reversal in dominance between surface and phloem 

 temperatures both in the thinned stand (fig. 5A) and the 

 unthinned stand (fig. 5B). Magnitude varies between 

 and 7 °C. After sunrise, there is a reversal in the tem- 

 perature curves, with the phloem temperature higher 

 than the surface temperature. The surface heat buildup 

 accelerates, and by afternoon surface temperature again 

 becomes dominant and remains so until the following 

 morning. 



Taking this comparison further, we contrasted the 

 phloem temperature curves for the thinned and unthin- 

 ned stands (fig. 5C). During late afternoon, there was a 

 peak difference of 8 °C, while during the remainder of the 

 day the two smoothed curves are quite similar. The 

 thinned stand had more heat building up in the phloem 

 than did the unthinned stand. 



Solar (23 days) — Incident solar radiation is a measure 

 of the amount of sunlight that strikes the tree surface or 

 forest floor and was expected to be strongly correlated 

 with temperature recorded for various points on or near 

 the sampled trees. 



The hourly averages for incoming solar radiation were 

 smoothed to show the daily solar curve for the 23 days. 

 Marked differences in solar radiation were observed be- 

 tween the thinned and unthinned stand at breast height 

 (fig. 6A), while not so striking a difference was shown for 

 the sensors placed on the towers (fig. 6B). It may be hard 

 to interpret trends seen here, particularly those at breast 

 height, because sensors placed on the trees were influ- 

 enced by occasional shade from various parts of the 

 sample tree. Therefore, the tower sensors were included 

 to serve as a reference for incoming solar radiation. 



25 



Julian Days 



Figure 4 — Smoothed curves for a 5-day period 

 contrasting bark surface temperatures on the south 

 side of two lodgepole pine trees between a thinned 

 and unthinned stand. 



The spread in the values obtained on the trees at breast 

 height was greater than the values obtained from the 

 tower. Therefore, it is assumed that shading is playing a 

 part in the measurement of the factors in figure 6A. 



Solar (5 Days) — The daily solar radiation curves 

 smoothed over a 5-day period more explicitly showed the 

 separation we observed earlier (fig. 6A and 6B). Less 

 separation was observed in the two smoothed curves at 

 breast height near the sampled trees when compared to 

 the amount of sunlight striking the sensors on the instru- 

 ment towers. These differences reflect, in part, placement 

 of the sensors in the stands. Those sensors in the inter- 

 spaces (on the towers) are probably more representative of 

 measured incident solar radiation within the stands. 



Windspeed (23 days) — Windspeed was not smoothed 

 as much as the previously mentioned factors. This al- 

 lowed some of the variance to remain in the data to more 

 clearly show trends. During a 24-hour period, windspeed 

 as measured on the tower varied between 1.6 and 

 5.6 km/h (fig. 7). The thinned stand had higher wind- 

 speed than the unthinned stand. The average (or overall) 

 difference was only about 1.6 km/h. However, during the 

 period of most MPB flight, between 4 and 6 p.m. (Ras- 

 mussen 1974), the difference was consistently 3.2 or more 

 km/h. 



Most wind movement occurred at the tower in the 

 thinned stand, while the least movement was within the 

 crown in the unthinned stand. Windspeed varied between 

 1.6 and 4.8 km/h (fig. 8). 



Windspeed (5 Days) — Consistency resulted between 

 the thinned and unthinned smoothed curves (fig. 9) for 

 windspeed on the instrument tower. This set of curves 

 was very uniform for the 5 days. However, smoothed 

 averages for the difference between the two curves varied 

 fi-om 1.0 to 1.6 km/h. 



5 



