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Years After Fire 



Figure 1 — Cumulative mortality by (a) season 

 of fire injury (autumn or spring and summer) and 

 (b) crown scorch class. 



of the first 3 years and last 3 years separated by higher 

 rates in the middle years, including a large increase 

 for trees dead 6 years. An important seasonal contrast 

 is shown as the cumulative fall rate for trees dead 

 longer than 6 years increased by only 5 percent for 

 autumn-killed trees compared to 18 percent for the 

 others. 



Even though tree fall differences were indicated 

 graphically among seasons of injury, significant differ- 

 ences were not found (p > 0.30) through regression 

 analysis. Small sample sizes and high variability likely 

 contributed to the lack of statistical significance. 



Figure 3 illustrates cumulative tree fall by diameter 

 class. Because only eight trees in the largest d.b.h. 

 class (midpoint 12 inches) died, these were pooled with 

 the 9-inch class to make a 10.5-inch class. The fall rate 

 pattern for the 3-inch class was consistent throughout 

 the study. Even with a slight decrease in fall rate in the 

 other two sizes after years 6 or 7, the average annual 

 rates among size classes were similar, ranging from 14 

 to 19 percent. Total tree fall percentages were not 

 statistically different (p > 0.25) among size classes, 

 ranging from 65 percent for the largest trees to 78 

 percent for the smallest. 



Contrasting fall rates were noted between trees that 

 died as a result of different levels of crown scorch. 

 Because of small numbers of dead trees in the lower 

 scorch classes (30, 50, and 70 percent) and similar 

 mortality among them, numbers of downed trees in 

 these classes were pooled and contrasted with pooled 

 values in the two highest scorch classes (90 and 100 

 percent) (fig. 4). The annual fall rates of trees that 

 died following low scorch was slightly greater than for 

 the other scorch class for years 2 and 3. However, for 

 the next 6 years, the fall rate of the lower scorched 



significantly higher (p < 0.07) than the 73 percent 

 scorch sustained by dead trees still standing. Average 

 d.b.h. of standing trees (5.8 inches) was not signifi- 

 cantly different from that of fallen trees (5.2 inches). 

 However, 75 percent of the fallen trees died in the first 

 postburn year, compared to 55 percent of the standing 

 dead. 



Over the 10-year study, 62 percent of the dead trees 

 in the autumn treatment fell compared to about 78 

 percent in the combined spring and summer treat- 

 ments. Because the spring and summer burns were 

 growing season treatments, the cumulative and an- 

 nual fall rates, which were similar, were combined. 

 Figure 2 shows cumulative tree fall percentages for 

 the seasonal treatments by year after death. The 

 autumn treatment had a highly variable 12 percent 

 average annual tree fall rate with the others averag- 

 ing about 18 percent annually. The high variability in 

 the autumn treatment was due to low fall rates in each 



-o- Autumn 



+ Spring and Summer 



Years After Death 



Figure 2 — Cumulative tree fall by season 

 of fire injury. 



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