100 



100 



2 3 4 5 6 7 



Years After Death 



Figure 3 — Cumulative tree fall by diameter 



size class. 



Year dead 



2 3 4 5 



Years After Death 



Figure 5 — Cumulative tree fall by time 

 between injury and death. 



trees decreased to an average of 6 percent per year, 

 compared to a rather constant rate of about 13 percent 

 for the highly scorched trees. 



Tree fall also varied by year dead after the fire, 

 shown in figure 5 for trees that died in the first 

 3 postburn years. Data for trees surviving until the 

 second and third year after injury were combined 

 because tree fall percentages were similar. Compari- 

 sons could only be made through 7 years after death 

 because trees dead in year 3 would only have 7 years 

 to fall before the end of the study. Therefore, for equal 

 comparison, falling of trees dead in year 1 was only 

 considered until year 8, and falling of trees dead in 

 year 2 was only considered until year 9. Results 



100 



0) 



80 



60 



40 



20 



Scorch 

 -o- 25 to 80 percent 

 + 80 to 100 percent 



2 3 4 5 6 7 



Years After Death 



indicate that the longer the trees survived after 

 mortal injury, the less the chance of early falling. 

 Seven years after death, 85 percent of the trees that 

 died in the first postburn year had fallen, compared to 

 65 percent of those that died in the second year, and 60 

 percent of those that died in the third year. Average 

 annual fall rate for trees killed in the first postburn 

 j'ear was 26 percent, 19 percent for the second post- 

 burn year, and 14 percent for the third postburn year. 



Analysis of the crown scorch variable indicated that 

 82 percent of the trees that died from high crown 

 scorch fell, which was significantly greater (p < 0.04) 

 than the 56 percent tree fall for those that died as a 

 result of low scorch (fig. 4). Also, the 85 percent tree 

 fall for those that died the first postburn year was 

 significantly greater (p < 0.08) than the 67 percent 

 total tree fall for those that died in the second or third 

 postburn years (fig. 5). Analysis of the interaction of 

 these two variables gives further insight into the 

 importance of each for probability of tree fall, as the 

 following tabulation shows: 



Scorch 



Low 

 High 



Years surviving 

 after fire 



1 2+3 



0.75 

 0.82 



0.27 

 0.77 



The 27 percent fall probability for trees that died 

 from low crown scorch but that survived 2 to 3 years 

 after the fire was about one-third and statistically 

 different (p < 0.01) from that of trees with high crown 

 scorch or those that died quickly. 



Figure 4 — Cumulative tree fall by 

 crown scorch class. 



4 



