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A Fire year 



Figure 3c — Approximate regeneration dates for individual overstory trees by species and ap- 

 proximate years of fire events for each moist site plot. (Flathead = F-1, F-2, Bitterroot = B-4). 

 Fire history (black triangles) could not be determined prior to 1600 on F-1 , 1817 on F-2, and 

 before 1630 on B-4. On B-4, trees with establishment dates of 1514, 1550, and 1581 were 

 substitutions for large cut stumps inside plot, as described in methods. 



of successful establishment came at different times in 

 different plots. Each plot, except the youngest stand 

 (B-1), also had one long period of 50 to 100 years with- 

 out successful pine establishment. These, too, occurred 

 at different times in different plots, suggesting the 

 causes were not regional phenomena. Presumably 

 the periods without new pine establishment occurred 

 when the site was already too heavily stocked to allow 

 recruitment of a shade-intolerant species or when 

 most of the pine regeneration was killed by fires, per- 

 haps partly because of suppression by the overstory 

 (Cooper 1960). 



The overstory Douglas-fir in the dry-site stands 

 with many-aged structures also became established 

 during extended periods, not necessarily coinciding 

 with periods of pine establishment. In plot B-1 most 

 of the Douglas-fir regenerated during the exception- 

 ally long fire interval between about 1756 and 1839. 



Because of extensive heart rot, many of the apparently 

 old Douglas-fir could not be aged. Thus, the continuity 

 of Douglas-fir establishment throughout the 1500-1900 

 period may be underestimated in some plots (table la). 

 Experimental (Kalabokidis and Wakimoto 1992) and 

 observational evidence (Arno 1988) indicates that 

 seedlings and saplings of pine are more fire-resistant 

 than those of Douglas-fir. Such differential fire resis- 

 tance might be a factor in the greater continuity of 

 ponderosa pine regeneration between 1500 and 1900 

 as compared to Douglas-fir. In all plots most of the 

 oldest trees were ponderosa pine. The greater average 

 age of ponderosa pine compared to Douglas-fir may be 

 linked to pine's ability to seal fire wounds with pitch; 

 the less-pitchy Douglas-fir usually develops extensive 

 rot as a result of multiple fire scars. 



Much of the present overstory on the two adjacent 

 plots, L-1 and L-2, regenerated in a wave between 



8 



