revealed that fires had occurred in each of these Bitter- 

 root plots at average intervals of about 50 years over a 

 300-year period ending with the 1889 fire (fig. 2). Fire 

 history literature and ecological process modeling of 

 serai ponderosa pine (Keane and others 1990) sug- 

 gested that a 50-year average fire interval is near the 

 maximiun that would edlow perpetuation of pine as 

 a major stand component, when in competition with 

 Douglas-fir. 



The three Lolo National Forest plots are located at 

 about 5,000 ft elevation on south-facing slopes, within 



the broad forest zone dominated by serai ponderosa 

 pine (fig. 1). We established one plot (L-3) at the 

 head of Whitehorse Gulch in the Fish Creek drain- 

 age west of Missoula and two other plots on a com- 

 parable south slope above Sawmill Creek, 8 miles to 

 the east. One of the Sawmill plots (L-1) had burned 

 in a 1953 lightning-caused underburn, still identifi- 

 able by charred bark extending several feet up on 

 many of the trees. The other plot (L-2) did not bum 

 because it was just across the fire control line. Plot 

 L-1 was unusual in having had surface fires nearly 



2000 



1900 



- •1889 •1889 



(D 



i£ 1800 



CO 



> 



T3 

 CO 



E 



1700 



w 

 LU 



• 1869 ^1869 ^1871 

 • 1852 



- ^1822 •1822 



•I ana 



• 1793 ^1793 



1600 



Lolo N.F. 



Bitterroot N.F. 



1 2 



•1953 



• 1919 ^1919 



Flathead N.F. 

 ~ 2 



•T897~ 



• 1908 



• 1889 ^1689 ^1689 ^1891 



• 1870 



• 1853 



• 1871 



• 1858 



• 1839 



- ^1751 ^1751 

 • 1734 •I 734 



• 1777 



• 1748 



• 1727 



• 1705 



► 1804 



• 1756 •1756 •1756 



• 1719 ^1719 ^1719 



• 1843 



• 1837 



• 1830 



• 1824 



#lflOJ_ 



•1796 



•1786 



• 1780 

 •1774 



•1760 

 •1750 

 •1742 



•1723 

 •1714 



• 1889 



• 1861 

 •1850 •I 850 



• 1839 



•1812 



• 1768 



• 1759 



• 1744 



• 1817 



• 1696 •1696 •1698 

 • 1687 



- ^1652 ^1652 



_ •1633 ^1633 •ISSe 



»1682 •1682 ^1682 



M631 ^1631 ^1631 



• 1673 



• 1658 



• 1649 



• 1638 



• 1678 



• 1670 



• 1660 



•4601— 



•1596 



•1559 



1500 



32 31 26 



Pre-1 900 mean tire interval, years 



47 52 50 13 



31 18 



Figure 2— Fire history from each detailed plot based on fire scar cross-sections. 



3 



