menziesii) (Morrison and Swanson 1990), giant se- 

 quoia (Sequoiadendron giganteum)-mixed conifer 

 (Stephenson and others 1991), red fir (Abies mag- 

 nifica) (Taylor 1993), and red pine-white pine {Pinus 

 resinosa-P. strobus) (Heinselman 1981). 



On both dry and moist sites, an understory of 

 Douglas-fir developed after fires were suppressed. 

 Similar understories may have developed occasion- 

 ally in some stands during the longest pre-1900 fire 

 intervals, which ranged from 41 to 97 years in our 

 stands and were about twice as long as the mean fire 

 intervals. Today, however, a large proportion of the 

 serai ponderosa pine type has been without fire for 

 periods exceeding former maximum intervals (Agee 

 1993; Amo 1988; Swetnam 1993), and succession has 

 also been advanced by removal of overstory pine and 

 larch trees. 



Recent management direction for National Forest 

 lands in the Western United States has focused on 

 designing treatments that are consistent with natu- 

 ral processes (Overbay 1992; Risbrudt 1992). This 

 management approach also seeks to maintain a range 

 of forest composition and structure somewhat similar 

 to that of presettlement forests. Reintroducing fire 

 alone will not restore most old growth stands because 

 of imprecedented accumulations of duff and ladder 

 fuels. The dense understories, including many trees 

 whose crowns extend into the overstory canopy, can- 

 not now be killed by fire without damaging the old 

 growth trees (Harrington 1991). Growth and vigor of 

 the old trees also have declined noticeably in many 

 stands while mortality has increased. A comparison 

 of growth from the most recent 50 years (1942-1991) 

 and an historic period (1851-1900), on overstory trees 

 in our six dry site plots indicates significantly greater 

 growth in the two plots that had fires since 1900 

 (Fiedler and others 1994). Slower growth and declin- 

 ing vigor in the four plots without fire are presum- 

 ably related to increased understory and stand basal 

 area density, and reduced nutrient availability. 



In the past, fi^equent underburns helped maintain 

 both uneven-aged and even-aged serai ponderosa pine 

 forests. Effects of these disturbance regimes suggest 

 that, to restore a semblance of self-perpetuating pine, 

 it will be necessary to reduce the understory mechani- 

 cally and thereafter control understory development 

 using prescribed fire. Periodic burning can remove 

 most Douglas-fir up to 4 inches in diameter and grand 

 fir of somewhat larger size (Kilgore and Curtis 1987). 

 If the stand is opened significantly (for example, re- 

 ducing basal area to about 40 to 60 square feet per 

 acre), natural or planted pine and larch could become 

 established (Fiedler and others 1988). If annosus 

 root disease (Heterobasidion annosum) is suspected, 

 a pathologist should be consulted before planning 



silvicultural treatment (Hawksworth and Shaw 1988). 

 Subsequent treatments through the use of selective 

 thinning and carefully applied prescribed burning, at 

 intervals of perhaps 20 to 25 years could favor these 

 serai trees over competing fir regeneration. 



BecaTise of prolonged fire exclusion, reintroduction 

 of fire must be done carefully, perhaps with successive 

 low-intensity bums, to prevent damage to old growth 

 trees (Harrington 1991; Harrington and Sackett 1992). 

 When reintroducing fire after a long period of exclu- 

 sion, some risk to old growth trees is unavoidable. In 

 some old growth stands, tree health is so poor that 

 major mortality will probably occur regardless of treat- 

 ment. Nevertheless, treatments that create openings 

 and establish regeneration of serai species will be 

 beneficial in the long term. Conversely, if prescribed 

 fire and fuels management are not initiated, loss of 

 ponderosa pine from the stand is virtually assured 

 due to successional replaceinent; this is often accompa- 

 nied by insect or disease epidemics and severe wUdfire 

 (Amo and others 1985; Keane and others 1990). 



A different sort of management challenge is implied 

 by knowledge that occasional stand-replacement 

 events were responsible for an even-aged ponderosa 

 pine stand stmcture in the Swan Valley study sites 

 on the Flathead National Forest. There is a need to 

 discover what natural conditions predisposed these 

 stands to these disturbances and allowed ponderosa 

 pine to reestablish itself as the major species. The 

 result of modem stand-replacing fires in both dry 

 and moist sites tends to be greater regeneration of 

 Douglas-fir (Amo and others 1985; Keane and others 

 1990). Unlike the pre-1900 replacement fires on the 

 Swan Valley sites, however, modem wildfires are oc- 

 curring after long periods of logging and successional 

 replacement of ponderosa pine across the landscape. 

 This has reduced the amount of pine seed source and 

 increased seed source for late-successional species. 

 Conversely, prior to 1900 underbums at 20 to 30 year 

 mean interveds would have helped maintain pine dom- 

 inance by removing much of the small Douglas-fir. 

 Thus, when a stand-replacing fire eventually occurred, 

 pine was the primary tree surviving at the periphery 

 of heavily burned patches of forest, and was able to 

 reseed much of the area. 



Today it may be undesirable to have stand-replacing 

 fires in the small natural areas that remain in this 

 ecological type. Fuels management with silviculture 

 and prescribed fire could be used to maintain pine and 

 larch while preventing replacement fires. Some of the 

 large even-aged ponderosa pine plantations on clear- 

 cuts in the Swan Valley could be converted gradually, 

 with the application of prescribed fire at 20 to 30 year 

 intervals, to old growth similar to the even-aged pre- 

 1900 stands on these sites. 



22 



