Conifer Regeneration after Forest Fire in the Klamath-Siskiyous: How Much, How Soon?

regime and have led to changes in forest structural characteristics (Agee 1993, Sensenig 2002). High-severity, stand-replacing fires also have been known in this region, where complex topography and fire behavior typically resulted in a patchy distribution of canopy openings, intact stands, and scattered surviving trees (Wills and Stuart 1994, Alexander et al. 2006). The prognosis of forest recovery after high-severity forest fire is uncertain. A history of regeneration failures after fires and logging raised concerns over the long-term sustainability of conifer forests in the region (Hobbs et al. 1992). Large brushfields dominated extensive areas in southwest Oregon in the mid-20th century and may have resulted from fires set by early settlers, ranchers, and miners (Hayes 1959). Limited conifer regeneration over long periods (10–50 years) fostered concerns that such areas would remain unforested indefinitely (Gratkowski 1961). Additional regeneration failures occurred after clearcut harvesting, and attempts to improve the regeneration environment through shelterwood cutting had mixed results (Stein 1986). Given this history of uncertainty, questions arose as to whether conifers would regenerate after the high-severity forest fires of recent times. Fears emerged that the brushfields common to the Klamath-Siskiyous highland in the early 1900s (Hayes 1959, Gratowski 1961) would become a dominate feature of the forests of the 21st century as well (Sessions et al. 2004). Of particular concern was the competitive advantage of broad-leaved shrubs and hardwoods that may result after the removal of the conifer overstory by fire. Hardwoods, particularly tanoak (Lithocarpus densiflora), madrone (Arbutus menziesii), and oaks (Quercus spp.), resprout vigorously after fire (Brown and Smith 2000). The rapid growth of seed-bank species such as Ceanothus and their association with nitrogen-fixing bacteria can lead to extensive shrub cover in early successional communities in the region (Hanson and Stuart 2005). Without active reforestation, conifers may have little or no window for regeneration amid the rapidly growing shrubs and hardwoods (Hobbs et al. 1992, Sessions et al. 2004). Along with competition for moisture and growing space, high levels of seed predation and high surface soil temperatures result in high mortality rates within the 1st year (Minore and Laacke [1992] and references therein). Extensive research has documented the advantage of planting conifers and controlling shrubs to increase tree density and growth over the early years of stand development (Hobbs et al. 1992, Zhang et al. 2006). Today, many postfire action plans regard treeplanting and vegetation control as a relatively straightforward and effective solution to the problem of forest renewal (Lindenmayer 2006). Little is known about how burned areas will recover on their own, how they might differ from stands managed after fire, or how these differences relate to the rate of forest recovery after fire over the short term (1–2 years) or longer (1–2 decades) time frames. The lack of information concerning ecosystem recovery, specifically natural conifer regeneration after wildfires, has allowed speculation on complex ecological processes. For example, in a recent 2-year study of conifer survival with and without salvage logging in southwest Oregon, Donato et al. (2006) concluded that postfire management activities 2 years after a fire killed most natural tree regeneration and may be counterproductive to forest recovery. This conclusion contradicted recommendations of a recent policy analysis for southwest Oregon, which argued that burned areas can develop into unproductive shrub fields that persist for “decades, perhaps centuries” and that postfire salvage logging and treeplanting would speed the recovery of complex conifer forests and provide revenue from timber extraction (Sessions et al. 2004). We report here on the abundance of natural regenerating conifers occupying sites 9–19 years after stand-replacing wildfires in northern California and southwest Oregon. Our findings redefine concepts of the role and reliability of natural regeneration in high fire frequency systems in the context of ecosystem management (Christensen et al. 1996). Additionally, they highlight the role of temporal and spatial variation as an inherent feature of forest development. Forest managers relying on natural regeneration should feel increased confidence and need to develop plans that can accommodate high levels of variation and accept the prolonged time line of the regeneration process.