Transition type | Transition frequency or length | Sources | Assumptions |
---|---|---|---|
Fuel build-up | After 25 years of uninterrupted growth | The cessation of surface fires around 1880 and the resulting accumulation of fuels (Covington and Moore 1994, Swetnam and Baisan 1996, Allen et al. 2002, Fulé et al. 2003) | It would take approximately 25 years since the last fire or management activity mimicking fire to move from an open canopy state (<30 % canopy cover) to a higher canopy state (>30 %). |
Wildland fire | Frequencies for nonlethal, mixed severity and stand replacing fire are based on empirical data in sources column. | Fire history data on the planning unit for the period 1960 through 2005 | Projected fire frequencies will be the same as those experienced the last half century. |
Management activities | Frequencies for management activities (fires and thinning) are based on empirical data in sources column. | Forest Activities Tracking System (FACTS) database of management activities recorded on the planning unit from 1985 through 2006 (M. Pitts, Forest Service, unpublished data) | Projected frequencies of prescribed burning, other fuels treatment, and harvest thinning will be the same as those experienced the last half century. |
Insect and disease | Frequencies for insects and diseases incidence are based on empirical data in sources column. | Insect and disease transitions were quantified using data from 1918–2006 (A. Lynch, Forest Service, unpublished report). | Projected frequencies of insect and disease incidence will be the same as those experienced since 1950. |
Regeneration from seed | Varies between 0 and 9 % per hectare per year after stand replacing fire | Savage and Mast (2005) | Projected frequencies of seedling recruitment are the same as those observed in the recent literature and in the planning area. |
Plant growth | 40 years between states | Transitions among model states are taken from silvicultural data summarized by Reynolds et al. (1992). | We assume that transitions between states (for example, from seedling and sapling to young forest, from young to mid-age forest) take 40 yr. |