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Table 4 Summary of transitions, frequency of transitions, sources of information used, and assumptions used to develop the frequency of transitions and their projected effects in the model. This table assumes no projected change in climate. The last section of this paper describes how to modify the models to incorporate the effects of projected climate change.

From: Evaluating the Ecological Sustainability of a Ponderosa Pine Ecosystem on the Kaibab Plateau in Northern Arizona

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database of management activities recorded on the planning unit from 1985 through 2006 (M. Pitts, Forest Service, unpublished data)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Insect and disease transitions were quantified using data from 1918–2006 (A. Lynch, Forest Service, unpublished report).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.