State 1
Reference

Community 1.1
Jeffrey pine-California red fir/needlegrass/lupine

This community phase is considered to be the likely future reference community phase. It is difficult to determine the exact species that will dominate this community phase. Within the Devastated Area Jeffrey pine (Pinus jeffreyi), white fir (Abies concolor), California red fir (Abies magnifica), and western white pine (Pinus monticola) coexist. It is likely that the upper elevation tree species (California red fir and western white pine) will not persist on the lower elevation debris flows and will be replaced by a Jeffrey pine-white fir forest. California red fir and western white pine may persist at the upper elevations of this site.

There are a few areas with older debris deposits mapped in the Manzanita Lake drainage. The older areas have developed mature Jeffrey pine or Jeffrey pine- California red fir forests. A small portion of the older debris material is located at higher elevations and is currently vegetated with dense California red fir thickets. The California red fir forests would normally be considered a separate ecological site, but is not in this case since the extent of debris deposits at upper elevations is minimal. The upper slope of the eruption is generally associated with debris flows, rather than debris fans and deposits. The ecological site associated with the upper elevations is F022BI115CA, a California red fir western white pine forest.

This community phase is maintained by low and moderate intensity fires that remove fire intolerant seedlings and saplings from the understory. Moderate intensity fires can kill some of the overstory trees as well, leaving canopy openings that are favorable for Jeffrey pine and western white pine regeneration. These moderate intensity fires breakup the uniformity of the older stands with pockets of young forests intermixed.

Forest overstory.Expected ovestory canopy will range from 35 to 65% with the possibility of multiple canopies beneath ranging from 5 to 15% cover. Age would be 125+ years and 60-125 years for lower tree canopies.

Forest understory. A number of species could develop with needlegrass and lupine expected.

Community 1.2
Jeffrey pine-California red fir-lodgepole pine/needlegrass/lupine

This regeneration community phase develops after a severe crown fire. It differs from primary succession because the soil has developed structure and accumulated organic matter, providing nutrients in the upper horizon. Seeds may be onsite that survived the fire, allowing tree seedlings, grasses, and forbs to establish quickly. The few surviving canopy trees are a valuable source of seed for tree regeneration. Nearby trees disperse their seed downwind to distances about twice their height, and possibly farther under windy conditions.

Forest overstory.Developing seedlings and saplings of Jeffrey pine, California red fir and lodgepole pine.

Forest understory. Forbs and grasses develop concurrently with the trees and include needlegrass and lupine.

Community 1.3
Jeffrey pine-California red fir-lodgepole pine/needlegrass/lupine

As this community phase develops during primary succession Jeffrey pine, white fir, California red fir and/or western white pine overtop the older but shorter Sierra lodgepole pines, and the understory is covered with a thin layer of pine needles. A young forest develops with several canopy layers.

This community phase also represents the young forest that would develop from community 1.2 the post fire conifer regeneration community. The conifer species diversity may be higher after primary succession than secondary succession. Seedling establishment and forest structure will most likely develop quicker during secondary succession because the soil has developed better structure, accumulated organic matter, microbes, and other physical properties which enhance seedling survival and plant growth.

This community phase develops over time and benefits from low to moderate intensity fire to maintain an open forest structure. The fires kill many of the young fire-intolerant seedlings in the understory, which reduces the competition between trees and lowers the potential for a severe canopy fire. The structure, composition, age, and moisture of this forest at the time of fire would determine the fire intensity and extent of damage to the young trees. Slope position, season of burn, and aspect also affect fire intensity and frequency.

Forest overstory.Total forest canopy cover ranges from 25 to 65 percent. Jeffrey pine and white fir are dominant.

Forest understory. Needlegrass and lupine are represented among other understory species.

Community 1.4
California red fir-Jeffrey pine/litter

Jeffrey pine and either California red for or white fir dominate over the Sierra lodgepole pines, with heavy recruitment of California red fir or white fir in the understory.

This community phase is defined by a dense canopy and high basal area of mixed conifers. Canopy cover ranges from 55 to 75 percent. The trees are overcrowded and often diseased and stressed due to competition for water and nutrients, making them more susceptible to death. Fire hazard is high in this community phase due to the deep accumulation of litter, the standing dead and down trees, and the dense multi-layered structure of the forest.

Community 1.5
California red fir-Jeffrey pine/litter

This community phase develops with the continued exclusion of fire. Depending upon the microclimate, seed source, snow load, elevation and other variables, California red fir or white fir will tend to dominate during this phase. They eventually shade out the associated pine species. This community is defined by a dense canopy and high basal area. Canopy cover ranges from 60 to 95 percent. The trees are overcrowded and often diseased and stressed due to competition for water and nutrients. The understory is almost absent because of lack of sunlight on the forest floor. Fire hazard is high in this community, caused by the deep accumulation of litter, standing dead and down trees, and the dense multi-layered structure of the forest.

Pathway 1.1a
Community 1.1 to 1.2

If this forest has a severe canopy fire, it will initiate forest regeneration (Community 1.2).

Pathway 1.1b
Community 1.1 to 1.5

This pathway is created when fire is excluded from this old growth community. White fir and/or California red fir continues to regenerate in the understory, increasing tree density and shifting this community toward the closed fir and Jeffrey pine forest (Community 1.5).

Pathway 1.2a
Community 1.2 to 1.3

The natural pathway is to community phase 1.3, a young open Jeffrey pine and fir forest. This pathway is followed with natural fire regime. Manual thinning with prescribed burns can imitate the natural cycle and lead to the same open community phase.

Pathway 1.2b
Community 1.2 to 1.4

An alternate pathway is created when fire is excluded from the system and leads to the closed red fir and Jeffrey pine forest (Community Phase 1.4).

Pathway 1.3a
Community 1.3 to 1.1

This is the natural pathway for this community phase, which evolved with a historic regime of relatively frequent surface and/or moderate severity fires, and/or partial tree mortality from a pest outbreak. This pathway leads to the mature Jeffrey pine and fir forest (Community Phase 1.1).

Pathway 1.3b
Community 1.3 to 1.2

A severe canopy fire would initiate forest regeneration (Community Phase 1.2).

Pathway 1.3c
Community 1.3 to 1.5

If fire does not occur, then the density of the forest increases. The increased density shifts this community phase toward the closed fir and Jeffrey pine forest (Community Phase 1.5).

Pathway 1.4b
Community 1.4 to 1.2

At this point, the density of ground fuels and the mid-canopy ladder fuels create conditions for a high intensity canopy fire. A severe fire would initiate forest regeneration (Community Phase 1.2).

Pathway 1.4c
Community 1.4 to 1.3

The natural event of a moderate or surface fire in this forest is unlikely due to the high fuels. Considerable management efforts would be needed to create the open forest conditions that should exist in this forest if it had developed with fire over time. Manual treatments to thin out the white fir and fuels in the understory, and/or prescribed burns, could be implemented to shift this forest back to its natural state of a young open mixed conifer forest (Community Phase 1.3). A partial mortality disease or pest infestation could also create a shift toward Community Phase 1.3 but with an increase to the already high fuel amounts.

Pathway 1.4a
Community 1.4 to 1.5

If fire continues to be excluded from this system, the mature closed fir and Jeffrey pine forest develops (Community Phase 1.5).

Pathway 1.5b
Community 1.5 to 1.1

The natural event of a moderate or surface fire in this forest is unlikely due to the high fuels. Considerable management efforts would be needed to create the open forest conditions that should exist in this forest if it had developed with fire over time. Manual treatments to thin out the understory trees and fuels, and/or prescribed burns, could be implemented to shift this forest back to its natural state of an open Jeffrey pine and fir forest (Community Phase 1.1). A partial mortality disease or pest infestation could also create a shift toward Community Phase 1.1 but tree mortality will increase the already high fuel amounts.

Pathway 1.5a
Community 1.5 to 1.2

At this point a severe fire is likely and would initiate forest regeneration (Community Phase 1.2).

State 2
Primary succession

Community 2.1
Debris deposits-primary succession

The 1915 eruptions of Lassen Peak left large swaths of debris material. This material has been subject to the slow processes of primary succession described in the ecological dynamics above.

Historic photos and research data reveal a 30 year delay in conifer establishment on the lahar and debris flow. The delay in conifer establishment could be due to several factors including:

1. The proximity to a nearby seed source.
2. Thick layers of ash may have inhibited tree establishment until the ash was washed away or weathered.
3. The trees may have been physiologically stressed to soil infertility (Kruh et al, 2000).

The dissemination of conifer seed and seedling establishment began from the periphery of the devastated area and has been moving inward. The intact forests adjacent to the debris flows provided the seeds for early colonization. As the forest on the periphery developed, more seed was produced and disseminated further into the debris flows. Heath, 1967 reports that strong winter winds come from the southwest, which would bring seed from the upper elevation forests dominated by red fir and western white pine and deposit them on the devastated area. Jeffrey pine and white fir seed would be blown away from the majority of the devastated area under this scenario. With normal wind conditions Jeffrey pine, red fir, white fir, Sierra lodgepole pine and western white disperse seed within 200 feet of the source. One report states that western white pine seed can be windblown over 2,000 feet. In addition to the wind, animals often cache the pine seeds. The presence of Sierra lodgepole pine in the early succession may be in part due to its high production of viable seeds, and the tolerance of the seedlings to open sunlight (Cope, 1993; Jenkinson, 1990; and Zouhar, 2001.).

After the 30 year delay, Sierra lodgepole pine was the initial invader, with Jeffrey pine, red fir and western white pine generally establishing later. However, Heath states that due to the complex interactions of seed dispersal, microsite characteristics, and climatic and other environmental variables, it is difficult to define a clear successional trend or even to determine the historic reference community phase.

With time, primary succession continues as conifers increase in abundance and size.

Community 2.2
Lodgepole pine forest development-primary succession

This community phase slowly develops as conditions become more hospitable for tree growth. The trees that established on the barren debris deposits have produced some litter accumulation, shade, and have reached reproductive maturity. Sierra lodgepole pine is the dominant tree and is about 10 to 12 feet tall. Total canopy cover may reach up to 35 percent. The ground is mostly bare of organic matter except directly under the young lodgepole pines. White fir or California red fir seedlings are present in the shadow of the lodgepole pines. The understory is limited, with some scattered forbs on the bare soil. There may be a range in tree age due to the continual establishment of seedlings in the open areas. As time progresses, forest canopy and structure develops. When this community phase develops it eventually becomes a forest capable of spreading fire and will undergo frequent natural understory burns.

As forest structure develops, this forest resembles the young Jeffrey pine-fir forest (Community Phase 1.3 in the state and transition model) and follows the same community phase pathways.

Pathway 2.1a
Community 2.1 to 2.2

Seedlings and saplings making the barren, primary conifer community phase succeeds to a more developed predominantly lodgepole pine forest. Canopy at 0 to 15% slowly develops to 15 to 35% with concurrent infill of forbs and sub-shrubs.

Transition T2a
State 2 to 1

As forest structure develops, this forest resembles the young Jeffrey pine-fir forest (Community Phase 1.3)and follows the same community phase pathways. The forest matures in both cover and species diversity.