State 1
Reference

Community 1.1
Old-growth forest

This community phase represents the most successionally advanced community for this ecological site and is largely absent. It can be characterized by an open, old-growth forest of white fir and Jeffrey pine with a multi-tiered forest beneath. Ages exceeded 125 years. White fir may reach maximal ages of 300-400 years. Jeffrey pine often lives to maximal ages of 400 or 500 years and is somewhat less likely to succumb to stress from drought and pests. Incense cedar was a common associate but of limited extent. Common shrubs likely included huckleberry oak, whitethorn ceanothus, greenleaf manzanita (Arctostaphylos patula), prostrate ceanothus (Ceanothus prostratus), creeping snowberry (Symphoricarpos mollis), gooseberry (Ribes spp.), and bush chinquapin (Chysolepis sempervirens).

Low to moderate intensity fires with a return interval of 3 to 40 years likely controlled overall stocking/cover of overstory trees by periodically killing some of the thin-barked seedlings, saplings and pole-sized trees (particularly white fir and incense cedar). Overall cover of understory species was also influenced by periodic fires because of species equilibration with shade of the overstory canopy.

Community 1.2
Stand initiation

Figure 7. Whitethorn ceanothus 3 years after wildfire.

This shrubland community thrives in the new openings created by large crown fires that kill the majority of overstory trees. Huckleberry oak is a fire-adapted species that is highly flammable and vigorously resprouts from the root crown after fire (Howard 1992, Nagal and Taylor 2005, Odion et al. 2009). Whitethorn ceanothus will resprout following light to moderate severity fire, and after severe intensity fire regenerates from heat activated seed that may survive in the soil for more than 200 years (Nagal and Taylor 2005, Reeves 2006). Greenleaf manzanita vigorously resprouts from underground lignotubers, and regerates from heat scarified seeds that may survive in the soil for more than 400 years (Nagal and Taylor 2005, Hauser 2007). With rapid regeneration from root sprouts, and recruitment from on site seed stores, this shrubland can resemble preburn coverage in 7 to 9 years (Risser and Fry 1988).

The size and the intensity of a burn may influence the shrub expression. Shrubs have been associated with large burn size, whereas trees were not able to establish across the landscape (Royce and Barbour, 2001). Shrubs can prevail in areas prone to frequent fire, such as ridges and wind tunnels. Greenleaf manzanita is a strong competitor for water. It continues to deplete water after conifer species have gone dormant for the drought season. This competition for water and sunlight between the shrubs and conifer seedlings can delay the establishment of a forest (Royce and Barbour 2001). The shrub community may persist for 50 years or more.

The surviving overstory trees are a valuable source of seed for tree regeneration. Seeds are dispersed downwind at approximately twice the height of the source tree, possibly farther under windy conditions. Jeffrey pine seed is also cached by squirrels and chipmunks, which aid in dispersing the seed. Studies have shown that Jeffrey pine seed germination and seedling survival is greater for cached seeds that have been buried in soil rather than for windblown seeds deposited on the surface.

Forest overstory.Canopy cover of remnant overstory trees surviving the causal disturbance may be up to 10 percent.

Forest understory. Shrubs varies in composition and cover as they dominate the area several years after disturbance. Tree regeneration typically is slow to infill in openings in shrub cover.

Community 1.3
Young forest

Figure 8. Community Phase 1.3

This is the most common community phase in the Lake Tahoe Basin. The community phase consists of white fir-Jeffrey pine stands with two to three layers, 40 to 60 percent canopy cover, and tree ages ranging from 30 to 125 years. It developed under natural succession with recurring low to moderate surface fires affecting overstory species canopy and composition as well as the amount of understory. Many of the communities in this phase are managed forests, with manual thinning and prescribed burns used to remove white fir and allow for more predominance of Jeffrey pine. The removal of some of the understory creates a somewhat more open forest with less competition between trees.

Forest overstory.This forest community phase is dominated by an even-aged stand of white fir and Jeffrey pine. The trees range from 30 to 125 years old. Canopy cover ranges from 40 to 60 percent, with an average of 50 percent cover. Incense cedar is common in the canopy and the understory with low cover.

Forest understory. The understory cover and diversity increases as the overstory canopy decreases. Average shrub cover is 15 to 45 percent, and huckleberry oak (Quercus vaccinifolia), whitethorn ceanothus (Ceanothus cordulatus), prostrate ceanothus (Ceanothus prostratus), and greenleaf manzanita (Arctostaphylos patula) are common species. Forb cover is low, averaging 3 percent. lambstongue ragwort (Senecio integerrimus and Brewer's fleabane (Erigeron breweri) are the most frequently present species, but a range of other forbs may be present at a given site. Grass cover is low, at less than 1 percent.

Community 1.4
Young forest infilling

This community phase begins with pole-sized white fir and Jeffrey pine, which eventually mature reaching 100 feet or taller. The age range for the phase is 30 to 125 years with a second story of trees developing beneath with ages down to 15 years. Canopy cover increases to 65 to 85 percent. White fir continues to reproduce and grow better in the understory than Jeffrey pine, so with time this forest will become dominated by white fir. This community phase is defined by a dense canopy and high basal area. The trees are often overcrowded and competition for water and nutrients increases stress, making this phase susceptible to death from pests and drought. Wildfire, if and when it occurs, will be severe due to the deep accumulation of litter, standing dead and down trees, and dense multi-layered structure of the forest. Decimation of the majority of trees can be expected. Forest understory is very sparse to absent.

Forest overstory.Young white fir and Jeffrey pine are mixed in the developing canopy. Combined canopy cover begins at 25 percent and increases to 65 to 85 percent. Tree regeneration continues throughout this phase, and if not removed by fire, overall stand density will increase. White fir continues to reproduce and grow better in the understory than Jeffrey pine, so with time this forest will become dominated by white fir.

Forest understory. The understory is densely shaded and covered with woody debris, which inhibits most vegetative growth other than white fir seedlings.

Community 1.5
Old-growth forest infilling

Figure 9. Community Phase 1.5

This community is defined by a dense canopy and high basal area of older white fir (125+ years in age). Canopy cover ranges from 60 to 90 percent including lower tree canopy stories. The trees are often overcrowded and stressed due to competition for water and nutrients, which makes this phase susceptible to death from pests and drought. Wildfire, if and when it occurs, will be severe due to the deep accumulation of litter, the standing dead and down trees, and dense multi-layered structure of the forest. Decimation of the majority of trees can be expected. Forest understory is very sparse to absent.

Forest overstory.White Fir dominates this forest with a dense canopy and multiple tree layers. Jeffrey pine is a common associate while incense cedar are occasionally present but with low cover.

Forest understory. The understory is very sparse to absent and typically only white seedlings are present.

Pathway 1.1a
Community 1.1 to 1.2

In the event of a severe canopy fire or a clear-cut and prescribed burn, the reference community phase would quickly transition to the stand initiation phase, 1.2.

Pathway 1.1b
Community 1.1 to 1.5

If low to moderate periodic fires are excluded from this community phase, tree density will continue to increase, favoring high stocking of shade-tolerant species (white fir and incense cedar) in lower and eventually mid-level canopy layers (phase 1.5).

Pathway 1.2a
Community 1.2 to 1.3

Stand initiation

Young forest

Time and growth of Jeffrey pine and white fir (tree age approximately 30 years) advances to a somewhat more closed-canopy, larger diameter forest (community phase 1.3) that may have two to three developing overstory canopy layers. A natural low to moderate intensity fire regime is assumed (return interval of about 4 to 12 years) which influences infill of additional species such as shade-tolerant white fir and possibly incense cedar. In the absence of recurring low to moderate intensity fires, manual thinning with prescribed burns can progress the forest to community phase 1.3.

Pathway 1.2b
Community 1.2 to 1.4

If low to moderate periodic fires are excluded from this community phase, tree density will continue to increase favoring high stocking of shade-tolerant species (white fir and some incense cedar) in lower and eventually mid-level canopy layers (phase 1.4).

Pathway 1.3a
Community 1.3 to 1.1

Time and growth of forests in this community phase allow development towards the reference community phase 1.1, as long as a natural low to moderate surface fire regime occurs. Partial tree mortality from pest outbreaks is another disturbance moving stands towards conditions of community phase 1.1. With control or suppression of fire and pests, manual thinning or prescribed burning can be implemented to emulate natural disturbances.

Pathway 1.3b
Community 1.3 to 1.2

Young forest

Stand initiation

In the event of a crown fire which decimates the majority of overstory trees or patch cutting, this community moves quickly to community phase 1.2.

Pathway 1.3c
Community 1.3 to 1.4

If low to moderate periodic fires are excluded, and other thinning management does not occur, tree density will continue to increase, favoring high stocking of shade-tolerant species (white fir and some incense cedar) in lower and eventually mid-level canopy layers (moving towards community phase 1.4).

Pathway 1.4b
Community 1.4 to 1.2

Should a wildfire occur, the density of ground and mid-canopy fuels create potential conditions for a high intensity canopy fire. A severe fire would move this phase quickly to 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 fuel loading. 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 treatment to thin out the white fir and fuels in the understory including the use of prescribed burns could be implemented to shift this forest to community phase 1.3. A partial mortality disease or pest infestation could also create a shift towards community phase 1.3.

Pathway 1.4a
Community 1.4 to 1.5

If fire continues to be excluded this community phase progresses to an older 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 recurring surface fires. Manual treatment to thin out the understory trees and fuels including prescribed burns could be implemented to shift this forest to the reference community phase 1.1. A partial mortality disease or pest infestation of white fir could also create a shift towards community phase 1.1.

Pathway 1.5a
Community 1.5 to 1.2

Old-growth forest infilling

Stand initiation

Should a wildfire occur, the potential for a severe crown fire is likely with decimation of the majority of trees. Such a fire would move this phase quickly to community phase 1.2.