Ecological dynamics
This ecological site consists primarily of a forest of Sierra lodgepole pine. It is more common in the southern portion of the Lake Tahoe Basin, especially within the Upper Truckee River and Trout Creek drainages. It is currently found in narrow strips between wet meadow areas, and in drier white fir-Jeffery pine forest. The moist meadow vegetation can be found in the understory. Some wetland plants are also found in this area due to the seasonally high water table of 12 inches.
The presumed historic most successionally advanced community phase is identified as Sierra lodgepole pine/Lemmon’s willow (Salix lemmonii). This phase likely consisted of multi-aged stands with areas of large older open Sierra lodgepole pines with intermixed small areas of dense young seedlings. White fir (Abies concolor), Jeffrey pine (Pinus jeffreyi) and incense cedar (Calocedrus decurrens) were occasionally present.
Sierra lodgepole pine can tolerate harsher conditions than many other conifers—especially cold, light, heat, drought, saturation, and hardpan soils (Kocher, 2005; Lotan and Critchfield, 1990). On these montane sites, lodgepole pine grows in the cold air drainages (Agee, 1994). They are moderately tolerant to shade and competition. The thin bark and shallow root systems of lodgepole pine makes it susceptible to fire and windfall (Lotan and Critchfield, 1990). Prolonged drought and flooding can kill the trees or make them vulnerable to disease and pest outbreaks.
Fire can play an important role in thinning and renewing Sierra lodgepole forests. Studies on fire frequency in Sierra lodgepole pine forests vary from 20 to 200 years, depending on location, elevation, and precipitation (Cope, 1993; Murphy and Knopp, 2000). This area has moderate precipitation, is at mid-elevations, and has seasonal wetness. The fire interval for moderate or severe fires was likely between 70 to 100 years, and was heavily correlated with mountain pine beetle infestations and the decline of the overstory trees. Sierra lodgepole pine is the only non-serotinous lodgepole pine. Therefore it does not need fire to open its cones to release seeds. In addition to a natural fire regime, it is believed the Washoe Tribe used fire to preserve meadow environments and to keep the forests open (Murphy and Knopp, 2000).
Human disturbance regimes have altered the historic community phase and its natural cycles. Much of the lodgepole pine forest terrain was clear-cut during the Comstock era from the mid-1870s to the mid-1890s although small scale logging occurred in sections from 1911 to the 1970s (Murphy and Knopp, 2000). Intense sheep and cattle grazing began as early as 1850, especially in the meadows. In 1924, fire exclusion became national policy (Murphy and Knopp, 2000), which led to an increase in forest density as well as the buildup of fuel in both the overstory and the understory. These disturbances and fire exclusion created lodgepole pine forests which are generally young, overcrowded, and do not necessarily resemble the historic forest.
The reference state consists of the most successionally advanced community phase (numbered 1.1) as well as other community phases that result from natural and human disturbances. Community phase 1.1 is deemed the phase representative of the most successionally advanced pre-European plant/animal community including periodic natural surface fires that influenced its composition and production. Because this phase is determined from the oldest modern day remnant forests and/or historic literature, some speculation is necessarily involved in describing it.
All tabular data listed for a specific community phase within this ecological site description represent a summary of one or more field data collection plots taken in communities within the community phase. Although such data are valuable in understanding the phase (kinds and amounts of ground and surface materials, canopy characteristics, community phase overstory and understory species, production and composition, and growth), it typically does not represent the absolute range of characteristics nor an exhaustive listing of species for all the dynamic communities within each specific community phase.
Community 1.1
Mature forest
Figure 7. Community Phase 1.1
The historic most successionally advanced community phase was presumed to be open old-growth stands of predominantly Sierra lodgepole pine occasional scattered white fir, Jeffrey pine and incense cedar, with establishment of secondary conifers limited by frost and high water table levels. The age for this community is estimated to have ranged from 100 to more than 200 years between disturbances. Stand-replacing fires would have initially established an even-aged forest. However, minor disturbances, such as windfall and insect infestation would have eventually led to openings, tree regeneration, and a mosaic of developing small stands forming an overall multi-aged forest. The understory cover was probably moderate in the openings with Lemmon’s willow, grasses, and sedges making up the majority of species.
Forest overstory. The overstory in this multi-aged forest is open, rarely exceeding 65 percent canopy cover. Mature Sierra lodgepole pine dominates with a cover ranging from 35 to 65 percent, with an average of 45 percent. White fir, Jeffrey pine, and incense cedar are occasionally present with low cover.
Forest understory. The understory of these sites consists of primarily grasses and willows and species composition is variable. The open canopy allows a high diversity of herbaceous species and graminoids.
Community 1.2
Stand initiation
This community may be dominated for a short time by Lemmon’s willow, grasses and forbs. Lemmon’s willow can resprout from the rootcrown or stembase after a fire. Several species of grasses and forbs, including bentgrasses and bromes, may regenerate from seed. Willow and grasses can have a potentially high cover. Remnant overstory lodgepole pines may be present in limited numbers.
Sierra lodgepole pine will regenerate from wind dispersed seed. The seeds will readily germinate in the spring in the mineral soil exposed by fire or scarification but require moist soil and full sun to establish in the first season. The seedlings develop into pole sized trees, with up to 40 percent canopy cover.
Forest overstory. If there is ample moisture and sunlight, Sierra lodgepole pine seedlings will germinate in thick patches in the spring following a fire or clear-cut.
Forest understory. Native grases and lemmon's willow can have high cover in this area.
Community 1.3
Young forest
This phase is dominated by an overstory of young Sierra lodgepole pine forest. White fir may germinate during this time in the shade of the young lodgepole pine and small shrubs. The estimated duration for this phase is up to approximately 60 years. Canopy increases with age and growth slows near the upper age of the phase.
Community 1.4
Dense young forest
The dense phase of the young forest develops in the absence of canopy disturbance. Periods without fire, windthrow, or pest ourbreaks maintain a closed overstory canopy. White fir and incense cedar seedlings are more shade tolerant than lodgepole pine seedlings, which allows them to continue to reproduce in the understory of the lodgepole pine canopy. The density of white fir increases over time and creates competition with lodgepole pine for sunlight and water. This stress makes the forest more susceptible to death from pests and drought, which in turn increases the fuel loads and potential for severe fires.
It appears that this site is not a conducive environment for the optimal growth of white fir. This is primarily due to the properties of the soil, the high water table, and the high frequency of frost. However, in some areas within this site, white fir is present and reproducing well.
Community 1.5
Dense mature forest
The mature dense forest will develop with the continued exclusion of fire, allowing white fir to reach the upper canopy and gain dominance over lodgepole pine. Competition for water and sunlight will cause the health and vigor of Sierra lodgepole pine to decline. An estimated age for this community phase ranges from 60 to more than 200 years. However, drought, pest attacks and water table fluctuations are disturbances likely to decimate this phase.
Community 1.6
Mountain pine beetle epidemic
Standing dead Sierra lodgepole pine forests can result following disease or pest outbreaks, sometimes in combination with prolonged drought or flooding. Large patches of forest remain standing dead for many years until fire or manual treatment remove the dead trees and surface fuels. If surface fuels are not too high, grasses and forbs may grow in the understory and in openings.
Pathway 1.1a
Community 1.1 to 1.2
In the event of a severe canopy fire, or a clear-cut with or without a prescribed burn, phase 1.1 would quickly develop into phase 1.2, the stand initiation phase. Sierra lodgepole pine is susceptible to death from fire at any age because of their thin bark and shallow root systems (Kocher, 2005).
Pathway 1.1c
Community 1.1 to 1.4
This pathway occurs with fire suppression.
Pathway 1.1b
Community 1.1 to 1.5
Plant community phase 1.1 may develop into phase 1.6 with the infestation of pests. The primary threat to Sierra lodgepole pines from pest invasion is from the mountain pine beetle (Dendroctonus ponderosae). Infestations can lead to a high mortality rate, sometimes leaving a stand of dead trees, and causing high fuel loads. Natural outbreaks of variable severity tend to occur every 20 to 40 years (Cope, 1993).
Pathway 1.2a
Community 1.2 to 1.3
Phase 1.2 will naturally move to phase 1.3 if given time without major disturbances. This pathway is facilitated with a natural fire regime and small scale canopy disturbances. An open multi-age forest develops (Community Phase 1.3). Reports vary on the natural fire return interval, but this pathway assumes that surface fires are relatively frequent with 20 to 40-year cycles (Cope 1993). Manual thinning with prescribed burns can imitate the natural cycle and lead to the same relatively open community.
Pathway 1.2b
Community 1.2 to 1.4
This pathway occurs with fire suppression that prevents thinning necessary for the natural patchy structure of this ecological site. Lack of ground fire allows white fir and incense cedar to establish and gain maturity in the understory.
Pathway 1.3a
Community 1.3 to 1.1
The natural shift for this phase is to grow and develop into community phase 1.1. This pathway evolved with a historic fire regime of occasional surface and moderately severe fires, with occasional pest outbreaks that can lead to partial tree death. Manual thinning or prescribed burning can be implemented to replace the natural disturbances that kept this forest relatively open.
Pathway 1.3b
Community 1.3 to 1.2
In the event of a canopy fire, this phase would quickly return to phase 1.2
Pathway 1.3c
Community 1.3 to 1.4
This pathway occurs with fire suppression that prevents thinning necessary for the natural patchy structure of this ecological site. Lack of ground fire allows white fir and incense cedar to continue to establish and gain maturity in the understory.
Pathway 1.3d
Community 1.3 to 1.6
This phase can transition to phase 1.6 with the infestation of pests. The primary threat to Sierra lodgepole pines from pest invasion is from the mountain pine beetle (Dendroctonus ponderosae). Infestations can lead to a high mortality rate, leaving a forest of standing dead trees, and causing high fuel loads. Natural outbreaks of variable severity tend to occur every 20 to 40 years (Cope, 1993).
Pathway 1.4c
Community 1.4 to 1.2
In the event of a severe canopy fire or clear-cut/scarification, phase 1.2 would develop.
Pathway 1.4a
Community 1.4 to 1.5
With continued fire suppression, this phase will transition to a dense mature forest.
Pathway 1.4b
Community 1.4 to 1.6
This phase can transition to phase 1.6 with the infestation of pests. The primary threat to Sierra lodgepole pines from pest invasion is from the mountain pine beetle (Dendroctonus ponderosae). Infestations can lead to a high mortality rate; leaving a forest of standing dead trees, and causing high fuel loads. Natural outbreaks of variable severity tend to occur every 20 to 40 years (Cope, 1993).
Pathway 1.5c
Community 1.5 to 1.1
A naturally occurring moderate or surface fire in this forest is unlikely due to the high fuel load. Considerable management effort would be needed to create the open forest conditions that should exist in this forest with a natural fire regime. Manual treatment or prescribed burns could thin out dense Sierra lodgepole pine, white fir and incense cedar. This would shift this forest back to its natural state of open, patchily distributed Sierra lodgepole pine forest (Community phase 1.1).
Pathway 1.5a
Community 1.5 to 1.2
Ladder fuels and the density of fuels formed from the dead and dying white fir in the mid and lower canopies create conditions suitable for a high intensity canopy fire, which would initiate regeneration similar to that seen in phase 1.2. Because of the likely proximity of a white fir seed source, further treatments would be needed to promote the predominance and reestablishment of Sierra lodgepole pines.
Pathway 1.5b
Community 1.5 to 1.6
A high mortality pest attack on white fir and lodgepole pine, drought or above normal water tables could create a dead and dying forest with conditions and fuel loadings similar or heavier than phase 1.6.
Pathway 1.6a
Community 1.6 to 1.2
After a prolonged period, this phase will progress to phase 1.2. Severe fire will accelerate this succession. Fire is the natural disturbance at this point in the Sierra lodgepole pine cycle and will allow for the regeneration of the open lodgepole pine forest seen in phase 1.3. Mechanical removal of the dead trees with partial scarification of the surface or a prescribed burn in the understory can also induce stand regeneration.
