Ecological dynamics
Abiotic factors
This site occurs on gently sloping glacial outwash at elevations of approximately 6200 to 6800 feet. Soils are very deep, with a weak fragipan at 12 to 65 inches and redoximorphic concentrations and depletions begin at 12 inches. Permeability is slow to very slow. The fragipan creates a perched water table, so soils are saturated at shallow depths during the wet season, and droughty during the dry season. This limits the forest canopy to dominance by Sierra lodgepole pine, which is tolerant of both saturated and droughty soil conditions. The understory is a sparse cover of native grasses, with squirreltail the most common species.
Ecological/Disturbance factors
The presumed most successionally advanced community phase is dominated by Sierra lodgepole pine forests. These forests are dense, single aged stands of Sierra lodgepole pine with an occasional white fir (Abies concolor) and Jeffery pine (Pinus Jeffreyi). The understory cover is sparse with scattered native grasses.
Sierra lodgepole pine can tolerate harsher conditions than many other conifers, inclduing cold, light, heat, drought, saturation, and hardpan soils (Lotan and Critchfield 1990, Kocher 2005). They are also moderately shade and competition tolerant. However, the thin bark and shallow root systems make Sierra lodgepole pine 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.
Historically, fire played an important role in thinning and renewing Sierra lodgepole pine forests. Studies on fire frequency in Sierra lodgepole pine forest 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 intervals for moderate and severe fires were most likely between 70 to 100 years, heavily correlated with mountain pine beetle (Dendroctonus ponderosae) infestations and the decline of overstory trees. In addition to a natural fire regime, it is believed the Washoe Indians used fire to preserve meadow environments and to keep forests open (Murphy and Knopp,2000).
Human disturbance regimes have altered the historic plant community and its natural cycles. Much of the Sierra 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. Almost a century of fire exclusion has led to increased forest density and over- and understory fuel build-up (Murphy and Knopp 2000). Consequently, this Sierra lodgepole pine community is younger and more overstocked than the pre-European settlement 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
This community phase is currently very rare, however it may become more extensive with appropriate management. This phase develops large old growth Sierra lodgepole pine with a mix of younger aged trees. The age for this community is estimated to have ranged from about 100 to more than 200 years. Small pockets of younger community phases intermixed to create a diverse forest structure. White fir and Jeffrey pine may be present at low cover due to high water table levels and a partially root restricting fragipan that limit establishment in this sites. Pine beetle infestations, wind throw and other small-scale disturbances create gaps for Sierra lodgepole pine regeneration. Over time these gaps break up the uniformity of the evenly aged stand that formed after the last large fire event. Old growth Sierra lodgepole pine that has not experience severe fire has an irregular forest structure and is able to regenerate in canopy gaps created by disturbances. The understory cover was probably sparse with scattered grasses.
Forest overstory. The overstory canopy cover may range from 40 to 70 percent. White fir and Jeffrey pine can be present with low frequency and cover.
Forest understory. The understory cover was most likely low with a range of 5 to 10 percent herbaceous cover. Data is unavailable for this historic community, but the species were most likely similar to those listed in community phase 1.3.
Community 1.2
Stand initiation
This short lived, community phase develops after a severe canopy fire. A carefully planned harvest and prescribed burn could imitate a canopy fire and initiate forest regeneration. Remnant overstory trees may be present in limited numbers. This community type was not observed, but grasses and sedges may dominate this phase, until Sierra lodgepole pine seedlings increase in cover. Sierra lodgepole pine readily germinates from seed in the spring in the mineral soil exposed by fire and can survive in the frost pockets that define these sites, where other tree seedlings cannot.
Forest overstory. Young, developing Sierra lodgepole pine seedlings.
Forest understory. Numerous species of grasses, including squirreltail (Elymus elymoides), Sandberg bluegrass (Poa Secunda), and Ross’ sedge (Carex rossii) regenerate from seed after fire and will dominate this community for several years. The seeds require moist soil and full sun to establish in the first season. Herbaceous species may include grassy tarweed (Madia gracilis), common yarrow (Achillea millefolium), and yampah (Perideridium spp.). In some instances, the grasses can dominate for a prolonged period from continual grazing or management that excludes establishment of lodgepole pine regeneration.
Community 1.3
Young forest
Figure 7. Community Phase 1.3
This young, open Sierra lodgepole pine community phase is dependent partially on the initial density of seedling establishment. In some cases, seedlings establish at different times, and in relatively open distribution. This depends in part on seed storage, time and intensity of fire, and post fire climate conditions. This community’s duration ranges up 60 years. Some reports indicate surface fires historically kept this forest open in the understory. However, it appears that a fire in these dense stands could be moderate to severe. The burns may be patchy, burning just the small dense groves and under the older forest nearby, which would create open conditions in some areas.
Forest overstory. In the young open Sierra lodgepole pine forest, the overstory is dominated by Sierra lodgepole pines with canopy cover ranging from 25 to 60 percent. White fir and Jeffrey pine each range from 0 to 5 percent canopy cover.
Forest understory. The understory is dominated by graminoid species. Ross' sedge (Carex rossii) and squirreltail (Elymus elymoides) are commonly represented along with a variety of other species.
Community 1.4
Dense young forest
The dense young forest may develop when fire suppression results in increased seed source and infill of white fir. White fir seedlings are more shade tolerant than lodgepole pine seedlings, which allows them to continue to reproduce in the understory of the lodgepole pine forest. The density of white fir increases over time and creates competition with the lodgepole pines for sunlight and water. This stress makes the trees more susceptible to death from pests and drought, which in turn increases the fuel loads and potential for a severe fire.
It appears that this site is not conducive for the optimum growth of white fir because of 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. If white fir does not infill, lodgepole pine can increase in density and create the same conditions mentioned above.
Canopy cover is high in this phase, at up to 80 percent.
Forest overstory. This phase is dominated by a relatively open overstory of 60 to 100 year old Sierra lodgepole pine trees. This community phase develops with occasional fire, pest outbreaks or tree fall, which create canopy gaps. White fir may germinate during this time in the shade of the young lodgepole pines and small shrubs.
Forest understory. The understory is dominated by graminoid species.
Community 1.5
Dense mature forest
The dense mature 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 Sierra lodgepole pine’s health and vigor 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.
Canopy cover is high, at up to 90 percent, and trees are 60 to over 100 years old.
Forest overstory. Sierra lodgepole pine is still dominant in the main canopy, but white fir is becoming increasingly dense in the understory. Overall density is high, with canopy cover ranging from 55 to 80 percent. The main canopy is composed of young, small-diameter trees around 60 feet tall, with several understory layers.
Forest understory. The high canopy cover and deep accumulation of woody debris causes a lack of sunlight and little to no understory.
Community 1.6
Mountain pine beetle epidemic
Standing dead forests can result following mountain pine beetle epidemics, 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.
Forest overstory. White fir is dominant in the main canopy and in the understory. Overall density is high with canopy cover ranging from 55 to 90 percent. The main canopy is composed of mature trees around 100 feet tall with several canopy layers beneath. An estimate for an age for this community is 60 to more than 200 years.
Forest understory. The high canopy cover and deep accumulation of woody debris causes a lack of sunlight and little to no understory.
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.
Pathway 1.1c
Community 1.1 to 1.5
This pathway occurs with fire suppression.
Pathway 1.1b
Community 1.1 to 1.6
Plant community phase 1.1 may develop into phase 1.6 with the infestation of pests. The primary threat to Sierra lodgepole pine from pest invasion is 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
The natural transition would be to community phase 1.3, the young Sierra lodgepole pine forest, if given time without severe disturbances. This pathway is followed with a natural fire regime. Reports vary on the natural fire return interval, but this pathway assumes that surface fires were 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 forest community phase 1.3.
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 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, the phase would quickly shift to community 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 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 1.4d
Community 1.4 to 1.3
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, western juniper and white fir. This would shift this forest back to its natural state of open, patchily distributed young Sierra lodgepole pine forest (community phase 1.3).
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, western juniper and white fir. 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
In the event of a severe canopy fire, or a clear-cut with or without a prescribed burn, this phase 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 1.5b
Community 1.5 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 1.6a
Community 1.6 to 1.2
After a prolonged period, this phase will progress to phase 1.2. Severe fire will accelerate this transition. Fire is the natural disturbance at this point in the Sierra lodgepole pine cycle and will allow for the regeneration of the 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.
