State 1
Reference

Community 1.1
Sierra lodgepole pine-aspen/blue wildrye

This is the reference community phase for this ecological site. Most of the ecological site is presently in this community phase as there has been very little disturbance since the debris flow of 1915. A dense forest of 80 to 90 year old Sierra lodgepole pine is present with a grassy understory. Areas of bark beetle infestations and wind throw have created small gaps within the dense forests. These gaps may allow for regeneration of Sierra lodgepole pine and stimulate aspen suckers. In order for the aspen suckers to survive, the gaps would have to have a low recruitment of lodgepole pine seedlings and be large enough to allow for direct sunlight to reach the aspen through the surrounding canopy. These gaps break up the uniformity of the forest overtime, but are probably not sufficient for healthy aspen regeneration. The mature aspen and young suckers occur in the denser areas of the forest as well, but are crowded and overshadowed by lodgepole pine. Aspen stands begin to deteriorate after about 80 years due to the build up of pathogens. Without sudden canopy disturbance there will not be a flush of aspen suckers and Sierra lodgepole pine may fill in the decaying aspen stand rather than younger aspen. Fossorial animal activity enhances germination of lodgepole pine under the decaying aspen canopy. Nearby in Pine Creek, Sierra lodgepole pine and white fir are established within the aspen stand. The young aspen suckers have a powdery mildew on their leaves caused by a fungi (Uncinula adunca) and a disease, most likely shepherd’s crook (Venturia macularis), is causing a blackening and wilting of the twigs and foliage of the young shoots. These are natural pathogens, but wetter than normal springs and/or increased shade from the conifer canopy may increase the rate of infection and reduce overall vigor of the aspens (Smith, et, 2006).

Forest overstory. Sierra lodgepole pine dominates this forest with up to 80 percent canopy cover. Trees are 85 to 100 feet tall with 15 to 20 inch dbh. Basal area ranges from 120 to 190 ft2/ acre. The height for the quaking aspen ranges from 80 to 90 feet. There is much standing dead and downed trees from both species.

Forest understory. The understory is dominated by grasses such as blue wildrye (Elymus glaucus), western needlegrass (Achnatherum occidentale), squirreltail (Elymus elymoides) and California brome (Bromus carinatus). Other common species include yarrow (Achillea millefolium), sedges (Carex spp.), spreading groundsmoke (Gayophytum diffusum), whitestem gooseberry (Ribes inerme) and Gray's licorice-root (Ligusticum grayi), with diverse other low cover plants. Quaking aspen (Populus tremuloides) sprouts are few and unhealthy.

Community 1.2
Aspen-Sierra lodgepole pine/blue wildrye

After a canopy replacing event such as fire, disease or insect infestation, young aspen suckers will sprout prolifically from the surviving roots. Very dense root mats are possible, which may suppress growth of other plants for a short period. Many of the young suckers will die during this time but overall canopy cover will remain high. Sierra lodgepole pine is a pioneer species and will also regenerate prolifically after fire via wind dispersed seed or from seeds stored in the soil. Seedling mortality will ordinarily be high during this phase, but young dog hair thickets can develop that will begin to self-thin and open up. The presence of aspen or Sierra lodgepole pine seems to be dependent upon the nearness and health of aspen roots after a disturbance and the proximity of a Sierra lodgepole pine seed source. After a fire, the cover of grasses and forbs will remain high since many of these species will re-sprout or germinate from seed. Disturbance dependent sun-loving annual and perennial forbs may have a short lived presence after a fire. Fires are not frequent in aspen stands because of the high moisture content associated with these areas. Some reports indicate that the fire frequency for aspen stands is similar or longer than for the surrounding forest, however. In this case, the surrounding forest would be comprised of white fir, Jeffrey pine or red fir. The natural fire intervals in these forests range from 5 to 65 years (Bekker and Tayler, 2001; Bancroft, 1979; Taylor et al., 1991).

Community 1.3
Aspen-Sierra lodgepole pine/blue wildrye

This is a healthy young aspen forest that quickly transitions to a mature aspen grove within 30 to 40 years. The understory is lush and diverse with patches of aspen suckers in areas of disturbance. Sierra lodgepole pine has established patches of forest on the upper stream terraces. The Sierra lodgepole pines are dense and overcrowded, in the absence of disturbance. The aspen and Sierra lodgepole pine forests form a patch-work across the flats. In areas where Sierra lodgepole pine and aspen co-exist they may have equal dominance in the upper canopy during this phase.

Community 1.4
Aspen-Sierra lodgepole pine/blue wildrye

This aspen forest tends to have a single canopy with 45 to 75 percent cover. Several clones may be present as well as suckers in the understory and a lush understory of grasses and forbs. Sierra lodgepole pine is present throughout this area, generally in-filling from the perimeter of the aspen stand or in the understory of the aspen. The Sierra lodgepole pine becomes taller than the aspens, casting shade upon the aspen canopy and reducing their vigor and growth. White fir is occasionally 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 old growth forest would return to the aspen regeneration community (Community 1.2). The overstory Sierra lodgepole pine will succumb to these fires because of their thin bark and shallow root systems (Kocher, 2005). A variable amount of Sierra lodgepole pine regeneration will co-develop with the aspen.

Pathway 1.2a
Community 1.2 to 1.3

With time and growth, Community 1.2 progresses to Community 1.3, the young aspen and Sierra lodgepole pine forest.

Pathway 1.3b
Community 1.3 to 1.2

In the event of a canopy fire or high mortality pest attack, this community would return to Community 1.2.

Pathway 1.3a
Community 1.3 to 1.4

This is the natural pathway for this community, which evolves with small patches of relatively frequent surface and moderate severity fires, and/or partial tree mortality from a pest outbreak. Manual thinning or prescribed burning can be implemented to replace the natural disturbances that would normally have removed portions of the tree canopy. This pathway leads to the aspen-lodgepole pine forest (Community 1.4).

Pathway 1.4a
Community 1.4 to 1.1

In the absence of canopy disturbance a Sierra lodgepole pine dominated forest will develop with few aspen (Community 1.1).

Pathway 1.4b
Community 1.4 to 1.2

Natural disturbances such as fire, flood or disease remove the overstory canopy of aspen and Sierra lodgepole pine, allowing for regeneration (Community 1.2).

State 2
Altered

State 2 develops due to a long period with-out canopy disturbance, so when disturbance finally comes during this state Sierra lodgepole pine will dominate and aspen will be absent in the regeneration community. Without canopy disturbance, mature aspen die out in the shade of the Sierra lodgepole pine. The hormones required to induce suckering are not activated and, denied the sunlight needed for photosynthesis, the aspen roots eventually die. If there is not a nearby aspen seed source, it is eventually eliminated from the area. After a long period of rest, and elimination of aspen, Sierra lodgepole pine reproduces prolifically from seed after canopy removal. The actual time it takes to cross this threshold is unknown but possibly ranges from 200 to 300 years.

Community 2.1
Sierra lodgepole pine/blue wildrye

This mature Sierra lodgepole pine forest develops with small scale disturbances which create gaps in the canopy. These gaps (single tree fall to 0.25 acre in size) provide suitable sites for Sierra lodgepole pine regeneration, and over time, create uneven forest structure and composition. Several age classes of Sierra lodgepole pine and white fir are present. Several Sierra lodgepole pines will persist in the tallest overstory and provide a seed source for gap areas. Mountain pine beetle (Dendroctonus ponderosae) epidemics are common in older Sierra lodgepole pine forests. Epidemics often occur in 20 to 40 years cycles and may last for 5 to 7 years. 1/3 to 2/3 of large trees in the forest can be killed during a severe infestation. After an outbreak, there are many standing dead trees, which gradually fall and create high amounts of down wood. Fine fuels from recently killed trees (dead needles and twigs both on the ground and remaining on trees) increase the probability of high mortality fire from ignition sources for several years. Sierra lodgepole pine will succumb to these fires because of their thin bark and shallow root systems. After death of the lodgepole overstory from fire or pest attack, watersheds can release up to 30 percent more water (Cope, 1993).

Community 2.2
Sierra lodgepole pine/blue wildrye

This community is dominated by grasses and Sierra lodgepole pine seedlings. This site generally has less than 500 stems per acre, and develops into a relatively open forest. The seedlings develop into pole sized trees, with up to 55 percent canopy cover. Grasses and forbs may increase in cover for a few years.

Community 2.3
Sierra lodgepole pine/litter

This regeneration community phase is defined by dense Sierra lodgepole pine seedlings. More research is needed to determine the cause of dense versus open seedling establishment, and appropriate indicators need to be defined which distinguish the two regeneration patterns. For now, it has been observed that more than 500 to 700 stems of Sierra lodgepole pine per acre can cause stagnant forest growth. There are many variables which influence seedling density. Sierra lodgepole pine produces good seed crops every 1 to 3 years, and seeds are dispersed from late August to mid October. These seeds can be stored in the soil for several years, but tend to regenerate from wind dispersed seeds deposited after the fire. Therefore, the season of burn and timing in relation to seed crop cycles may affect seedling density. Smaller fires may have higher seedling density, due to the proximity of an available seed source. Fires leave bare soil and disturbed duff with open sunlight, which are ideal conditions for Sierra lodgepole pine seed germination. Seasonal precipitation patterns and air temperatures, during the season and germination, influence the survival of seedlings. As the seedlings develop they form dense thickets. The trees thin out there lower branches as they grow tall and thin. They self thin to some extent, but most trees persist even with limited sunlight on their canopy. Growth becomes stagnant, due to competition for light, water and nutrients. After a certain point in development Sierra lodgepole pine may not respond to competitive release from thinning, disease, or fire.

Community 2.4
Sierra lodgepole pine/blue wildrye

This forest is multi-aged with an irregular canopy distribution due to small scale or patchy disturbances. This community phase is common at this time. Mountain pine beetle infestations are the most significant disturbance that can create canopy openings. After a pest infestation, patches of the stand die, leaving gaps for lodgepole pine regeneration. Low intensity fire is often fatal to mature lodgepole pine, so even low severity fire can be a stand replacing event. So the event of fire creating small gaps is uncommon. However low intensity smoldering fires have been documented which spread through downed trees after a mountain pine beetle infestation. Minor damage to the live trees was noted, but some with fire scars were more susceptible to mountain pine beetle attack. It does not seem that fire would ignite easily in the moist understory or in the nearby meadow until the end of summer. Shallow roots make lodgepole pine is susceptible to wind throw which also creates canopy gaps.

Community 2.5
Sierra lodgepole pine/litter

This dense Sierra lodgepole pine forest develops after dense seedling establishment and absence of canopy disturbance. This forest is even-aged with a high basal area of tall thin trees. The forest is stagnant. Only the upper crowns get sunlight, and the understory branches die back. The self-thinning process is slow and does not eliminate competition. There is almost no regeneration due to the lack of openings in the forest. Understory production and cover decreases due to the lack of sunlight. The potential for a severe pest infestation or disease is high because the trees are stressed from competition for sunlight, water, and nutrients. The close proximity of the trees will enable the pathogens to spread quickly. Severe fire is likely during this phase because of the high accumulation of fuels on the forest floor.

Forest overstory. Dense, even-aged lodgepole pine with canopy ranging from 60-90 percent.

Forest understory. Little to no understory vegetation; litter predominates.

Pathway 2.1b
Community 2.1 to 2.2

This pathway is created by a high mortality fire or forest infestation, followed by relatively open Sierra lodgepole pine seedling regeneration (Community 2.2).

Pathway 2.1a
Community 2.1 to 2.3

This pathway is created by a high mortality fire or forest infestation, followed by relatively dense Sierra lodgepole pine seedling regeneration (Community 2.3).

Pathway 2.2a
Community 2.2 to 2.4

With time and growth, with small scale canopy disturbances Community 2.2 progresses to the open Sierra lodgepole pine forest, Community 2.4.

Pathway 2.3a
Community 2.3 to 2.5

With time and growth, in the absence of disturbance, Community 2.3 progresses to the dense lodgepole pine forest, Community 2.5.

Pathway 2.4a
Community 2.4 to 2.1

With time and growth with small scale disturbances this forest continues to develop into a Sierra lodgepole pine forest (Community 2.1) with a multi-aged, complex forest structure.

Pathway 2.4b
Community 2.4 to 2.2

This pathway is triggered by a high mortality fire, which initiates open Sierra lodgepole pine regeneration (Community 2.2).

Pathway 2.4c
Community 2.4 to 2.3

This pathway is triggered by a high mortality fire, which initiates dense lodgepole pine regeneration (Community 2.3).

Pathway 2.5b
Community 2.5 to 2.2

This pathway is triggered by a high mortality fire, with appropriate conditions for open lodgepole pine regeneration (Community 2.2).

Pathway 2.5a
Community 2.5 to 2.3

This pathway is triggered by a high mortality fire, with appropriate conditions for dense lodgepole pine regeneration (Community 2.3).

Pathway 2.5c
Community 2.5 to 2.4

This pathway is initiated by repeated small scale canopy disturbances caused by mountain pine beetle infestations, low-mortality fires, or wind throw. The forest becomes a more open Sierra lodgepole pine forest (Community 2.4) with several age classes, with continued small scale disturbances can eventually develop into Community 2.1.

Transition T1
State 1 to 2

The transition to State 2 may occur with the prolonged absence of fire or other disturbances, which would cause canopy mortality. If the lodgepole pine forest exists for a long enough period the aspen clones may completely die out and not regenerate after fire

Restoration pathway R2
State 2 to 1

Restoration of this site would be easiest after a natural disturbance, but considerable expense and maintenance would be needed. Aspen seed or seedlings would need to be reintroduced to the area while the Sierra lodgepole pine seedlings may need to be removed to eliminate competition.