Ecological dynamics

Below is a State and Transition Model diagram to illustrate the “phases” (common plant communities), and “states” (aggregations of those plant communities) that can occur on the site. Differences between phases and states depend primarily upon observations of a range of disturbance histories in areas where this ESD is represented. These situations include tree harvest, grazing gradients to water sources, fence-line contrasts, patches with differing dates of fire, herbicide treatment, tillage, and kinds and times of timber harvest, etc. Reference State 1 illustrates the common plant communities that probably existed just prior to European settlement.

The major successional pathways within states, (“community pathways”) are indicated by arrows between phases. “Transitions” are indicated by arrows between states. The drivers of these changes are indicated in codes decipherable by referring to the legend at the bottom of the page and by reading the detailed narratives that follow the diagram.

The plant communities shown in this State and Transition Model may not represent every possibility but are probably the most prevalent and recurring plant communities. As more monitoring data are collected, some phases or states may be revised, removed, and/or new ones may be added. None of these plant communities should necessarily be thought of as “Desired Plant Communities.” According to the USDA NRCS National Range & Pasture Handbook (USDA-NRCS 2003), Desired Plant Communities (DPC’s) will be determined by the decision-makers and will meet minimum quality criteria established by the NRCS. The main purpose for including descriptions of a plant community is to capture the current knowledge at the time of this revision.

This site provides poor grazing for livestock because of the short growing season, limited numbers of forage species, and low productivity resulting from shade associated with the generally continuous tree canopy. However, it does provide valuable summer range for big game.

State 1 Reference State
The Reference State is a description of this ecological site just prior to Euro-American settlement but long after the arrival of Native Americans. At the time of European colonization, what would have been observed on these sites would have primarily depended on the time elapsed since the last wildfire occurred. Had the site been relatively undisturbed (i.e. without fire) for approximately 400 years or longer, the late seral climax of Subalpine fir and Engelmann spruce co-dominate forest would have been found (1.1). The understory would have been relatively sparse due to tree competition, overstory shading, and duff accumulation. Wildfire (1.1a) would have replaced these stands with diverse herb-dominated vegetation (1.2). In the absence of any major disturbance (1.2a, 1.3a, 1.4a, 1.5a), the vegetation would have progressed into more of a shrub-herb co-dominance (1.3), followed by aspen (Populus tremuloides) and possibly lodgepole pine (Pinus contorta) (1.4), then would have become a mature stand of subalpine fir (Abies lasiocarpa) (1.5). Ultimately the site would have been reinvaded by Engelmann spruce (1.1). Wildfire (1.1a, 1.5b) would have been the primary disturbance factor prior to colonization. Livestock grazing and fire exclusion can accelerate natural succession of woody species.

Community Phase 1.1: Mature Engelman Spruce – Subalpine Fir
Subalpine fir and Engelmann spruce co-dominate the climax overstory; few stands exhibit Engelmann spruce dominance over subalpine fir. Douglas fir and aspen occur as seral trees in some stands. The understory would be sparse consisting of shade-tolerant herbs such as heartleaf arnica, Geyer’s sedge, slender wheatgrass, and spike trisetum. This community would have existed approximately 400 years post fire.

Community Pathway 1.1a:
A stand-replacing wildfire or intensive logging will set the vegetation back to an early seral herb-dominated phase. Logging opens the forest canopy, allowing shrubs and herbs to flourish for 20 to 30 years.

Community Phase 1.2: herb-dominated meadow
This plant community will develop within the first 5 years following the last fire or complete tree removal. This would have been dominated by shade-intolerant forbs and grasses.

Community Pathway 1.2a:
After about 5 years, shrubs will establish, and the understory will diminish due to natural succession. Heavy season-long livestock grazing will accelerate woody plant recovery and diminish the understory.

Community Phase 1.3: shrub-herb
Between 5 and 30 years after fire, shrubs and herbs would co-dominate the site. The increasing shrub component would have included common juniper (Juniperus communis), grouse whortleberry (Vaccinium scoparium), gooseberry currant (Ribes montigenum), and Oregon boxleaf (Paxistima myrsinites). Geyer’s sedge, spike trisetum, heartleaf arnica, and meadow-rue would have been beginning to be present in the understory.

Community Pathway 1.3a:
Woody plant recovery continue to occur due to natural succession. Heavy season-long sheep grazing, deer and elk grazing, and fire exclusion will accelerate woody plant recovery and diminish the understory. About 30 years after fire, aspen would have become established in the site.

Community Phase 1.4: aspen
This plant community would have been dominated by aspen, a seral species. Understorys are forb-rich beneath early successional aspen canopies. Subalpine fir would have been present only as an understory species at this time. Aspen would have dominated these sites for approximately 30 to 100 years following the last fire. The understory would have had a mixture of shrubs and herbaceous species. Lodgepole pine may become established following aspen. Lodgepole pine may occur as an important seral species up toward Leadville and Denver.

Community Pathway 1.4a:
With approximately another century without fire, subalpine fir would have out competed the aspen to become the dominant overstory species at the site. Heavy season-long livestock grazing, and fire exclusion will accelerate woody plant recovery and diminish the understory.

Community Phase 1.5: mixed age subalpine fir
A stand of mature aspen and/or lodgepole pine with an inter-mixing of subalpine fir, and Engelmann spruce will develop approximately 100 to 400 years following fire or complete tree removal. Only shade-tolerant understory species would have been present. During this time, Engelmann spruce would become established in the understory.

Community Pathway 1.5a:
After approximately 400 years following the last wildfire, Engelmann spruce would have out-competed subalpine fir to become the dominant overstory species at the site. Fire exclusion will accelerate woody plant recovery and diminish the understory.

Community Pathway 1.5b:
A stand-replacing wildfire or intensive logging will set the vegetation back to an early seral shade-intolerant herb-dominated phase. Logging opens up the forest canopy allowing shrubs and herbs to flourish for 20 to 30 years.

Transition T1a: from State 1 to State 2
Sites that have had the most intense logging pressure have also had greatest degree of forest soil erosion and soil compaction. Once the forest reaches a certain level of degradation, managers often decide to focus on favoring one tree, usually lodgepole pine because of its greater growth rate and merchantability. This requires a clear cut and slash disposal followed by planting.

A less costly alternative compared to logging/slashing/replanting is to defer logging and control livestock grazing to allow whatever self-regenerating trees that occur on the site to recover. This process could, however, be thwarted by heavy game usage (i.e. elk utilization of aspen, or snowshoe hare utilization of subalpine fir).

State 2: Logged Forest
This state is forest plantation with trees like lodgepole pine planted specifically to replace previously degraded forests and to increase productivity of the site for economic profitability. Subsequent harvests and replanting will take place at maximum wood accumulation. Thinning to reduce insect or pathogen outbreaks will help maintain the resiliency of this State. Conversely, no management action may reduce the resiliency of this State.

With the large spruce trees being targeted during the first rounds of logging, what was left of these trees was minimal to none. Instead, sites that would have been dominated by Engelmann spruce became more often dominated by subalpine fir with only a scattering of Engelmann spruce (1.1). Logging effects, along with associated mechanical and fire disturbances, open the canopy and allow for the expansion of the herbaceous understory