STONY MAHOGANY SAVANNA
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition A More details
- Transition B More details
- Transition A More details
- Transition B More details
- Restoration pathway A More details
- Transition A More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
The Reference State 1.0 is a representative of the natural range of variability under pristine conditions. The Reference State has three general community phases; a tree-shrub dominant phase, a sprouting shrub and perennial grass dominant phase and a shrub dominant phase. State dynamics are maintained by interactions between climatic patterns and disturbance regimes. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These include the presence of all structural and functional groups, low fine fuel loads, and retention of organic matter and nutrients. Plant community phase changes are primarily driven by fire, periodic drought and/or insect attack.
Submodel
Description
This state is similar to the Reference State 1.0. It has similar community phases with the addition of the 2.4 at-risk community phase. Ecological function has not changed, however the resiliency of the state has been reduced by the presence of invasive weeds. This state has the same three general community phases. These non-natives can be highly flammable, and can promote fire where historically fire had been infrequent. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These include the presence of all structural and functional groups, low fine fuel loads, and retention of organic matter and nutrients. Positive feedbacks decrease ecosystem resilience and stability of the state. These include the non-natives’ high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate, and adaptations for seed dispersal.
Submodel
Description
This state has two community phases and is characterized by singleleaf pinyon and/or Utah juniper dominating site resources. Evergreen trees outcompete and overtop the mountain mahogany overstory. The understory is reduced due to shading and competition with tree overstory. This state may be compounded by grazing of livestock and wildlife further reducing perennial understory species. Annual non-native species may be increasing.
This state will not occur above the pinyon/juniper tree zone (>9000 ft).
Submodel
Description
The primary characteristic of this state is a dominance of non-native annual grasses like cheatgrass. The community may be dominated by sprouting shrubs, annual non-native grass and forbs, and Sandberg bluegrass. This state is a product of many years of heavy grazing during time periods harmful to perennial bunchgrasses, and/or severe wildfire or repeated fires. Sandberg bluegrass will increase with a reduction in deep rooted perennial bunchgrass competition and become the dominant grass. Annuals, Sandberg bluegrass, and sprouting shrubs dominate site resources such that soil water, nutrient capture, nutrient cycling and soil organic matter are temporally and spatially redistributed.
Submodel
Mechanism
Trigger: This transition is caused by the introduction of non-native annual plants, such as cheatgrass, mustards, and thistle.
Slow variables: Over time annual non-native species increase within the community.
Threshold: Any amount of introduced non-native species causes an immediate decrease in the resilience of the site. Annual non-native species cannot be easily removed from the system and have the potential to significantly alter disturbance regimes from their historic range of variation.
Mechanism
Trigger: Time and lack of disturbance such as fire allows for pinyon trees to dominate.
Slow variables: Over time abundance and size of pinyon will increase.
Threshold: Pinyon pine dominates ecological processes. Trees overtop and outcompete mountain mahogany and shrubs for water and sunlight. Shrub skeletons exceed live shrubs with minimal recruitment of new cohorts.
Mechanism
Trigger: Time and lack of disturbance such as fire allows for pinyon and juniper trees to dominate.
Slow variables: Over time abundance and size of pinyon will increase.
Threshold: Pinyon pine dominates ecological processes. Trees overtop and outcompete mountain mahogany and shrubs for water and sunlight. Shrub skeletons exceed live shrubs with minimal recruitment of new cohorts.
Mechanism
Trigger: High-severity or stand-replacing fire that significantly reduces or eliminates Mountain mahogany and sagebrush. Bunchgrass plants significantly damaged by the fire may be further reduced or eliminated with inappropriate post-fire grazing management. Cheatgrass becomes the dominant grass. Sandberg bluegrass may be a significant component.
Slow variable: Cover and production of annual non-natives and/or Sandberg bluegrass will increase.
Threshold: Loss of mahogany overstory, sagebrush, and deep-rooted perennial bunchgrasses changes nutrient cycling, nutrient redistribution, and reduces soil organic matter. Increased continuous fine fuels modify the fire regime by changing intensity, size and spatial variability of fires.
Mechanism
Removal of singleleaf pinyon and Utah juniper from the site may allow mountain mahogany to reestablish and become dominant in the overstory.
Relevant conservation practices
| Practice | External resources |
|---|---|
|
Brush Management |
Mechanism
Trigger: To community phase 4.1: Overgrazing in the presence of non-native annual species can cause a decrease in perennial bunchgrasses and an increase in annual species. Spring and/or fall moisture may also increase annual species. To community phase 4.2: Catastrophic fire.
Slow variables: Cover and production of annual non-native species increase in the understory.
Threshold: Loss of mahogany overstory, mountain big sagebrush, and deep-rooted perennial bunchgrasses changes nutrient cycling, nutrient redistribution, and reduces soil organic matter and soil moisture. Increased, continuous fine fuels modify the fire regime by changing intensity, size and spatial variability of fires.
Model keys
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