RNG341 OSU State And Model Transitions of A Grassland System 1. Pick a desert, grassland or shrubland system with which you are familiar or would like to b

RNG341 OSU State And Model Transitions of A Grassland System 1. Pick a desert, grassland or shrubland system with which you are familiar or would like to become more familiar.2. List the top 5-7 primary plants in the system, as well as two disturbances. 3. Create a STM that has THREE states and within each state 2-3 communities. Be sure to clearly label the following:drivers of community pathways thresholds (abiotic or biotic) and what drives the system across a thresholdkeep in mind that communities there is disturbance within states that cause a system to reach a threshold; and a primary disturbance that pushes the state over a threshold to a new state. I find the best way to create an STM is utilizing PPT, however you may utilize any software you wish and you may draw it by hand… just be sure its clear so I can read it. There are no right or wrong answers for this assignment, but rather thoroughness and thoughtfulness of the diagram. Meaning it should reflect all the elements of an STM and disturbance and community/state shifts should be fairly logical. I don’t expect you to know exactly how a system may respond to a disturbance. I do expect you to understand the difference between a state, community, transition and threshold. I will give you ample feedback on this assignment so you are clear on the purpose of an STM and how to craft one for future assignments. State and Transition Model (STM)
State-and-Transition Model: Components & Structure
State 2
State 1
Reference State
Community Pathway: mechanism (succession,
fire, grazing, drought) that results in community
Transition – Vector of system change leading to
a new state without removing the stressor,
defined by a systems ability to self-repair
Plant community phase
Community pathway
(within states)
Reversible transition
Irreversible transition
State: the recognizable, resistant and resilient
complex of the soil and vegetation structure,
connected through integrated ecological
processes (hydrology, energy capture, nutrient
Phase: different plant communities that exist
within a state
State 3
Threshold – when one or more of the ecological
processes degrades beyond self-repair
Stringham, T.K., W.C. Krueger, and P.L. Shaver. 2003.
State and transition modeling: an ecological process approach.
Journal of Range Management 56:106-113
State-and-Transition Model: Reference vs. Current States
• The “reference state” = what is possible
based on ecological site potential
• Primary standard for assessment
• Provides data and information on
ecological processes
• Plant community assemblages
• Full range of ecological services
• Communities within a current state = what
is realistic
• Secondary standard for assessment
• Provides data and information on
current process function
• Provides options for management
• Provides options for restoration
opportunities (including risk)
State-and-Transition Model: States
STATE – a recognizable, resistant and resilient complex of
two ecosystem components, the soil base and the
vegetation structure
•soil – developed through time from specific parent
material, climate, landscape position and
interaction with biota
– determine the site’s capability
– interaction between soil and vegetation determines
functional status of site and inherent resistance to change
Stringham, et al., 2003
Vegetation attribute(s)
State-and-Transition Model: States
Ecological process function
State-and-Transition Model: Transitions & Thresholds
TRANSITION – the trajectory of a change
– change is precipitated by natural events,
management actions, or both
– degrades the integrity of one or more of the state’s primary
ecological processes beyond the point of self repair
THRESHOLD- boundary in space and time between two states
– irreversible for practical purposes without input of
outside energy
Stringham, et al., 2003
State-and-Transition Model: Transitions & Thresholds
Vegetation attribute(s)
State-and-Transition Model: Transitions & Thresholds
Vegetation attribute(s)
State-and-Transition Model: Ecological Resilience
• ECOLOGICAL RESILIENCE – Amount of change
required to transform a system from being
maintained by one set of mutually reinforcing
processes to a different set of processes.
(Briske et al 2008)
Process function
(% of capacity)
State-and-Transition Model: Function, Resistance and Resilience
High resistance
Low resistance
and high resilience
Low resistance
and low
Time (years)
(Modified from
Seybold, et al, 1999)
State-and-Transition Model: States, Thresholds, Transitions,
Vegetation attribute(s)
Ecological process function
State-and-Transition Model: Community Phases & Pathways
-Different assemblages within a state that do not
represent a state change since a threshold has not
been crossed
– Vegetation dynamics within a state
(succession/regression and/or non-equilibrium)
– Causes of change between plant communities
Vegetation attribute(s)
Ecological process function
Juniper Encroachment
Juniper captures
Decrease in understory
Decrease in litter
Increase in
bare ground
Deterioration in soil
Decreased soil stability
Decrease in juniper
Increase in
herbaceous production
Decrease in bare
Increased organic
matter inputs
Increased soil surface
Increased infiltration
Increased herbaceous
The STM below is one I developed for a project in SW Colorado. I know it looks complicated, but really if you follow it through you will see its fairly straight forward and its really about shifts in community composition as
a result of management and/or disturbance. Your assignment this week will be crafting an STM similar to this example for a system you chose.
State A: Pinyon-Juniper Savanna Historical
Community 1
Community 2
Pinyon-Juniper 15-30%
Pinvon Juniper 25-45%
reduction of
Shrubs Rotbrtosh Satbus 15-30% Shrubs Riba, 20-35%
State B: Post-Restoration Grass/Forb Dominated
Grasses but 15
Grasses de gesterweel 5-15% tree & shrub
Forbs 2.8%
canopy: Seed
Forte 6 10%
native grasses &
Community 1
Un-Managed over time
Grasses begrama westem wheat) 25-40%
Biotic Threshold Forbs 15-25%
Community 3
Pinyon Juniper 30-50%
Pinyon Juniper 10-20%
Shrubs Rabbal, Boy 25-40%
Struts Bas Salt 15-25%
Grasses de grans de what 1-5%
Forbs 1-5%
Community 2
Pinyon-Juniper 25-30%
Shrubs (Ratibus. Salbrush 25-30%
Un-Managed dominance of Pinyon-
Perennial Invasive Forb 5-10%
Juniper and shrubs reduces soil
Grasses (blue cromo, westom whoat 10-20%
quality and water availability and LA
Forts 5-10%
accelerates soil loss.
Abiotic Threshold Crossed
Prolonged drought and/or overgrazing reduces soil
State C: Degraded Pinyon-Juniper Woodland
quality and water availability and accelerates soil loss.
Invasive species establishment
Community 2
Community 1
Abiotic & Biotic Thresholds Crossed
Pinyon-Juniper 25-40%
Pinyon Juniper 30-45%
Un-Managed overtime
Shrubs 25-30%
Shrubs 30-35%
Perennial Invasive Forb 15-28%
Perennial Invasive Forb 10-15%
Native Grasses & Forbs 1-2%
Native Grasses & Forts 1-5%
Heavy Grazing
Not Probable
Time Passing
Threshold Crossed
Community 3
Fire Disturbance
Annual Invasive Grasses 50-90% Juniper, Shrubs & Perennials 5-25%
Biotic Threshold
Abiotic Threshold
Dominant and/or Key Increasing Species Community at Risk
Site Name: Savanna Site Type: Rangeland
Site ID: RO35XG127NM
MLRA: 035Colorado Plateau
These readings won’t tell you exactly how to craft an STM, but they will provide you with background and contextual information to guide you. Plus, they are standard readings within the discipline on the topic of STMs.
READ: Briske, Fuhlendorf, & Smeins. (2005). State-and-Transition Models, Thresholds, and Rangeland Health: A Synthesis of Ecological Concepts and Perspectives e. Rangeland Ecology & Management, 58(1), 1-10.
READ: Bestelmeyer, B. et al. 2010. Practical Guidance for Developing State and Transition Models 2. Rangelands, 32(6) pp. 23-30.

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