Ecological Site Descriptions (ESD) synthesize information concerning soils, hydrology, ecology, and management into a user-friendly document. A crucial component of an ESD is the state-and-transition model (STM) that identifies the different vegetation states, describes the disturbances that caused vegetation change, and suggests restoration activities needed to restore plant communities. State-and-transition models are powerful tools that utilize professional knowledge, data, and literature to describe the resistance and resilience of an ecological site. The STM then captures various disturbances, triggers leading to ecological thresholds, feedback mechanisms maintaining ecological states, and the restoration techniques required for moving from one ecological state to another (Briske et al. 2008, Stringham et al. 2003).
Many ecological sites are similar in their plant composition and other important physical attributes such as soils, but may differ in total production or landscape setting. Thus, often these similar ecological sites will respond to the same disturbance in a similar manner. The rate of response to disturbance may be different but the endpoint of the change will be very similar. In order to expedite development of STMs, a process developed by Dr. Stringham, referred to as Disturbance Response Grouping was utilized in this project. The Disturbance Response Group process is conducted at the Major Land Resource Area (MLRA) scale, making it a highly efficient method for STM development. The process requires a team of experts with years of experience working in the area of interest.
The core team for this project consisted of:
- Tamzen K. Stringham is a Professor with the University of Nevada, Reno
- Devon K. Snyder is a Rangeland Ecologist with University of Nevada, Reno
- Patti Novak-Echenique is a Rangeland Management Specialist with the Bureau of Land Management, Sparks, Nevada
- Kelsey O’Neill was a Rangeland Ecologist with University of Nevada, Reno
- Alexa Lyons is a research technician with University of Nevada, Reno
- Mattie Johns is a research technician with University of Nevada, Reno
Soil support was provided by:
- Joseph Chiaretti, Soil Scientist, NRCS Nevada (retired)
- Edward Blake, Soil Scientist, NRCS Nevada (retired)
- Matt Cole, NRCS Soil Scientist
- Chris Savastio, NRCS Soil Scientist and MLRA Soil Survey Leader
- John Fisher, Soil Scientist, NRCS Nevada (retired)
Additional support members of the team:
- Martin Oliver, Botanist, BLM Bishop, CA
- Casey Boyd, Rangeland Management Specialist, BLM, Bishop, CA
- Robin Tausch, Professor Emeritus, UNR
- Keith Barker, Fire Ecologist, BLM Carson City, NV
- Rachel Williams, U.S. Fish and Wildlife Service
- Martina Middione, BLM Bishop, CA
- Sarah Johnson
- Alyssa Badertscher
- Sarah Kidd
Initial office meetings were conducted with all Core Team members present to group sites into preliminary Disturbance Response Groups (DRGs) (Stringham et al. 2016). During the DRG office exercise, the Core Team examines characteristics of each existing range site, including but not limited to the following:
- Dominant Vegetation
- Soils: depth, texture, parent material, diagnostic horizons, chemical properties, soil temperature and moisture regimes
- Precipitation
- Slope and Elevation
- Plant productivity
- Response to various disturbances based on all the above characteristics, plus management history
The Core Team spends an extensive amount of time on the topic of response to disturbance. Discussions on different disturbances such as fire, grazing, long-term drought, insects, flooding or ponding, invasive species, and combinations of disturbances are recorded. The Core Team makes a determination as to which DRG each ecological site or range site will be assigned to for modeling purposes. After the initial DRG is finalized, the “modal” ecological site for the DRG is chosen. This ecological site typically represents the site in each DRG with the most mapped acres in the NRCS soil survey. Dr. Stringham then develops a “Tier I” state-and-transition model for the modal ecological site for each DRG. This generalized STM represents each ecological site within the DRG until field validation is complete, and changes to the STM are deemed necessary based on field observations.
Field validation occurs primarily with the Core Team and at times with assistance from others interested in the process. To facilitate the field component, the GIS specialist builds a geodatabase with relevant data. These include NRCS soil survey data (i.e. ecological site type locations, soil map units, ecological site polygons, soil pit sampling locations), historical wildfires dating back at least 30 years, BLM land treatment layers, land ownership, roads, any available vegetation monitoring data, NAIP imagery, and USGS Digital Raster topography. The GIS specialist or the soil scientist utilizes this geodatabase while in the field to inform the team of recent fires, multiple fires, or mechanical treatments performed on the site. The Core Team attempts to visit every ecological site at least once, and visits the modal ecological site for each DRG multiple times in different locations, and in different conditions. At each site visit the following information was recorded:
- GPS coordinates
- Photos
- Elevation
- Slope and aspect
- Landform
- Soil description to 20” depth or to restrictive horizon
- Soil is identified to series if possible
- Known disturbances: fire, drought, insects, management practices, and others
- Plant species composition by weight, estimated ocularly and sometimes clipped
- Shrub and tree cover
- Rangeland Health
- State-and-transition model state and community phase, including any relevant notes on ecological dynamics
Dr. Stringham modifies the STM if needed based on field notes, this then becomes the “Tier II” model. The Core Team reconvenes in the office and reviews the Tier II state-and-transition models. Members of the interested public are invited to the meetings to provide input and critical review. Models are modified if warranted. STMs are built using Microsoft Visio, and a shorthand “key” is written for each Community Pathway and Transition. Dr. Stringham, along with her staff, complete the STMs by developing the “STM narrative,” which explains the ecological dynamics associated with the various States, Community Phases, Community Pathways and Transitions. An extensive literature review is conducted and added to the knowledge gained from the field investigations. The Core Team and interested agency partners peer review and provide critical feedback for the ecological dynamics section and the STM.
This project produced 158 field notes over the course of 3 field seasons and 15 weeks of field work. The Final Report contains the Disturbance Response Group list for MLRA 26, a robust literature review and Ecological Dynamics section for the modal ecological site of each DRG, State-and-Transition Model diagrams for each ecological site contained within a DRG, and supplemental information with field notes for all site visits.
For the complete 710 page report, use the link below to download the PDF version.
