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 the 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 to various disturbances, the triggers leading to ecological thresholds, the 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 and referred to as Disturbance Response Grouping was utilized on 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.

Disturbance Response Groups (DRGs). During the DRG exercise the Core Team examines characteristics of each existing range site including but not limited to:

  • 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 extensive 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 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 with the most mapped acres for that DRG. Dr. Stringham develops a Tier I state-and-transition model for the modal ecological site for each DRG. This STM represents each ecological site within the DRG until field validation is complete and changes are warranted.

Field validation occurs primarily with the Core Team and at times with assistance from additional members and others interested in the process. To facilitate the field component the GIS specialist builds a geodatabase with spatial layers of ecological site type locations, ecological site polygons, soil modal and soil sampling locations, soil map unit polygons, historical wildfire locations dating back at least 30 years, BLM land treatment layers, land ownership, roads, NAIP imagery and USGS Digital Raster topography. The GIS specialist or the soil scientist utilized this geodatabase while in the field to provide information to the Core Team on necessary information such as when did this area burn or how many times has this area burned in the last thirty years. The Core Team attempted to visit every ecological site at least once and the modal ecological site for each DRG was visited multiple times in different locations and it different conditions or states. At each field site visit the following information was recorded:

  • GPS coordinates and photos
  • Elevation and aspect
  • Landform
  • Soil description to 20” depth and/or soil series and soil map unit
  • Fire history if relevant
  • Other known disturbances
  • Plant species composition by weight estimated ocularly and sometimes clipped
  • Shrub and tree cover
  • Rangeland Health
  • State-and-transition model state and community phase: ecological dynamics

Dr. Stringham modifies the STM if needed based on field notes. 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. Dr. Stringham along with her staff consisting of rangeland ecologists Amanda Wartgow and Devon Snyder complete the STMs by developing the narrative explaining 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. Patti Novak-Echenique peer reviews the ecological dynamics section and the STM and provides critical feedback.

This project produced 89 field notes over the course of one field season and three weeks of field work. The FINAL REPORT contains the Disturbance Response Groups, State-and-Transition Models for each ecological site contained within a DRG, a robust Ecological Dynamics section for the modal ecological site, Field Notes for all site visits and an extensive literature review for each DRG.

map of mlra 24

Introduction

MLRA 24 is located in Nevada (94 percent) and Oregon (6 percent). It makes up about 12,680 square miles (32,855 square kilometers). The towns of Winnemucca and Battle Mountain, Nevada, are along Interstate 80, which crosses this MLRA. A small portion of the Humboldt-Toiyabe National Forest and numerous wilderness study areas occur in this area. The Fort McDermitt Indian Reservation and the very small Battle Mountain and Winnemucca Indian Reservations also are in this area.

Physiography

This MLRA is in the Great Basin Section of the Basin and Range Province of the Intermontane Plateaus. A series of widely spaced north-south trending mountain ranges are separated by wide valleys filled with alluvium and lacustrine materials. The isolated ranges are dissected, uplifted fault-block mountains. Elevation ranges from 3,950 to 5,900 feet (1,205 to 1,800 meters) in most of the area, but it is more than 8,850 feet (2,700 meters) on some mountain peaks.

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Black Rock Desert-Humboldt (1604), 84 percent; Central Nevada Desert Basins (1606), 10 percent; and Oregon Closed Basins (1712), 6 percent. The Humboldt River flows through this area on its way to the Humboldt Sink.

Geology

Most of this area consists of wide valleys filled with deposits of alluvium washed in from the adjacent mountain ranges. Playas occur in the lowest areas in valleys with closed drainage systems. Most of the valleys, however, are drained by tributaries to the Humboldt River.
Mesozoic and Paleozoic volcanic rocks and marine and continental sediments are exposed in the mountain ranges. Some young andesite and basalt layers (6 to 17 million years old) occur at the margins of the mountains. These north-south trending ranges are uplifted fault blocks. Alluvial fans consist of coarser alluvium near the mountains and fine grained sediments at their distal ends.

Climate

In most of this area, the average annual precipitation is 6 to 12 inches (150 to 305 millimeters). It is as much as 40 inches (1,015 millimeters), however, in the mountain ranges. Most of the rainfall occurs as high-intensity, convective thunderstorms in spring and autumn. Precipitation occurs mainly as snow in winter. Summers are dry. The average annual temperature is 38 to 53 degrees F (3 to 12 degrees C). The freeze-free period averages 135 days and ranges from 100 to 175 days, decreasing in length with elevation.

Water

The total withdrawals average 985 million gallons per day (3,730 million liters per day). About 30 percent is from ground water sources, and 70 percent is from surface water sources. The low precipitation provides a small amount of water. Surface water is available from perennial and intermittent streams that carry snowmelt from the mountains. Late-season surface water supplies are deficient. Most of the water is used for irrigating grain and hay grown for cattle feed.

Irrigated areas are on alluvial fans and along streams in the valleys. Diversions from the Humboldt River are common. Because of additions of poor-quality drainage water from the irrigated areas, the quality of water in the Humboldt River deteriorates as the river flows west. Rye Patch Reservoir, on the lower reaches of the Humboldt River, in the southwest corner of this area, is the only large irrigation storage reservoir in this MLRA. Surface water from mountain runoff is generally of excellent quality. As the water seeps through the alluvial fan deposits, salts left in the soil as a result of evapotranspiration are dissolved. In the wetter years, when springs discharge this seepage water at the toe of the fan, local surface water quality can be degraded.

Limited quantities of ground water in valley fill are being rapidly developed for irrigation of crops. This water is typically of good quality and generally meets the national standards for drinking water. In some areas of geothermal activity or in shallow alluvial-lacustrine and volcanic deposits, high levels of arsenic (more than 50 parts per billion) exceed the national standards for drinking water. Ground water from the basin fill aquifers is slightly hard and has 200 to 400 parts per million (milligrams per liter) total dissolved solids.

Soils

The dominant soil order in the MLRA is Aridisols. Entisols, Inceptisols, and Mollisols also are important. The soils in the area dominantly have a mesic soil temperature regime, an aridic soil moisture regime, and mixed mineralogy. They generally are well drained, loamy, and very deep. Torriorthents (Boton series) formed in loess and alluvium over lacustrine sediments on lake plains and basin floors. Somewhat poorly drained Halaquepts (Wendane series) formed in alluvium on flood plains and terraces. Natrargids (Beoska and Oxcorel series) formed in loess over alluvium on fan piedmonts and plateaus. Haplocambids formed in loess over alluvium on alluvial fans and alluvial flats (Broyles, Orovada, and Weso series) and in alluvium on alluvial fans and lake terraces (Davey, Enko, and McConnel series). Shallow Argidurids formed in alluvium on fans and terraces (Tumtum series) and in loess and alluvium on fan remnants and plateaus (Dewar series). Moderately deep Haplargids (Roca series) formed in colluvium and residuum on hills and mountain slopes. Moderately deep Argixerolls (Reluctan series) formed in colluvium and residuum on hills, mountains, and plateaus.

Biology

This area supports shrub-grass vegetation. In areas where the average annual precipitation is about 8 inches (200 millimeters) or more, big sagebrush is the characteristic plant. Low sagebrush is characteristic on some soils with a clayey subsoil. Thurber needlegrass, bluebunch wheatgrass (scarce on the drier sites), basin wildrye, squirreltail, Sandberg bluegrass, forbs, spiny hops age, and Douglas rabbitbrush are common associated plants. Locally important are Idaho fescue and snowberry on sites where moisture is favorable, Utah juniper in a few high rocky areas, and Indian ricegrass and needle and thread on sandy soils. Shadscale and bud sagebrush associated with Indian ricegrass and bottlebrush squirreltail are dominant on the drier sites. Black greasewood, basin wildrye, and Nuttall saltbush are locally important on some low terraces and flood plains. Winterfat is prevalent in some areas.

Some of the major wildlife species in this area are mule deer, coyote, bobcat, beaver, muskrat, jackrabbit, cottontail, pheasant, chukar, Hungarian partridge, sage grouse, quail, ducks, and geese. The Humboldt River supports some warm-water fish. Trout are in some of the mountain streams.

Land Use

About three-fourths of this area is federally owned. The rest is used for fams, ranches, industrial enterprises (mining), and some urban and transportation purposes. Livestock grazing on native range is the principal agricultural enterprise. About 3 percent of the area, generally consisting of narrow strips along the major streams and margins of valleys, is used for irrigated hay, grain, pasture, alfalfa seed, or potatoes. The hay produced in the area is used principally for winter feeding of resident livestock.

The major soil resource concerns are control of wind erosion and reduction of the content of salts and sodium in the soils in areas used for crops or pasture. The main management considerations include proper grazing practices and the efficient use of the available supplies of surface water and ground water. Conservation practices on cropland generally include irrigation water management, crop residue management, and toxic salt reduction. Important practices on rangeland include prescribed grazing, brush management, and development of watering facilities.

For the complete research report contact Tamzen Stringham

T.K. Stringham, P. Novak-Echenique, A. Wartgow, D. Snyder 2017, USDA Ecological Site Description State-and-Transition Models Major Land Resource Area 24, Experiment Station, University of Nevada, Reno, RR-2017-03

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