Rangeland Ecology & Management

Current Rangeland Ecology and Management Research at EOARC

Rangeland Carbon Dioxide Flux

Carbon dioxide (CO2) is an important component of our atmosphere. It is used by plants during photosynthesis to capture and store energy from sunlight. The concentration of CO2 in the air never has been constant, however during the last century, levels of CO2 in the atmosphere have increased at an accelerated rate. This becomes important to mankind for two reasons.

First, since carbon dioxide is used by plants to capture and store energy, increasing concentrations of this compound probably have a fertilizing effect for plants. This has several important implications relating to plant productivity, water use efficiency and nutritional quality. In native ecosystems, differing abilities to use CO2 may lead to shifts in community composition and structure.

Second, carbon dioxide is one of those gasses which contributes to what is called the greenhouse effect, the warming of the earth's surface temperatures by the "insulating" effect of gasses such as carbon dioxide. There is considerable

 debate over the consequences of any such warming effect.

To help address this issue, this research center, along with several other Agricultural Research Service locations has undertaken a long-term study to measure the amount of carbon dioxide taken up and released by plants and soil on rangelands throughout the United States. Here at EOARC, we have established a study looking at the dynamics of CO2 flux on burned and unburned sagebrush rangeland.

The study is still underway, however we are finding that these rangelands are acting as sinks for carbon dioxide for most of the year. What that means is that the plants take up more CO2 than is released by above and below ground respiration.

The picture to the right shows the equipment we use to estimate the direction and magnitude of CO2 movement between the atmosphere and surface. In a nutshell, the system measures carbon dioxide concentration at two heights, along with other needed information, and we then use these data to estimate the rate of movement toward or away from the surface.

If you are interested in this study, check these recent publications, or contact Ray Angell or Tony Svejcar

Rainfall Distribution Study

Rainout Shelters One of the challenges of living and working in the Great Basin is the variable climate. However, there has been surpisingly little research on the effect of weather variation on rangeland vegetation. The difficulty in manipulating weather is part of the reason for the lack of prior research. One can attempt to document year-to-year changes in vegetation and relate the changes back to weather patterns. However, this approach requires very long time frames and there is still the problem of many variables to sort out (weather is more complex than just rainfall and temperature).

In this study we chose to focus on one question, "How does precipitation timing influence Great Basin vegetation?" This is a difficult subject to study because one cannot easily manipulate precipitation timing. Our approach was to exclude all precipitation with fixed location rain shelters and use an overhead sprinkler system to "rain on" three different zones under each rain shelter at the desired time.

Layout of Plots at Rainout Shelter We have five 30'x100' rain shelters each with three 30'x30' zones to which rain is applied at different times. Our three rainfall treatments (zones) are : 1) average current rainfall distribution, 2) a higher proportion of rainfall during winter, and 3) a higher proportion of rainfall during the spring. All three treatments recieve the same amount of precipitation.

Our measurements include variables such as plant development and productivity, species composition and cover, rooting activity, reproductive output, and soil moisture and nitrogen.

We hope the results of this study will help land managers better understand the impacts of weather on vegetation trends. Managers are faced with the challenge of separating the effects of weather from those induced by management. We also know that the Great Basin has undergone large changes in weather patterns in the past and will likely do so in the future. The results of this study might help us predict how climatic shifts will influence vegetation.

If you would like more information on this, contact Tony Svejcar , Jon Bates , Rick Miller , or Ray Angell.

Grazing Exclosure Study

exclosure in 1937 The 16,000 acre experimental range was established in 1937. The original directors of the experimental range had the foresight to establish thirteen 4-acre exclosures that have not been grazed by livestock since 1936. There was a detailed sampling of the vegetation when the exclosures were established, and several additional samplings over the past 60+ years. Most recently we have sampled for plant species compostion and cover inside and outside the exclosures in 1991, 1994, and 1997. The data is being analyzed for both changes over time, and grazing effects.

In three of the exclosures we added a burning treatment to the mix thus, we have grazed and ungrazed plots that were either burned, or left unburned. This arrangement will allow us to determine if there are interactions between burning and grazing. The burning treatments were applied during the fall of 1993 and sampling was conducted during 1992, 1993, 1994, and 1999. The first two samplings were prior to the burn, the second two after. An article detailing this study is currently in preparation. We will continue to take vegetation measurements in the exclosures in the foreseeable future.

grazed vs. ungrazed in 1993 dormant season burned treatment outside of exclosure 1995 grazed vs. ungrazed in 1997 growing season

For more information about this research contact Tony Svejcar or Rick Miller.

Expansion of Western Juniper

Western juniper (Juniperus occidentalis Hook var. occidentalis Vasek) currently occupies 5 million acres in Oregon, 3 million acres in northeastern California, a ½ million acres in Nevada and Idaho, and a few limited stands in southeastern Washington. In Oregon, western juniper is the most extensive conifer type. This species occupies a broad array of environments and soils varying from poorly drained heavy clays to excessively drained pumice sands. It is a relatively long lived species, exceeding ages of 1,000 years with the oldest living tree reported at 1600 years (Oregon's oldest tree recorded to date). On dry rocky sites, dead trees can remain standing for up to 600 years with the center growth ring dating as far back as 50 to 100 BC. However, an estimated 95% of western juniper is less than 100 years old.

Despite the large degree of variability of environments occupied by western juniper and the varying stages of woodland succession occupying today's landscapes, juniper woodlands are frequently treated generically in management, resource inventories, and wildlife habitat assessments. Our woodland expansion research program is; (1) documenting the chronology of expansion, (2) evaluating the impact of increasing tree dominance on understory plant composition across different soils and plant communities, and (3) evaluate the affects of woodland succession on abundance and diversity of avian populations.

Early successional juniper woodland Since the late 1800s western juniper has been actively encroaching or increasing in density in Intermountain plant communities ranging from shallow rocky heavy clay soils occupied by low sagebrush to deep clay loam or loam soils occupied by mountain big sagebrush or aspen groves. Accelerated juniper establishment began during the 1870s. The most rapid period of establishment occurred between 1885 and 1925, a period of wetter than average conditions, few fires, and intensive livestock grazing. The majority of western juniper woodlands are still in a state of change, succeeding from open juniper shrub steppe communities to closed woodlands.

As juniper dominance increases on a site the shrub understory declines. In the mountain big sagebrush alliance, sagebrush cover declined to approximately 80% of maximum potential as juniper increased to about 50% of maximum canopy cover. Mountain mahogany, bitterbrush, and aspen also declined as juniper dominance increased. Herbaceous cover and species diversity declined and bare ground increased with increasing juniper dominance in the mountain big sagebrush/Thurber needlegrass association. However, herbaceous cover on the deeper soils characterized by Idaho fescue did not decrease with increasing juniper dominance.

If you are interested in this study, check these recent publications , or contact Rick Miller , Tony Svejcar , or Jon Bates at this location.

Old Growth Juniper Woodlands

Oldest known living tree in Oregon at 1600 years old In the Intermountain West, it is estimated that 3 to 5%, or nearly 1.25 million ha, of western juniper woodland is old-growth. Old growth juniper has largely been ignored throughout this region. Attention has primarily focused on the rapidly expanding postsettlement stands of juniper throughout the western United States. Resource inventories, management plans, range improvement practices, research, and wildlife habitat evaluations typically have not differentiated between old-growth juniper and postsettlement woodlands. In addition, work describing old growth stand characteristics has been derived from more mesic heavily forested communities. These stand characteristics may not directly apply to semi-arid woodlands in the Intermountain West. Future work and inventories of old growth woodlands requires criteria for defining old growth across different habitats.

Increasing recognition by land managers and land owners of the existence of these communities has prompted questions about how to recognize old-growth, old growth community structure and composition, ecological importance of old growth, and appropriate management. Our recent efforts have focused on determining the age of old growth woodlands, describing composition and structure, developing criteria for identifying old growth woodlands based on community structure and tree growth form, and measuring abundance and diversity of birds and small mammals in old growth stands.

This study is still ongoing, however, facts of interest are: (1) trees can exceed ages of 1,000 years with the oldest living western juniper aged at 1600 years, (2) trees on arid sites can remain standing dead for hundreds of years, (3) the most extensive stands of old growth typically grow on the wind blown pumice sands of central Oregon, (4) most of these old stands are relatively open, ranging between 10 and 20% tree cover, (5) old woodlands in central Oregon support a relatively high abundance of birds during the breeding season, and (6) these old woodlands provide important avian wintering habitat. We have identified one extensive old growth woodland in the High Desert Ecological Province, which is typically characterized by widely scattered presettlement trees growing on shallow rocky soils. Woodland structure is very different on these igneous soils. Canopy cover ranges from 30% on the south aspect to 50% on the north aspect and few shrubs exist in the understory.

If you are interested in this study, check these recent publications , or contact Rick Miller.

Fire History in Sagebrush Communities

The recent expansion of western juniper throughout eastern Oregon and northeastern California began during the late 1800s. Postsettlement juniper woodland expansion in the West has been most frequently attributed to the introduction and overstocking of livestock, the reduced role of fire, and optimal climatic conditions during the late 1800s. However, few studies have been conducted that directly support this idea. Only a handful of studies have documented mean fire intervals in the sagebrush steppe biome, and few if any have evaluated the chronosequence of the introduction of livestock, the reduced role of fire, and climatic conditions with the initiation of postsettlement woodland expansion.

This study was designed to: (1) document the chronology of western juniper age distribution; (2) document pre- and postsettlement mean fire intervals in a mountain big sagebrush steppe community; and (3) determine the proportion of large to small fires, and evaluate their relationship to growing conditions in years preceding and concurrent with fire events. The work is being conducted throughout central and southeast Oregon, and northeast California. Old juniper killed in 1717 by fire

We are still constructing fire histories for many mountain big sagebrush communities throughout the study area. However, we have completed our work in the Chewaucan River Basin. In this 5,000 ha watershed we found western juniper expansion began between 1875 and 1885, with peak expansion rates occurring between 1905 and 1925. The fire record spans 1601 to 1996. Before 1897, mean fire intervals within individual clusters ranged from 12 to 15 years with years between fires varying between 3 to 28. Nearly one third of the fires in the basin were large and usually proceeded by one year of above-average growing conditions. Two fire events were recorded in the sparsely vegetated low sagebrush site, 1717 and 1855. The last large fire occurred in the study area in 1870 and the last small fire in 1897. The time sequence of wet climatic conditions between 1870 and 1915, introduction of livestock, and the reduced role of fire support the hypothesis that these factors contributed to the postsettlement expansion of western juniper.

We are in the process of developing fire histories for 7 additional sites. The fire record ranges from the early 1500s to present. Mean fire return intervals vary from 12 to 20 years, however, not all samples have been analyzed.

If you are interested in this study, check these recent publications , or contact Rick Miller at this location.

Fire Effects in Mountain, Wyoming, and Low Sagebrush Communities

Juniper stand after burning Fire played an important role in shaping many of the shrub steppe communities in the Intermountain West prior to Eurasian settlement. However, the role of fire was very dependent on plant community type. Presettlement fires occurred every 15 to 25 years in the relatively wet mountain big sagebrush communities decreasing to 50 to 100 years in the more arid Wyoming big sagebrush communities, to less than 100 years in low sagebrush stands. However, the role of fire has significantly changed across sagebrush communities since the late 1800s.

Recent concerns about fire, prescribed and wild, have increased the need for information on whole system responses. The lack of this type of information makes it difficult to address some of the questions raised by burning. Our research effort has focused on the response of plant and animal communities in sagebrush steppe community types to wild and prescribed fire. This ongoing effort is currently looking at; (1) changes in plant composition and structure in mountain and Wyoming big sagebrush, and low sagebrush communities, and (2) evaluate the affects of fire on abundance and species composition of birds, small mammals, and butterflies in mountain big sagebrush communities. The work is being conducted in southeast Oregon, northwest Nevada, and northeast California.

Preliminary results for mountain big sagebrush prescribed and wild fires:

1. Response of perennial grass cover was inconsistent, however, perennial and annual forbs consistently increased in the burned areas.
2. Litter cover is reduced from 4.5% to less the 1% following a fire but approaches preburn levels after 3 growing seasons.
3. Bareground is increased from 1 to 3 years following fire.
4. Introduced annual grasses, which accounted for less than 1% cover prior to burning, did not increase following fire.
5. Bird abundance on burn communities varied from being similar to greater than unburned sites.
6. The abundance of butterflies appear to be unaffected by fire, however, species composition is altered.

If you are interested in this study, check these recent publications , or contact Rick Miller .

Aspen Ecology and Rehabilitation in Eastern Oregon

It is generally accepted that aspen stands in the Blue Mountains and Northern Great Basin are in an ongoing state of decline. In some cases only one or two trees remain in a stand, and it is reasonable to conclude that extensive stand loss has occurred during the last several decades. The purpose of this study is to investigate the status and trend of aspen stands in the Blue Mountains and evaluate the success of ongoing aspen rehabilitation methodologies. The primary objectives are:

  1. Field reconnaissance of existing stands in the study area with emphasis on identifying historic extent of aspen; reviewing ongoing USFS and BLM inventory work; assisting or supplementing ongoing USFS and BLM inventory work in locating stands and sites; and characterizing existing structure (including age), condition and function. 
  2. Identify and evaluate exclosures; and previous, ongoing, and planned stand treatment projects. 
  3. Obtain funding for an extensive proposal to study aspen ecology and evaluate and monitor rehabilitation methods in these unique environments. 
  4. Continue to work with all interested potential partners or cooperators, and volunteers. 
  5. Develop a progress report for the RMEF, USFS, BLM, ODFW, and BMEI that summarizes the fieldwork. 

From the stated objectives we hope to 1) develop a better understanding of the past and present status, and trend of aspen; 2) identify aspen rehabilitation methods now in use and evaluate their level of success; 3) identify factors leading to aspen decline; 4) develop a working partnership between EOARC, BLM and USFS to initiate an intensive study of aspen in the Blue Mountains and northern Great Basin that will provide managers with methodologies of rehabilitation that have a high expectation of success and increase the knowledge base of aspen ecology.
Aspen with young stand of juniper encroaching


Western Juniper Encroachment into Aspen Communities in the Northwest Great Basin

In the Northwest Great Basin, aspen communities uniquely contribute to the biodiversity of a semi-arid, sagebrush-dominated landscape. In this same region, western juniper is encroaching into aspen stands. Aspen stands below 2,133 m elevation were sampled in northwest Nevada, northeast California, and southeast Oregon for density, canopy cover, age, stand structure, and recruitment of western juniper and aspen. Soils and tree litter from both species were collected to analyze the effects of western juniper in areas previously influenced by aspen. Additionally, two large aspen complexes in southeast Oregon were intensively aged to determine disturbance (fire) frequencies.

Western juniper encroachment into aspen stands peaked from 1920 to 1939 with 77% of all juniper trees sampled establishing during this period. Five percent were greater than 100 years and none exceeded 145 years. Three-fourths of aspen stands sampled have established populations of western juniper. Twenty-three percent have a dominant canopy of western juniper. Twelve percent of aspen stands sampled were completely replaced by western juniper. Average density of western juniper was 1,573 trees per hectare of aspen. Seventy percent of aspen stands sampled had zero recruitment of new aspen. Within the study area aspen stands averaged 98 years old. Forty-eight percent of stands were greater than 100 years old. There was an inverse correlation between aspen canopy cover and western juniper canopy cover (r2 = .80, p = .0001).

Soils influenced by western juniper had a higher C:N ratio and pH; higher amounts of salts, lime, and sulfate; and lower amounts of magnesium, iron, copper, and manganese (p < .05). Aspen litter had a lower C:N ratio than western juniper litter (p < .05). Prior to 1870, the two major aspen complexes sampled had mean fire return intervals of 10 and 11 years. However, the most recent disturbance in either complex was 80 to 90 years ago. This lack of disturbance (fire) coupled with aspen stand decadence and low recruitment levels leaves aspen communities in the Northwest Great Basin vulnerable to western juniper encroachment and replacement.

If you are interested in this study, contact Rick Miller , or Marty Vavra.

Riparian Plant Community Classification Study

Sawtooth Creek near Burns Oregon

Attempts to classify the “health” or “functionality” of riparian systems typically focus on morphology of the stream channel and associated banks, and attempt to relate this information to the potential hydrologic activity of the stream. In this paradigm, riparian vegetation composition is often viewed as a consequence of stream morphology, or, alternatively, a direct result of management actions (i.e. livestock grazing). This view of riparian plant community ecology is incomplete, in that it does not take into consideration other site factors (e.g. soil texture, limiting layers…) which may influence the presence or absence of a given plant community type. At present, there is little empirical information on the site factors required for establishment and persistence of specific plant community types in riparian zones in southeast Oregon. In upland areas, the type of “ecological site” denotes the particular suite of environmental conditions present at a given site and serves as a useful reference for deducing the range of plant community types capable of existing at that site. It is our view that a similar approach applied to riparian areas may increase our understanding of plant community dynamics in these systems. Our overall aim in this project is to delineate environmental factors that influence plant community composition of riparian areas in southeast Oregon. We will simultaneously examine the specific and interactive effects of management actions.

Fieldwork will take place on Rattlesnake Creek, Sawtooth Creek, and Nicoll Creek, in northern Harney County, OR during the 2000 and 2001 growing seasons. We will attempt to sample a set of sites that represents our interpretation of the range of plant community types extant on a given drainage. At each site we will estimate vegetation composition and record soil properties, stream characteristics. Management information will be obtained from the appropriate management agency or landowner. We will attempt to sample a total of 25 sites per creek during the 2000 and 2001 growing seasons, for a total of 150 sites.

In the data analysis phase of this project we will use statistical procedures to group similar plant communities and define important environmental variables which influence plant community type (e.g. soil texture, soil moisture, elevation). Similar procedures will be used to determine what environmental factors most influence plant species composition within a given community type.

The end product of our efforts will be a publication detailing riparian plant community types along with the environmental and management factors influencing plant species composition. Information gained from this effort should allow managers to more accurately separate the influences of management actions and site conditions on plant community dynamics, and should serve as a useful reference for stream rehabilitation/re-vegetation efforts.

If you are interested in this study, contact Chad Boyd.

Riparian Vegetation Regrowth Study



Professional activities

Dr. Boyd is a member of the Oregon Sage-grouse planning team, and organized a diverse group of authors in developing and invited synthesis paper on the ecology and management of sage-grouse for the Journal of Range Management.  He currently serves on the technical review panel for the Natural Resource Conservation Service’s “Sage-grouse Restoration Project”.


Research activities (Livestock grazing study)

Livestock grazing has been indirectly related to sage-grouse declines in the western United States and southern Canada; however, there is a lack of scientific research that directly relates the two. We used grazing trials conducted in the summer of 2003 and 2004 to determine the level of utilization at which cattle begin to access herbaceous vegetation adjacent to and under the canopy of sagebrush. This vegetation is thought to provide important screening cover for nesting sage-grouse, providing a degree of protection from potential nest predators.  Four pastures 15 acre pastures were fenced in a Wyoming big sagebrush community and each stocked with 3 to 4 yearling heifers. Within each pasture 30 sagebrush plants were randomly located and a randomly selected perennial grass was permanently marked under the canopy of each sagebrush and a second marked in the interspace between shrubs.  Visual obstruction for a potential nest site was measured using a modified Robel pole to document changes in screening cover with increasing herbaceous utilization. Grass plants were checked every second day and given a grazed or ungrazed score. Changes in standing crop and utilization (by weight) were assessed weekly by clipping 20 random 1-m² plots in each pasture. Grazing of under-canopy plants was negligible at light to moderate levels of utilization (e.g. < 10% of under canopy plants were grazed at 30% pasture utilization). At utilization levels >30% by weight, under canopy plants were used with increasing frequency. There was no statistical effect on visual obscurity with consumption of forage for this environment. Overall, our data suggest that sagebrush constituted the bulk of screening cover at this site and that utilization of understory grasses will be minimal with light grazing.



Related Publications

Crawford, J.A., R.A. Olson, N.E. West, J.C. Mosley, M.A. Schroeder, T.D. Whitson, R.F. Miller, M.A. Gregg, and C.S. Boyd.  2004.  Ecology and management of sage-grouse and sage-grouse habitat.  Journal of Range Management 57:2-19.


France, K.A. 2005.  Interspace/Under-canopy Foraging Patterns of Beef Cattle in Sagebrush Communities: Implications to Sage-grouse Nesting Habitat. M.S. Thesis, Oregon State University, Corvallis.

2005.  Greater Sage-Grouse Conservation Assessment and Strategy for Oregon:  A plan to Maintain and Enhance Populations and Habitat.

If you are interested in this study, contact Chad Boyd.

Monitoring Willow Abundance

Few logistically feasible techniques exist for monitoring changes in the biomass of willow and other woody riparian species. In this ongoing project, we are attempting to develop a method for monitoring changes in willow biomass which is based on evaluating percent visual obstruction and incorporates the use of scanned 35mm images. The relationship between visual obstruction and willow biomass is determined using a sequential removal technique. Harvested willow branches are placed in a holding device such that they are oriented perpendicular to the ground and located in front of a 70 x 50cm photoboard. The leaves obstructing view of the photoboard are then incrementally removed, with each successive removal representing an approximately 25% decrease in visual obstruction of the photoboard. A photo is taken, before and after each removal, and harvested leaf material is dried and weighed. Camera placement is 3.5 meters from the photoboard with a lens focal length of 80mm. Slides are then scanned and cropped to encompass the dimensions of the photoboard. Visual obstruction is estimated for all scanned images, using Sigma Scan 5.0 computer software, by determining the amount of the photoboard visible in the image and comparing that to its' actual area. The relationship between percent visual obstruction and leaf biomass is evaluated by regressing the amount of leaf biomass covering the photoboard against percent visual obstruction. Preliminary results indicate a strong relationship between visual obstruction and willow leaf biomass.
Photo Analysis of Willow Biomass

We are currently exploring the idea of using permanent photo monitoring stations to evaluate changes in willow biomass over time. Each monitoring station will consist of two 2 x 12" boards placed behind a willow clump (Figure 1). willow sampling diagram

The boards will be placed at roughly 1/2 and 2/3 the height of the willow clump. If the clump is immature, an average willow height of nearby mature willows will be used to determine height placement of boards. Annual photographs will be taken from a permanent photo point located perpendicular to the visual obstruction boards. We will use a minimum focal length of 50mm to minimize distortion of scale, and the photo-point will be located just far enough from the willow clump to frame the mounting posts in the photograph. Photos will be scanned and visual obstruction of each board will be determined. This setup will facilitate determination of visual obstruction at two levels in the tree canopy. Changes in these readings from year to year can be used to imply changes in biomass of the willow clump. The boards will be of known length and can be used as scale references for determining the height and width of the clump.

If you are interested in this study, contact Chad Boyd at this location.