States, transitions, and thresholds : further refinement for rangeland applications

Published March 2001. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalo

Application of nonequilibrium ecology to managed riparian ecosystems

Seasonal trends in water table level and soil moisture for four plant community types within an irrigated eastern Oregon riparian zone were described. Aboveground biomass, species composition, litter, percent bareground and percent basal cover of key plant species and life forms were measured. The relationship between water table levels and soil moisture content were analyzed using simple linear regression. Transition zones between plant community types based on soil moisture and/or depth to water table during the growing season were determined. The soil moisture-water table relationship can be used to predict changes in plant community composition induced by a permanent depth to water table change. Irrigation impact on meadow water table levels and stream temperature were determined. Water table levels responded to irrigation manipulations within days. The permanent cessation of irrigation would shrink the riparian meadows contained within this study from widths in excess of 300 m to less than 60 m. Continuous stream temperature data were collected on a stream running through adjacent non-irrigated and irrigated meadows. Daily maximum stream temperatures in the segment contained within the irrigated meadow were 1.0° to 3.0° C cooler than the reach contained within the non-irrigated meadow. Management impact on plant community attributes, forage production and forage quality were assessed under three pasture management alternatives. Comparison of stubble height, litter, forage production, forage quality, species composition, percent bareground and percent basal cover of key plant species and life forms indicated all three management alternatives are sustainable from both a plant community and a livestock production perspective

Infiltration, Runoff, and Sediment Yield in Response to Western Juniper Encroachment in Southeast Oregon

Infiltration was measured in a western juniper (Juniperus occidentalis Hook.) watershed to characterize the hydrologic processes associated with landscape position. Infiltration rate, runoff, and sediment content were measured with the use of a small-plot rainfall simulator. Study sites were located in each of the four primary aspects (north, south, east, and west). Research sites were located in two ecological sites—South Slopes 12-16 PZ and North Slopes 12-16 PZ. Within aspect, plots were located in three juniper cover levels: high (> 22%), moderate (13%-16%), and low (<3%) juniper canopy cover. During rainfall simulation, water was applied at a 10.2-cm h-1 rate, levels comparable to an infrequent, short-duration, high-intensity precipitation event. Runoff was measured at 5-min intervals for 60 min. Comparing canopy cover levels, steady-state infiltration rates on control plots (9.0 cm h-1) was 68% greater than high juniper cover sites (2.87 cm h-1) and 34% greater than moderate juniper cover sites (5.97 cm h-1) on south-facing slopes. On north-facing slopes, no differences in infiltration rates were observed between juniper cover levels, demonstrating differential hydrologic responses associated with ecological site. Generally, all water applied to control plots infiltrated. Highest infiltration rates were positively associated with increased surface litter and shrub cover. In addition, depth of water within the soil profile was lowest in high juniper cover plots. This suggests that less water is available to sustain understory and intercanopy plant growth in areas with high juniper cover. Accelerated runoff and erosion in juniper dominated sites (high level) across east-, west-, and south- facing slopes can lead to extensive degradation to the hydrology of those sites. These data suggest that sustained hydrologic processes are achieved with reduced western juniper canopy cover. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Ecological Site Descriptions: Consideration for Riparian Systems

The Rangelands archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform March 2020Legacy DOIs that must be preserved: 10.2458/azu_rangelands_v32i6_rep

Use of Felled Junipers to Protect Streamside Willows From Browsing

Willow (Salix) communities are important components of riparian ecosystems. However, browsing by livestock and wildlife species can negatively impact willow size and abundance, and make restoration efforts difficult. A common solution has been fencing of affected willows to exclude ungulates, but fencing is expensive and may not complement desirable land management strategies. An alternative to fencing is the use of structures that limit access to streamside willows, without excluding ungulate access to the entire riparian zone. We examined the use of felled western juniper trees (Juniperus occidentalis Hook) placed over streamside willow shrubs. Four replicates of felled western juniper treatments (covered) and noncovered treatments were applied to a 1.2-km length of stream in southeastern Oregon. Willows (< 2 m) within treatment areas were censused, tagged, examined for evidence of browse-use, and measured for maximum height during August 2002, before treatment. Posttreatment measurements were made in August and October 2003. Results indicate that by August 2003 (posttreatment) the average growth of willows in covered treatments was 25 cm (480%) greater than in noncovered treatments. By October 2003 (posttreatment), more shrubs were browsed in noncovered (84%) than covered (39%) treatments. Our data suggest that covering small willow shrubs (< 2 m tall) with felled western juniper is an effective deterrent to browsing.  The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 2020Legacy DOIs that must be preserved: 10.2458/azu_rangelands_v58i6_boy

State and transition modeling: An ecological process approach

State-and-transition models hold great potential to aid in understanding rangeland ecosystems’ response to natural and/or management-induced disturbances by providing a framework for organizing current undersanding of potential ecosystem dynamics. Many conceptual state-and-transition models have been developed, however, the ecological interpretation of the model’s primary components, states, transitions, and thresholds, has varied due to a lack of universally accepted definitions. The lack of consistency in definition has led to confusion and criticism indicating the need for further development and refinement of the theory and associated models. We present an extensive review of current literature and conceptual models and point out the inconsistencies in the application of nonequilibrium ecology concepts. The importance of ecosystem stability as defined by the resistance and resilience of plant communities to disturbance is discussed as an important concept relative to state-and-transition modeling. Finally, we propose a set of concise definitions for state-and-transition model components and we present a conceptual model of state/transition/threshold relationships that are determined by the resilience and resistance of the ecosystems’ primary ecological processes. This model provides a framework for development of process-based state-and-transition models for management and research.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Classification of Willow Species Using Large-Scale Aerial Photography

The distribution characteristics of willow (genus Salix) can be evaluated with the use of remote sensing, geographic information systems (GIS) technologies, and spatial analysis. This information can be used to better understand willow ecology, such as willow community composition, species relationships, and associations with other landscape attributes (i.e., soils, elevation gradients, water sources, and landscape position). Aerial photographs of a willow-dominated riparian area located in southeastern Oregon were taken in November 1999 at a 1:2 400 scale. Four basic techniques were used to separate willow species from each other in both color and infrared images using ERDAS Imagine® GIS. Willow species included Geyers willow (Salix geyeriana Anderson), Booth willow (Salix boothii Dorn), and Lemmon’s willow (Salix lemmonii Bebb). The techniques used to analyze aerial photographs included image resampling (degrade), image filtering (smoothing), unsupervised classification, and supervised classification. Highest accuracy was obtained using a supervised classification of the color images smoothed with a low-pass convolution filter (84.6% accuracy). Spectral samples were collected using a polygon digitizing method, which had superior results compared to the seed or region growing method. The infrared image was least effective in separating the plants into species classes (58.6% accuracy). This may be due to the lack of the blue band in the infrared image. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 2020Legacy DOIs that must be preserved: 10.2458/azu_rangelands_v58i6_stringha

A Process-Based Application of State-and-Transition Models: A Case Study of Western Juniper (Juniperus occidentalis) Encroachment

A threshold represents a point in space and time at which primary ecological processes degrade beyond the ability to self-repair. In ecosystems with juniper (Juniperus L. spp.) encroachment, ecological processes (i.e., infiltration) are impaired as intercanopy plant structure degrades during woodland expansion. The purpose of this research is to characterize influences of increasing juniper on vegetation structure and hydrologic processes in mountain big sagebrush-western juniper (Artemisia tridentata Nutt. subsp. vaseyana [Rydb.] Beetle-Juniperus occidentalis Hook.) communities and to identify and predict states and thresholds. Intercanopy plant cover and infiltration rates were sampled in relation to juniper canopy cover. Study plots, arranged in a randomized complete-block design, represented low shrub-high juniper, moderate shrub-moderate juniper, and high shrub-low juniper percentage of canopy cover levels at four primary aspects. In field plots, percentage of plant cover, bare ground, and steady-state infiltration rates were measured. In the laboratory, juniper canopy cover and topographic position were calculated for the same area using high-resolution aerial imagery and digital elevation data. Parametric and multivariate analyses differentiated vegetation states and associated abiotic processes. Hierarchical agglomerative cluster analysis identified significant changes in infiltration rate and plant structure from which threshold occurrence was predicted. Infiltration rates and percentage of bare ground were strongly correlated (r2 = 0.94). Bare ground was highest in low shrub-high juniper cover plots compared to both moderate and high shrub- low juniper cover levels on south-, east-, and west-facing sites. Multivariate tests indicated a distinct shift in plant structure and infiltration rates from moderate to low shrub-high juniper cover, suggesting a transition across an abiotic threshold. On north- facing slopes, bare ground remained low, irrespective of juniper cover. Land managers can use this approach to anticipate and identify thresholds at various landscape positions. The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202