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    • Rangeland Ecology & Management, Volume 62 (2009)
    • Rangeland Ecology & Management, Volume 62, Number 2 (March 2009)
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    A Process-Based Application of State-and-Transition Models: A Case Study of Western Juniper (Juniperus occidentalis) Encroachment

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    Author
    Petersen, Steven L.
    Stringham, Tamzen K.
    Roundy, Bruce A.
    Issue Date
    2009-03-01
    Keywords
    landscape ecology
    phase-shift
    state-and-transition
    succession
    thresholds
    transition
    western juniper
    
    Metadata
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    Citation
    Petersen, S. L., Stringham, T. K., & Roundy, B. A. (2009). A process-based application of state-and-transition models: a case study of western juniper (Juniperus occidentalis) encroachment. Rangeland Ecology & Management, 62(2), 186-192.
    Publisher
    Society for Range Management
    Journal
    Rangeland Ecology & Management
    URI
    http://hdl.handle.net/10150/643019
    DOI
    10.2111/06-171.1
    Additional Links
    https://rangelands.org/
    Abstract
    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. 
    Type
    text
    Article
    Language
    en
    ISSN
    0022-409X
    ae974a485f413a2113503eed53cd6c53
    10.2111/06-171.1
    Scopus Count
    Collections
    Rangeland Ecology & Management, Volume 62, Number 2 (March 2009)

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