Variation in sagebrush communities historically seeded with crested wheatgrass in the eastern great basin

Authors: Monaco, Thomas; Williams, Justin; MORRIS, LESLEY - Oregon State University; GUNNELL, KEVIN - Utah Division Of Wildlife Resources; Johanson, Jamin

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2017
Publication Date: 11/1/2017
Citation: Monaco, T.A., Williams, J.R., Morris, L.R., Gunnell, K.L., Johanson, J.K. 2017. Variation in sagebrush communities historically seeded with crested wheatgrass in the eastern great basin. Rangeland Ecology and Management. 70:683-690.

Interpretive Summary: Although crested wheatgrass (CWG; Agropyron cristatum [L.] Gaertn.) has been one of the most commonly seeded exotic species in the western United States, long-term successional trajectories of seeded sites are poorly characterized, especially for big sagebrush (Artemisia tridentata Nutt.) ecosystems in the Great Basin, USA. Interpreting successional trajectories is particularly difficult because many seeded sites were actively managed with subsequent treatments to kill sagebrush and sustain high forage productivity of CWG plants. In addition, inherent differences in climate, topography, soils, and disturbance regimes may lead to variable vegetation structure and species composition among ecological sites. To clarify variation in successional trajectories, we measured vegetation composition, plant species diversity, ground cover, and soil properties in 38, 30-50 year-old, historical CWG seedings that lacked subsequent sagebrush treatments and distributed across 15 Ecological Sites. The multivariate dataset was analyzed using principal components analysis (PCA), to identify "defining factors" that best explained variation among and within ecological sites. Among-site variation was primarily attributed to an inverse relationship between CWG and sagebrush abundance (R2 = 0.69; P < 0.0001) and their affinity for either silty or sandy soil textures, respectively, as well as a negative association between CWG abundance and species diversity (R2 = 0.67; P < 0.0001). In contrast, variation within three extensively sampled ecological sites was defined by unique factors, yet all sites were best partitioned into two distinct vegetation states dominated by either CWG or sagebrush with hierarchical cluster analysis. These results do not support the assumption that crested wheatgrass seedings uniformly remain in vegetation states with low diversity and sagebrush re-establishment over the long-term (i.e., 30-50 years). We suggest that a broader interpretation of plant community dynamics is needed within contemporary state-and-transition vegetation models while avoiding generalizations of how historically seeded Wyoming big sagebrush sites will respond over the long-term.

Technical Abstract: Although crested wheatgrass (CWG; Agropyron cristatum [L.] Gaertn.) has been one of the most commonly seeded exotic species in the western United States, long-term successional trajectories of seeded sites are poorly characterized, especially for big sagebrush (Artemisia tridentana Nutt.) ecosystems in the Great Basin, USA. Interpreting successional trajectories is particularly difficult because many seeded sites were actively managed with subsequent treatments to kill sagebrush and sustain high forage productivity of CWG plants. In addition, inherent differences in climate, topography, soils, and disturbance regimes may lead to variable vegetation structure and species composition among ecological sites. To clarify variation in successional trajectores, we measured vegetation composition, plant species diversity, ground cover, and soil properties in 38, 30-50 year-old, historical CWG seedings that lacked subsequent sagebrush treatments and distributed across 15 Ecological Sites. The multivariate dataset was analyzed using principal components analysis (PCA), to identify "defining factors" that best explained variation among and within ecological sites. Among-site variation was primarily attributed to an inverse relationship between CWG and sagebrush abundance (R2 = 0.69; P < 0.0001) and their affinity for either silty or sandy soil textures, respectively, as well as a negative association between CWG abundance and species diversity (R2 = 0.67; P < 0.0001). In contrast, variation within three extensively sampled ecological sites was defined by unique factors, yet all sites were best partitioned into two distinct vegetation states dominated by either CWG or sagebrush with hierarchical cluster analysis. These results do not support the assumption that crested wheatgrass seedings uniformly remain in vegetation states with low diversity and sagebrush re-establishment over the long-term (i.e., 30-50 years). We suggest that a broader interpretation of plant community dynamics is needed within contemporary state-and-transition vegetation models while avoiding generalizations of how historically seeded Wyoming big sagebrush sites will respond over the long-term.