Demographic characteristics of 3 Artemisia tridentata Nutt. subspecies
KeywordsArtemisia tridentata spp. wyomingensis
artemisia tridentata subsp. vaseyana
artemisia tridentata subsp. tridentata
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CitationPerryman, B. L., Maier, A. M., Hild, A. L., & Olson, R. A. (2001). Demographic characteristics of 3 Artemisia tridentata Nutt. subspecies. Journal of Range Management, 54(2), 166-170.
PublisherSociety for Range Management
JournalJournal of Range Management
AbstractPrevious research suggested that woody plant recruitment may occur in pulses in semi-arid areas. The overall objective of this study was to determine if this pulse phenomena was recorded in the demographic structures of big sagebrush (Artemisia tridentata Nutt.) stands in Wyoming. In 1997, approximately 75 stem cross sections were collected from 9 stands of each of 3 subspecies of big sagebrush in Wyoming along elevation and climatic gradients. Annual growth-rings were used to identify year of establishment and demographic characteristics were analyzed from age-class frequencies. Mean stand ages of the 3 subspecies were different (P = 0.002), and analyses revealed that Wyoming (A. tridentata ssp. wyomingensis) and mountain big sagebrush (A. tridentata ssp. vaseyana) stand ages (32 +/- 9 and 26 +/- 9 years, respectively) were significantly older than basin big sagebrush (A. tridentata ssp. tridentata) (17 +/- 3) stands (P < 0.05). Mean recruitment intervals (years) were shorter for basin (1.6) than for Wyoming (2.3) and mountain (2.2) sagebrush (P = < 0.01). The number of cohorts did not differ among the subspecies (P = 0.11), but the percent of years with recruitment was significantly higher for basin (59%) compared to Wyoming (37%) and mountain (39%) subspecies (P 0.0001). Age-class frequency distributions of each stand and regional stand combination were assessed for dispersion across each associated period of record. Chi-square goodness-of-fit tests were performed for the negative binomial distribution. All stands (with one exception) and all 3 regional stand combinations fit the negative binomial distribution. Age-class frequency patterns indicate that recruitment is clustered or aggregated across each period of record. Recruitment in big sagebrush stands occurs in pulses throughout Wyoming.
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Point sampling for leaf area index in sagebrush steppe communitiesClark, P. E.; Seyfried, M. S. (Society for Range Management, 2001-09-01)Although point sampling has been used for more than 30 years to quantify leaf area index (LAI), this field technique has not been rigorously evaluated in sagebrush steppe plant communities. Leaf area index estimates obtained using different sampling pin inclinations or combinations of pin inclinations were evaluated in Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young), low sagebrush (Artemisia arbuscula Nutt.), and mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) communities within the Reynolds Creek Experimental Watershed near Boise, Ida. Leaf area index values determined by clipping and processing green foliage through a leaf area meter were used as evaluation standards. Pins inclined at 13 degrees from the horizontal, used alone or in combination with pins of 52 degrees and/or 90 degrees inclinations, performed poorly for estimating LAI in the Wyoming big sagebrush and low sagebrush communities. Estimating total LAI with either the combination of 52 degrees and 90 degrees angle pins or with 52 degrees or 90 degrees pins alone explained at least 96% of the variability in LAI standard values from the Wyoming big sagebrush and mountain big sagebrush communities. Using 52 degrees angle pins alone produced model fits similar to those obtained when the combination of 52 degrees and 90 degrees angle pins were used to estimate shrub, graminoid, and forb LAI across all 3 communities (P > 0.1). Collecting point data using 52 degrees angle pins often provided better or similar model fits with LAI standards compared to other pin angles but using 90 degrees angle pins offers a better compromise between practicality, efficiency, and accuracy.
Climatic influences on recruitment of 3 subspecies of Artemisia tridentataMaier, A. M.; Perryman, B. L.; Olson, R. A.; Hild, A. L. (Society for Range Management, 2001-11-01)Previous research suggested that big sagebrush (Artemisia tridentata Nutt.) recruitment occurs in pulses consistent with favorable climatic conditions. In 1997, 75 stem sections were collected from 9 stands of each of the 3 subspecies of big sagebrush in Wyoming along elevation and climatic gradients. Annual growth rings were used to identify the year plants were established. Large cohorts of Wyoming big sagebrush (A. tridentata ssp. wyomingensis Beetle and Young) appeared in 1982, 1981, 1964, 1961, and 1955. Basin big sagebrush (A. tridentata ssp. tridentata Beetle and Johnson) cohorts flourished in 1991, 1986, 1985, 1982, and 1977. Mountain big sagebrush (A. tridentata ssp. vaseyana [Rydb.] Beetle) cohorts prospered in 1985, 1982, 1981, 1979, and 1974. Mean monthly precipitation and temperature records were compared to years with high and low recruitment using logistic regression models at 3 geographic scales (single-stand, regional, statewide). Wyoming big sagebrush recruitment was greatest in years with above-average December and January precipitation occurring after the first growing season (r2 = 0.10, 0.04, P < 0.05). Basin big sagebrush recruitment was most successful in years with above-average March, May, and June precipitation during the first growing season (r2 = 0.06, 0.09, 0.18, P < 0.05). Mountain big sagebrush recruitment was greatest in years with below-average February, April, and May precipitation after the first growing season (r2 = 0.03, 0.04, 0.04, P < 0.05). While variable precipitation patterns appear to contribute significantly to recruitment of big sagebrush, responses among the 3 major subspecies were quite variable. More complex models need to be developed to foster our understanding of the mechanisms affecting big sagebrush establishment.