Growth Rate Differences among Big Sagebrush [Artemisia tridentata] Accessions and Subspecies

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Abstract
Even-aged plants of 21 big sagebrush (A. tridentata) accessions were grown in a uniform garden to test growth parameter variation. Growth parameter measures (height, crown diameter, yield, and annual nonfloral leader growth) were scored after the 1975, 1976 and 1977 growing seasons. Nested analyses of variance and mean comparison tests showed significant (P < 0.05) accession and subspecies differences in each measure, each year. On a subspecies level, basin big sagebrush (A. t. tridentata) exceeded the other 2 subspecies (mountain big sagebrush = A. t. ssp. vaseyana, Wyoming big sagebrush = A. t. ssp. wyomingensis) for each character. In general, the values for the last 2 subspecies were not significantly different, but mountain big sagebrush tended to have larger values. Using 1975 data for yield and 1976 data for the other growth parameters, basin big sagebrush accessions averaged 147.9 .+-. 14.7 (se) cm in height, 193.0 .+-. 12.1 cm in maximum crown spread, 2217 .+-. 444 g current yield, and 12.7 .+-. 1.1 cm in annual leader growth. Corresponding values for mountain big sagebrush were 95.8 .+-. 2.2 cm, 157.3 .+-. 3.4 cm, 890 .+-. 77 g and 8.8 .+-. 0.6 cm. For Wyoming big sagebrush the values were 77.1 .+-. 4.1 cm, 129.6 .+-. 6.4 cm, 545 .+-. 84 g and 8.5 .+-. 1.1 cm. Comparison of 3 accessions'' performances at 2 uniform gardens and their native sites indicated that growth parameters, while subject to environmental influences, are under genetic control. The fastest growing and largest growing plants were diploid, 2n = 18, whereas the slowest growing ones were tetraploid, 2n = 36. Growth rate characteristics of big sagebrush should be considered for management purposes and in plant improvement programs [for forage].