ABSTRACT
Summary Knowledge of plant phenology and live weight dynamics is necessary for intensive management of semiarid rangelands. Thirteen sites in Wyoming were sampled for plant phenological development and culm weights of western wheatgrass (Agropyron smithii) and bluebunch wheatgrass (A. spicatum). These species are sympatric and allopatric within these rangelands. Such a distribution allows site comparisons between these species. Environmental data were collected for use in differentiating sites. Data on all variables were collected at 14-day intervals throughout the growing seasons of 1979 and 1980. Permanently marked plants were sampled for phenology, and plants of similar development were collected for culm-weight estimates. Cumulative precipitation, degree days, soil water potentials at three depths (0-15, 16-30, and 46-60 cm), soil temperature at 25 cm, and Julian dates were recorded. A two-way analysis of variance performed on culm-weight and phenological data identified nine groups of sites. For culm weights, western wheatgrass formed four distinct groups, bluebunch wheatgrass formed two distinct groups, and both species together formed three groups. Phenological data revealed the same groupings of sites. Discriminant analysis of micrometeorological variables showed that western wheatgrass produced the greatest culm weights at moderate amounts of degree-day accumulation and cumulative precipitation. Bluebunch wheatgrass culm weights were greatest at higher values of both variables. Phenological development was species related, with bluebunch wheatgrass developing more rapidly. Phenology on sites with low culm weights developed more rapidly than on sites with high culm weights. Micrometeorological variables were utilized to distinguish sites with bluebunch wheatgrass and western wheatgrass according to culm weights and phenological development. Dominant factors affecting the species were Julian date, degree-day accumulation, and cumulative precipitation to the sampling site. These variables were able to account for 91% of between-site variability in culm weights and phenology.
