Seasonal forage dynamics of three grasses with different origins and photosynthetic pathways in a rural North American cold steppe

摘要

Sustainable pastoralism on North American high-elevation cold steppes requires an understanding of forage dynamics relative to potential compositional changes. I sampled forage quality monthly and peak forage mass of a native C4 grass (Bouteloua gracilis), a native C3 grass (Pascopyrum smithii), and an exotic C3 grass (Agropyron cristatum) in 2016, an average precipitation and temperature year, on a 2,195 m elevation steppe grassland in Wyoming USA. Constrained ordination of the forage quality data displayed the first axis by photosynthetic pathways and the second axis by different native/exotic origins (86.3% fit variation explained; permutation test p = 0.003). Forage species, day of year, and their interaction were significant for all forage quality metrics (p 0.001) indicating that species-specific forage quality characteristics respond to seasonal changes differently. For example, A. cristatum had the earliest crude protein peak in April, followed by P. smithii from May – July, followed by B. gracilis in August. Other examples include lower lignin values for B. gracilis, and P and K peaks for P. smithii. A. cristatum yielded greater forage mass than P. smithii or B. gracilis. Relative to plant succession and potential compositional change, these three species combined match a broader range of livestock nutritional needs than any single species.