With his collaborator, R. Kent Beattie, he surveyed the Palouse area of southeastern Washington, and expanded the study to the entire state in 1906.
In 1902, he issued and distributed bryophyte specimens in an exsiccata-like series entitled Musci Occidentali-Americani.
On a trip to Africa, he found Sudan grass and introduced it to North America as a forage plant (vegetable matter eaten by livestock).
Piper's knowledge of grasses led him to become Chairman of the United States Golf Association's Green Section from 1920 until his death.
The botanist was instrumental in establishing this plant as a successful crop in the U.S.[6][7] It became a fundamental part of U.S. agriculture.