Seedling emergence and seed production of curlycup gumweed

Abstract

Native rangeland forbs are in demand among Intermountain restorationists, but they are underrepresented in revegetation projects because of high seed cost, limited availability, and poorly understood establishment requirements. Curlycup gumweed (Grindelia squarrosa (Pursh) Dunal [Asteraceae]) is a short-lived forb, native to semi-arid sites in the Intermountain West, with potential for broadscale use in restoration activities. We conducted a glasshouse experiment examining seedling emergence of curlycup gumweed planted at depths of 0, 1, and 2 cm (0, 0.4, and 0.8 in) in 3 different soil textures (sand, loam, and clay loam). We also compared 3 seed harvest methods of curlycup gumweed in a replicated field trial and evaluated seed yield, purity, and viability. In a third experiment, we tracked viability of seed stored under dry, cool conditions over 3 y using tetrazolium (TZ) staining. Our seedling emergence experiment indicated that maximum emergence can be achieved by planting seed on the soil surface (0 cm) regardless of soil texture. Soil texture had no effect on seedling emergence at any depth. Seed yields from harvesting once via mechanical swathing, simulated using a hedge clipper, were comparable to yields from multiple hand harvests using a racquet-and-hopper, while harvesting with a Flail-Vac resulted in poor yields. Average seed purity and viability did not differ among harvesting methods. Finally, seedling vigor changed little under storage conditions and stayed above 95% over 3 y. Our results suggest curlycup gumweed has excellent potential for larger scale seed production and marketability.