Four Native Wildflower Species Differ in Their Seed Yield Response to Irrigation

Native grasslands and their associated shrubs and wildflowers have been disappearing from the Great Basin.  Seed of native wildflowers are needed in restoration efforts.  Four key characteristic native wildflower species (Eriogonum umbellatum, Lomatium dissectum, Penstemon speciosus, and Sphaeralcea grossulariifolia) that grow in the same region were established at the OSU Malheur Experiment Station in 2006 and supplied with 0, 100, and 200 mm of irrigation per year.  Irrigations were divided in four equal increments from budding to seed set with four replicates per irrigation rate.  The irrigation timings differed by species. Seed was harvested over multiple years and optimal irrigation was determined by regression.  The four native wildflower species differed in their response to irrigation.  Lomatium dissectum seed yields were optimized with 140 mm of irrigation.  E. umbellatum seed yields were optimized with nearly 200 mm of irrigation in dry years and progressively less to no irrigation in the wettest year.  P. speciosus seed yields were optimized with 100 to 125 mm of irrigation in dry years and were reduced by irrigation in wet years. S. grossulariifolia seed yields did not respond to irrigation.