Influence of Soil Color on Seedbed Microclimate and Seedling Demographics of a Perennial Bunchgrass

Perennial bunchgrasses are critical to maintaining sagebrush plant communities, but seeding of native bunchgrasses following fire has had limited success. Previous research indicated that blackened soils beneath burned sagebrush canopies have increased bunchgrass seeding success when compared with interspace locations. We investigated soil moisture and temperature across white, neutral, and black soils and tested the relationship between soil color and seedling demographics for bluebunch wheatgrass. We used a randomized block design with three treatments and five replications conducted in a Wyoming big sagebrush community in southeast Oregon. The study site was rototilled before establishing 50 x 50 cm plots in each of 2 yr. We installed soil temperature/moisture probes at 3-cm depth in each plot. Plots were seeded in November of each year with 125 viable seeds and covered in a < 1-mm layer of white, brown, or black aquarium sand. We counted emergent seedlings weekly through May of the year following planting. Soil moisture during the emergence period (March-May) was highest for white soils and lowest for black or neutral soils (P< 0.001); soil temperature was highest for black or neutral soils and lowest for white soils (P< 0.001). Year 1 was characterized by a relatively warm and dry emergence period, and year 2 was relatively cool and moist. Emergent seedling density was highest (P< 0.05) for white soils; surviving seedling density (on June 1) was highest (P< 0.05) for white soils in year 1 and black soils in year 2. Black soils had greater success in a year with lower soil temperatures and adequate soil moisture. When soil moisture was limited, and spring temperatures warmer, increased soil temperature on black soils led to seedling desiccation and death.