Microenvironment of a dynamic annual community in relation to range improvement

Available soil moisture permitted seed germination, seedling emergence, and growth of plants in this community. Temperature controlled the general rate of growth, and also created detectable differences in plant response when it dropped low enough to affect germination of seeds or caryopses or rose high enough to stress plants directly, or indirectly by more rapid depletion of soil moisture. The overriding factor of competition which prevented establishment of hardinggrass and perlagrass was interception of light by the canopy of annual plants during the growing season. The shading effect was most severe at ground level. During crucial periods of emergence and growth of the seeded species, this shading was virtually restricted to 1 or 2 cm above the surface. Soil-moisture depletion mattered primarily at the end of the growing season, but in some restricted periods during the season it became an important factor.