GERMINATION, LIGHT REQUIREMENTS, AND COMPETITIVE INTERACTIONS OF STIPA-LEUCOTRICHA (GRAMINEAE)

Reasons for the atypical distribution of Stipa leucotricha (Texas wint er grass), a C-3, cool season perennial bunchgrass, strictly south of 35 degrees N latitude are unknown. Germination requirements, light req uirements, and competitive abilities of S. leucotricha were investigat ed to better understand the biology and possibly explain its persisten ce in an area reported as more suitable for C-4 species. Aerial, chasm ogamous seeds (florets) were dormant, bur when scarified with concentr ated sulfuric acid for 15 minutes, germination increased from 18.5 +/- 7.7% to 82.7 +/- 4.6% which suggests seed bank longevity uncharacteri stic of most grasses. Aboveground, belowground, and total dry mass of seedlings were significantly, linearly related to light level, with gr eatest dry mass produced in the highest light treatment. Intraspecific competition for both S. leucotricha and Schizachyrium scoparium (litt le bluestem, a co-occurring C-4 perennial) was found at a density as l ow as 2 plants per pot. Interspecific competition studies demonstrated that growth of both species was greatest in the high light and high n itrogen treatment, and reduced at low light and low nitrogen levels. C omparisons of species differences between mixtures and monocultures in dicated that S. leucotricha was a better competitor al high light and nitrogen levels. At low levels of nitrogen and light interspecific com petition was equal. These characteristics do not fully explain its dis tribution strictly south of 35 degrees N latitude; however, its abilit y to compete with a climax prairie grass species under conditions typi cal of late successional grassland communities, along with growth duri ng a time of reduced temperature, increased soil moisture, and dormanc y of irs competitors are possible causes of the southern distribution of this C-3 grass.