Germination Preferences And Effects Of Micro-Site Variation

On Lupinus Perennis Establishment In An Oak Savanna

Scott D. Kelly and Helen J. Michaels

Complex patterns of variation in environmental factors are found in the open areas (gaps) of oak savannas. This environmental variation will influence both seed germination and emergence as well as early seedling growth. To understand the factors influencing recruitment of Lupinus perennis, a dominant species of Midwestern oak savannas that is the only known larval food source for the Federally Endangered Karner Blue Butterfly, a field experiment examined the effects of micro-site variation on successful emergence and first season establishment. In addition, a growth chamber study was conducted to determine the optimal dormancy breaking requirements for L. perennis seeds. Four single effect (stratification, scarification, heat, and control) and 3 crossed-effect treatments were compared using failure time analysis of the growth chamber data. In the field experiment, 1568 seeds were placed into 32 grids in a savanna gap for which environmental data were collected through the season. Seeds given the combined scarification + stratification treatment maximized both the rate and numbers of seeds germinating. Field emergence and growth in May was best explained by light, soil moisture and phosphorus, with late afternoon light in May increasing growth but decreasing seedling numbers. Although pH varied within a very narrow range (pH 4.8 to 5.2), June seedling growth increased in response. By July, light had the dominant effect: numbers tended to decline in locations exposed to morning light, while mid-day and late afternoon light increased growth.