| The purpose of these experiments is to provide a framework for understanding the distribution of C. cardunculus. In a four year experiment to determine which of several common southern California plant communities provided habitat suitable for germination and establishment, areas already invaded by C. cardunculus and south-facing coastal sage scrub communities provided the most suitable germination habitat. However, in above average precipitation years, annual grasslands previously uninvaded by C. cardunculus provided the best establishment habitat.; To build on those results, a series of experiments investigated temperature and water potential interactions, planting depth, and presence and type of leaf litter on the surface and how these environmental variables impact seed germination. High temperature and low water potential delayed germination and reduced germination percentage. Increased planting depth did not decrease germination, but did reduce emergence when seeds were planted more than 10 cm below the soil surface. Hypocotyl length and crown burial depth increased with increasing planting depth. Leaf litter had little effect on germination or growth of C. cardunculus, but presence of leaf litter did result in a more shallow shoot apex.; In competition experiments simulating both colonization and restoration, C. cardunculus seedling measurements of diameter and number of leaves were reduced. The contribution of root competition was greater in the restoration simulation than the colonization simulation. In other experiments, the rate of taproot formation and timing of perennation was examined. Rate of taproot formation is similar to that found in other invasive species. Shoot removal did not activate any axillary meristems in this experiment. In a shading experiment, shading simulating that found under C. cardunculus plants reduced carbon assimilation by one quarter.; Finally, using data from a phenology experiment, a degree-day model was developed to predict seedling emergence and early development. The model, with low and high temperature thresholds of 10 and 20 C, respectively, and a vertical cutoff was validated with field data. The ability to predict emergence and early development is critical to battling C. cardunculus in the seedling stage where the likelihood of control success is much higher. |
