Estimating Arundo donax ramet recruitment using degree-day based equations

Arundo donax is a tall perennial reed. Once established, it spreads by producing new shoots (ramets) from rhizomes. We performed two separate experiments to test the hypotheses that temperature (7, 8, 14, 16, or 20 °C) and combinations of temperature and nitrate concentration (0, 0.3, 0.6,1.2, 2.4, 3.6, 4.8, and 6.0 mg/l nitrate) regulated the initiation of ramet production. No ramets emerged from rhizome sections at 7 or 8 °C, but ramets emerged at 14, 16, and 20 °C. Neither time to ramet emergence nor the number of ramets that emerged was influenced by nitrate level in the watering solution. We used the above results in combination with ramet emergence data from plants grown outdoors at Davis, California to develop degree-day equations for three separate ramet cohorts. When compared to ramet emergence from different plants in different years, there was very good agreement between predicted and actual ramet emergence indicating that these equations provide a realistic representation of processes involved in ramet emergence. This is an important step in developing integrated management plans for this species.