Survival of cabomba (Cabomba caroliniana) during lake drawdown within mounds of stranded vegetation

Abstract Control of submerged aquatic vegetation during drawdown is known to be hindered by mounds of stranded vegetation that protect underlying stems from desiccation. This study investigated the viability of stranded cabomba (Cabomba caroliniana) during a winter drawdown of Lake Benalla, Victoria, Australia. The viability of stems and crowns, determined by their ability to generate new shoots, was related to substrate exposure status, location in lake, mound height, and soil moisture, at 34 and 69 days after exposure (DAE). Stem viability at 34 and 69 DAE was most closely associated with exposure status, where ∼20% of stems under mounds on relatively dry substrate were viable, compared to ∼95% of stems under mounds on saturated substrate, and 92% of unexposed stems. Stem viability was similar when collected 34 and 69 DAE and was similar under naturally occurring mounds of differing thickness. In contrast, viability of exposed crowns was usually 40% or less, compared to 72% for unexposed crowns, and their viability was not influenced by substrate moisture. Instead, their viability was influenced by location in the lake and was proportional to mound thickness. Like stems, viability of crowns did not decrease over the duration of the drawdown. We concluded that for drawdown to be effective in minimizing viable stems, the substrate below them needs to dry out. Even then, viable crowns may be a source of recolonization.