The historic flowering behaviour of River Red‐gum and Black Box in a flooding forest

Abstract

AbstractRiver Red‐gum (Eucalyptus camaldulensis) and Black Box (E. largiflorens) are the dominant tree species of Barmah forest, Victoria; part of a floodplain ecosystem which has been identified as being under threat due to the reduced frequency and duration and altered timing of flooding associated with river regulation, water extraction and drought. The flooding regime plays a significant role in the phenology in both these species. Hence, establishing past flowering behaviour using long‐term records (1934 to 1973) provides a historical baseline against which current and future flowering behaviour can be judged. Black Box was more consistent in its flowering, with an annual failure recurrence interval of 1 in 36 years less compared to 1 in 9.25 years for River Red‐gum. Black Box was also the more intense flowering species and flowered for longer (4.0 ± 1.9 months compared to 2.1 ± 1.4 months), with its flowering period encompassing River Red‐gum’s. The flowering of the two species was therefore synchronous. River Red‐gum displayed evidence of flowering more intensely every second year and therefore some dependence on the previous year’s flowering; this was absent in Black Box. The influence of flooding on flowering intensity over this 40‐year interval indicated that flooding 10 years out of 13 years with an inundation period greater than 6 months has a depressive effect on flowering intensity while flooding in 7 out of 13 years with an inundation period of no greater than 5 months enhances flowering intensity. This is more so for Black Box than River Red‐gum. However, flooding is a recurring event in this study, and therefore, it is difficult to isolate the effect of a single flood on flowering.