Phenology is the study of periodic biological functions, such as reproduction. We have examined the timing and relative density of new leaves, buds, flowers and fruits in river red gum (Eucalyptus camaldulensis) and coolibah (Eucalyptus coolabah). Previously, river red gum phenology has been studied in the southern Murray-Darling Basin (MDB), while coolibah phenology has received little attention. We hypothesised that the phenology of these species would differ between the southern and northern MDB as a response to climatic differences.
Observations were made at nine sites along the Condamine-Balonne River (northern MDB) over seven years. The mean timing of phenological events was consistent across sites and years for both species. The results did not differ from those reported for the southern MDB, however first flowers occur earlier in the north. Density did not differ between sites but differed significantly between years. Our data also supports findings from the southern MDB that light fruit crops alternate with heavy crops.
The production of new leaves and immature buds in both species was correlated with higher rainfall, river discharge and warming temperatures. Number of days flooded was correlated with new leaves in river red gum and immature buds in coolibah. Coolibah were found to retain closed fruit in the canopy for longer under dry conditions and are likely to release their seeds in autumn/early winter.
Spring rainfall was important to stimulate reproduction in river red gum and coolibah, and summer/autumn flooding was important to provide for germinants and seedlings and may trigger seed release. Moreover, reproduction and recruitment in these species relies on a series of flows and flood events that occur on decadal, not annual time scales. The outcomes of this project will inform water planning in the Queensland MDB by improving understanding of important vegetation and its link to the flow regime.