We’ve long associated autumn with leaf fall and spring with blossoms, but this autumn you may have noticed something odd. Several locals spotted unseasonal flowers on pear and apple trees. In most cases it was just a few blossoms, but one very confused, smaller ornamental pear had almost a full spring bloom.
There have also been reports of other species flowering out of season, including guinea flowers, sweet bursaria (Bursaria spinosa), native pea (Dillwynia sericea) and hawthorn bush (Crataegus monogyna). What’s going on? We’re not really sure.
The study of these types of observations is called phenology. It includes the timing of biological events like spring blossoming, fruit development in summer and leaf colouration in autumn. In animals it can include the timing of migration, hibernation, hatching, and mating.
Depending on the species, phenological events are triggered by climatic variables such as the onset of rainfall, reaching a threshold temperature, the number of hours of sunshine or a combination of variables.
So what triggered our recent blooms? The Bureau of Meteorology’s Albury data showed that overnight temperatures in March and April were about a degree warmer than average, while day temperatures were around 1.5 degrees cooler than average. We also received approximately three times the average rainfall in March. It’s unclear which variable or combination of variables triggered the flowering, but it’s certainly got us curious. We’re also concerned about the impacts, particularly in the long term. Buds that burst in autumn won’t flower again in spring, resulting in reduced fruit yields, with consequences for humans and other species depending on that fruit.
In an article in The Conversation, ‘Why phenology is key in tracking climate change’, Associate Professor Jennifer Fitchett argues that phenology is one of the most sensitive biological indicators of climate change. ‘Phenological shifts are often detected long before irreversible ecosystem responses are apparent,’ she writes. Fitchett also stresses the importance of monitoring these changes in timing of phenological conditions.
It’s great to see the increasing numbers of local citizen scientists recording their nature observations on platforms like iNaturalist. If you’re tuned into nature and want to notify us of unseasonal observations, please email us so we can add them to our database: firstname.lastname@example.org. For information on our past observations see: watch.id.au/local-climate-impacts/
Note: An abridged version of this article by Lizette Salmon appeared as a ‘Living Lightly’ article in The Border Mail on 6/5/20.