Supra-annual Masting: When Will Those Trees Flower?

by Kris Fricke · Australian Bee Journal, August 2026 · pp. 22–28

Fricke, K. (2026). “Supra-annual Masting: When Will Those Trees Flower?” Australian Bee Journal, 107(8), 22–28.Suggested citation

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When Will Those Trees Flower?

Supra-annual masting explained By Kris Fricke

I had been a beekeeper for 15 years already before I came to Australia. I thought I knew a thing or two about beekeeping. Arriving here, however, I discovered beekeeping is only like 10% of beekeeping here! The rest is the trees!

In most other countries you can do the same thing every single year. In California I overwintered in the desert lowlands, hit the citrus in spring, and then it was up the mountains for wild sage in the chaparral, and the meadow flowers of the oak forests in the narrow valleys. Wild buckwheat at the end of summer. Every year, the same pattern, up and down the mountain.

Here in Australia, however, everything seems to flower every 3 years, every 4 years, every 7 years, when it rains, or when it doesn’t. No one year is the same. As a new arrival, it was a challenge not just learning these patterns, but how to distinguish one type of tree from another, and where they could be found, and then of course, finding a site near them. This can be a real challenge, although it’s also part of what I enjoy about beekeeping here – when telling non-beekeepers about what we do I like to characterize it like a giant scavenger hunt across the entire region, challenging your knowledge of the climate and ecosystem to come up with the winning hive movement choice.

Thanks to a 2001 RIRDC (the predecessor of Agrifutures) report1 I can put solid numbers to this behaviour. This study was conducted in 1996 in collaboration with the Victorian Apiarist Association.

Above: Fig 1. Top nectar sources in Victoria identified in the 1996 survey.

Recent Podcasts Of Interest Two Bees in a Podcast – Varroa Biology and Pesticite Research with Kirsten Traynor What’s the Buzz – SE QLD is screaming for help as unknown viruses cause mass bee losses Beekeeping Today – Beekeeping Around the World with Dr Robert Owen [Author of the Australian Beekeeping Guide and founder of Melbourne based Bob’s Beekeeping]

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When Will Those Trees Flower?, cont’d

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And now, keeping the same order from the above chart, here’s how frequently those same plants flower:

Exploring honey’s anti-aging properties in human skin cells SOCIETY FOR EXPERIMENTAL BIOLOGY Ongoing research reveals that multifloral honey is a promising candidate for protecting human skin cells from premature ageing and cell damage caused by UV radiation, with the potential for developing future clinical and cosmetic applications. Honey is already well known in the medical and cosmetic industries for its antioxidant, antimicrobial, antiinflammatory and wound-healing properties, and sterile honey-derived medical products already exist in the form of dressings, gels and ointments for burns and difficult-to-heal wounds. “I have always been interested in the fact that certain honeys, such as Manuka honey, are used in medical-grade applications,” says Dr Fikiye Fulya Kavak, a member of Prof. Margherita Maioli's research team at the University of Sassari, Italy, whose background in medical biology and personal interests in beekeeping and cosmetic science inspired this project. “This led me to ask whether high-quality multifloral honey could also show measurable protective effects for human skin cells.” Read more here

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And finally, just one more chart, this is looking at all apiary sites identified in Victoria, how frequently they have major flows:

As you can see, only 10% of Victorian beekeeping sites have a flow every year, and over 60% of them are less frequent than every two years. This illustrates the degree to which one must be able to anticipate where the next flow will be, and find a place there you can put your bees. Let me tell you this is a bit of a hurdle to someone trying to break into beekeeping here.

Okay, so this may not be news for most of you, but why eucalypts do this is a different gumnut entirely. Recently, I’ve been taking a pollination ecology class, and chose to do my big report on this, so now I’m all learned up

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on it.

This is called supra-annual masting. Supra-annual means less frequently than once a year, and “masting” is heavily synchronized flowering/seeding at a variable interval.

Why do flowering plants do this? There’s two theories: Predator satiation – basically to overwhelm the ability of predators to consume all the flowers or seeds before they can germinate. We’re not used to thinking of predators of seeds but consider the most prominent old-world mast-flowering plant – the oak. Squirrels, famously, and many other animals, love to eat their seeds (acorns), so they practice supra-annual masting to overwhelm the ability of animals to eat all their seeds – though squirrels respond with hoarding. Here in Australia this is less an issue, gumnuts are generally small and granivorous animals such as cockatoos do eat them but surprisingly the real threat is harvester ants which can take and consume significant portions of fallen gumnuts;

Pollination efficiency – you know flowers need to be pollinated, and they need to be pollinated by the same kind of plant as themselves (a “conspecific”). If there’s an overwhelming number of the same species in an area that’s more likely to happen. But usually plants find other means of ensuring pollination by conspecifics or a simple pattern of always flowering at the same time every year is usually enough to accomplish this. But what’s unique about Australia is a lot of the pollinators - lorikeets, honeyeaters, flying foxes - are migratory. Flying foxes exercising “facultative latitudinal migration” migrate 45 km a day.2 Basically the pollinating animals do as the beekeepers do and follow the flow, but they have countless generations of instincts telling them where to go.

What Triggers Masting?

It seems it is not simple. There are seven factors that feed into whether one of these trees flower (then we’ll deal with how they get in sync).3

Vernalization – prolonged cold ambient temperatures switch off a repressor gene (which is there to prevent flowering before winter);

Autonomus pathway – this is a set of genes that put automatic pressure towards flowering that triggers flowering if there are not sufficient repressors against it;

Photoperiod – day length cues;

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Age – genes prevent flowering below a certain age; Sugar – reports if the sugar resources to flower are available; Ambient temperature – several genes have been shown to be activated by warm ambient temperatures, and repressed by cool temperatures;

Hormonal – plant hormones contribute to keying on flowering when these other factors reach a certain point. How Do they Get in Sync?

So the trees obviously don’t get together for annual AGMs to vote on when they’ll next flower, after approving the minutes and treasury reports and wrangling over inconsequential changes to their bylaws, and we can envy them for it, but how do they decide when they’ll all flower then? There’s several different possibilities linking to different pathways:

The “Moran Effect” (not to be confused with a “moron effect,” which pertains to beekeepers never checking their brood) is basically that they are all responding to the same climatic conditions and therefore all respond to the cues at the same time. The ambient temperature, photoperiod and vernalization pathways would feed in to this.4

Resource matching – trees don’t flower unless they have the resources to, as controlled by the sugar pathway. As they’re all accumulating resources at about the same rate this would keep them on a synchronized schedule, even if it takes years to get to the necessary sugar threshold.

Pollen coupling – this is a neat one and I think is the real key as to how something that only flowers once every four years can get all in sync. Once flowers are pollinated, they then become seeds, into which the tree pours much more resources. This sets the tree back much further than if it hadn’t made all those seeds. So the tree that flowers in the off years gets barely pollinated, produces few seeds, and is able to flower again much sooner, maybe every year; meanwhile the ones that got well-pollinated produce mass seeds and the resource cost sets them back enough that it’s years before they have enough to flower again. The tree flowering every year eventually catches up with the others in the mass flowering event that brings all the pollinators, and then it’s in sync with them.

Facultative masting – this is your fire, flood, or draught cued flowering. The fire cue comes from compounds called karrikins (from an Australian aboriginal word actually) which cue germination, an effective signal for trees to cue from since it honestly signals bare nutrient-rich ground will be available. Droughts can trigger flowering in some species (in the anticipation, presumably, that it will make fire likely and then their seeds will have that nutrient rich bare ground), and floods as well, both of which work through the sugar/resource pathway.5 Facultative masting doesn’t necessarily just mean events such as fire and flood, but can mean specific climatic triggers. For example many box-ironbark trees such as grey box, yellow box, and red ironbark are facultatively triggered by temperature,6,7, which is part of what makes predicting flow in Victoria so difficult. River red gum, coolabah and black box are all cued by flooding.8 In fact, high rainfall or flooding effect not just budding, but seed fall and germination – and flood control measures have in some cases negatively affected the ability of these trees to reproduce.9,10,

Let’s dive a bit deeper into the box-ironbark facultative masting as I’m sure it’s a topic many readers are keenly interested in, and we are fortunate to have a paper specifically focusing on it. The study looked at trees in Havelock and Rushworth, Victoria. They found yellow gum, red box, and red ironbark flowering were all correlated to the temperature (accumulation of degree-days) in the two months prior to the start of flowering. Rushworth always flowered earlier than Havelock in direct proportion to the warmer days there. For yellow gum specifically, the flowering always stopped when the average daily temperature exceeded 18°C. It seems they assume the other trees have a similar stop-cue but weren’t able to determine it, and “the reasons for E. melliodora [yellow box] at Havelock having such a different month [March, compared to December for the others] of finishing are not readily explainable.” They note that genetics play a significant factor and is “perhaps the main reason” for Havelock yellow box being different. Yellow gum flowered every year (in keeping with the Goodman finding), and red box was most variable. They noted that the red ironbark trees in their two study areas fell into two distinct set types, an early flowering (January) and late flowering (July) variant. The variants could be intermingled together. It should be noted this paper primarily looked at within-year flowering rather than the supra-annual patterns, so there could be more to it that determines in which years these trees flower.

Now this is what the scientists say, let’s validate that against / compare it to the knowledge of experienced Victorian beekeepers. I asked John Edmonds about the ironbark flowering and he said “around parts of central Victoria it starts flowering mid January to March, and is called early flowering ironbark. Tarnagaulla, Bendigo and Rushworth have large stands of it. Mid-flowering ironbark is in the Wellsford Forest, Bendigo, and some other areas. The largest amount of ironbark is winter flowering type and it starts usually April to September but can be later. Beekeepers are cautious of it as it has no pollen and plenty of thin nectar resulting in weak spring bees.”

Which is all to say, while I’m obviously a big believer in science, you can see how much more comprehensive and deeply nuanced the knowledge carried by our experienced beekeepers is.

How Do Beekeepers Cope With This?

There’s one attribute of eucalyptus trees that makes what would be extremely difficult guesswork much much

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easier. While many flowering trees may set buds months in advance, they’re usually so small only a close examination would reveal them. But eucalypts make large visible buds (the meaning of the name eucalyptus in fact) visible to the trained eye from the ground (it helps to carry a pair of binoculars in the glovebox, which many beekeepers do for this purpose) many months before flowering. River red gums for example bud for over two years before flowering, the mountain ash buds for 27-29 months before flowering. For this reason you’ll often hear the old seasoned beekeepers planning the whole year ahead based on what they’ve seen budding.

A Biosecurity Problem

Reading up about masting, a biosecurity threat posed by the phenomena is often mentioned. Bamboo masting in India causes rodent plagues, as do oak mastings in the northern hemisphere. To this I would add another one – the erratic flowering patterns here in Victoria cause all the migratory beekeepers to rush into close concentrations wherever the biggest flow is, and this caused some secondary varroa mass-spreader events (after the main one, almonds), and likely will in the future. These can actually be worse than the almonds if they happen March-April when brood areas are shrinking and many more mites are hitching rides out of hives.

A Conservation Problem

As mentioned with the river red gum, a failure to properly plan for and work with the necessary cues to make a tree flower can cause very poor pollination and thus poor regeneration of the population.

And so there you have it. If you’re just breaking in to migratory beekeeping you’re going to need to get in the habit of looking for buds at the tops of trees with your binoculars and knowing what flowers under what conditions. If you want to read more, the Wright 2022 paper is publicly available and a good thorough overview of Australian masting plants – if you happen to be an aspiring student looking for a PhD topic, every study on this subject mentions that it’s a severely under-studied area.

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References 1 Goodman, R. (2001). Beekeepers' Use of Honey and Pollen Flora Resources in Victoria. A report for the Rural Industries Research and Development Corporation (RIRDC), Barton, ACT. RIRDC Publication No. 01/050, RIRDC Project No. DAV-109A. ISBN 0 642 58272 6; ISSN 1440-6845.

2 Roberts BJ, Catterall CP, Eby P, Kanowski J (2012) Long-Distance and Frequent Movements of the Flying- Fox Pteropus poliocephalus: Implications for Management. PLoS ONE 7(8): e42532. https://doi.org/10.1371/ journal.pone.0042532

3 Samarth, Kelly, Turnbull & Jameson (2020), "Molecular control of masting: an introduction to an epigenetic summer memory," Annals of Botany 125(6): 851–858 (doi:10.1093/aob/mcaa004)

4 Moran, P. A. P. (1953). "The statistical analysis of the Canadian lynx cycle. II. Synchronization and meteorology." Australian Journal of Zoology 1(3): 291–298.

5 Flematti, G. R., Ghisalberti, E. L., Dixon, K. W., & Trengove, R. D. (2004). "A compound from smoke that promotes seed germination." Science 305(5686): 977. https://doi.org/10.1126/science.1099944 (PMID: 15247439).

6 Wright BR, Franklin DC, Fensham RJ. (2022) The ecology, evolution and management of mast reproduction in Australian plants. Australian Journal of Botany 70, 509–530. https://doi.org/10.1071/BT22043

7 Keatley, M. R., & Hudson, I. L. (2007). "A comparison of long-term flowering patterns of Box–Ironbark species in Havelock and Rushworth forests." Environmental Modeling & Assessment, 12: 279–292. DOI: 10.1007/s10666-006- 9063-5

8 Roberts, Jane., & Marston, F. (2011). “Water regime for wetland and floodplain plants: a source book for the Murray –Darling Basin.” National Water Commission, Canberra.

9 Bren, L. J. (1988). "Effects of river regulation on flooding of a riparian red gum forest on the River Murray, Australia." Regulated Rivers: Research & Management 2(2): 65–77.

10 Di Stefano, J. (2002). "River red gum (Eucalyptus camaldulensis): a review of ecosystem processes, seedling regeneration and silvicultural practice." Australian Forestry 65(1): 14–22.

Deadline for the next journal is Tuesday 1st of September 2026 Please send any submissions to new email address abjeditor@vicbeekeepers.com.au

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