Learnings from the Land Down Under

Photos and story by: Tessa Maurer, PhD, Senior Project Scientist

The hills of Mount Buffalo National Park in the Australian state of Victoria are covered in lush, forested hills, scrub, and rocky outcroppings. The only evidence that this landscape was heavily impacted by the 2019-2020 “Black Summer” bush fires, is the skeletons of mature eucalypts that can still be seen in some areas above the new forest growth. If you’d asked me when the fire occurred, I would have said 7 to 10 years ago — not 3 to 4.

It turns out that, despite sharing a vulnerability to weather extremes of fire and floods, Australia’s landscape can behave in ways that are very different from California’s and the Western U.S. Over the (northern hemisphere) winter this year, I was lucky enough to escape the cold and spend some time visiting friends, sight-seeing, and learning more about the conservation challenges that face our friends in the land of Oz. In this month’s blog post, I’ll share some of those learnings with the Blue Forest community.

Much of Australia, particularly the southeast where I spent most of my time, is dominated by eucalypt (or, colloquially, “gum”) forests. These are fire adapted ecosystems just like the conifer forests of the Western U.S., but the exact ways that these trees respond to fire are distinct, with implications for management. Whereas North American species like Giant Sequoia have evolved to germinate in the wake of a fire without damage to mature trees, eucalypt forests may at least partially depend on more intense fires for new growth.

There are two primary mechanisms for eucalypt germination in the wake of a fire: the first is epicormic sprouting where buds lie dormant under the bark of the tree, suppressed by hormones until the crown of the tree is damaged, which triggers new growth. This mechanism thus relies on crown fires, which may be one reason the bark and oil of eucalypts are so good at transmitting fire from the ground upwards (rue the day these trees made it to California!). The other way that eucalypt regenerate after a fire is through lignotubers, a trait shared with coast redwoods. A lignotuber is a large mass at the base of the trunk where it meets the root system that contains a high density of dormant buds; after a fire, these allow the trees to re-sprout from an already-mature root system.

Neither of these mechanisms necessarily requires entirely killing off mature eucalypts to trigger a regeneration event, but another characteristic of eucalypt forests that makes them distinct from Western North American forests is that they are highly productive. In other words, gum trees grow back much more quickly than conifers.  This is the reason I was so wrong about the fire history at Mount Buffalo: even if a severe crown fire does blow through an area, in just a few years, it can be hard to tell.

This has some very tangible implications for management and fire cycles. For example, managing forests to reduce fire risk often means removing fuels from the landscape, which does release some carbon that was stored in that biomass. In the U.S., we know that severe fires can lead to forests becoming grass or shrubland, since these smaller plants regenerate faster after a fire. These landcover types store much less carbon than healthy forests, so the relatively small amount of carbon released from fuels reduction is offset by the benefits of long-term storage in fire-resilient forests. In Australia, however, there is less danger that post-fire landscapes will turn into grass and shrubland as trees establish themselves quickly enough to compete with other types of plants. As a result, the trade-off between fuels reduction and long-term carbon storage is less clear.  While there is still an argument for fuels reduction for fire risk benefits, the co-benefits may not always be aligned.

Another important difference between Australia and the U.S. are the large-scale climate drivers that influence extreme weather events. On the most basic level, Australia’s fire season is different from California’s just due to having different seasonality. But even on a larger scale, Australia is on the opposite end of the El Niño-Southern Oscillation (ENSO) cycle from California. This means that El Niño and La Niña conditions will tend to have the opposite effect in each place: La Niña, not El Niño, is likely to make Australia wetter. To complicate things, ENSO is only one of multiple climate drivers that Australia has to contend with. The other major driver is the Indian Ocean Dipole(IOD), which is similar to the ENSO cycle but in the Indian Ocean. If the IOD shifts out of neutral to be positive or negative, Australia tends to face drier or wetter conditions, respectively.  Secondary impacts include the Southern Annular Mode (SAM) and East Coast Lows. When one or more of these converge on the same conditions, which is not infrequent, the country can face incredible extremes, whether dry or wet.

Indeed, the Pacific Ocean is coming off of a rare three consecutive years of La Niña conditions, and during most of that time, the IOD was also in a negative mode.  This resulted in intense and prolonged flooding along Australia’s east coast, including in the Murray-Darling River system, Australia’s largest watershed. The results have been devastating for both people and wildlife, and the satellite imagery is startling.  In short, Australia has known for some time what California has been reminded of this year: floods can be just as much of a management challenge as fires. As Blue Forest’s work in riparian areas grows, it will be interesting to see what opportunities and challenges will come with trying to leverage the co-benefits of flood risk reduction, and perhaps this will create more opportunities to trade conservation knowledge across the Pacific Ocean!