The science of plant selection, and why the species matters

Who are you planting it for?

Put a Glossy Black-Cockatoo in a healthy forest and it can still starve.

Not because the forest is degraded. Because it is the wrong forest.

Last time we wrote that a bush is a building, and that its structure matters more than its tree count. This is the part where you decide who moves in. Because “we planted a bunch of trees ” is a volume statistic. The ecological question is narrower, and much harder. Which trees, and for whom.

One bird, two trees, no substitutes

The South Australian Glossy Black-Cockatoo feeds almost exclusively on the seed of the drooping sheoak, Allocasuarina verticillata. Not sheoaks in general. That one. And it does not forage evenly across the trees available to it either. Researchers on Kangaroo Island have spent years working out which cone and tree characteristics decide where these birds will and will not feed.

Then there is the second requirement, and it has nothing to do with food. Glossies nest in hollows, in large old eucalypts.

So the bird needs two entirely unrelated species, delivering two entirely different things, on two entirely different timelines. Plant only sheoaks and you have fed a bird that cannot breed. Plant only eucalypts and you have housed a bird that cannot eat. Plant both this decade and the food arrives in years, while the nest sites arrive next century.

The South Australian population climbed from 158 birds in 1995 to around 453 by 2023, which is a genuine recovery story. Then the Black Summer fires destroyed at least 54 per cent of their feeding habitat and 38.5 per cent of known nests in a single season.

That is what a species list is really deciding.

Timing is a species trait

Fewer than 400 Regent Honeyeaters remain in the wild. They are critically endangered, they depend on flowering eucalypts, particularly yellow box and mugga ironbark, and they range across more than half a million square kilometres chasing blossom.

They have to, because eucalypts are unreliable. Flowering is irregular, heavy in some years and absent in others, and it varies between individual trees in the same stand. A nectar feeder cannot settle down. It follows the food or it does not eat.

Which means a species list is not only what you plant. It is when those plants flower. A revegetation site that blooms gloriously in spring and offers nothing in July is a feast followed by a famine, and the famine is the part that decides whether anything stays.

Sometimes the plant is not the food

At Winton Wetlands in Victoria, we funded the translocation of around 60 Growling Grass Frogs to establish a new population, in a targeted recovery plan.

Frogs do not eat the vegetation. They need it for something else entirely. Growling Grass Frogs require cover in and around the water, and they also need to bask. Raising their body temperature helps them resist chytrid fungus, the disease behind amphibian collapses worldwide. So habitat work for this species means planting for shelter while deliberately leaving open, sunlit places to warm up in, and adding rock.

Same principle, completely different logic. Here the vegetation is chosen for what it physically does, not for what it feeds.

A thousand plants can be one plant

Here is the part almost nobody outside the sector thinks about.

Collect seed from three convenient trees, grow a thousand seedlings, and you have not planted a thousand plants. You have planted a very small number of plants, a thousand times over. The genetic variation that lets a population survive drought, disease and heat is simply not in the box.

And it gets worse in exactly the places restoration tends to happen. Small, isolated remnants produce less seed, of poorer quality, with narrower genetic diversity, because the plants that remain are increasingly related to each other. A landmark Australian paper by Broadhurst and colleagues concluded that the emphasis on strictly local seed sourcing will, in many cases, lead to poor restoration outcomes, and argued for concentrating less on how local the seed is and more on how genetically diverse and high quality it is.

This is why “locally sourced” in our reporting means seed collected across many parent plants, not simply seed collected nearby. It is also why community nurseries and seedbanks are infrastructure rather than sentiment.

Planting for a climate that has not arrived yet

Which brings us to the most interesting unresolved question in Australian restoration right now.

The traditional rule is local provenance. Use seed from as close to the site as possible, because local plants are adapted to local conditions. It is sound logic and it has guided planting for decades.

But the conditions are moving. So Australian researchers have proposed alternatives, most prominently climate-adjusted provenancing, which mixes local seed with seed collected from populations lying in the direction the climate is travelling, typically hotter and drier. The aim is to give a planting the genetic raw material for the climate it will face in fifty years, not only the one it faces today.

Both positions carry real risk. Stay strictly local and you may plant something exquisitely adapted to a climate that is on its way out. Move seed too far and you risk outbreeding depression, where mixing distant populations produces less fit offspring.

There is no settled answer yet, and anyone who tells you there is has stopped reading.

Which is why the nursery matters

We support community nurseries across four states, with living seedbanks and community groups that tend to them, and we have propagated and planted more than 110,000 fire-resilient natives.

Not because growing plants locally is charming. Because the species list, the seed source and the genetic spread are the three decisions that determine whether a planting becomes habitat, or just becomes trees.

The question is never how many.

It is who are you planting it for.

Help us bring back the bush.