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Australia’s most innovative green homes will be open to the public on Sustainable House Day, taking place on Sunday 17 September.

Guam's trees are struggling without the birds that spread their seeds. Author provided

Can a snake bring down a forest? If we’re talking about the Pacific island of Guam, the answer may well be yes.

Our research adds to mounting evidence that the killing of many of the island’s bird species by an invasive species of snake is having severe knock-on effects for Guam’s trees, which rely on the birds to spread their seeds.

Invasive predators are known to wreak havoc on native animal populations, but our study shows how the knock-on effects can be bad news for native forests too.

Globally, invasive predators have been implicated in the extinction of 142 bird, mammal and reptile species, with a further 596 species classed as vulnerable, endangered or critically endangered. But the indirect effects of these extinctions on entire ecosystems such as forests are much harder to study.

Read more: Invasive predators are eating the world’s animals to extinction – and the worst is close to home.

The brown tree snake was accidentally introduced to Guam in the mid-1940s and rapidly spread across the island. At the same time, bird populations on Guam mysteriously began to decline. For years, no one knew why.

In 1987 the US ecologist Julie Savidge provided conclusive evidence that the two were linked: the brown tree snake was eating the island’s birds. Today, 10 of Guam’s 12 original forest bird species have been lost. The remaining two are considered functionally extinct.

The brown tree snake has caused a cascade of problems. Isaac Chellman, Author provided

But the ecological damage doesn’t stop there. The loss of native bird species has triggered some unexpected changes in Guam’s forests. Both the establishment of new trees and the diversity of those trees is falling. These changes show how an invasive predator can indirectly yet significantly alter an entire ecosystem.

Birds and trees

Birds are very important to trees. In the tropics, up to 90% of tree species rely on animals, often birds, to spread their seeds. Birds eat fruit from the trees and then defecate the undigested seeds far away from the parent tree’s canopy, where there are fewer predators and pathogens that specialise on that species, where competition for light, water and nutrients is less intense, and where seeds can take advantage of promising new real estate when old trees die.

Without birds, roughly 95% of seeds of two common tree species on Guam (Psychotria mariana and Premna serratifolia) land directly beneath their parent tree. Compare that with the nearby islands of Saipan, Tinian and Rota – none of which have brown tree snakes – where less than 40% of seeds land near their parent tree. On Saipan, seeds that escape their parent tree are five times more likely to survive.

Close neighbours, but very different situations. Author provided

What’s more, passing through the gut of an animal can actually increase the likelihood that a seed will germinate. On Guam, seeds that had been eaten by birds were two to four times more likely to germinate than those that hadn’t.

Overall, for the roughly 70% of tree species on Guam that rely on birds to spread their seeds, research suggests that the bird deaths caused by the brown tree snake have reduced the establishment of new tree seedlings by 61-92%, depending on the species.

Forests’ future threatened

These numbers suggest that many tree species in Guam are under serious threat, which in turn threatens the species diversity of the island’s forests.

Our new research, published in Proceedings of the National Academy of Sciences, examined the number of seedling species growing in treefall gaps on Guam compared with Saipan and Rota, which still have their birds.

Treefall gaps appear when an adult tree dies, opening up the canopy and increasing the light that reaches the forest floor. Many species rely on this increased light for germination and early growth, so these gaps are hotspots for new seedlings.

Birds such as the Mariana fruit dove are a big help to the islands’ trees. Lainie Berry, Author provided

We found that Saipan and Rota had roughly double the number of species of seedlings growing in these gaps, compared with Guam. What’s more, seedling species on Guam tended to be clumped together, as you might expect if more than 90% of seeds are falling beneath their parent trees.

We also found that birds are important in moving the seeds of certain types of species to gaps. In forests, “pioneer species” are those that rapidly colonise gaps, exploiting the increased light to grow fast and reproduce young. Crucially, we found pioneer species in all gaps on islands with birds, but in very few gaps on Guam, where these species could be at risk of being lost entirely.

Read more: Pristine paradise to rubbish dump: the same Pacific island, 23 years apart.

Invasive predators are a reality for many ecosystems, particularly on islands, and the situation on Guam is particularly extreme. Perhaps nowhere else in the world has experienced such dramatic losses of native fauna as a result of invasion.

While these direct impacts of invasion are astounding, the indirect impacts cascading through the ecosystem are just starting to unfold, and may prove to be similarly catastrophic.

Haldre Rogers receives funding from the US National Science Foundation (NSF) and the Strategic Environmental Research and Development Program (SERDP). She is a faculty member at Iowa State University.

Elizabeth Wandrag does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond the academic appointment above.

Llanbedr, Gwynedd With sadness I realised a proposed road, improving access to the planned spaceport, would cut across the floodplain I had just explored

The train along the Cambrian coast route stops at Llanbedr only by request, and on this occasion I was the only passenger to alight. To the west fields of wet grassland, divided by drainage channels brimming with rushes, spread towards the sea.

Related: Snowdonia fears impact of UK spaceport decision

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The list of places that tell our nation’s story now has its own place in print with the launch of the book Australia’s National Heritage List – The Story So Far.

Australian government’s draft Reef 2050 Water Quality Improvement Plan provides new water quality targets, but has very few other concrete changes

Australia’s draft plan to improve water quality on the Great Barrier Reef has ignored official government scientific advice, which was published by the Queensland and federal governments alongside the new plan this week.

The draft Reef 2050 Water Quality Improvement Plan is an update to the plan released in 2013, and provides new water quality targets for specific parts of the reef, but has very few other concrete changes overall.

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Climate Council ranks state efforts on renewables and climate targets as they race to fill the federal government void.

A guide of what we know about the links between climate change and Harvey to help unpack the elements that contributed to this historic and unfolding storm

Wind output in Australia hits record highs in August, with wind and rooftop solar combining to provide 59 per cent of South Australia's consumption.

Two of India’s leading public sector banks at risk of losing a “significant proportion” of US$7.4 billion loaned over three years to private power producers

Australian homes and businesses have installed almost 2.8m small-scale renewables systems, pushing total installed capacity to the 6GW mark – 5.9GW of it rooftop solar.

Vet Amir Khalil goes into conflict areas to save the zoo animals left behind.

Abbotsford Convent in Melbourne today became the 111th place on our National Heritage List. This outstanding site shows the role of religious and charitable institutions in Australia’s social and welfare history during the 19th and 20th centuries.

Canberra's public transport bus fleet will trial two pure electric buses and one electric-diesel hybrid, as it transitions away from ageing diesel fleet.

New data has shown that in North Sydney, alone, 74% of residents can’t access solar because they are renters or live in apartment buildings. But there are ways to solve the problem – as well as new companies making it their mission.

State and Federal Governments are currently working on a strategy for national environmental accounting — with the goal to have an agreement signed by the end of the year.

Kenyans producing, selling or even using plastic bags will risk imprisonment of up to four years or fines of $50,000, as the world's toughest law aimed at reducing plastic pollution comes into effect.

US authorities approve a treatment which re-designs a patient's own immune system to attack cancer.

Judge says president Michel Temer went beyond his authority in issuing decree to dissolve Renca, after fury from activists

A Brazilian court has blocked an attempt by the president, Michel Temer, to open up swaths of the Amazon forest to mining companies after an outcry by environmental campaigners and climate activists.

The federal judge Rolando Valcir Spanholo said the president went beyond his authority in issuing a decree to abolish Renca, an area of 46,000 sq km (17,760 sq miles) that has been protected since 1984.

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Critics say authorisation of supplementary culls shows the programme, which began four years ago, is not working

Another 1,000 badgers are set to be killed this autumn and winter in the two UK counties where the controversial cull began four years ago.

Natural England confirmed on Wednesday that supplementary culls had been authorised in Gloucestershire and Somerset.

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Are American lives simply worth more, wonder Lynne Edwards, Peter Williams, and Susan Howe. Plus letters from Bob Pike and Sheila Rigby

While I have the greatest sympathy for those who have lost friends, family, pets or property in the Texas floods (Report, 30 August), I am disgusted at the relative number of column inches and amounts of airtime devoted to its coverage. During precisely the same period huge areas of Bangladesh, Nepal and India are suffering an even greater catastrophe, with 1,200 plus lives lost and millions made homeless. Let’s get some balance here. America is a rich country and will cope, despite inept leadership. Or are we saying that American lives are worth more?.
Susan Howe
Ross on Wye, Herefordshire

• The contrast between the coverage of floods in Texas and floods in South Asia is stark. Live updating of trivia as well as important events from Houston; the odd report from India, Nepal, Bangladesh and elsewhere. There are probably many more people of South Asian heritage in this country than American. The implicit message is that they, and their relatives, are far less important than a pet in Houston. I don’t want Texas coverage reduced, but please take more notice of the rest of the world.
Lynne Edwards
New Quay, Ceredigion

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