Guam’s forests are being slowly killed off – by a snake

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

Elizabeth Wandrag, University of Canberra and Haldre Rogers, Iowa State University

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.

The ConversationWhile 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.

Elizabeth Wandrag, Postdoctoral Fellow, Ecology, University of Canberra and Haldre Rogers, Assistant Professor, Iowa State University

This article was originally published on The Conversation. Read the original article.


The world protests as Amazon forests are opened to mining

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The Amazon is the largest rainforest in the world.
Author provided

Beatriz Garcia, Western Sydney University

The Amazon, often described as the “lungs of the Earth”, is the largest rainforest in the world. Its extraordinary biodiversity and sheer scale has made it a globally significant resource in the fight against climate change.

But last week the Brazilian president Michel Temer removed the protected status of the National Reserve of Copper and Associates, a national reserve larger than Denmark.

The reserve, known as “Renca”, covers 46,000 square kilometres and is thought to contain huge amounts of copper, as well as gold, iron ore and other minerals. Roughly 30% of Renca will now be open to mining exploration. Renca also includes indigenous reserves inhabited by various ethnic communities living in relative isolation.

The decision, which has been denounced by conservation groups and governments around the world, comes as the unpopular Temer struggles with a crushing political and economic crisis that has seen unemployment rise above 12%.

Read more: With Dilma Rousseff impeached, Brazil is set for years of political turmoil

Political and economic turbulence

Brazil is currently in the middle of the largest corruption scandals in its history. Since 2014, an ongoing federal investigation called Operation Car Wash has implicated elite businesspeople and high-ranking politicians, uncovering bribes worth millions of dollars exchanged for deals with the state oil company Petrobas. According to the BBC, almost a third of President Temer’s cabinet is under investigation for alleged corruption.

There is no doubt that Brazil needs to find ways out of recession and unemployment. As the minister of mining and energy has said, “the objective of the measure [to allow mining] is to attract new investments, generating wealth for the country and employment and income for society.”

However it’s not clear that this move will benefit ordinary Brazilians. This is not the first gold rush into this area, and the Amazon still has high indices of poverty and many other challenges.

During the 1980s and 90s tens of thousands of miners flocked to gold deposits in the Amazon, driven by high international prices. One of the most famous examples, “Serra Pelada,” saw 60,000 men dig a massive crater in the Amazon Basin.

These mining operations typically provided little economic benefits to the local populations. Instead, they attracted thousands of people, which led to deforestation, violent land conflicts and mercury pollution in the rivers.

In reality the Amazon and its people deserve a sustainable model of development, which takes advantage of the outstanding biodiversity and beauty of its standing forests. The historical record shows mining is likely to lead to a demographic explosion, and further deforestation, pollution and land conflicts.

The principle of non-regression

One important aspect of international environmental law is called the “principle of non-regression”. The principle states that some legal rules should be non-revokable in the name of the common interest of humankind. Essentially, once a level of protection has been granted there is no coming back.

This principle is reflected in article 225 of the Brazilian constitution, which lays out the right to a healthy environment:

All have the right to an ecologically balanced environment […] and both the Government and the community shall have the duty to defend and preserve it for present and future generations.

The Brazilian constitution also describes the Amazon forest as a “national heritage”. It must then be treated accordingly.

Read more: Deep in the Amazon jungle, Brazil’s ‘hidden cities’ are in crisis

While the Amazon is a fundamental part of Brazil’s history, it’s also an essential part of the global battle against climate change. The Amazon contains half the worlds’ tropical rainforests, and its trees absorb and store vast amounts of carbon dioxide.

According to the Intergovernmental Panel on Climate Change, land use, including deforestation and forest degradation, is the second-largest source of global emissions after the energy sector.

Developed countries around the world have committed resources to help Brazil offset the costs of safeguarding their forests. One example is the Amazon Fund, created in 2008. It has received billions of dollars from foreign governments such as Norway and Germany, to combat deforestation and to promote sustainable practices in the Brazilian Amazon.

But with 14 million Brazilians unemployed, further assistance is required to ensure that they can protect their forests.

As well as governments, companies have also committed billions of dollars to fight climate change and support projects that reduce carbon emissions and promote energy efficiency. Most businesses have also created self-regulatory standards to ensure compliance with international laws and ethical standards.

The decision of the Brazilian government leaves us with two questions. How will the international community honour their commitments to keep global warming below 2℃, if countries begin rolling back their environmental protections? And how will companies involved in mining projects in the Amazon honour their social responsibility commitments and moral obligation towards present and future generations?

The degradation of the Amazon will affect the entire world. The clearing of the Amazon for mining will lead to the emissions of thousands of tons of greenhouse gases, furthering global warming and causing the irreversible loss of biodiversity, and water resources, as well as damage to local and indigenous communities.

The ConversationLet us not take a step back towards more destruction. Rather, let us strengthen the protection of our remaining forests.

Beatriz Garcia, Lecturer, Western Sydney University

This article was originally published on The Conversation. Read the original article.