Planting non-native trees accelerates the release of carbon back into the atmosphere



native forest.

Lauren Waller and Warwick Allen, University of Canterbury

Large-scale reforestation projects such as New Zealand’s One Billion Trees programme are underway in many countries to help sequester carbon from the atmosphere.

But there is ongoing debate about whether to prioritise native or non-native plants to fight climate change. As our recent research shows, non-native plants often grow faster compared to native plants, but they also decompose faster and this helps to accelerate the release of 150% more carbon dioxide from the soil.

Our results highlight a challenging gap in our understanding of carbon cycling in newly planted or regenerating forests.

It is relatively easy to measure plant biomass (how quickly a plant grows) and to estimate how much carbon dioxide it has removed from the atmosphere. But measuring carbon release is more difficult because it involves complex interactions between the plant, plant-eating insects and soil microorganisms.

This lack of an integrated carbon cycling model that includes species interactions makes predictions for carbon budgeting exceedingly difficult.




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How non-native plants change the carbon cycle

There is uncertainty in our climate forecasting because we don’t fully understand how the factors that influence carbon cycling – the process in which carbon is both accumulated and lost by plants and soils – differ across ecosystems.

Carbon sequestration projects typically use fast-growing plant species that accumulate carbon in their tissues rapidly. Few projects focus on what goes on in the soil.

Non-native plants often accelerate carbon cycling. They usually have less dense tissues and can grow and incorporate carbon into their tissues faster than native plants. But they also decompose more readily, increasing carbon release back to the atmosphere.

Our research, recently published in the journal Science, shows that when non-native plants arrive in a new place, they establish new interactions with soil organisms. So far, research has mostly focused on how this resetting of interactions with soil microorganisms, herbivorous insects and other organisms helps exotic plants to invade a new place quickly, often overwhelming native species.

Invasive non-native plants have already become a major problem worldwide, and are changing the composition and function of entire ecosystems. But it is less clear how the interactions of invasive non-native plants with other organisms affect carbon cycling.




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Planting non-native trees releases more carbon

We established 160 experimental plant communities, with different combinations of native and non-native plants. We collected and reared herbivorous insects and created identical mixtures which we added to half of the plots.

We also cultured soil microorganisms to create two different soils that we split across the plant communities. One soil contained microorganisms familiar to the plants and another was unfamiliar.

Herbivorous insects and soil microorganisms feed on live and decaying plant tissue. Their ability to grow depends on the nutritional quality of that food. We found that non-native plants provided a better food source for herbivores compared with native plants – and that resulted in more plant-eating insects in communities dominated by non-native plants.

Similarly, exotic plants also raised the abundance of soil microorganisms involved in the rapid decomposition of plant material. This synergy of multiple organisms and interactions (fast-growing plants with less dense tissues, high herbivore abundance, and increased decomposition by soil microorganisms) means that more of the plant carbon is released back into the atmosphere.

In a practical sense, these soil treatments (soils with microorganisms familiar vs. unfamiliar to the plants) mimic the difference between reforestation (replanting an area) and afforestation (planting trees to create a new forest).

Reforested areas are typically replanted with native species that occurred there before, whereas afforested areas are planted with new species. Our results suggest planting non-native trees into soils with microorganisms they have never encountered (in other words, afforestation with non-native plants) may lead to more rapid release of carbon and undermine the effort to mitigate climate change.The Conversation

Lauren Waller, Postdoctoral Fellow and Warwick Allen, Postdoctoral fellow, University of Canterbury

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Non-native species should count in conservation – even in Australia



Australia is home to many new species, including wild camels found nowhere else on Earth.
Author provided

Arian Wallach, University of Technology Sydney; Chelsea Batavia, Oregon State University; Danielle Celermajer, University of Sydney; Daniel Ramp, University of Technology Sydney; Erick Lundgren, University of Technology Sydney, and Esty Yanco, University of Technology Sydney

As the world struggles to keep tabs on biodiversity decline, conservation largely relies on a single international database to track life on Earth. It is a mammoth and impressive undertaking – but a glaring omission from the list may be frustrating conservation efforts.




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The International Union for the Conservation of Nature’s Red List aims to be a “complete barometer of life”. But non-native wildlife is excluded from the list.

Our study, published today in the journal Conservation Biology, questions the wisdom of this omission. It means, for example, vulnerable species facing existential threats in their “home country” may be exterminated freely in another. Excluding these animals, such as wild camels in Australia, and rare Australian frogs living overseas, distorts conservation science.

What counts as ‘native’?

The concept of “native” draws a sharp line between species that count and those that don’t. It is essentially an ethical choice, and a disputed one at that. Regardless of whether one defends or disputes the concept, it is problematic to use a moral term to filter a critical source of scientific data.

Trash Animals: How We Live with Nature’s Filthy, Feral, Invasive, and Unwanted Species.

The invisible components of biodiversity – those populations excluded from conservation’s definition of life – can be found in trash lists, where they are described as invasive, aliens, pests, and feral.

So what does the world look like if we include all wildlife in biodiversity assessments? We rummaged around in the “trash piles” to find out.

When all life counts

By focusing on Australian non-native vertebrate species – amphibians, birds, fishes, mammals, and reptiles – we did something many conservationists would find unthinkable. We added unloved species such as feral cats, cane toads, the Indian myna, and carp to Australia’s biodiversity counts.

We created maps showing the range of 87 species whose ancestors were introduced into Australia, and 47 species native to Australia that were introduced elsewhere, since European colonisation.

Many of these so-called invasive species are at risk of extinction in their native ranges; 32% are assessed as threatened or decreasing in the Red List. For 15 of them, non-native ranges provide a lifeline.

Australia’s vertebrate species that are threatened or near threatened in their native ranges with significant populations overseas. From left-to-right: Indian hog deer, banteng, wild cattle, wild water buffalo, wild camel; wild goat, carp, wild donkey, brumby, Mozambique tilapia; European rabbit, Javan rusa, sambar deer, and (emigrants) green and golden bell frog, growling grass frog.
Arian Wallach et al

Not only does Australia contribute to the survival and flourishing of these species, but immigrant vertebrates have also added 52 species to the number of vertebrate species in Australia (after accounting for extinctions).

This number in no way indicates that non-native species replace or make up for those that have been lost. And it does not exonerate humans of their role in causing extinctions. But the current data do not even allow us to acknowledge that these species exist.

Because they are not counted in conservation, these non-native populations are subjected to mass eradication programs. Paradoxically, in assessing how such programs are justified, we found conservation is the most frequently cited reason for killing these wild animals.

Dromedary camels were extinct in the wild for some 5,000 years until they “went feral” in Australia, where they are now endemic. Rather than celebrating what is arguably the most extraordinary rewilding event in the world, wild camels were declared a pest. Between 2009 and 2013, Australia spent A$19 million to gun down 160,000 individuals of a species found nowhere else on Earth in the wild.

Likewise, 89% of the global distribution of Javan rusa, a deer species vulnerable to extinction, is in Australia. As pest, they are culled and hunted for sport.

Stated motivations for killing Australia’s immigrant vertebrate wildlife, shown as percentages of species targeted per taxonomic group. Numbers above bars indicate absolute number of species targeted.

Nativism not only renders countless species invisible, along with their unique and fascinating ecologies; it also exposes them to unfettered, unscientific, unmonitored, and unlamented mass killing programs.




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Mass killing of non-native species, if questioned at all, is generally explained as protecting native species. But ecology is complex. One cannot simply assume that all non-native populations, in all contexts, do nothing but harm.

Where non-native species do contribute to the loss of native species, humans need to confront the ethical complexities and shoulder real responsibility, rather than simply reach for a gun as a first solution.

In many situations changing harmful human behaviours, like persecuting apex predators such as dingoes, can solve problems that appear to be caused solely by non-native species.

Irrespective of whether we value non-native species or not, there is no scientific justification for expunging large swaths of the living world from conservation data. Smuggling ethically dubious distinctions into data harms conservation science, and has grave repercussions.




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Persisting with the assumption that we have the right to pick and choose which species “count” looks like playing God. By now, we should have learned we must not.The Conversation

Arian Wallach, Lecturer, Centre for Compassionate Conservation, University of Technology Sydney; Chelsea Batavia, Postdoctoral research associate, Oregon State University; Danielle Celermajer, Professor of Sociology and Social Policy, University of Sydney; Daniel Ramp, Associate Professor and Director, Centre for Compassionate Conservation, University of Technology Sydney; Erick Lundgren, PhD Student, Centre for Compassionate Conservation, University of Technology Sydney, and Esty Yanco, PhD Candidate, Centre for Compassionate Conservation, University of Technology Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.