How invasive weeds can make wildfires hotter and more frequent



File 20171218 17860 8i8ehc.jpg?ixlib=rb 1.1
Mixed grill: burning combinations of invasive and native plants helps us understand how invasive plants make fires hotter and more likely.
Sarah Wyse, CC BY-ND

Tim Curran, Lincoln University, New Zealand; George Perry, and Sarah Wyse

Over the past year the global media has been full of reports of catastrophic fires in California, the Mediterranean, Chile and elsewhere. One suggested reason for increases in catastrophic wildfires has been human-induced climate change. Higher temperatures, drier weather and windier conditions all increase the impact of fires.

While climate change indeed raises the risk of wildfires, our research shows that another way humans can change patterns of fire activity is by introducing flammable plants to new environments.


Read more: How will Canada manage its wildfires in the future?


Plantations of highly flammable exotic species, such as pines and eucalypts, probably helped to fuel the recent catastrophic fires in Portugal and in Chile. In arid regions, such as parts of the US southwest, the introduction of exotic grasses has transformed shrublands, as fires increase in severity.

Invasive plants and fire

How do invasive plants change fire patterns? We burned species mixtures (aka “mixed grills”) on our plant barbecue to help find out.

Invasive plants are responsible for changing the patterns of fire activity in many ecosystems around the world. In particular, invasive species can lead to hotter and more frequent fires.

Invasive plants can also reduce fire frequency and fire intensity, but there are fewer examples of this occurring worldwide.

One of the main ways flammable invasive plants can have long-lasting impacts on an ecosystem comes from positive fire-vegetation feedbacks. Such feedbacks can occur when a flammable weed invades a less fire-prone ecosystem. By changing the available fuel the invader makes fires more likely and often hotter.

If the invading species has characteristics that allow it to outcompete native species after a fire, then it will further dominate the ecosystem. Such traits include thick bark, the ability to resprout following fire, or seeds that survive burning. This invasion will likely lead to more fires, changing the species composition and function of the ecosystem in a “fire begets fire” cycle. Extreme examples of this dynamic are where flammable grasses or shrubs invade forests, leading to loss of the forest ecosystems.

Mixed grills

We wanted to understand how invasive plants interact with other species when burned in combination. To explore the mechanisms underpinning such feedbacks, we examined how invasive plants might change the nature of a fire when burned together with native species.

We collected 70cm shoots of four globally invasive species (of both high and low flammability) and burned them in pairwise combinations with New Zealand native trees and shrubs to determine which characteristics of a fire could be attributed to the invasive plants.

Samples of Hakea sericea (foreground) and Kunzea robusta (rear) arranged on the grill of our plant barbecue.
Sarah Wyse, CC BY-ND

We found that overall flammability was largely driven by the most flammable species in the mixture, showing how highly flammable weeds could set in motion fire-vegetation feedbacks.

We established that a greater difference in flammability between the two species led to a larger influence of the more flammable species on overall flammability. This outcome suggests weeds that are much more flammable than the invaded community can have larger impacts on fire patterns.

Importantly, we also showed the influence of the highly flammable species was independent of its biomass, meaning highly flammable weeds may impact community flammability even at low abundances.

When we looked closer at the different components of flammability (combustibility, ignitability, consumability and sustainability) we found some important nuances in our results.

While the maximum temperature reached in our burns (combustibility) and the ignition speed (ignitability) were both most influenced by the more flammable species, consumability (the amount of biomass burned) and sustainability (how long the fire burns) were equally influenced by both the more flammable and less flammable species.

In short, more flammable weeds will cause a fire to ignite more quickly and burn hotter.

However, less flammable species can reduce the duration of a fire compared to when a more flammable species is burnt alone. These results could have important ecological implications, as the longer a fire burns the more likely it is to kill plants: low-flammability plants could reduce this impact.

Measuring how long a fire burns on our plant barbecue.
Tom Etherington, CC BY-ND

Managing weeds to reduce fire impacts

Even low abundances of highly flammable invasive weeds could set in motion positive fire-vegetation feedbacks that lead to drastic changes to ecosystems. If this result holds when our shoot-scale experiments are repeated using field trials, then land managers should work quickly to remove even small infestations of highly flammable species, such as gorse (Ulex europaeus) and prickly hakea (Hakea sericea).

Conversely, the role of low flammability plants in extinguishing fires further supports the suggestion that the strategic planting of such species across the landscape as “green firebreaks” could be a useful fire management tool.

The ConversationIn any case, our “mixed grill” study further highlights the role of exotic plants in fuelling hotter wildfires.

Tim Curran, Senior Lecturer in Ecology, Lincoln University, New Zealand; George Perry, Professor, School of Environment, and Sarah Wyse, Early Career Research Fellow, The Royal Botanic Gardens, Kew and Research Fellow, School of Environment

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

Ethiopia’s Lake Tana is losing the fight to water hyacinth



File 20170830 23702 17vlg7u.jpg?ixlib=rb 1.1
The aquatic weed water hyacinth is causing major problems in Ethiopia’s Lake Tana.
Shutterstock

Solomon Kibret, University of California, Irvine

Lake Tana is the largest lake in Ethiopia. It holds 50% of the country’s fresh water. It is also the source of the Blue Nile, which contributes up to 60% of the Nile’s water. Not only is the lake important as a water source for over 123 million people in the Nile Basin, it is also a source of food in the form of fish. But weeds are threatening this life-giving resource.

The lake has been listed in the top 250 lake regions of Global Importance for Biodiversity. It has 28 species of fish, of which 21 are endemic. Commercially, the lake’s most important fishes include the large African barbs, Nile tilapia and African catfish. The annual commercial value of fish production at Lake Tana is about USD$1.1 million.

The potential fish production of the lake is estimated to be 13 000 tons yearly. But its current fish production is less than 1000 tons a year. Recent studies show a serious decline in fish stocks due to the spread of the aquatic weed water hyacinth around fish spawning grounds.

Water hyacinth, Eichhornia crassipes, is an exotic free-floating invasive plant that is native to South America. People who tend aquariums and gardens are believed to have spread the plant inadvertently across the Atlantic to Africa and Asia.

It restricts water flow, blocks sunlight from reaching native water plants and depletes the oxygen in the water – often choking aquatic animals like fish. It also has an economic impact by interfering with navigation, irrigation, power generation and fishery.

The infestation

The weed forms thick mats that cover the open water. Recent data show that Lake Tana is critically infested with water hyacinth and it’s putting the aquatic biodiversity at extreme risk.

In 2011, the Regional Environmental Bureau named water hyacinth as the most dangerous weed affecting Lake Tana. By then, about 20 000 hectares of the north-eastern shore of the lake was infested. In 2014, researchers from Ethiopia found out that about one-third of the lake’s shoreline, around 128km, was invaded by water hyacinth.

In just two years, the estimated coverage of the weed doubled from 20 000 to 40 000 hectares. The weed is now estimated to cover 50 000 hectares of the lake. To make matters worse, inflowing rivers carry heavy loads of soil and suspended sediment into the lake, which affects the water quality and creates favourable conditions for the spread of the weed.

The release of untreated waste water from industries around the lake adds to the deterioration of the lake ecosystem. As a consequence, the lake has lost 75% of its fish stock in recent years.

Farmers trying to remove water hyacinth from Lake Tana.
CGTN Africa

Control measures

A water hyacinth infestation is hard to get rid of. But there are three ways to do this: removal, chemical spraying (using herbicides) and biological control.

Removing the weed, either manually or using machines, could reduce coverage and slow its spread. But it’s expensive and takes time. Local authorities are mobilising an estimated 162 000 people to remove the weed by hand. This happens only when the lake shores are accessible and when farmers have time.

Lake Victoria, lying in Tanzania, Uganda and Kenya, offers lessons for dealing with the water hyacinth problem. An estimated 60 000 hectares is covered by the weed in Kenya alone. A weed harvesting machine can clear only 10 hectares a day, so it would take 6 000 days (more than 16 years) to remove the weed entirely. Methods like biological control have been shown to be more effective.

Herbicides have been widely used to reduce the spread of the weed, but they may harm the environment. They can kill native plants that are necessary for a healthy functioning of the lake’s ecosystem.

This control method is expensive for developing countries and requires highly skilled people. In Sudan, the costs of chemical treatment for water hyacinth control were estimated to be £1 million each year.

The best approach

Biological control has been widely used. It appears to be the most economical and effective approach to manage water hyacinth in the long term. It uses natural enemies, with little cost and usually no negative environmental impact. Two weevil – or beetle – species, Neochetina eichhorniae and Neochetina bruchi, have been widely used with success. They have shrunk the coverage of the weed and controlled its spread in 33 countries, including the United States, Uganda, Nigeria, Ghana, India and Australia. But this method takes years of work by the insect to clear the weed. For instance, the weevils took two years to control the weed at Lake Victoria in Uganda.

Neochetina weevils eat only water hyacinth. Studies show that these weevils rely on the water hyacinth’s root system for crucial stages of growing. They feed heavily on the plant tissue: larvae eat the inside of the plant and adults eat the outside. Feeding damage by both life stages inhibits the growth of the plant by slowing the flowering process.

Biological control using weevils has been successful in Lake Victoria. A recent study on the adaptability and efficacy of weevils for water hyacinth control in the Ethiopian Rift Valley showed promising results. Potential negative effects, however, should to be studied before realising the weevils to new environment. Once the weevils are released, there is no operational cost as they naturally reproduce and continue feeding until all the weed is cleared.

The ConversationResearchers are also looking at the potential of using weevils for water hyacinth control around Lake Tana. At least 2-3 million people living around the lake will be relying on the success of all these efforts.

Solomon Kibret, Postdoctoral researcher, University of California, Irvine

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

Tiny desert mice could help save Australia’s grasslands from invasion


Christopher Edward Gordon, University of Wollongong and Mike Letnic, UNSW Australia

You should stop skylarking about with those bloody desert mice and try and stop those woody weeds. I could see clear through that paddock in the ‘60s. Now look at it. That scrub costs us tens of thousands of dollars in lost fodder and it’s almost impossible to muster the livestock.

That blunt assessment of our research, first offered by a local farmer in Australia’s arid rangelands almost seven years ago, raised an irresistible question for us as field ecologists. Why are Australia’s (and many others around the world) grasslands becoming woodier?

It certainly was a question worth asking. Shrub encroachment – an increase in the cover of woody shrubs in areas once dominated by grasses – is not just an issue in Australia.

In two recent papers published in the journals Ecography and the Journal of Animal Ecology, we looked at one key reason why trees are invading grasslands, and how we could stop them. And it all comes down to tiny desert mice.

Shrub invasion

“Invasive native vegetation”, as bureaucrats call it, is a major problem for livestock producers in drylands throughout the world. This is because the shrubs compete for space and light with the grasses needed to feed their cattle and sheep.

Shrub encroachment ‘inside’ the Dingo Fence.
Dr Ben Moore

It is a hard problem to tackle. Clearing and fire are the most common methods of controlling woody shrubs. But these methods are laborious and often hard to implement on large scales.

Removing shrubs is also contentious because these are typically native species that provide important habitat for wildlife. The New South Wales parliament’s controversial relaxation in November of regulations governing vegetation clearing were designed partly to allow farmers to remove invasive native vegetation.

What’s going on?

The causes for the spread are complex and poorly understood. Shrub encroachment is often attributed to overgrazing by livestock, which favours the growth of shrubs over grasses. It has also been linked to a reduction in bushfires that wipe out the shrubs and an increase in atmospheric carbon dioxide, which can promote their growth.

However, we suspected another important factor could be at play. And it was those little desert mice that provided us with a big clue – and a possible solution.

Since European settlement, livestock grazing and the introduction of foxes, feral cats and rabbits have decimated Australia’s native mammals, especially in arid and semi-arid areas.

The bilbies, bettongs, native rodents and other small mammals that became rare or extinct across much of the continent in the early 20th century once played essential roles in Australian ecosystems, by shifting vast amounts of soil and consuming vegetation and seeds.

Historical accounts suggest that shrub encroachment quickly followed European settlement and mammal extinctions in many areas. This coincidence led us to ask: could the loss of native mammals be making Australia’s drylands woodier?

Hopping to it

To answer this question, we went to the northwest corner of NSW. Here the Dingo Fence marks the border with Queensland and South Australia.

The Dingo Fence.
Ben Moore

We wanted to know whether the local extinction of a native mammal, the dusky hopping mouse, which eats shrub seeds and seedlings, would allow more shrubs to grow. The Dingo Fence was the perfect study site because dusky hopping mice are common on the northwest side, “outside” the fence, where dingoes are present.

Dingoes keep fox numbers down, which are the mouse’s major predator. However, dusky hopping mice are rare on the “inside” of the fence (the NSW side), where dingoes are less common and foxes roam.

We first used historical aerial photographs to show that shrub cover was consistently higher inside the dingo fence (rodents rare) than outside (rodents common). We then did field surveys, which showed that the numbers of shrubs, their seedlings and their seeds were greater where rodents were rare.

We also showed that dusky hopping mice were major consumers of shrub seeds and capable of keeping the numbers of shrub seeds in the soil down.

Fieldwork in the Strzelecki Desert.
Dr Ben Moore

Going wild again

These results are exciting because they suggest that the loss of native mammals such as the dusky hopping mouse may be an important and overlooked driver of shrub encroachment, not only in arid Australia but also globally.

Perhaps more exciting, however, is how we can apply our work. Our research suggests that “rewilding” drylands by re-establishing rodents and other native mammal species that eat shrub seeds and seedlings, such as bettongs and bilbies, could curb the shrub invasion.

Although an abstract and even controversial idea, rewilding of native mammals would provide a long-term solution to a problem that has affected pastoralists for more than a century.

Further, it would represent a natural and cost-effective strategy with enormous benefits for the conservation of imperilled native mammals.

Before we can do so, we have to control foxes and feral cats across vast areas, which is no small feat. However, the economic and conservation potential make it an approach that is well worth taking seriously.

The Conversation

Christopher Edward Gordon, Associate Research Fellow, University of Wollongong and Mike Letnic, Associate Professor, School of Biological, Earth and Environmental Sciences, UNSW Australia

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

Media Release: Myall Lakes National Park and Booti Booti National Park


The link below is to a media release concerning park closures in Myall Lakes National Park and Booti Booti National Park, due to the annual Bitou Bush control aerial spraying program.

For more visit:
http://www.environment.nsw.gov.au/media/OEHmedia13050902.htm

Antarctica: Weed Invasion Threat


The article below reports on the threat to Antarctica posed by weeds brought in by human visitors. This is a threat that will continue to grow with climate change.

See also:
http://www.nytimes.com/2012/03/20/opinion/seeding-the-southern-continent.html

India: Kaziranga National Park – The Rhinoceros now Threatened by Weeds


The link below is to an article about the threat posed to Rhinos in India by the weed Mimosa diplotricha. According to the article poaching is somewhat under control (poaching for horns), but now the Rhino is threatened by the rapidly spreading Mimosa weed that is smothering out grasses that provide feed for the Rhino.

For more visit:
http://ipsnews.net/news.asp?idnews=106803