On the trail of an ancient invasive

‘if men were not employed to prune these trees… they would cover the country, completely invading it.’

Sound familiar? It could be a description of any number of invasive trees, from the trumpet tree (Cecropia peltata) spreading through West Africa to the candlenut tree (Aleurites moluccanus) currently invading Pacific islands. But it’s actually an account by Mas’ūdī, writing over a thousand years ago in the Islamic year 332 (943 CE).

Ficus benjamina

Has Ficus been a problem for over a thousand years?    © K.M. Kochummen.

Born in Baghdad around 890 CE, Mas’ūdī was a prolific writer and adventurer extraordinaire. His world-history-meets-travelogue, The Meadows of Gold, contains many fantastic stories, from jewelled tombs to Viking battles, but it was his account of an apparent invasive – referred to simply as the banyan tree – that caught my attention, and I was keen to find out more.

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The impacts of invasive weeds in Chitwan National Park, Nepal

Mikania (Mikania micrantha) is a tropical vine which is native to the Americas. Often referred to as the ‘Mile-a-Minute Weed,’ mikania grows rapidly in areas of high rainfall and has become highly invasive in parts of Asia and the Pacific. Under the Convention on Biological Diversity, invasive species are defined as alien species that threaten native ecosystems, habitats or species and in Nepal, mikania and other invasive plants such as chromolaena (Chromolaena odorata) are becoming increasingly problematic within the Chitwan National Park (CNP). There, the plants are having a serious negative impact on native grasses, shrubs and the one-horned rhinoceros, and by implication, deer and tiger populations. They are also affecting the local people who reside in the buffer zones and rely on the park for fodder and other materials.

A rhino amongst chromolaena

A rhino amongst chromolaena


In a specific study on mikania, scientists from the National Trust for Nature Conservation, Nepal with support from CABI and the Zoological Society of London have found a significant negative relationship between high mikania coverage and the population of rhinos. This is because the mikania vine smothers the fodder plants that the rhinos feed on. This could also be influencing their movement to other areas of the park where they feed on resources and crops important to local people. This in turn may exacerbate conflict between the residents of the buffer zones and the wildlife in the area.

Deer and Tigers

The reduction in fodder plants is likely also to cause a mirrored decrease in the number of deer in the park. Deer feed on similar plants to the rhinos and the impact of mikania on native vegetation is therefore likely to affect their feeding behaviour in a comparable manner. As a result a decrease in deer numbers is likely to have a negative impact on tiger populations, with tiger numbers being directly related to the populations of their prey.

Local people

The residents of the buffer zones surrounding the CNP are known to rely on the core area of the park for resources such as fodder, which they use to feed their livestock. These residents recognise that fodder availability within the park has decreased and report that collecting materials now takes three times as long as it has in previous years to gather the same amount of fodder. Reduced fodder has been attributed to flooding of the park and the spread of invasive plant species. In particular, a high proportion of local residents report that mikania has a significant negative impact on the fodder growing in the park.

Sustainable control of mikania weed

CABI piloted using a rust fungus (Puccinia spegazzinii) as a classical biological control agent for mikania weed in India. This highly host specific and damaging pathogen has now been released in Papua New Guinea and Taiwan, where it is having a significant impact on the growth of the weed. The rust has recently been released on a number of other Pacific Islands, and could be considered for release in Nepal.

New Strategy Receives Thumbs Up

Group photo GA 2015

This week in Douala, Cameroon, the General Assembly of the African Union’s InterAfrican Phytosanitary Council (IAPSC) gave the thumbs up to IAPSC’s new strategic plan. IAPSC Director Dr Jean Gerard Mezui M’Ella thanked all the organisation’s partners who had assisted in the preparation of the plan, especially FAO’s Regional Office for Africa for funding the work. Titled “For Better Plant Health in Africa”, the plan identifies four key impact areas, and names a number of partners, including CABI, whose support will be important in its operationalization.

Following on from earlier discussions with IAPSC, CABI Africa’s Roger Day made a presentation on “A Plant Health Management System (PHIS) for IASPC”, corresponding to output 2.3 of the strategy. The ideas were well received by the General Assembly, which immediately appointed a small task force to develop a proposal as a basis for mobilising resources. The General Assembly also adopted a resolution saying it “Welcomes the cooperation between CABI and IASPC on Plant Health Information Systems, and urges them to develop further the ideas for putting in place an effective PHIS, and calls upon international partners to avail financial and technical resources for implementing such an important project”.

For further information contact IAPSC (au-cpi@au-appo.org) or CABI (Africa@cabi.org).

New in May 2015 from the ISC

In May 2015 the following datasheets were published on CABI’s Invasive Species Compendium (ISC). You can explore the open-access ISC here: www.cabi.org/isc


Bubalis bubalis (Asian water buffalo) – domesticated herds of the Asian water buffalo are widely kept across Asia and southern Europe, where they are considered naturalised and not invasive. However, introduced populations in Australia and South America have proved more problematic. B. bubalis competes with cattle in South American grazing land, and has significant negative impacts on rainforests, floodplains and tropical savannahs in northern Australia.

Fibropapillomatosis – thought to be caused by Chelonid herpesvirus 5, fibropapillomatosis is a disease of sea turtles that causes internal and external tumours. Although considered benign, these tumours can hinder swimming, feeding, sight, buoyancy and even breathing, sometimes leading to death. Fibropapillomatosis occurs most commonly in green turtles, but has been reported in six other species, and is now considered a tropical pandemic, with infection rates above 70% in some regions.

Lygodium microphyllum (old world climbing fern) – native to tropical and subtropical Africa, Asia and Oceania, the old world climbing fern was introduced to the USA as an ornamental in the mid-1900s. It has aggressively invaded forested wetlands, particularly in Florida, where it smothers undergrowth, shrubs and even tall trees – you may recognise L. microphyllum as the rampant invasive in the banner at the top of the ISC homepage.

Other invasive species datasheets recently published include:

Alopecurus myosuroides (black-grass)

Ammophila arenaria (marram grass)

Batis maritima (saltwort)

Conium maculatum (poison hemlock)

Leiothrix lutea (red-billed leiothrix)

Linaria vulgaris (common toadflax)

Pastinaca sativa (parsnip)

Poecilia latipinna (sailfin molly)

Rhizophora mangle (red mangrove)

Salsola paulsenii (barbwire Russian thistle)

Stachytarpheta cayennensis (blue snakeweed)

Vicia villosa (hairy vetch)

Villagers front-line in the battle against Prosopis in Ethiopia


Prosopis invading a flood channel near Badahamu

Paul Rogers, Business Development Manager at CABI, visits Badahamu to understand how invasive weeds affect their livelihoods

As we arrived in Badahamu, in eastern Ethiopia, negotiating the by-now familiar thickets of Hara Dergi, “Derg weed” as Prosopis is known in the local Afar language, the impact of last autumn’s floods were painfully apparent. We passed rows of half-destroyed and half-built houses and were warned to avoid local water due to the risk of cholera, which is now endemic.

The story of Badahamu is common across southern Afar. One best told in the words of its inhabitants, it is a tale of the usual challenges of drought and flood being complicated by an invasive species, which removes land from productive cultivation and pasture, and challenges the wealth and identity of households and communities.


Food Aid being delivered to Badahamu

The real human impact of this stressed and vulnerable habitat was apparent when we found the group of community members who we had arranged to interview. They had gathered near the village storage barns, where the latest consignment of food aid was being unloaded. A hundred or more villagers were waiting around the trucks, keen to see what was being delivered and what would temporarily alleviate their chronic hunger.

When we started to discuss Hara Dergi the community listed a number of critical indigenous species that are disappearing due to the invasion of three-quarters of their land. These included trees like cassalto (Acacia nilotica), which is used to feed camels, build houses and as a fuelwood, angalita (Cadaba rotundifolia), which goats and camels browse on, and hedayito (Commiphora habessinica) which provides good grazing. When it invades the banks of the Awash river, the region’s lifeblood, it causes silting which obstructs and deviates the flow, increasing the frequency and severity of floods and reducing the community’s ability to manage dry season droughts.


Focus group respondents at Badahamu

There were bitter complaints over the cost of clearance, which places a significant financial burden on households and the community. The fierce thorns of Hara Dergi are causing both lameness and jaw deformity in livestock, and is likened locally to “AIDS for cattle”. It is also reducing income that could be used to fund local measures to control the spread of the weed.

It is not just the animals that suffer from thorn injuries – the local administrator estimated that the thorns had caused over 30 disabilities within the community, a human tragedy worsened by the effect Prosopis has on obstructing access to the local health centre.

Hunger and despair are driving the community to increasingly drastic and destructive measures. The encouragement, and then discouragement, of charcoal production by the government has caused anger and conflict amongst pastoralists who suspect that the few remaining local trees, rather than the intended Hara Dergi, are being used. Then there is the sugar cane plantation.  Positioned adjacent to the community’s lands as a tauntingly green, year-round oasis, over 15 of their members have been imprisoned for illegally grazing their herd around its edges. Despite warnings and sanctions, the scant rewards outweigh these evident risks.

This is the real tragedy. Such is the devastating impact on their livelihoods, and the desperation that this causes, that members of the community are engaging in illegal activities that risk ostracization by officials whose support is crucial in improving their circumstances. Once proud, the community now recognizes that it cannot confront Hara Dergi alone but is coincidentally conscious of the fact that it was introduced not by them, but by foreigners – tempering shame with indignation. Whoever’s ultimate responsibility it is, a solution will only be found through collective action, action which above all must be quick.

New in April 2015 from the ISC

In April 2015 the following datasheets were published on CABI’s Invasive Species Compendium (ISC). You can explore the open-access ISC here: www.cabi.org/isc.


Triumfetta semitriloba (burweed) – this weedy perennial shrub species, native to large parts of tropical and subtropical America, has been introduced to a number of Pacific islands, where it is now invasive. Its international spread is something of a mystery, though the barbed burs allow local spread via passing animals and people to occur very easily.

Stachys arvensis (staggerweed) – native to parts of Europe, Asia and North Africa, this poisonous herb has been introduced to a range of habitats around the world. S. arvensis has become a serious weed in many places, with negative environmental and economic impacts. It can cause nervous disorders in livestock, especially sheep, causing them to stagger – hence the common name staggerweed.

Solanum mammosum (nipplefruit nightshade) – known by a veritable smorgasbord of colourful names, S. mammosum is an annual or short-lived perennial that has been introduced to Asia, Africa, the Americas and Pacific islands. It is reported invasive in Cuba, the Philippines, Fiji, Tonga and parts of Hawaii.

Other invasive species datasheets recently published include:

Lythrum maritimum (pukamole)

Opuntia engelmannii (cactus apple)

Salvia splendens (scarlet sage)

Solanum erianthum (potato tree)

Solanum rostratum (prickly nightshade)

New edition of weed biocontrol catalogue gives information on more than 2000 releases

The Plantwise Blog

Himalayan balsam infected with Puccinia rust Himalayan balsam infected with Puccinia rust – a method of biocontrol being used in the UK. Photo credit: Rob Tanner © CABI

The fifth edition of Biological Control of Weeds: A World Catalogue of Agents and Their Target Weeds has been released after years of literature searches and the involvement of 125 weed biocontrol specialists.

The publication of this catalogue, available as a searchable online database and as a PDF book, was led by Mark Schwarzländer, University of Idaho CALS professor of entomology and biological control of weeds (and a former CABI researcher), and current CABI biological weed researcher, Hariet Hinz. Several prominent invasive species researchers co-edited the catalogue, including CABI’s Chief Scientist, Matthew Cock.

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