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

Rhinos

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 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 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)

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.


May

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)

Ebola and IAS

A conversation with Dr Arne Witt

Dr Arne WittThe recent outbreak of Ebola virus disease in West Africa made headline news around the world. During the outbreak this fatal disease, endemic to parts of Central and West Africa, rapidly spread from Guinea, Sierra Leone, and Liberia to other countries in the region such as Nigeria, Mali and Senegal and then further afield to the USA, UK and Spain, mainly through infected health workers. This prompted decisive action from governments around the world and led to the implementation of strict controls at most national points of entry – as a result of this action and increased awareness, the further spread of this disease was effectively halted. No new infections have been reported for a number of months now but the cost has been significant – more than 10,000 people lost their lives, mainly in Guinea, Sierra Leone, and Liberia. However, it is highly probable that without significant interventions the costs could have been far higher. For example, the outbreak of bubonic plague or Black Death in Europe in the 17th century resulted in the death of 34 million people. The accidental introduction of potato blight, a crop disease which affects potatoes, from the Americas to Ireland in the mid-1800s contributed to the starvation of about 1 million people. Rinderpest, a disease affecting livestock was accidentally introduced to Africa from Asia in the late 19th century resulting in the deaths of, it is claimed, a third of the human population of what is now Ethiopia and two-thirds of the Maasai, an ethnic group of pastoralists in East Africa who are totally dependent on livestock. We may ask what Ebola, potato blight and rinderpest have in common – well obviously they have all have had a devastating impact on humanity but what binds them all together is that they are all INVASIVE ALIEN SPECIES (IAS). Fortunately, due to concerted efforts by a range of agencies rinderpest has been eradicated from the planet but as a result of increased trade, travel and tourism more and more species are being moved around the world and many are establishing and are continuing to have devastating impact on livelihoods. Read more of this post

Tuta absoluta on the rampage in Africa

Watch a new video illustrating the devastating impacts that Tuta absoluta is having on tomato yields, and what this means for farmers who rely on these crops for sustenance and income.

Dr Arne Witt, from CABI commented on the implications of Tuta absoluta infestation across Africa

“Tomatoes are one of the most widely cultivated crops in Africa and are grown in the backyards of almost every homestead across sub-Saharan Africa. This important cash crop and source of vitamins is now threatened by the recent arrival of the tomato leafminer, Tuta absoluta.

This Invasive Alien Species is rapidly moving down the African continent, having already decimated crops in Egypt, Ethiopia, Kenya and northern Tanzania. Growers are at their wits end as to how best they can control this pest and many have abandoned tomato growing altogether. The race is on to prevent its spread further south with various interventions planned to mitigate its impact in areas where it is already present.”

For more information on Tuta absoluta visit the Invasive Species Compendium and the Plantwise Knowledge Bank.

New in February 2015 from the ISC

In February 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

February

Furcraea foetida (Mauritius hemp) – native to Central America, this evergreen perennial has been introduced worldwide as an ornamental, for its fibre and for erosion control. However, F. foetida can grow up to three metres across, compete with surrounding vegetation and displace native plants, and as a result has become dominant on many tropical islands and atolls around the world.

Hypostomus plecostomus (suckermouth catfish) – as a popular ornamental fish, H. plecostomus has been introduced to the Americas, Asia and Europe from its native range in northern South America. But this armour-plated, egg-guarding, hypoxia-proof omnivore can quickly monopolise resources and inhibit other aquatic organisms. By building nests in river banks and sediment, the suckermouth catfish contributes to bank erosion and increased turbidity, with associated environmental and socioeconomic impacts.

Bythotrephes longimanus (spiny waterflea) – the invasion of the crustacean B. longimanus in the North America Great Lakes has resulted in a marked decline of both the density and diversity of many copepod zooplankton species, with long-lasting effects in invaded systems. It has also been responsible for a large-scale shift in the zooplankton community and competes directly with planktivorous fish for food.

Other invasive species datasheets recently published include:

Adenostoma fasciculatum (chamise)

Adiantum hispidulum (rosy maidenhair fern)

Belonesox belizanus (pike killifish)

Bromus hordeaceus (soft brome)

Buddleja asiatica (dog tail)

Desmodium incanum (creeping beggerweed)

Euphorbia hypericifolia (graceful spurge)

Hymenachne amplexicaulis (hymenachne)

Lepomis microlophus (redear sunfsh)

Mikania scandens (climbing hempvine)

Polistes dominulus (European paper wasp)

Salvelinus namaycush (lake trout)

Simosyrphus grandicornis (flower fly)

New in January 2015 from the ISC

In January 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.

Clerodendrum thomsoniae Invasive Species Compendium datasheet

Clerodendrum thomsoniae Invasive Species Compendium datasheet

Clerodendrum thomsoniae (bleeding glory bower)native to West Africa, this vine has been widely cultivated in tropics and subtropics worldwide, and is naturalised in many places, including the USA, Australia and the Galapagos Islands. Despite being related to some particularly serious invasives, such as C. chinense and C. quadriloculare, the impacts of bleeding glory bower are so far limited.

Cortaderia jubata (purple pampas grass)familiar to many of us as a garden ornamental, C. jubata is a multipurpose tussock grass native to South America. Surprise surprise, this towering, fast-growing, prolific plant has become a serious invasive in several places around the world, displacing native vegetation and suppressing the growth of young trees. Dense stands of C. jubata can also pose a fire hazard.

Opuntia monacantha (common prickly pear) – another introduced Opuntia, another tale of woe. Opuntia monacantha has been introduced around the world as a fruit and fodder plant since the 1700s. Its ability to regrow from broken and scattered cladodes allows it to quickly form dense, impenetrable thickets. Fortunately, biocontrol of the common prickly pear has proved successful in several countries.

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