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What is an Invasive specie?
 
If you look around the ocean or the forest you can see different species living around, either small or big. These species might be hunting their prey or be hiding to avoid being eaten by their harmful predators. In the habitat, there are some species that can have a beneficial relationship, which can help each other when they are together. However, there are some species that can harm other natural resources in an ecosystem. Invasive species is a harmful relationship in an ecosystem. An invasive species is a biotic or an abiotic factor that aggressively takes over habitats. So it is also known as exotic species, since exotic means when something is from another place. When these species takes over it allows it to exclude the community. These species can also threaten humans by their resource (What Is an Invasive Species?). 
 
 
What is the Invasive specie that I chose?
 
 The invasive species that I chose is chromolaena odorata, which is known to be one of the 100 most world's worst invasive species.Chromolaena odorata is a fast growing, and everlasting shrub, it can grow 1.5 to 5m tall but it can grow about 6~20 m when they have a supported tree or other objects that they can go up. Chromolaena Odorata is woody in the base but it has a soft stem. The stems are yellowish, straight and sprawling, glandular/hairy that gives strong odor when they are squeezed. The leaves have 3 prominent veins, 4 to 10cm long, 3 to 8cm wide, triangular or oval shape and a pointed apex. Likewise the stem, the leaves also have a pungent odor when it is squeezed. The flower doesn’t have petals but the color of it is known to be pale pink/ mauve. It will turn brown when it dries up. The number the flower is about 15 to 30 each and it is 10~12mm long. The root will first grow horizontally for few centimeters, when if develops it will result in a lignified storage. The Black/ brown seeds that are 4 to 5 mm long, has pappus hair which is very light that gets easily blown by the wind (Chromolaena Odorata (Siam Weed).

Invasive Species name

Chromolaena Odorata has multiple names. The full scientific name is Chromolaena odorata (L.) R.M. King & H. Robinson. Chromolaena odorata has a meaning to the name. Chroma, in Greek, means color and Laena, in Latin, means cloak. Which means a flowering plant that has a colorful appearance. While Odorata means the smell of the leaves when it is crushed. The aliases is known to be Eupatorium Odoratum L. and the preferred common name is Siam weed. It is also known as Siam weed, which shows the plant's occurrence and importance in Siam, known as ThailandIn different countries this plant is named differently. Below is the list of common names that other countries prefer to use. (Plants Profile for Chromolaena Odorata (Jack in the Bush).)

 

English

  • Archangel

  • Bitterbush

  • Christmas bush

  • Chromolaena

  • Siam weed

  • Triffid

Spanish

  • Chimuyo

  • Crucit

  • Eupatorio Oloroso

  • Hierba de chiva

  • Paleca

  • Rey del todo

French

  • Eupatoire odorante

  • Fleurit-Noël

  • Herbe du Laos

Australia

  • Butterfly-weed

  • Devil weed

  • Jack-in-the-bush

China

  • Feijicao

Germany

  • Siam-Kraut

South Africa

  • Amstrong's weed

  • Armstrong weed

  • Kingsweed

  • Paraffin weed

 

Origin and Distribution

In the 1840s, Chromolaena odorata was supposedly introduced as an ornamental in India, which then was spread. Chromolaena odorata is originated in the native of Central and South America, which soon widely spread through tropical areas of the world. In 1994, Australia was the first to identify this plant. In Queensland, they have suspected the introduction of the seeds from oversea. But after couple of years, people wanted to eliminate the specie. It wasn't a serious weed in the native area but it colonized the areas of the forest, which made other plants unable to grow. Now this weed is rapidly wide spreading into Africa, tropical America, Southeast Asia and India. The spread of the seeds happen by water or wind since it was very light. Also it moved by mud by the movements of animal, humans or machinery. The seeds have a fine barbs around the seeds so it may stocked to clothing, equipment or animals. The most spread happened during World War II, the troop movements of people and materials. In 1937, in West Africa during the forestry seeds, the plants were accidentally introduced.  Soon in 1952 it was introduced to Côte d’Ivoire and continued to spread. (Issg Database: Ecology of Chromolaena Odorata.)

Habitat

Chromolaena Odorata lives in agricultural areas, riparian zones, shrub lands, grasslands, planted forests or natural forests. In order for a good growth it should be on places where there are some shades with an annual rainfall about 1200mm. The temperature of the soil should be 30˚C and the humidity should be in a range of 60 to 70 percent. It won't grow well when there is too much water, high salinity of soil, lots of shades or if the humidity is higher than 80%. ((Issg Database: Ecology of Chromolaena Odorata.)

This plant is almost everywhere; it is at Asia, Africa, North America, Central America and Caribbean, South America and Oceania. Although there are known to be an invasive species in some areas it is just a normal plant, for example in South America the plants are populated but they aren't invasive specie. 

 

Impacts

Chromolaena odorata can give Social impacts, environmental impacts and Economic impacts. In some regions like the South Western China, traditional agriculturalists are growing Chromolaena odorata by their attractive appearance. Also these plants were used as ornamental plants during the nineteenth century. Some regions are using it as traditional medicine. For example in Vietnam, Chromolaena odorata is the ingredient of one of their traditional medicine, which is called "Co hoi". The leaves of this plant were used in Vietnam for treating soft tissue wounds, skin infections and burn wounds. It proved scientifically when they experience whether the medicine was working or not. These results show that traditional medicine can be examined as a scientific manner while developing the wound-healing model. However it can also give negative impacts. Chromolaena Odorata is toxic to human. It can cause skin problems, Asthma in allergy prone people. (Chromolaena Odorata (Siam Weed))

 

Apart from having a positive impact on humans it may have some negative impacts on the environment. It was known to be 100 of the world's worst invasive species. These species can be affected to other natural plants since it rapidly dominates the native area and alter or takes away their habitat. It can also decrease the animal population. When these plants take away the area, then the food sources will be replaced also they will lose their shelter, the breeding site will no longer be suitable. For example the Nile crocodile in South Africa have lost their breeding habitat since the nesting site's temperature decreased by shading and became more crowded. Nesting sites for the Nile Crocodile should be open, sunny and sandy area. In dry seasons, Chromolaena Odorata represents a fire hazard. It is because of the volatile oils in their leaves and stems which will promote a bushfire. Dried Chromolaena Odorata has a much hotter flame comparing with the pure forest fires. Uncontrolled fires created by this plant can harm the village, the crops and destroy plantation. For example in South Africa, even it is a season that is green (growing season) it is still available to burn. In this plant, on the flower there is Alkaloid, which kills animals such as goats while they eat the flowers. For instance in Philippines it had mentioned that it killed more than three thousand cattle. (Chromolaena Odorata (Siam Weed))

 

Lastly it can give economic impacts. Chromolaena odorata can be a serious weed when it comes to plantation. The crops are usually grown in humid areas so when the plants are colonized it will completely kill the crops such as cocoa or coffee. Killing these crops will have negative impacts to the farmers since they will produce fewer crops. When the crops replace Chromolaena odorata, then it will be dominant specie that can grow in that area. It may have some negative impacts to farmers since they have lost their land to produce crops. But it can still be considered as a benefit since Imperata Cylindrica will not grow anymore. Also the growth of this plant can make the soil more fertile. Chromolaena odorata can also communicate with fungi and host for recognized pests and pathogens including Zonocerus variegatus. (Chromolaena Odorata (Siam Weed))

 

 

 

Prevention and Control

Cultural control

 

Cultural control can have a high labor cost since this is controlled by humans, also it may not be as effective comparing with other controls it may bring up another problem. In the cultural control there are 3 ways to prevent the spread of the Chromolaena Odorata. People can be mulching. Mulching is known to cover with organic matter to be a protective covering to the tress, to maintain a healthy root. Mentioned previously, this have a hight labor cost and have a limited materials. The second method is people allowing other competitive species to involve with the Chromolaena Odorata. For example in 1977, Castillo et al planted Leucaena Leucocephala and Tephrosia Purpurea in Philippines and was able to reduce the population. Other plants such as, Neolamarckia Cadamba, Pueraria phaseoloides, Calopogonium mucunoides, Centrosema pubescens and Vigna unguiculata were suggested to cover crop on other countries. In 1989, Torres and Paller found out that Calopogonium mucunoides and Centrosema pubescens suggested to cover crop after burning the infested area. Lastly, slashing and hand pulling is another example. Since slashing can't kill Chromolaena Odorata, it has to take of the whole root, so they have to hand pull it. During the growing season, this action should be taken at least twice. To make sure that the contact is not remained in the soil, it may result for the plant to grow.

 

Mechanical control

 

The mechanical control is slashing, burning or ploughing. Mentioned previously, this action should be taken at least twice to prevent from regrowth. So this labor, in large areas or dense infestation, be slow and will cost highly Rather than doing this with hands, in this process it will be using a mechanized equipment such as hoes, machetes, tractor and bush knives. This mechanical control should be done by a trained operator since other might mistakenly destroy an untargeted species.

 

Chemical control

 

The chemical control is the most used method by other countries and most successive. It is well used because it can quickly reduce the population in a particular agricultural land but the cost can be effective. During this control, a trained operator that is able to use specialized equipment will be needed. There are some expectation in order to do this control. Such as the weather, the plant status and also the high cost. Chemical controls are widely used on Chromolaena Odorata. In Australia, it was able to reduce 98% of this species in 5 years by using herbicidal treatment in a particular area. However it was a small infestation, in West Africa it failed on 100% mortality with lots of money. The testing was mostly in Philippines, Indonesia, India, West Africa and South Africa. This chemical control can be used before the mechanical control or after. When it is used before, the herbicides will be applied before the seedling stage/ early regrowth. When people are using this control, they have to beware of the options of the herbicide since it is expensive and ecological concerns. When they are applied before the seedling stage/ early regrowth, after the regrowth it will only reach a height of 50 to 100 cm. Another way is the cut-stump method. After slashing the Chromolaena Odorata they can apply the herbicides.

 

 

 

 

 

 

 

 

 

 

Biological control

 

The biological control is known to be a low cost control, eco-friendly, less disturbance but a long term method on the control of invasive species. This method had showed positive results. But, a survey showed that only twenty-five percent to forty percent was considered to be effective. The Nigerian Oil Palm Research Institute, in 1996, recognized the serious spread of Chromolaena Odorata, and asked the CIBC (aka CABI Bioscience) to manage the rapid population growth. Cruttwell McFadyen, a weed bio control entomologist have found 207 types of insects and 2 types of mite that was able to reduce the amount of Chromoloaena Odorata in America. But, the quarter of these type of species have actually affected Chromoloaena Odorata. These species will help removing the potential growth and the flowering point. Chromolaena Odorata has a photosynthetically active stems that regenerates after the defoliation, so these agents can use the stems as their key in controlling the infestation. There are 3 species that was selected to be the most helpful agent on reducing the amount of Chromolaena Odorata. Firstly, Pareuchaetes Pseudoinsulata, it was the first species identified by the CIBC. Pareuchaetes Pseudoinsulata was first released in Malaysia in 1970-1972 but only some places were able to reduce them. After it was released on Sri Lanka in 1973, Sabah in the mid 1980s, Guam in 1985, Northern Mariana Islands in 1986-1987, India in the late 1980 and early 1990, Yap in 1989-1991, Pohnpei in 1988-1990, and Indonesia at 1991. As a result, they found out that it had less impact to larger areas comparing to smaller areas since Guam was able to reduce the number. The second species was the mite called Acalitus Adoratus Keifer. Unlike the previous species, this species was accidentally introduced to Malaysia from Trinidad through shipment. This species had spread to Philippines, Mariana Islands, Thailand, Indonesia and India. Lastly the Procecidochares Connexa. In 1996, it was established at Indonesia and currently it is being hosted in Palau, Philippines and Guam.

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