Wednesday, September 28, 2011

Alien invasion!

Flowers of Lantana camara. Look closely- each one of those blooms is
a small flower on a bigger 'head.' Each head can have up to 20 flowers.

I have met the enemy, and its name is Lantana.

Lantana camara is a plant species originally from Central and northern South America. Sixty years ago this beautiful plant was still in its native range, but it was taken to Europe as an ornamental. People then took it around the world, and now sixty countries or major islands are grappling with its effects on their ecosystems.

Lantana thick and tall in Agahozo-Shalom Nature Park, 7:30 am one morning.
You can barely make out the tree inside.

Lantana is all over East Africa (Kenya, Tanzania, Uganda, Rwanda, Burundi). On our hillside in Rwanda, outside of landscaped and cultivated areas, Lantana is the dominant plant. You pass it on the way to the dining hall and school, you sit near it in the amphitheater, and you see it in Parike W’Agahozo (Agahozo-Shalom Nature Park). In the park especially, where we are promoting the growth of native species, Lantana is a major problem; it is a non-native (alien), invasive species.

The same view of the tree as above five hours later with Lantana removed.
There is still more to remove from the back and sides, and several stumps
still need  to be removed. Clearing Lantana from this tree was particularly
tricky because there are swarms of honeybees that live in it!

Most non-native plants do not cause problems. Generally plants are adapted to a certain climate, soil type, variety of pollinators, and other environmental factors and thus do not succeed outside of their established range. Some plants are extremely tolerant of different conditions. It is these plants that can become problematic when they are introduced to new areas. They can have devastating consequences when other plants, animals, bacteria, and all the forms of biodiversity are not adapted to such a new factor. Lantana outcompetes the local plants and quickly forms a dense monoculture of Lantana. Any associated animals must either move on from their former habitat or adapt to living with Lantana.

The small shark-tooth shaped thorns that can make removing Lantana
tough on the hands, arms, and any other part of the body they scratch.

To understand Lantana’s imposing grasp on the landscape, we need to examine its biology. Lantana is a flowering plant that produces fruits. These small berries are eaten by birds (other animals) and are spread through their feces. This takes Lantana far and wide across the landscape.

Lantana fruits

Once the seeds germinate, they grow quickly. In just its second growing season, Lantana can produce flowers. The flowers are very small, but grow on heads that can contain twenty flowers per head. A mature plant “flowers prolifically” and can produce 12,000 seeds annually.

I counted 87 flower heads (assuming just 10 flowers per head, that is 870
flowers). Each one of these flowers may produce a fruit. Now, try to count
the heads that have already fruited. You get the picture.

In addition to its reproductive attributes, Lantana grows quickly and shades out all other species in an area. In shaded areas, their shoots grow tall and sprout leaves above the cover. They can grow thick stems that lean on trees and within just a couple years, they can completely shade out a 3 meter tree. Taller trees in a dense forest may prevent Lantana growth, but in an area that is being reforested like Parike W’Agahozo, Lantana will plague native regrowth until the trees are tall enough to shade it out.

Lantana regrowth, just two months after we cut away the rest of the plant.
Because of its ability to regrow quickly, we have to remove the roots.

It is difficult to estimate how much Lantana is in the 1.7 hectares of Parike W’Agahozo. Mature plants might be easy to count, but many younger plants have small stems and number in the 1000s. Young plants that have sprouted in the past year number in the tens or hundreds of thousands.

A student uses a saw to cut Lantana.

Upon realizing the depth of the problem, it became apparent to me that without mitigation, the park would become a protected place of Lantana, a stronghold for it to continue its spread. In order to plant native trees and to conserve the native species we already have, we had to get rid of the Lantana.

Students removing the roots of Lantana.

But is not as easy as cutting it down. Lantana can grow back from any part of itself. We have to remove the roots to fully disrupt Lantana regrowth. Agahozo-Shalom students participate in removing Lantana from the park each Saturday. Our tools include hand saws, pruners, hoes, pitchforks, and gloves. We have removed maybe half the Lantana in the park, but we have a long way to go.

Students participate in Lantana removal each week.

Looking back on my photographs of birds at ASYV, it is telling that a large number of them are on Lantana branches. I do not believe we can fully remove Lantana from East Africa. What we can do is find the places that need protection the most, like parks and Important Bird Areas, and make sure that Lantana does not invade them. We also need to educate people outside these areas to certainly not plant Lantana, but also to remove it and favor other plants so we can reduce its spread.

In the much bigger picture, we cannot blame the plant. We brought this plant here. We transport invasive species all over the planet. Everyone in every environment can promote native species and help stop the spread of non-native, invasive species.

Works Consulted
  • "Invasive Species in Eastern Africa: Proceedings of a workshop held at ICIPE, July 5-6, 1999." UNEP Convention on Biological Diversity. Accessed September 29, 2011 at
  • Walton. C. "Lantana camara." Global Invasive Species Database. Accessed September 29, 2011.
  • “Invasive Pest Fact Sheet: Lantana camara.” Asia-Pacific Forest Invasive Species Network. Accessed September 29, 2011.
  • “Pest Plants- Lantana camara.” Rwanda’s the Eye Magazine. Accessed September 29, 2011.

1 comment:

  1. Hello Jared,
    I like this post.
    I would like to reproduce extracts on my page:
    I have already used one photo.
    Ray Perry