The rabbit has been an invasive species all across the globe for over 2000 years, but is
most commonly known as a pest in Australia. Image courtesy of J.J. Harrison (creative commons)
In agriculture we often have to ask ourselves a very serious question. Are we planting invasive species? This question deals with some incredibly important scenarios. Over the past few centuries humans have unintentionally done some pretty serious damage by introducing a new plant, animal, or fungus in a new area. Before we can answer the question though, we need to learn more about what an invasive species is, and what makes it that way. Lets look at a few examples taken from the website of Invasive Species Specialist Group.(1)
Oryctolagus cuniculus (English Rabbit): Originally domesticated in the year 600 in French monasteries, the rabbit was introduced to Australia in 1788 as a food source for the new colonists. The rabbit population grew rapidly, and in 1920 the population had soared to over 10 billion. This invasive pest is a problem because in such high numbers they completely destroy native vegetative lands. Not only does this endanger the survival of native plants, but it also leaves little or no food for native herbivorous mammals such as the Bilby or the Burrowing Bettong.(2)
Opuntia stricta (Common Prickly Pear): The native range of Optunia stricata is the Eastern coastline of North, Central, and South America, in all tropical and subtropical areas. It was intentionally introduced to Australia with the first colonists in order to create two-meter high hedges that cattle would not pass through. This species of cactus very rapidly got out of hand and took over the rangeland intended for cattle, rendering it a dangerous wasteland. Only with the introduction of a moth that is known to feed on the cactus in its native habitat was the population growth able to be curbed.(1)
Acridotheres tristis (Indian Myna): The Indian Myna is a bird that was originally confined to Central and Southern Asia, most specifically India. In India the Myna is considered to be an important animal for pest control for farmers. However, outside of its native habitat the Myna itself becomes the pest. Mynas compete with native species for food, nesting sites, and other resources. In Hawaii they are know to destroy the eggs of other native birds. The Myna also is a carrier of many viruses that can infect humans.(1)
Achatina fulica (Giant African Snail): Originally found on the Eastern coastline of Africa from Mozambique North to Somalia, the Giant African Snail has been unintentionally introduced to tropical and subtropical countries around the world. This snail is a crop pest, destroys native vegetation, alters ecosystems, and carries diseases. Efforts to curb population growth have not been successful.(1)
Why are these organisms invasive?
So, why are some organisms such terrible pests in an introduced region, but sometimes have limited populations in their native ranges? It all has to do with the ecosystem as a whole. When an organism is introduced into another ecosystem, whether intentionally or not, it tries to carry on doing the exact same thing it did in its original ecosystem: obtain nutrition, grow, and reproduce. The potential food sources, the physical environment, possible predators, weather variations, and other things about the new area may be quite different. These factors:
- can cause the organism to become extant (extinct in a certain region) in its introduced ecosystem,
- could provide no advantage or disadvantage at all to the organism, or
- could provide a more suitable habitat where the organism will thrive.
This last option is what happens in the case of an invasive species. Often, there is no control for the new organism (predators or pests) and the organism becomes a better competitor than other similar species in its new habitat because of this. The population begins to grow quickly, and native species start to get pushed out as a result.
Now, lets look at some agriculturally significant plants and animals that have been introduced around the world. As you read this section, ask yourself, have these plants out-competed the native species? Do they grow in areas that were once inhabited by different organisms? Does this make them “invasive”?
Triticum sp. (Wheat): Originally cultivated in the Middle Eastern area now comprising Syria, Jordan, and Turkey, wheat has become the most planted crop in the world. It wasn’t till 1602 that wheat was grown in the new world!
Oryza sativa (Rice): Rice is the second most grown crop in the world. Rice has its origins in South East Asia near the border of China and India.
Zea mays (Corn): First cultivated by Pre-Colombian Natives in Mexico, corn is now one of the most widely distributed agricultural plants in the world.
Solanum tuberosum (Potatoes): Potatoes are the 4th most important food crop in the world — originally farmed by the Inca Indians in the Andes Mountains in Peru. Over five centuries ago, potatoes were brought back to the old world where most civilized cultures initially felt that potatoes were morally wrong to eat since they had been the food of pagans in the New World. Eventually, following many campaigns by monarchs to encourage the eating of potatoes, it is now an essential part of the diet in many of the world’s cultures.
Gossypium sp. (Cotton): Most historians suggest that cotton originated in India. It has become a very important crop for textile industries.
Solanum lycopersicum (Tomato): First grown by the native Aztec people in Central America, the tomato was brought to Spain as early as 1493. At one point it was even considered a poison in England! The tomato did not make it to Asia until about 1825.
Cucumis sativus (Cucumber): Originally from Nepal, where it has been cultivated for about 3000 years, the cucumber spread to Europe through the Middle East. By the reign of Emperor Tiberius (42 BC-37 AD) the cucumber had become a staple food and was even grown in primitive greenhouses. Emperor Tiberius was known to eat these every day, summer and winter.
Apis mellifera (European Honeybee): Based on genetic research, all seven different species of honeybees are originally from South East Asia, more specifically from the Philippines. The honeybee only made it to the New World (North, Central, and South America) with the arrival of European colonists.
Bos premigenius (Cattle): The first evidence of domestic cattle are thought to be either in the area now known as Iraq or in Egypt. Cattle were domesticated from a wild animal called an Auroch.
Then use natives instead!
So what does this mean? Should we eschew the use of these plants and animals outside of their original habitats based on the evidence that they have displaced millions and millions of hectares of native species and surely been the cause of the extinction of many plants and animals? Well, some people might take the position of saying yes. Let’s take a look at what it would mean if we were only able to use native organisms for our daily needs. As an example I have used the nation (and surrounding connected ecosystems) of Kyrgyzstan, as this is where I live. Actually, Kyrgyzstan has enough native species to keep you pretty healthy, but in other locations you would have a much harder time just keeping your belly full.
Malus Sieversii is the ancestor of our domestic apple.
Image courtesy of Lukasz Szczurowski (creative commons)
Malus domestica (Apple): Apple trees are originally from Central Asia and we can still find the original species, Malus Sieversii, in Kyrgyzstan. Malus Sieversii is, however, quite endangered, with less than 1000 trees left in the wild in Kyrgyzstan.
Juglans sp. (Walnut): The town of Arslanbob, Kyrgyzstan has the largest wild fruit and nut forest in the world, dominated by wild walnut trees. These nuts are generally smaller than domestic varieties and are usually considered to be more bitter.
Prunus cerasifera (Plum): Wild plums can be found in a few remote pockets in Kyrgyzstan, but the domesticated plum has nearly pushed this wild ancestor to extinction.
Prunus avium (Cherry): The wild cherry shares the same fate as the wild plum and is also at risk.
Mentha sp. (Mint): Wild Asian mint grows everywhere in the country but is not as useful as domesticated varieties of mint.
Allium cepa (Onion): There are many different species of wild onion in Kyrgyzstan, but few of them produce large enough tubers to make them viable for eating. In addition to that, most wild onion species in Kyrgyzstan grow in very specific elevation zones, which are often above 2000 meters.
Cannabis sp. (Hemp): Used in ancient China and the Central Asian region as a source for fibre to produce paper, clothing, and rope, it has also been used for thousands of years as a medicinal plant.
This list is by no means comprehensive, as there are many more native plants in Kyrgyzstan that are the ancestors to our modern day varieties. These wild ancestors are genetically important resources as they often exhibit tolerance to diseases, temperature fluctuations, limited water availability, and predators. However, the reason these wild varieties are not our “garden varieties” is because they generally do not taste as good.
The answer is control
So, are we planting invasive species? Most often the answer could be construed as yes. If left to its own devices, could wheat become an invasive species? Absolutely. Cattle? Definitely, and in many places cattle has become exactly that. Any organism has the potential to become an invasive species given the correct set of variables that allows it to have perfect growing conditions with no predators. But, this is where we come in. Do you water your garden? Pull up the weeds? Pick the fruits? Fence your animals? This is called control. Without control, many of the plants and animals we use could potentially become invasive. Control is what keeps this from happening. Of course you should be wise in what you plant. If a certain plant is already known to be quite invasive, even in its home habitat, it might be best to avoid using this species. The air potato comes to mind as an example.
Should our worries about causing ecological ruin on our planet stop us from planting new and exciting varieties of purple potatoes, or trying to see if the North American Pawpaw tree will grow in Europe, or maybe an American Persimmon in Kyrgyzstan? I should think not. If we impose limits on ourselves to despise all species that are non-native to our area, then in reality we need to backtrack and remove a lot of non-native plants from our agricultural playbook that we have become dependent on. To do this would be extremely unreasonable, if not impossible.
So next time you plant an apple tree on your farm, just remember, you aren’t in Kyrgyzstan anymore and technically this tree is a non-native with the potential to become invasive. But, as practitioners of Permaculture, we must be willing to pioneer new varieties of a plant, try new species that may have the potential to grow in a different continent, or bring in a new breed of animal that could be beneficial to our system. However, if you choose to do this, it is up to you to take responsibility for your actions. Be wise in what you plant or use. Do the research to see if there is the potential for things to get out of hand. But don’t forget that you’ve already been planting non-natives since day one!
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