I is for Invasive

When we lived in the country, part of our yard was filled with brilliant orange flowers.  The petals were bright yellow-orange in the centre shading to deep red-orange at the edges, and the leaves were covered with bristly hairs.  The flowers grew in clusters on the tops of long stems, and I loved their bright, cheerful colours.  But these flowers were in fact Orange Hawkweed, an invasive plant that can dominate meadows and fields, forming dense mats and outcompeting native species.  What was once a brilliant summer wildflower now was an abhorred invader – or was it?

An invasive species is a non-native plant, animal, or other organism that can survive, reproduce, and expand its population in a landscape where it has few predators or pathogens to check its growth, negatively influencing native plants and animals and often causing the native biodiversity to decline.  European Starlings, Zebra Mussels, and Purple Loosestrife are examples of invasive species in North America.  Most invasive species are introduced by humans, either intentionally or unintentionally.  Sometimes they are brought in as ornamental or crop plants, or as livestock, game animals, or pets, while others arrive as stowaways, pathogens or parasites carried by other introduced species, or seeds in animal feed.  While most of these non-native introduced species do not become problematic, some species are able to quickly take advantage of their new environment and thrive, often at the expense of native species.

Invasive plants, Orange Hawkweed (Hieracium aurantiacum) and Oxeye Daisy (Leucanthemum vulgare)

Invasive plants, Orange Hawkweed (Hieracium aurantiacum) and Ox-eye Daisy (Leucanthemum vulgare)

Many invasive species first become established in areas where the native species have been removed or disturbed – such as in cities, agricultural areas, and regions disturbed by mining, logging, or overgrazing.  Many invasive plants are adapted to disturbed and nutrient-poor soils; they spread quickly, often producing high volumes of seeds or forming dense mats through rhizomes or runners.  Some, such as Spotted Knapweed (Centaurea maculosa) are allelopathic – they produce toxins in their roots that inhibit the growth of nearby, competing species.  Others may be directly harmful to livestock or humans, such as Giant Hogweed (Heracleum mantegazzianum), which has sap that can cause blistering and scarring.

Once established, invasive species can start invading undisturbed ecosystems as well, where they often outcompete native species.  Where I live, grasslands are especially vulnerable to invasive plants; many grasslands have suffered from overgrazing in the past, decreasing the abundance of native plants, and both humans and grazing livestock can easily spread the seeds.  European Starlings (Sturnus vulgaris), introduced in New York as part of a plan to introduce all birds mentioned in Shakespeare’s works to North America, are now found throughout the continent and number in the millions.  Although they may be most often found in urban and suburban areas, they can outcompete native woodpeckers and bluebirds for nesting cavities.  Zebra Mussels (Dreissena polymorpha), introduced to North America’s Great Lakes in ballast water from ships, can reduce the amount of plankton available to native fish, promote the growth of toxic algae, and block water intakes – and they are easily transported to new lakes on boats and equipment.  Invasive species may also bring with them diseases that can infect native species, which may have little natural resistance.

We have often attempted to eradicate invasive species through the use of herbicides and pesticides, physical removal of the species (through weeding, mowing, trapping, etc.) from the environment, or biological control (introducing other species that eat or parasitize the invasive).  Such actions are understandable.  Having seen the damage that an invasive species has wreaked on a native ecosystem and having realized that we are to blame for introducing the invasive, of course we want to do whatever we can to fix our mistake and bring the environment back to its original state.  But such a goal is an impossibility.  Usually, by the time an invasive is recognized, it has already become well-established over a relatively large area.  Many invasives are by nature adaptable species that can survive in diverse environments, cope well with disturbance, and multiply rapidly.  At best, we can only hope to manage most invasive species, not eradicate them.  No management method is 100 percent effective, and some may even lead to further harm: pesticides can affect non-target species, physical removal is costly, and introduced predators or pathogens, if not carefully researched beforehand, may attack related native species as well.  Struggling with invasive species may feel like fighting a battle that will never be won.

But once we recognize the futility of being in a constant battle against invasives, we can accept that neither we nor the invasives need to “win.”  We can choose instead the middle way that will allow all of us – humans, invasives, and native species alike – to co-exist.  Because, like us, the invasives are here to stay.  There is no easy fix to the problem of invasive species – no magic pesticide or other treatment that will completely eliminate the invasives and bring our environment back to its pristine state.  We will never go back to that state.  But recognizing that we will never win against the invasives does not mean doing nothing or giving up.  I believe that we must seek to work with them in a way that will promote healthy ecosystems, biodiversity, and the growth of native species, while acknowledging that the invasive species are a part of the landscape that we can connect with and learn from.  I believe that invasive species are a call for us to adopt a more involved relationship with our environment.

Invasive species are not inherently evil or bad.  Like anyone else, they are trying to survive as best as they can in an ever-changing world (although they are perhaps a bit better at dealing with that change than some).  In their native habitats, these species have natural checks on their growth (predators, competitors, pathogens, parasites) and they co-exist in an ever-shifting balance with other plants, animals, fungi, and microbes.  One reason they become invasive is that when introduced to a new environment, these natural checks are not present and there is little to halt their growth and spread.  I believe that by working with invasives in our backyards, parks, forests, and grasslands, we can take on those roles and become those checks on the invasive species in their new environment.  In this perspective, we are no longer seeing ourselves as apart from the environment and looking at the invasives from outside, trying to “fix” our mistakes, but we are seeking to become a part of the healthy functioning of our ecosystems.

When we approach invasive species with openness, I believe that it will be easier for us to learn and benefit from them, even as we strive to minimize their negative impacts.  Invasive species should not be viewed as a “problem” for government officials and resource managers to deal with, but an opportunity for all of us to become more involved members of our more-than-human community.  For example, by working together on the landscape, we can work to harvest invasive plants (ideally using simple tools rather than heavy equipment that can further disturb native plants and animals, and avoiding pesticides and herbicides).  These activities can help to bring ordinary people into contact with their non-human environment and foster personal relationships with the non-human.  The harvested plants may be used as food or other products by the local community or sold.  Sheep or goats may also be encouraged to graze on invasive plants.  Many of these activities would have direct benefits to the local human population, by providing opportunities for employment, income, and sustenance.  They would also help to encourage a sense of connection through small, local actions that bring people together to honour their local landscape.

Invasive species are not our enemies, or the enemies of our native species.  Many of them are fascinating organisms in their own right.  I believe that we should at least have some respect for their ability to succeed in diverse, non-native environments.  And by engaging with them, I believe that they can teach us much.

What are your thoughts on the issue of invasive species?  How have you worked with invasives in your environment?


I is for Invasive” is part of a year-long series of posts exploring plants, animals, and other beings.  Previous post: H is for Hen.  Next post: J is for Juniper.

This entry was posted in A to Z, Ecology and Environment and tagged . Bookmark the permalink.

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