Being Watchful For Invasive Species
It is now widely accepted that a diverse ecosystem is a robust ecosystem. Every time we lose a species, we lose information, potential and interactions that we will never know appreciate or comprehend; we also lose another interspecific link in our ecosystem, the importance of which can only be conjectured. Whether we regard other species as economic opportunities, scientific curiosities, ecological consociates, aesthetic delights or ethical responsibilities it is imperative that they be conserved.
Threats to biodiversity come in many forms but the two most serious threats are habitat loss and invasive species (itself a type of habitat loss). Invasive species may be animals, plants or disease organisms that are released without control into areas where they can thrive, spread, kill or displace native species and thereby alter the species composition of an area. Alien species that fail to persist, that persist without spread, that remain only in disturbed habitats are not invasive even though, in the case of agronomic weeds, they may inflict serious economic losses. It is their spread and increase in hitherto undisturbed native habitats that earns their status as invasive.
Over the course of history, people have moved from place to place and usually have brought along plants and animals for food, medicine and aesthetics. Many of our greatest explorers brought back food plants and today their cultivation is often far from their origins. Coffee is from Africa though we usually think of Colombia ; potatoes evolved in Central and South America before being taken to Europe in the 1800’s and thence to North America . This movement and introduction of species into new areas has resulted in many of the invasive species that trouble us today. On the island of Newfoundland one of our most serious invasive species is our largest land animal, the moose. Introduced in the early 1900’s the moose has spread throughout the island, bred without check and is now inflicting serious damage in our national parks and many parts of rural Newfoundland. A voracious browser, moose have stripped tree branches as high as they can reach and munched native shrubs down to their crowns. Their partner in crime, the snowshoe hare, is another newcomer. It too browses native vegetation, but is fond of young shoots and seedlings. The result is a dramatic change in boreal forest recovery, age structure and understory species.
Newfoundland and Labrador 's flora of approximately 1,500 vascular plant species comprises perhaps 1,000 native species and 500 naturalized species. The latter were brought here intentionally or accidentally and have flourished. Certainly, we do not have the vast stretches of purple loosestrife (introduced as packing material), English ivy or Scotch broom (introduced as ornamentals) that have damaged many parts of Canada but within our naturalized species we have several invasive plant species and we need to be vigilant lest more occur.
Just what makes a plant invasive? Well we can look at its characteristics, especially its reproductive characteristics to give clues as to its capacity to become a pest. Below is a short list of factors to be concerned about:
- Does the species have a widespread native distribution?
- Does it have high genetic variability and is adapted to range of conditions?
- Is there close correspondence between native climatic conditions and those of the new area?
- Are there natural predators of the introduced species?
- Does it have highly effective seed dispersal mechanisms?
- Is it associated with humans?
- Does it have a short juvenile period?
- Is it self-compatible?
- Does it have high reproductive output and show several reproductive strategies?
Reichard and Hamilton (1997) constructed a very useful ‘decision tree' when considering new plant introductions. The more widespread such decision-making becomes the less new invasives will be seen.
Let us turn our attention to our own province. Sometimes used as a windbreak or hedge, Japanese knotweed a.k.a. mile-a-minute (Polygonum cuspidatum) is a pernicious weed that quickly gets established on roadsides, dumps and waste ground. It has become a major problem in most temperate countries since its introduction as fodder and as an ornamental from Japan in the mid- 19th century. A far more charming herald of spring is the coltsfoot, but it too arrived in Newfoundland in the early 1900’s probably in ballast on the west coast. It has since spread across the island establishing in open disturbed ground but spreading into native stands. It is particularly abundant on the western side of the island where it has been observed mixed (and apparently out-competing) the native creeping arbutus (Epigaea repens). I well remember strolling along a stream on the Bonavista Peninsula . Stream banks are usually lush with many species like willows and sweetgale, violets and ferns. Not here though, the entire vegetation comprised of just one species, European mint (Mentha spicata) massed along the banks and into the water. Certainly a wonderful smell, but just how much mint sauce can one community need!
MUN Botanical Garden encourages everyone to participate and enjoy gardening and horticulture. It is a healthy and rewarding hobby. Also healthy is the horticultural industry of Canada that has developed into a significant employer and economic driver. While most garden plants are not invasive and can be grown without worry, please remember these few pointers:
- Never bring seed or plants back into Canada without having them inspected. Over 80% of all plants intercepted at US airports were found in regular passengers' baggage. Often the plant's identification is unknown and we have little knowledge of their potential for invasiveness once released in a new area.
- Never take garden trash and dump it in a natural habitat. Seed, sods and clippings can easily re-establish themselves in this new site.
- Never plant ‘extra' plants or seed in a natural area regardless of their attractiveness; they are not native and should not be introduced artificially.
- If you do see a garden plant spread from your garden into some native habitat then remove it.
We are all stewards of this land and stewardship requires taking responsibility. If we can all be watchful for invasive species and take action if they are encountered, then Newfoundland and Labrador 's wonderful native flora will continue to co-exist with our new arrivals.
Reichard, S.H. and Hamilton , W.H. (1997). Predicting invasions of woody plants introduced into North America . Conservation Biology 11, 193 – 203.
