Friday, May 3, 2013

Native vs non-native vs invasive; weed vs wildflower - what's the difference?

Happy Spring! Gardening weather has returned to the northeast! With it comes an interest in landscaping and getting outside to enjoy our local biodiversity.

Gardening and the biodiversity of our natural habitats sometimes clash because some species that are planted intentionally for landscaping purposes escape cultivation and wreak havoc in nearby forests, wetlands, and grasslands. Government agencies and non-profit organizations such as The Nature Conservancy spend millions of dollars each year trying to prevent the introduction of such plants and to reverse their impacts.

There are many terms associated with this issue - native, non-native, and invasive species are only a few of the descriptions that are thrown around. Weed and wildflower are similarly vague and not always defined. What do they all mean? Let me try to help.

    Japanese maple tree
  • Typically a native species is one that naturally occurs in a particular region. The opposite is a non-native species, which is one that has been transported outside its native range to another place. So, a red maple tree is native to the northeast; the common ornamental Japanese maple tree is non-native to the northeast but native to Asia. Usually the introduction of non-native species is associated with human transportation, trade, etc., though with shifts in species ranges due to climate change, there may be more and more examples of species entering new areas with relatively little human assistance.
Japanese barberry in a forest understory
  • An invasive species is a non-native species that is particularly worrisome because it is capable of expanding into natural areas or protected habitats. While Japanese maples are non-native, they for the most part stay in the yards in which they are planted - I have two in my own yard - rather than produce new offspring that grow into surrounding forests. Therefore, they are not considered invasive. The term invasive is reserved for species whose ranges are able to expand in size or whose populations are able to grow in number. Another species from Asia, Japanese barberry, is also widely planted in landscaping, but it is also a highly invasive shrub in surrounding forest understories. Barberry seeds are transported by birds to neighboring habitats where they grow and reproduce in abundance. So, not all non-native species are invasive, while the term "invasive" is pretty much reserved for non-native species (though there are some exceptions).
    Dandelion in a salad - not a weed
    Dandelion in a lawn - a weed
  • Weed is a term that is basically defined by the context of its presence retaliative to human uses. Many native species are weeds in agricultural fields because they decrease a farmer's productivity. And the same species may be a weed in one context and not a weed in another context – for example dandelions in your lawn versus in your $10 salad.
    Red trillium
  • Lastly, the term wildflower is usually reserved for native, often herbaceous species. However, it is important to note that many non-native – including invasive – species were specifically cultivated and sold for their pretty flowers. There are few if any prohibitions against selling non-native species in nurseries in NY state – many plants that are the target of expensive eradication programs are widely sold in garden centers.
So, what is a gardener to do armed with this knowledge? By all means, get out there, enjoy the outdoors, and get dirt under your fingernails. When you do, give a special nod to your native vegetation that can support diverse pollinators and birds and that values the unique ecological and environmental history of our region.

I recommend following this hierarchy:
  1. Where you can, plant a native species. There are excellent resources for gardeners interested in native landscaping. This is an excellent resource by Donald Leopold for the northeast region. Better Homes & Gardens has a list of the top 15 native plants for northeastern gardens. There are many other similar publications and lists for other regions. Also consider planting native species that support native pollinators such as butterflies and bees. Many of these pollinators' populations are struggling due to loss of habitat, climate change, and increasing pollution. So they need all the help they can get.
  2. When you do plant a non-native species, make sure it is not invasive. The innovative "Don't Plant a Pest" program is a cooperation between the California Invasive Plant Council and the state's horticultural community to offer alternatives - both native and non-native - to invasive species that might be planted in people's gardens. Similar programs exist elsewhere, and you can also visit sites such as New York's Invasive Species Clearinghouse to see lists of priority invasive species.
  3. Get out there and pull! There are many opportunities to volunteer to control invasive species in parks and natural areas near your home. Contacting your park or local chapter of The Nature Conservancy is an excellent way to get involved in biodiversity conservation.

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