Skip to content

More reflection on exotic invasives

2010 July 29

PHOTO BY KEN MOORE. Self-seeding chaste tree, sometimes called hemp tree (see the leaves), attracts pollinating bees and wasps but has nothing else to add to the local natural ecosystem.

By Ken Moore
Flora Columnist

I’ve targeted chaste tree, Vitex agnus-castus, (above) and crape myrtle, Lagerstroemia indica, (back page) to be chopped out of my landscape. You’ll not be happy to read on for the reasoning.

Mention of one’s position on exotic invasives usually initiates heated discussions among gardeners. While many such plants cause multi-million-dollar disruption to agriculture and natural areas, others are objects of pride in private and public gardens.

It’s good to pause and recognize that no individual or organization introduced exotic plants to America intending to create the environmental/economic disasters we now have. Exotic plants date back to the pioneers’ cherished herbs and medicinals from their homelands. Thomas Jefferson and other colonial horticulturists introduced exotics of beauty and culinary appeal. Some invasive plants were accidental stowaways.

Rather than feel guilty for exotic species, we can simply appreciate where we are and how to proceed.

As described in the July 8 issue of The Citizen , our town has taken a bold step. New developments are not allowed to include plant species that appear on the Invasive Exotic Species List, Rank 1-Severe Threat, of the N.C. Native Plant Society (ncwildflower.org). Not surprisingly, that list includes plants like tree of heaven, mimosa and Chinese wisteria, already so ubiquitous that few would dare plant more, though some still plant Chinese wisteria.

I am bewildered by the absence of Bradford pear on that list. Though it’s listed on Rank 2 of the society’s list, it is allowed for new plantings in Carrboro. That is unbelievable (see past Floras featuring the Bradford pear). Observing the flowering of trees along the N.C. 54 bypass around Carrboro, I have noted that at least 50 percent of the forest edge is filled with Bradford pear, tree of heaven, princess tree and mimosa.

Federal, state and conservation organizations have compiled numerous lists of undesirable exotics. To view those lists and understand more about exotic invasives, visit the N.C. Botanical Garden website (ncbg.unc.edu). Under “conservation” is “Invasive Exotic Plants: Publications and Resources.” Among other references, you’ll discover the N.C. Department of Transportation has a sizeable publication with identification guides, historical notes and eradication recommendations. Amazingly, Bradford pear is not considered a “Threat” or “Moderate Threat.” Rather, it’s included on its “watch” list

Why do we have to wait until plants have successfully invaded hundreds and hundreds of acres of landscape before we declare them pests to avoid?

Tree of heaven was introduced to Philadelphia in 1784. It’s taken 200 years for it to reach the current level of disturbance. In contrast, the cultivar Bradford pear was introduced in the 1960s; within 40 years, it’s displacing natives from local fields and roadsides.

My chaste tree, a gift from a friend, is now seeding around like a weed in less than 10 years. During that same period, my beautiful so-called dwarf cultivar of crape myrtle, now higher than 20 feet, has been reseeding for six years. Don’t know how long I can keep it confined to my yard.

The botanical garden has a list of “Plants to Avoid in the Southeastern United States.” I recommend that as the list for folks to adopt as a guide. It’s not perfect, because it doesn’t include my chaste tree or crape myrtle, nor do any other lists.

So I am developing my own list of plants to exclude from my garden. Whatever one chooses to retain and/or introduce in a private garden is whatever one chooses. The real damage to larger landscapes is from large-scale plantings on public landscapes of exotics that eventually escape to adjoining public and private lands.

To be truly responsible, all roadways, parks and residential and commercial developments should be landscaped only with plant species indigenous to the region. Indigenous species are the natural components that thread together a healthy regional ecology (environment).

The native plant society welcomes feedback, so I hope they will bring Bradford pear up to the “Severe Threat” list soon. I hope the Town of Carrboro will take a truly bold step and require all new landscapes to reflect only the native flora of our region.

Email Ken Moore at flora@carrborocitizen.com.

PHOTO BY KEN MOORE. Inappropriate annual pruning never allows crape myrtles, approved to meet the town’s parking lot shade-tree requirement, to become shade trees.

Comments are closed.