Tree of heaven, Ailanthus altissima, Lakeside, California. Tree of heaven is considered one of the five most invasive trees in the Netherlands. It was brought to both Europe and the Americas by Chinese immigrants in the eighteenth century.
San Diego’s “most annoying tree,” proclaimed the tree service’s website. They were cagy when I called to ask where I could find the trees, suggesting along the highway by Lakeside, adding that they could only tell me about trees on public property. Having walked as close to the highway as I could get, I was about to give up when realized that the trees were everywhere, in alleys, parking lots and the yards of old homes, sometimes covered by other introduced plants including purple morning glories and golden honeysuckle. When I asked a mechanic if I could photograph by his shop he responded, “you want to photograph that weed tree?” Nonetheless on my next trip, I found a plant sale set up by the local garden club. One of the salespeople pointed to a tree of heaven telling me she’d bought it to serve as a shade plant. Yes, she knew others called it an invasive weed, but her barren lot needed something that would grow fast.
Tree of heaven, Ailanthus altissima growing in Hidden Meadow Preserve, Valley Center, California.
Having learned that the tree of heaven grows in many protected areas of San Diego County, I contacted the Escondido Creek Conservancy. To see the tree, the manager of the preserve took me to former farmland they’d saved from suburban sprawl and planned to rehabilitate as native wildlife habitat.
When we arrived, volunteers were gathered to plant seedlings of native plants they brought from their property to replace the introduced plants that flourished on the abandoned land. Eliminating the tree of heaven had proven difficult. Although they had tried to dig them up, they always missed roots, which resprouted in abundance causing further spread. Therefore, the preserve manager decided to use triclopyr, carefully applying it directly to the tree’s stem away from bodies of water.
The herbicides triclopyr and glyphosate (Round Up) are frequently used to remove invasive plants in the United States. Are the benefits of removing an invasive plant greater than the negative impacts of herbicides on other organisms?
Spotted Lanternfly, Lycorma delicatula, whose preferred host is the tree of heaven, is stealthily following its host around the world on imported goods.
For a decade I have walked with tanoak in northern California killed by sudden oak death, a microorganism that arrived on nursery plants from Asia. Now lanternflies have arrived in Japan, South Korea and the eastern United States and are expected to spread everywhere that tree of heaven has been planted. The sale of tree of heaven has been banned in much of the eastern United States. However, it is unclear how much eliminating the tree will stop the spread of the lanternflies, as the larvae are not fussy, enjoying many native species and agricultural crops. Public officials suggest citizens can play a crucial role in spotting new infestations. With current rate of global shipping these infestations are a constant challenge. Insects and microorganisms inadvertently brought to new places on plants and shipping materials have the potential to eliminate entire species in their new locales.