In­va­sives threaten Na­tional Ar­bore­tum

For­eign pests take toll on trees

The Washington Times Daily - - FRONT PAGE - BY EMMA AY­ERS

For­eign plants and in­sects in­tent on wip­ing out na­tive flora have in­vaded the Na­tional Ar­bore­tum and the sur­round­ing D.C. area, forc­ing gar­den­ers and hor­ti­cul­tur­al­ists alike into a silent war against de­struc­tive pests.

At the ar­bore­tum’s New York Av­enue NE en­trance, green creep­ing vines — English ivy — hugs the ground, block­ing sun­light from reach­ing the plants be­neath. In other spots around the ar­bore­tum, the weed can be seen cling­ing to trees and shrubs.

Else­where, woody vines — some with black round berries, oth­ers with fra­grant white flow­ers — have grown up thick and for­mi­da­ble. These plants may look harm­less at first glance, but they have ex­acted a toll on the na­tive plant life in the ar­bore­tum and the D.C. re­gion.

“There are a ton of in­va­sives we have to fight here,” said Ar­bore­tum hor­ti­cul­tur­al­ist Joe Meny. “But if you look, you can see the prob­lem pretty much any­where.”

These plants — of­ten woody vines — have taken over many

ar­eas in which plenty of sun­light is avail­able.

“His­tor­i­cally, you would find vines in these types of places where there was light — where, say, a hur­ri­cane had knocked down some trees. Now, par­tic­u­larly in ur­ban ar­eas, lighted ar­eas are ev­ery­where,” said Lea John­son, an ecol­ogy pro­fes­sor at the Univer­sity of Bal­ti­more.

So much avail­able sun­light speeds up the al­ready-rapid growth of these ag­gres­sive vines — Ja­panese hon­ey­suckle and English ivy among them — and forces the ar­bore­tum spe­cial­ists into a con­stant fight to slow their growth.

Ferns and aza­leas, as well as oaks and dog­woods, are just a few of the species be­ing threat­ened by the weeds.

But ash trees in the Ar­bore­tum and around the coun­try are tak­ing a hit too.

Emer­ald ash bor­ers orig­i­nated in Asia, and were first found in Michi­gan in 2002. The bright-green bee­tles now are found in 22 states and wreak­ing havoc on the in­ner bark of valu­able ash trees.

Borer lar­vae gorge them­selves on the chan­nels the trees use to re­ceive wa­ter and nu­tri­ents, and can kill them within two years of in­fes­ta­tion.

This in­sect men­ace has be­come so large that many states have out­lawed the in­ter­state transportation of ash wood for fear of spread­ing the prob­lem even fur­ther.

Eco­nom­ics plays a role as well. Con­sider the ash tree, which of­ten is planted in ur­ban ar­eas like the Dis­trict and Bal­ti­more be­cause of its beauty.

“It de­pends on the size of the tree, but a full-grown ash tree can be a great deal of money to re­move,” Mr. Meny said.

The vines and weeds that cause so much en­vi­ron­men­tal dam­age are not cheap to get rid of ei­ther.

Ja­panese hon­ey­suckle, English ivy and Porce­lain­berry have deep root sys­tems that are al­most im­pos­si­ble to re­move com­pletely, de­spite the many her­bi­cides the Ar­bore­tum uses against them.

Even so, some­thing must be done quickly as the weeds are chok­ing out the na­tive plants that in­habit D.C. and be­yond.

For in­stance, English ivy can gir­dle a tree or block its leaves from sun­light, in­hibit­ing pho­to­syn­the­sis. Gar­den­ers some­times al­low the dark-green vine to grow on its own be­cause the ivy is thought to be at­trac­tive. How­ever, the weight of years-old ivy can cause a tree to fall in a strong wind or heavy rain.

Sim­i­larly, Porce­lain­berry and Ja­panese hon­ey­suckle are of­ten bought and planted by those who be­lieve them to be harm­less. But these Asian weeds grow along the ground and block light from na­tive plants. Birds spread their seeds, and the in­va­sive process be­gins anew in an­other area.

These weeds and in­sects, like the borer, en­dan­ger the ar­bore­tum’s plants and trees, re­quir­ing per­sis­tence by hor­ti­cul­tur­al­ists and ar­borists to stem the in­va­sion. Still, house­hold gar­den­ers should be aware of their role in spread­ing the prob­lem.

Sandy Kem­per, a long­time vol­un­teer at the ar­bore­tum, sug­gests sign­ing up to help, as he did years ago. “I ab­so­lutely rec­om­mend vol­un­teer­ing. I love it here. If you en­joy plants, Wash­ing­ton, D.C., is the vir­tual plant mecca,” Mr. Kem­per said.

For Ms. John­son, the bat­tle against in­va­sive species is a must-win ef­fort.

“The Ar­bore­tum has done a lot for the hor­ti­cul­ture world. It is a great place to get in­spi­ra­tion for what you might want to plant in your own gar­den, and it is re­ally just beau­ti­ful,” she said.

Ms. John­son said she takes her Univer­sity of Bal­ti­more stu­dents to the Ar­bore­tum ev­ery year. “It’s truly a great ex­am­ple of a nat­u­ral habi­tat right in the city.”


English ivy is an in­va­sive plant that has crept into the Na­tional Ar­bore­tum and through­out the D.C. re­gion. The plant’s fast-grow­ing green vines block sun­light from reach­ing na­tive flora be­neath it. Na­tion­wide bee­tle in­fes­ta­tions have also killed many na­tive trees.

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