‘Su­per in­vader’ tak­ing over

Sci­en­tists look at im­port­ing in­sect to help con­trol spread of tal­low trees in U.S. South

St. Thomas Times-Journal - - SPORTS - STACEY PLAISANCE

NEW OR­LEANS — The tal­low tree, a “su­per in­vader” with toxic leaves and no nat­u­ral ene­mies in North Amer­ica, is con­quer­ing the Amer­i­can South.

Over­tak­ing forests from Texas to Florida, tal­lows grow three times faster than most na­tive hard­woods, and each one casts off 100,000 seeds a year. Con­trolled burns haven’t stopped their spread, nor have her­bi­cide sprays from he­li­copters. Cut­ting them down works only when each stump is im­me­di­ately doused with chem­i­cals. Har­vest­ing them for bio­fuel re­mains more a prom­ise than a prac­ti­cal so­lu­tion.

Some sci­en­tists say in­tro­duc­ing a flea beetle from the tal­low’s na­tive habi­tat in east­ern China may be the best al­ter­na­tive.

Yes, they’re aware of “night­mare sce­nar­ios” with other non-na­tive plants and bugs, en­vi­ron­men­tal sci­en­tist Michael Mas­simi said.

But he also points to suc­cess sto­ries, such as the aquatic weevil that munches on gi­ant salvinia, a float­ing fern from Brazil that had been clog­ging wa­ter­ways in Florida and Texas un­til its in­sect en­emy was brought in. The weevil un­der­went a sim­i­lar line of test­ing through the U.S. Depart­ment of Agri­cul­ture, and like the flea beetle, the weevil spends its en­tire life-cy­cle on one plant, he said.

“Im­port­ing an or­gan­ism to help con­trol an­other or­gan­ism right off the bat doesn’t sound very in­tu­itively smart to do, but it turns out that es­pe­cially with in­sects and plants, they’ve co­e­volved over many mil­lions of years, and in a lot of cases, the in­sect is very host-spe­cific,” said Mas­simi, the in­va­sive species co-or­di­na­tor for the Barataria-Ter­re­bonne Na­tional Es­tu­ary Pro­gram along the Louisiana Gulf Coast.

In this case, the flea beetle (Bikasha col­laris) gen­er­ally ig­nores other plants as it eats the roots and leaves of the tal­low (Tri­ad­ica seb­ifera), a host-spe­cific ten­dency tested on about 150 other plant species in a decade of lab­o­ra­tory work in the U.S. and China, re­searchers said.

The USDA’s An­i­mal and Plant Health In­spec­tion Ser­vice has been work­ing on an en­vi­ron­men­tal im­pact as­sess­ment, which will in­clude a pub­lic com­ment pe­riod. If ap­proved, the bugs could be re­leased some­time in 2018. Mean­while, re­searchers in Louisiana are study­ing tal­lows to gain a bet­ter un­der­stand­ing of the beetle’s ef­fec­tive­ness once they are let loose.

Ben­jamin Franklin sent tal­low seeds from London to a friend in Georgia in the 1700s, but ge­netic test­ing cleared the found­ing fa­ther of blame for the kind of tal­lows grow­ing so ag­gres­sively today — those trees were ap­par­ently in­tro­duced by fed­eral bi­ol­o­gists around 1905, ac­cord­ing to re­search led by Evan Sie­mann, an evo­lu­tion­ary bi­ol­o­gist at Rice Univer­sity, that was pub­lished in The Amer­i­can Jour­nal of Botany in 2011.

U.S. For­est Ser­vice data show tal­low now spread­ing across 10 states. Its growth nearly tripled in Texas in the past two decades, and in­creased 500 per cent in Louisiana, where its higher tol­er­ance for salin­ity en­ables it to crowd out moss-cov­ered bald cy­press in swamps and bayous. Pop­u­la­tions also are up along the At­lantic coast, from Florida to the Caroli­nas.

“Tal­lows take ad­van­tage of dis­tur­bances,” said Nancy Loewen­stein, an in­va­sive plant spe­cial­ist at Auburn Univer­sity. “Storms, floods, con­struc­tion sites, log­ging sites, any­thing that dis­rupts the en­vi­ron­ment will give an in­va­sive like tal­low an op­por­tu­nity to take over.”

The help can’t come too soon for the keep­ers of Amer­ica’s suf­fer­ing forests. Tal­lows grow into fully ma­ture trees in just three years, far out­pac­ing na­tive maples, oaks, cy­press and elms. Their leaves are toxic to some an­i­mals, and they cast off lit­ter that changes soil chem­istry and dis­ad­van­tages com­peti­tors.

“Chi­nese tal­lows are very com­pet­i­tive, and they have no nat­u­ral preda­tors here like in their na­tive China,” said Karan Rawl­ins, an in­va­sive species spe­cial­ist at the Univer­sity of Georgia’s Cen­ter for In­va­sive Species & Ecosys­tem Health. “Very few if any in­sects rec­og­nize it as a food source, so it has ba­si­cally be­come a su­per in­vader.”

Also known as the pop­corn tree and can­dle­berry tree, tal­lows have been planted widely since their first seeds ar­rived. Cov­eted as or­na­men­tals for their vi­brant fall fo­liage, they have seeds en­cased in small green cap­sules that split when ripe, re­veal­ing a small clus­ter re­sem­bling a puffy ker­nel of pop­corn. Their oils have been used in can­dle and soap-mak­ing, and bee­keep­ers like their boun­ti­ful nec­tar.

But ecol­o­gists say they do more harm than good, de­creas­ing the di­ver­sity of plants, trees and in­sects, and weak­en­ing the food chain for birds and an­i­mals. At least one study found that frog eggs are less likely to hatch into tad­poles in wa­ter lit­tered with tal­low. And since the seeds don’t pro­vide much nu­tri­tion, Mas­simi said they’re like “junk food” for mi­grat­ing birds.

It has taken more than a decade to clear tal­low from just half the 35-hectare Audubon Louisiana Na­ture Cen­ter af­ter floods from hur­ri­canes Ka­t­rina and Rita.

“We still have 40-plus acres (16 hectares) that are 95 per cent Chi­nese tal­low, so we have a lot of work to do, and it’s go­ing to be a long, long haul,” said Llewellyn Ever­age, who di­rects vol­un­teers and in­terns at the site. “This is not a quick prob­lem to fix.”


A flea beetle is seen at the USDA/ARS In­va­sive Plant Re­search Lab­o­ra­tory in Ft. Laud­erdale, Fla. The in­sect is a po­ten­tial bio­con­trol agent that may be re­leased as early as next year to com­bat the spread of the Chi­nese tal­low tree, a highly in­va­sive tree rapidly over­tak­ing forests from Texas to Florida.

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