Ash dieback screen­ing could in­vite deadly bee­tles

China Daily (Hong Kong) - - NATURE - By HENRY BODKIN

At­tempts to stall the spread of Ash dieback may back­fire be­cause trees se­lected to with­stand the dis­ease are par­tic­u­larly vul­ner­a­ble to deadly at­tacks by in­sects, new re­search re­veals.

The “un­ex­pected” data has prompted warn­ings from sci­en­tists about the hid­den dan­gers of screen­ing projects, such a ma­jor ini­tia­tive cur­rently be­ing run by the Forestry Com­mis­sion.

The cur­rent out­break of dieback, also called Chalara, was first de­tected in a nurs­ery in Buck­ing­hamshire in 2012, lead­ing to fears the UK ash tree pop­u­la­tion could be all but wiped out.

Caused by the hy­menoscy­phus frax­ineus fun­gus, the dis­ease is ca­pa­ble of killing young trees in a sin­gle sea­son, and older trees over sev­eral years.

Screen­ing re­place­ment trees in or­der to plant only those re­sis­tant to the dis­ease is seen as the “best hope” of sav­ing Bri­tain’s ash pop­u­la­tion.

Since 2013, the Forestry Com­mis­sion has planted around 155,550 trees across 14 lo­ca­tions in the South East in an at­tempt to find out which types are dis­ease re­sis­tant.

But the new re­search from the univer­si­ties of Ex­eter and War­wick sug­gests the types able to re­sist the fun­gus also have very low lev­els of the chem­i­cals needed to de­fend against in­sects.

In par­tic­u­lar, it leaves them de­fence­less against the Emer­ald Ash Borer bee­tle, which has al­ready dev­as­tated vast tracts of ash in the US and is cur­rently spread­ing west­wards across Europe.

It means choos­ing saplings on the ba­sis of their abil­ity to with­stand dieback could sim­ply re­place one lethal prob­lem with an­other.

“Our re­search high­lights the danger of se­lect­ing trees for re­silience to ash dieback at the ex­pense of re­sis­tance to in­sects that threaten this iconic UK tree species, said Dr Chris­tine Sam­bles, who co-led the re­search.

Ash is Bri­tain’s most com­mon hedgerow tree, with 60,000 miles of tree lines, and the sec­ond most com­mon wood­land tree af­ter oak.

An in­fec­tion of dieback is usu­ally fa­tal for a tree, and the dis­ease can be spread on the wind and by the move­ment of in­fected logs.

The Forestry Com­mis­sion has said its strat­egy to se­cure the longterm fu­ture of Bri­tain’s ash trees lies in un­der­stand­ing the species’ genet- ic struc­ture and how some va­ri­eties can survives dieback.

How­ever, the team from Ex­eter and War­wick also ex­am­ined in the dif­fer­ences in the chem­i­cal com­po­si­tion be­tween tol­er­ant and sus­cep­ti­ble ash trees.

“Plants use a vast range of chem­i­cals to de­fend against fun­gal at­tack, and the pri­mary ob­jec­tive was to iden­tify dif­fer­ences which could be used to screen young ash trees and choose the best ones for re­plant­ing, said Pro­fes­sor Mur­ray Grant, from War­wick.

“Our find­ings un­der­line the need for fur­ther re­search to en­sure that we select ash trees re­silient to present and fu­ture threats.”

Emer­ald Ash borer, a bee­tle which kills ash trees within two or three years, is not yet in the UK but is high on the Gov­ern­ment’s plant risk reg­is­ter.

In Oc­to­ber the Wood­land Trust an­nounced it would launch an ac­cred­i­ta­tion and la­belling scheme for trees sold at nurs­eries as a guar-

Our re­search high­lights the danger of se­lect­ing trees for re­silience to ash dieback at the ex­pense of re­sis­tance to in­sects.” Dr Chris­tine Sam­bles, co-lead of a study con­ducted by the univer­si­ties of Ex­eter and War­wick

an­tee that they have been grown in Bri­tain from Bri­tish seed.

The “Buy Bri­tish” ini­tia­tive is in­tended to try to pre­vent for­eign pests en­ter­ing UK wood­lands.

An es­ti­mated six mil­lion trees were brought into Bri­tain in the past three years, in­clud­ing 1.1 mil­lion oaks.

PHILIPPE HUGUEN

Betty, a cop­pice Ash has the right genes to with­stand Dieback.

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