Spread by trade and cli­mate, bugs butcher Amer­ica’s forests

Un­der­min­ing for­est ecosys­tems

Kuwait Times - - HEALTH & SCIENCE -

PETERSHAM, Mas­sachusetts: In a tow­er­ing for­est of cen­turies-old eastern hem­locks, it’s easy to miss one of the tree’s neme­ses. No larger than a speck of pep­per, the Hem­lock woolly adel­gid spends its life on the un­der­side of nee­dles suck­ing sap, even­tu­ally killing the tree. The bug is one in an ex­pand­ing army of in­sects drain­ing the life out of forests from New Eng­land to the West Coast. Aided by global trade, warm­ing cli­mate and droughtweak­ened trees, the in­vaders have be­come one of the great­est threats to bio­di­ver­sity in the United States.

Sci­en­tists say they al­ready are driv­ing some tree species to­ward ex­tinc­tion and are caus­ing bil­lions of dol­lars a year in dam­age and the sit­u­a­tion is ex­pected to worsen. “They are one of the few things that can ac­tu­ally elim­i­nate a for­est tree species in pretty short or­der - within years,” said Har­vard Uni­ver­sity ecol­o­gist David Or­wig as he walked past dead hem­locks scat­tered across the uni­ver­sity’s 5.8-square -mile re­search for­est in Petersham.

This scourge is pro­jected to put 63 per­cent of the coun­try’s for­est at risk through 2027 and car­ries a cost of sev­eral bil­lion dol­lars an­nu­ally in dead tree re­moval, de­clin­ing prop­erty val­ues and tim­ber in­dus­try losses, ac­cord­ing to a peer-re­viewed study this year in Eco­log­i­cal Ap­pli­ca­tions.

That ex­am­i­na­tion, by more than a dozen ex­perts, found that hun­dreds of pests have in­vaded the na­tion’s forests, and that the emer­ald ash borer alone has the po­ten­tial to cause $12.7 bil­lion in dam­age by 2020.

Species go­ing ex­tinct

In­sect pests, some na­tive and oth­ers from as far away as Asia, can un­der­mine for­est ecosys­tems. For ex­am­ple, sci­en­tists say, sev­eral species of hem­lock and al­most 20 species of ash could nearly go ex­tinct in the com­ing decades. Such de­struc­tion would do away with a crit­i­cal sponge to cap­ture green­house gas emis­sions, shel­ter for birds and in­sects and food sources for bears and other an­i­mals. Dead forests also can in­crease the dan­ger of cat­a­strophic wild­fires.

To­day’s con­nected world en­ables for­eign in­vaders to cross oceans in pack­ing ma­te­ri­als or on gar­den plants, and then reach Amer­i­can forests. Once here, they have rapidly ex­panded their ranges.

While all 50 states have been at­tacked by pests, ex­perts say forests in the North­east, Cal­i­for­nia, Colorado and parts of the Mid­west, North Carolina and Florida are es­pe­cially at risk. Forests in some states, like New York, are close to ma­jor trade routes, while oth­ers, like in Florida, house trees es­pe­cially sus­cep­ti­ble to pests. Oth­ers, like New Hamp­shire, Mas­sachusetts and Maine, are ex­pe­ri­enc­ing record warm­ing.

“The pri­mary driver of the in­va­sive pest prob­lem is glob­al­iza­tion, which in­cludes in­creased trade and travel,” An­drew Lieb­hold, a For­est Ser­vice re­search en­to­mol­o­gist in West Vir­ginia. “But there are cases where cli­mate change can play an im­por­tant role. As cli­mates warm, species are able to sur­vive and thrive in more northerly ar­eas.”

The emer­ald ash borer, first found in 2002 in Michi­gan, is now in 30 states and has killed hun­dreds of mil­lions of ash trees. The gypsy moth, dis­cov­ered in 1869 in Bos­ton, is now found in 20 states and has reached the north­ern Great Lakes, ac­cord­ing to the US Depart­ment of Agri­cul­ture.

Na­tive bark bee­tles have taken ad­van­tage of warm­ing con­di­tions and a long western drought to rapidly range from Mex­ico into Canada. An out­break in Colorado spread across 3.4 mil­lion acres of for­est from 1996 to 2013, ac­cord­ing to the For­est Ser­vice, and in Cal­i­for­nia 100 mil­lion-plus trees have died in the Sierra Ne­vada since 2010. Though small, bugs can eas­ily over­whelm big trees with sheer num­bers. “They drain the resin that oth­er­wise de­fends the tree,” said Matt Ayres, a Dart­mouth Col­lege ecol­o­gist who worked on the Eco­log­i­cal Ap­pli­ca­tions study. “Then, the tree is toast.”

For­est pests in the era of cli­mate change are es­pe­cially con­cern­ing for tim­ber­land own­ers, said Jasen Stock, ex­ec­u­tive di­rec­tor of the New Hamp­shire Tim­ber­land Own­ers As­so­ci­a­tion. “We’re deal­ing with pests we’ve never been around be­fore, never had to man­age around be­fore,” Stock said. “It’s some­thing we’re go­ing to be deal­ing with for­ever.”

Ur­ban forests, too, are at risk from out­breaks. In Worces­ter, Mas­sachusetts, a city of about 180,000, an Asian long horned beetle in­fes­ta­tion in 2008 re­sulted in the re­moval of 31,000 trees. “You would leave for work with a tree-lined street, and you come back and there was not a tree in sight,” re­called Ruth Se­ward, ex­ec­u­tive di­rec­tor of the non­profit Worch­ester Tree Ini­tia­tive. Most trees have since been re­placed.

Though trees can die off quickly, the im­pact of pests on a for­est ecosys­tem can take decades to play out. Dead hem­locks, for ex­am­ple, are giv­ing way to black birch and other hard­woods. Gone are fa­vorite nest­ing spots for two types of war­blers, as well as the bark that red squir­rels love to eat, Har­vard’s Or­wig said. The birds won’t die off, he said, but their ranges will be re­stricted. “It’s a great ex­am­ple of how one species can make a dif­fer­ence in the for­est,” Or­wig said. As pests pro­lif­er­ate, sci­en­tists seek to con­tain them. Among the meth­ods are bio con­trols, in which bugs that feed upon pests in their na­tive lands are in­tro­duced here.

— AP

SYRA­CUSE, New York: In this Oct 6, 2016 still im­age from video, Ph.D. can­di­date Andy Ne­w­house looks over young Amer­i­can ch­est­nut trees, some of them ge­net­i­cally mod­i­fied, grow­ing in a rooftop nurs­ery at the State Uni­ver­sity of New York’s Col­lege of En­vi­ron­men­tal Science and Forestry.

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