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Flaws found in research on the impact of log­ging on biodiversity

pub­lished 20 July 2013 | mod­i­fied 13 Sep­tem­ber 2014

Stud­ies about the impact of log­ging on bio­di­ver­sity in trop­i­cal regions should be scru­ti­nised, con­clu­sions toned down or even dis­counted, accord­ing to a recent pub­li­ca­tion (online on 2 Jan­u­ary) in the jour­nal Con­ser­va­tion Biol­ogy that has revealed wide­spread method­olog­i­cal flaws.

Logging Koh KongDou­glas Sheil, senior asso­ciate with the Cen­ter for Inter­na­tional Forestry Research (CIFOR) Forests and Envi­ron­ment Pro­gramme and a col­lab­o­ra­tor on the study “Pseudorepli­ca­tion in trop­i­cal forests and the result­ing effects on bio­di­ver­sity con­ser­va­tion“, said his team set out to deter­mine why research about the impact of log­ging on trop­i­cal for­est ecosys­tems often yields con­tra­dic­tory results.

In rainforest-​specific stud­ies, they found, sci­en­tists often treat sites that have been logged and those that haven’t as if they were iden­ti­cal before the tim­ber cut­ting, and per­form sta­tis­ti­cal com­par­isons that can­not sup­port the con­clu­sions that are drawn from them, an exam­ple of a method­olog­i­cal flaw known as “pseudorepli­ca­tion”.

In many cases, the impor­tance of local vari­a­tions among study sites has been ignored while inter­pret­ing the research – so that all the dif­fer­ences, includ­ing those that were nat­ural, are ascribed to tim­ber cut­ting and removal. As a result of the flawed inter­pre­ta­tion, changes result­ing from log­ging have often been exag­ger­ated, Sheil said.

“Con­fronting pseudorepli­ca­tion is essen­tial for accu­rately assess­ing bio­di­ver­sity in logged forests, iden­ti­fy­ing the rel­a­tive mer­its of spe­cific man­age­ment prac­tices and land­scape con­fig­u­ra­tions, and effec­tively bal­anc­ing con­ser­va­tion with tim­ber pro­duc­tion in trop­i­cal for­est land­scapes,” he added.

For­est bio­di­ver­sity is threat­ened by defor­esta­tion and for­est degra­da­tion, hunt­ing and the intro­duc­tion of inva­sive species from other habi­tats. At least 13 mil­lion hectares (50,000 sq miles) of for­est – an area almost the size of Nicaragua — are dis­ap­pear­ing each year, accord­ing to the United Nations Food and Agri­cul­ture Orga­ni­za­tion.

Method­olog­i­cal prob­lems and pit­falls are much more preva­lent than we had anticipated
Ben­jamin Ram­age, lead author, Uni­ver­sity of Cal­i­for­nia Berkeley »

Of 77 stud­ies analysed, only five were defin­i­tively free of pseudorepli­ca­tion, said Ram­age. “We may need to dis­card some past results, while in some other cases, we may be able to esti­mate the corrections.”

The poten­tial for sta­tis­ti­cal inac­cu­ra­cies in for­est assess­ment calls into ques­tion the results of an untold num­ber of stud­ies, as well as some estab­lished “truths” derived from lit­er­a­ture that appears now to be “rife with unwar­ranted infer­ences,” the paper said. Sheil said researchers some­times use short cuts to com­pile data on species affected by log­ging, either due to lack of fund­ing or to make results look more impressive.

“Rain­for­est stud­ies are dif­fi­cult to do well, and often there is a lot of pres­sure to make strong claims based on stud­ies where bud­gets are con­strained,” he said. We are used to say­ing ‘some infor­ma­tion is bet­ter than none.’ But, of course, this is true only if we do not allow our­selves to be misled.”

The knock-​on effects of the team’s find­ings could be huge.

With opin­ions already divided over whether well-​managed log­ging areas are a pos­i­tive step for the con­ser­va­tion of bio­di­ver­sity, the new results are likely to rekin­dle the var­i­ous debates on when and where tim­ber pro­duc­tion should be viewed as a friend or a foe to con­ser­va­tion. It also has the poten­tial to change the way we think about pro­duc­tion forests which — unlike many other land-​uses, such as oil palm and sugar cane — sup­port a much higher level of for­est species.

If we don’t recog­nise and address the prob­lem of pseudorepli­ca­tion, we can­not accu­rately assess bio­di­ver­sity in logged forests
« Dou­glas Sheil, CIFOR Forests and Envi­ron­ment Programme

For the moment, Sheil said, researchers have lit­tle choice but to return to square one. “There is also no way of know­ing how to effec­tively bal­ance con­ser­va­tion with tim­ber pro­duc­tion in trop­i­cal forests. And how can we pos­si­bly say which man­age­ment prac­tices are effec­tive and which are not.”

Both authors empha­sised that their analy­ses should not be read as deny­ing that log­ging has neg­a­tive impacts on bio­di­ver­sity. “We under­line that some of these effects are real and jus­tify con­cern,” Sheil said. “But it appears that many past results are unsound and likely to have been exag­ger­ated. We would all be bet­ter able to focus our con­cerns and efforts if we had a more reli­able knowl­edge of these log­ging effects.”

The preva­lence of pseudorepli­ca­tion in trop­i­cal forestry research, mean­while, begs the ques­tion of how so many sci­en­tists failed to spot it in the first place. Accord­ing to Sheil, it is all about aware­ness. “It is about recog­nis­ing the prob­lem and know­ing why it mat­ters. If researchers recog­nise when and where these approaches lead to prob­lems we can avoid them,” he said.

Ram­age says he hopes the report will encour­age researchers to start think­ing more crit­i­cally about the con­clu­sions they draw from their data and try to find ways to cor­rectly repli­cate log­ging treatments.

The above news item is reprinted from mate­ri­als avail­able at Forests news. Orig­i­nal text (Cre­ative Com­mons Attribution-​Noncommerical-​Share Alike License) may be edited for con­tent and length.
(Source: Forests news – a blog by the Cen­ter for Inter­na­tional Forestry Research, 19.07.2013)

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