For­est fire preven­tion forces hard choices

We need to al­ter our ap­proach as our cli­mate changes, Robert Gray writes.

Vancouver Sun - - OPINION - Robert Gray is a fire ecol­o­gist and prin­ci­pal of R.W. Gray Con­sult­ing.

The area burned by wild­fires this sum­mer in B.C. is enor­mous by any mea­sure. Over 1.2 mil­lion hectares as of Aug. 22, and there are still sev­eral weeks of fire sea­son re­main­ing. This wild­fire sea­son adds to an ever-in­creas­ing area burned over the past decade. Will we ever see an end to sum­mers with this much area on fire? Ac­cord­ing to cli­mate sci­en­tists, not likely. Cli­mate pre­dic­tions in­clude longer fire sea­sons, more sig­nif­i­cant droughts (mean­ing more dead trees and thus more fuel for fires), more fire starts, and larger and more se­vere fires.

A rea­son­able ques­tion is whether or not at some point enough area will be burned that it will ac­tu­ally start to im­pede fire ac­tiv­ity. The an­swer de­pends on fu­ture cli­mate and what we as so­ci­ety do with re­gard to veg­e­ta­tion and dead fu­els. There is not much we can do about the cli­mate pre­dic­tions — un­for­tu­nately, we’re locked into this cli­mate pat­tern for the fore­see­able fu­ture. The only place we can make a dif­fer­ence is with what is avail­able to burn when fire re­turns the next time.

Within a few short years of a high-sever­ity fire (one that kills the ma­jor­ity of the for­est), the dead trees start to fall. With in­creased sun­light hit­ting the for­est floor, grasses, forbs and shrubs take hold and cre­ate a con­tin­u­ous layer of fine, flashy fuel ca­pa­ble of quickly spread­ing a fire once lit.

If another fire oc­curs in quick suc­ces­sion, it is re­ferred to as a re-burn. This sub­se­quent fire tends to spread slowly but can burn very in­tensely as it con­sumes the downed trees and of­ten kills re­gen­er­at­ing trees. Once again, grasses, forbs and shrubs re­turn, and once they are fairly con­tin­u­ous, can sup­port another fire. If most of the downed wood was con­sumed in the re-burn, the next fire is not likely to grow very large or to burn very in­tensely.

Fires burn­ing in grass, forbs and shrubs are highly sus­cep­ti­ble to in­creases in rel­a­tive hu­mid­ity and are quickly ex­tin­guished dur­ing a typ­i­cal sum­mer’s night in­crease in hu­mid­ity or are halted by abrupt changes in to­pog­ra­phy or fuel breaks. To sur­vive, they need to smoul­der in a re­main­ing log or stump close to the burn­ing perime­ter of a fire. The next day, as the tem­per­a­ture rises and hu­mid­ity falls, the smoul­der­ing fire moves out of the log and into un­burned ar­eas of cured grass, al­low­ing the fire to spread for another day. If there are no logs or stumps for smoul­der­ing, the fire burns out.

His­tor­i­cally, when much of the west was burn­ing fre­quently, many fires burned in fine, flashy fu­els in­clud­ing grass, forbs and shrubs, and even small changes in to­pog­ra­phy and fu­els were ef­fec­tive bar­ri­ers to fire spread. Large fires were rel­a­tively in­fre­quent. So how do we em­u­late that process?

This is where there are very dif­fi­cult com­pro­mises that need to be made. Tra­di­tion­ally, our ap­proach to post-burn land­scapes is to sal­vage any re­main­ing eco­nomic value from burned stands, of­ten leav­ing log­ging slash and re­plant­ing the site. This pat­tern sim­ply per­pet­u­ates the prob­lem. Downed logs of­fer im­por­tant wildlife habi­tat, and forests that quickly re­gen­er­ate fol­low­ing fire con­tain valu­able tim­ber. How­ever, if we are on the cusp of our new nor­mal, we may have to em­u­late the re-burn model over large ar­eas. This means heav­ily thin­ning re­cently burned ar­eas (leav­ing some dead stand­ing trees and few logs), pre­scribed burn­ing them and re­plant­ing to very low den­sity. It will be dif­fi­cult to em­brace the re-burn model, but we need to care­fully con­sider the ben­e­fits.

Newspapers in English

Newspapers from Canada

© PressReader. All rights reserved.