AT WHAT THICK­NESS IS A TREE IM­MUNE TO FLAMES?

World of Knowledge (Australia) - - Nature -

It’s a spec­tac­u­lar sight: 100-me­tre­high, 1,500-year-old bush spread­ing across the primeval land­scape of the north­west­ern United States. The gi­ant red­woods of Yosemite Na­tional Park in Cal­i­for­nia are some of the tallest and old­est trees in the world – even though they’re rooted in one of the most bush­fire-prone re­gions on the planet. The se­cret of their longevity lies in their tough bark, which, at 50cm thick, of­fers a nat­u­ral form of fire pro­tec­tion. This means small fires pose no risk to the gi­ant se­quoias. In fact, the op­po­site is true: by get­ting rid of pesky com­peti­tors and de­liv­er­ing nu­tri­ent-rich ash to the red­woods, bush­fires ac­tu­ally have a pos­i­tive im­pact. Cer­tain trees have even adapted to the fire so their seed pods only burst un­der ex­treme heat.

How­ever, red­woods aren’t the only fire re­tar­dant trees: bark with a thick­ness of just five cen­time­tres can pro­tect against flames, as the 60-me­tre-high yel­low pines of New Mex­ico have shown. These ever­green pines stretch across the south­ern tail of the Rocky Moun­tains and have sur­vived count­less fires over the years, es­cap­ing al­most all of them un­scathed, although the un­der­growth has fre­quently not been so lucky. Even some de­cid­u­ous trees can stand up to bush­fires: Quer­cus suber, an oak that grows in south­west Europe, has fire­proof ar­mour made of cork. The tree is the pri­mary source of cork for wine bot­tle stop­pers.

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