Ancient Trees Are Key to Healthy Forests, Scientists Say

The planet’s forests rely on a small group of ancient trees to sur­vive and with­stand envi­ron­men­tal changes and other per­ils, new research has found.

However, these long-lived trees can only repro­duce in primeval forests and are cur­rently threat­ened by cli­mate change and defor­esta­tion.

Scientists from the University of Barcelona, Tuscia University in Italy and the Morton Arboretum in the United States used a math­e­mat­i­cal prob­a­bil­ity model to assess the num­ber of trees that exceed the aver­age age of other trees in a for­est.

They also ana­lyzed data from pre­vi­ous stud­ies to under­stand how these ancient trees affect the rest of the flora in the ecosys­tem.

In their study, pub­lished in Nature Plants, the researchers noted that ancient trees account for less than one per­cent of the tree pop­u­la­tion in a for­est and can reach 10 or even 20 times the age of other trees in the wood­land.

Despite their rar­ity, how­ever, the forest’s vet­er­ans are vital to pre­serv­ing the health and bio­di­ver­sity of forestry ecosys­tems.

The chances are that trees that achieve excep­tional longevity might pass on their genetic resilience to new gen­er­a­tions of trees in their vicin­ity, enabling them to deal with their alter­ing envi­ron­ment and pur­sue con­tin­u­ance.

“We exam­ined the demo­graphic pat­terns that emerge from old-growth forests over thou­sands of years, and a very small pro­por­tion of trees emerge as life-his­tory ​‘lot­tery win­ners’ that reach far higher ages that bridge envi­ron­men­tal cycles that span cen­turies,” said Chuck Cannon, the direc­tor of the cen­ter for tree sci­ence at the Morton Arboretum and one of the study’s authors.

“In our mod­els, these rare, ancient trees prove to be vital to a forest’s long-term adap­tive capac­ity, sub­stan­tially broad­en­ing the tem­po­ral span of the pop­u­la­tion’s over­all genetic diver­sity,” he added.

The sci­en­tists added that the advan­ta­geous traits of cen­ten­nial and mil­len­nial trees are not lim­ited to pre­vent­ing the wear and tear of aging. They also out­per­form typ­i­cal mature trees in absorb­ing car­bon diox­ide and pro­vide a unique habi­tat for endan­gered species.

The researchers also said that ancient trees do not fol­low a nat­ural life cycle sim­i­lar to other plant species or even humans; instead, their exis­tence is mainly due to ran­dom events such as dis­ease or fire.

“Mature, well-estab­lished trees are not pro­grammed to senesce at a par­tic­u­lar size or age,” they wrote. “[They] die in con­se­quence of seri­ous dam­age due to exter­nal biotic and abi­otic fac­tors, such as pests and dis­eases, fires, wind and ice storms, or sus­tained poor envi­ron­men­tal con­di­tions.”

However, the exis­tence of old-growth trees is threat­ened by cli­mate change and defor­esta­tion, and no phys­i­cal mech­a­nism exists to replace the loss of their parental pres­ence in the for­est.

“As the cli­mate changes, it is likely that mor­tal­ity rates in trees will increase, and it will become increas­ingly dif­fi­cult for ancient trees to emerge in forests,” Cannon said. ​“Once you cut down old and ancient trees, we lose the genetic and phys­i­o­log­i­cal legacy that they con­tain for­ever, as well as the unique habi­tat for nature con­ser­va­tion.”

The researchers finally noted that, while for­est restora­tion is an essen­tial tool to pre­serve ecosys­tems, it is also cru­cial to pro­tect the forest’s elders and pre­serve the evo­lu­tion­ary his­tory writ­ten into them.

“Ancient trees are known to be unique bio­di­ver­sity hubs that pro­vide key or unique ecosys­tem func­tions unpar­al­leled by man­aged forests,” they said.

“Losing these trees is like species extinc­tion, in that an irre­place­able genetic resource is being lost,” the researchers con­cluded. ​“For all of these rea­sons, old-growth forests with their unique stock of ancient trees are becom­ing increas­ingly impor­tant to pro­tect.”

• Nature Plants
• The Morton Arboretum