How to tell if tree will stand or fall

Winnipeg Free Press - Section F - - HOMES - MICHAEL ALLEN

IS your tree safe? Home­own­ers who have lived on their prop­erty for years rec­og­nize their large trees are usu­ally safe and un­likely to top­ple if they’re sta­ble. But new res­i­dents who are not fa­mil­iar with their newly ac­quired trees are of­ten ap­pre­hen­sive.

The most com­mon ur­ban trees to fail are poplars and Man­i­toba maples that have been poorly pruned and ne­glected. Both types of trees are great abun­dance in Win­nipeg and south­ern Man­i­toba. Many poplars grow tall, so the po­ten­tial dam­age from their fail­ure if they have been poorly treated is greater than the maples.

Hy­brid poplars were planted widely in ur­ban ar­eas in the 1950s, ’60s and ’70s, mainly for their fast growth and shade-pro­duc­ing na­ture. Ini­tially de­vel­oped by tree-breed­ing sci­en­tists for use as a farm shel­ter­belt, hy­brid poplars are rel­a­tively short-lived. Af­ter 50 years or less, many of these trees suc­cumb to in­ter­nal wood de­cay and branch break­age. Oc­ca­sion­ally, a fully leafed po­plar may sud­denly fail at its base and top­ple.

As they age, grow in size and de­cay, hy­brid poplars be­come haz­ardous. Of­ten there is less than on inch of liv­ing wood close to the bark that keeps the tree up­right. The re­main­ing area and vol­ume of the po­plar is full of de­cayed wood sur­round­ing a hol­low core. Even with that thin layer of liv­ing wood, there are enough con­duc­ing ves­sels to sup­ply wa­ter and nu­tri­ents to the top of a 15.25-me­tre po­plar for a while, but the leaves will be smaller and their dis­tri­bu­tion through the crown will be­come more sparse over time.

Both poplars and Man­i­toba maples tend to pro­duce more de­cayed wood than most other tree species in our area. Of­ten, the de­cay oc­curs be­cause of poorly pruned branches that have been topped or crowned. The cut ends of the branches are made in­dis­crim­i­nately with no care given to proper lo­ca­tions that will ac­tu­ally help the tree seal over the prun­ing wound.

The af­fected branches are re­ferred to as stubs. The el­e­ments of weather, in­sects such as wood bor­ers, de­cay fungi, and some­times pathogenic dis­eases en­ter these stubs and cause the wood to pro­gres­sively de­cay through­out the tree.

Iron­i­cally, many peo­ple are con­vinced their trees should be heav­ily cut back to make them safer. Topped trees are more dan­ger­ous than prop­erly pruned trees be­cause of the greater weak­ness in struc­tural strength that oc­curs in the wide­spread dis­tri­bu­tion of de­cayed wood. A good ar­borist can em­ploy crown-re­duc­tion tech­niques when it is ap­pro­pri­ate to re­duce some of the tree’s height.

I see many hun­dreds of poplars and maples that I would de­scribe as haz­ardous, es­pe­cially on pri­vate prop­er­ties. Look for large de­cayed wounds on the trunks and up­per branches. Im­proper lawn-mow­ing that has dam­aged the lower bark of a trunk has likely re­sulted in in­ter­nal wood de­cay. Look for bark scar­ring and weep­ing de­cayed bark. Has there been some no­tice­able wind dam­age of up­per limbs?

I use a de­vice called a Re­sis­to­graph that al­lows me to as­sess the in­ter­nal struc­ture of wood in trees. On oc­ca­sion, a climb­ing ar­borist will ask to use this tool in the up­per part of a tree to as­sess sus­pi­cious-look­ing wood sit­u­a­tions that may not be ap­par­ent from the ground.

If you have a large tree that you are con­cerned about call a pro­fes­sional ar­borist to have it prop­erly as­sessed. I rec­om­mend only those ar­borists that have a valid Man­i­toba ar­borist li­cence and at least $2 mil­lion in gen­eral busi­ness li­a­bil­ity in­surance. These are manda­tory legal re­quire­ments for com­mer­cial ar­borists.

En­joy your well-main­tained trees; don’t let them cause you grief.

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