Case Study: Improper pruning and spurred tree work


Orange arrows indicate spur wounds. Notice the proximity of the failure point to the uppermost spur wound.

Large big leaf maple tree located very close to a house and spreading over the deck. Three years ago, the tree was aggressively pruned back off the house and deck. Approximately 40% of the canopy was removed and spurs were worn to access the tree.


  • Excessive water sprouts are produced at large cuts and overall form has been destroyed.
  • The infection of a decay pathogen (that entered through the spur wound) weakened a stem which then failed and damaged the glass railing around the deck.


Damage was caused by the method of pruning. An improper pruning cut can compromise the tree’s ability within the branch socket to stop the spread of decay pathogens.

More than 25% of canopy loss has potential to stress the tree. Excessive removal of one portion of a tree’s canopy can:

  • increase the chance of sun scald (especially a south facing portion of the canopy) and leaves the remaining canopy compromised.
  • expose large branches and limbs that were once protected to new windthrow causing increased potential of failure.

Notice the concentration of decay at the failure
point which is also the location of a spur wound.

Spurs can significantly damage the tree, opening up the cambium to infection and decay. When climbing on spurs, every step creates a puncture wound that has the potential for fungal or bacterial infection. Fungus and bacteria can penetrate the trees’ natural defences and cause premature failures.

Spurs should only be used on trees slated for removal.