What causes the trees to develop gnarls? I can't find anything on internet other than dictionary definitions.

Are they caused by a mold, like the burls?


If I understand what you're talking about by "gnarl", they are usually caused by a bacterium like Agrobacterium tumescens infecting and creating a gall.

Update: Forgot, also in some cases caused by insects.

  • $\begingroup$ Thanks, that means that "gnarl" is the same thing with "crown gall" ? By gnarl I meant the most common dictionary definition of it - a rough, knotty protuberance, especially on a tree. $\endgroup$ – Ark25 Apr 13 '20 at 18:04
  • $\begingroup$ @Ark25 I guess it depends what you mean by "gnarl"- it doesn't appear to be a very specific technical term. Looking at what shows up when you google image search, it shows both extreme twistedness and protuberances. If protuberances are what you mean, they indeed mostly seem to be caused by pathogens such as insects or microbes. $\endgroup$ – Maximilian Press Apr 13 '20 at 18:15

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