# "Growth Factor" Lists?



## Padre05 (Sep 30, 2014)

My son is putting together a tree inventory for the local city park as a service project. He's already gone to a lot of work measuring, counting, identifying around 400+ trees with the hopes to estimate their age based off of the formula of: Diameter in inches x growth factor = tree age. The city understands this method is only a rough estimate and is okay with this approach; I don't want this thread to be a debate on if this is the best method but rather hoping I could get some advise/guidance from the experts on where to find a comprehensive list that show the growth factor for various tress in the US? I've already been directed to: http://mdc.mo.gov/your-property/your-trees-and-woods/backyard-tree-care/how-old-tree which seems to be the resource several websites point to. This site did help but there are several more trees we're not able to find the growth factor on and we've both seem to have "googled" ourselves out trying to search lol. Any suggestions of a more comprehensive list of growth factors?

Thanks in advance


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## BC WetCoast (Sep 30, 2014)

I think this is great project for your son to be working on. Having said that, I don't know of any growth factor lists, but let me explain why they aren't common and your son may be able to include this in his project. 

Trees, like humans and most living organisms, don't grow linearly, that is if you graphed the diameter vs age the line wouldn't be straight. Rather it would have an 'S' shape. When a tree is young it's diameter grows very slowly (like a baby), when it reaches a certain age it grows very quickly (teenager) and as it gets older it slows down (senior). So in giving out a growth factor, the author of the web site is just giving an average over time. Now the growth rate can be highly influenced by light competition, soil fertility and moisture availability. 

There are many growth curves developed, but they have been developed by foresters for lumber species and are usually developed on an ecosystem basis. Urban trees grow on a much more variable environment and there is not the demand for this information, so the research hasn't been done.

Here is a web site that explains it. It may be a little more technical than your son needs. http://www.sfu.ca/~heaps/861/T_GROWTH.htm

Here's a couple of approaches you son could use if you can't find a 'growth factor'. 
- see if the parks dept would be receptive to your son using an increment borer to determine tree age. This is an instrument that is a hollow screw. You screw it into the tree and extract a 1/8" core of wood, which will show the annual rings. You can then count the rings to determine the tree age. Do a couple of the species you don' t have factors for and develop your own growth factor to use on the rest of the trees of that species in the park.
- If all the trees in the park are approximately the same age ie it was established after the area was logged, storm, forest fire, then you could assume the trees you don't have factors for are the same age and work backwards to develop your own factor.

Where's the park, and what species do you need help with?

Hopefully this wasn't too complicated.


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## ATH (Sep 30, 2014)

"How old is that tree"? My least favorite question. My favorite example: I cut a 36" diameter ash in OK, not great soil. It was in a back yard, so probably lots of water, no competition. When I noticed how huge the rings were, I counted: 58 years old. Later that same week, I was visiting a timber sale I had marked. Great soil. The owner was in his 70s, and there wasn't a significant timber harvest going back to his grandfather. I only counted in about 4-5" worth and got to 75 rings - so the tree was probably pushing 150-200 years. It was all about the competition.

One thought to keep in mind with the growth factors/formulas: look up from the paper!!! Often there are historical records or common sense history to help figure out how old a tree is. Was it likely here when the building was constructed? Was the park established in the woods, in a field, or a pasture with some trees in it? For example: "That one is very tall and straight...it more than likely grew up in the woods." or "That one has many low limbs...it obviously did not grow up in the woods." etc...

I know you said you don't want this to be a debate about the method...but there is a reason it is worth debating!


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## BC WetCoast (Sep 30, 2014)

I've seen two trees growing next to each other in a forest stand. Same species, same age; one was 40" in diameter and 140' tall and the other was 8" in diameter and 40' tall. The larger one was dominant when they were younger and took all the light. The smaller one became suppressed and struggles to survive.


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