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Author Topic: Calculating tree canopy  (Read 935 times)

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Offline NCPeavey

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Calculating tree canopy
« on: December 21, 2016, 09:50:43 pm »
Greetings all,  my first post though been following the forum for a long time.

This might be a simple question, but no amount of "googling" has found me the answer.  Trying to calculate the estimated canopy coverage for a single mature tree, for the purpose of putting together a mitigation table for a tree ordinance.

For example, if we have a tree where the estimated canopy of a mature tree is a 30'-50' foot spread, I assume we work with 40' as the average.

If that's the case, the radius would be 20'.  With that, does the basic math formula of pi X r squared (area of a circle) work? Or are there other variables that need to be taken into account?  Does species matter? (Leaf vs needles?).

I've found some tables on-line that give a value for certain species but the math doesn't always jive with the estimated canopy spread estimates for mature trees.

Hope this makes sense...appreciate any insight from this knowledgeable group!

Scott

Offline WDH

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Re: Calculating tree canopy
« Reply #1 on: December 22, 2016, 08:00:29 am »
Measure the crown spread from the drip line on one edge of the crown to the drip line to the other edge.  Then take another measurement perpendicular to the first.  Average the two measurements.  The formula for the area of a circle that you referenced would then give you the area covered by the crown.  An acre covers 43560 square feet.  So, you could calculate how many trees with crowns that size that it would take to cover an entire acre.
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Offline DelawhereJoe

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Re: Calculating tree canopy
« Reply #2 on: December 22, 2016, 10:12:13 am »
There should be many mature canopy guides in landscape design, years ago when I took a landscape design class we had to do many projects, designing yards with mature trees. We had a hard plastic template and we would just match scale to scale for certain trees, generally the most popular types of ornamental and shade trees.
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Offline DelawhereJoe

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Re: Calculating tree canopy
« Reply #3 on: December 22, 2016, 10:21:37 am »
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Offline NCPeavey

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Re: Calculating tree canopy
« Reply #4 on: December 22, 2016, 11:20:38 am »
Thank you gentlemen for the replies.  Yes, I have found several charts with the sq. ft. canopy size noted both for "mature" trees, as well as the projected 10 year canopy like the chart DelawhereJoe shared.  What got me thinking about it was that some of the charts have different values for the same species (could be locality generated I suppose).  Also, using the basic match calculation for the area of a circle (even averaged as WDH pointed out) sometimes gives a value well above what the charts provided.  Bottom line, I was wondering if there was a standard formula of some sort for trees.

FYI - what we're trying to do is shoot to have residents or developers maintain a minimum of tree canopy cover.  For example if you have a 75x100 town lot (7500 sq ft) and you want to maintain 40% canopy cover (3000 sq ft) then you could "save" canopy, or replant so that at full maturity you get the desired coverage.  I'm working on a chart of trees native to our town (Coastal NC) with a projected mature canopy size - some I've had no problem finding that figure, others I'll have to compute, hence the original question. 

Again, thanks for the replies!

Offline DelawhereJoe

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Re: Calculating tree canopy
« Reply #5 on: December 22, 2016, 11:57:20 am »
Have you considered the possibility of root intrusion into water, sewage lines, sidewalk and curbs?
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Offline DelawhereJoe

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Re: Calculating tree canopy
« Reply #6 on: December 22, 2016, 12:07:21 pm »
Back in my youth I was state licensed to inspect septic systems and have seen what roots can easily do to a concrete septic tank , pipes and drain fields. Cypress tree roots will do a number on blacktop and all tree roots will warp sidewalks.
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Offline ESFted

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Re: Calculating tree canopy
« Reply #7 on: December 22, 2016, 12:38:01 pm »
PLEASE! Save yourself and those attempting to implement your regulation a lot of frustration by keeping the rules as simple as possible.  Ordinances that require complicated plant material coverage calculations that are not detailed in a crystal clear manner are a nightmare to satisfy and almost guarantee a plan will get bounced, frustrating all involved and adding to the cost of development.

Consider using tree caliper rather than canopy.  The Chesapeake Bay Riparian Buffers Guidance Manual, Appendix D-Vegetative Replacement Standards does a pretty good job of laying out mitigation requirements using a caliper based standard that could easily be adopted for your purpose. 
http://www.deq.virginia.gov/portals/0/deq/water/publications/riparianbuffermanual.pdf

If you do use canopy, realize that it's not a precise science and that a range of anticipated canopy is OK. I've been doing this a long time and have found no coordinated standardization in the way ordinances specify canopy. However, if the empirical data on a tree suggests a 20-30' spread at maturity (or 20 years), then the canopy will usually have a commensurate range.  Just put a footnote on your chart that says to use the largest canopy figure to satisfy requirements.  Don't complicate the process.

Consider how plant materials are specified when you craft your ordinance and use the appropriate size references contained in this document.
https://americanhort.org/documents/ansi_nursery_stock_standards_americanhort_2014.pdf

Here's a tree canopy reference I've used a lot.  I actually have an older version of this as a spread sheet that includes caliper.  Send me a PM if you would like a copy.

http://dendro.cnre.vt.edu/predictions/canopy.cfm

I'm sure you have checked out how other municipalities handle this.  An example:
https://www.vbgov.com/government/offices/eso/boards-commissions/Documents/landscaping-guide-2009.pdf
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Offline DelawhereJoe

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Re: Calculating tree canopy
« Reply #8 on: December 22, 2016, 01:01:50 pm »
I know someone who owned a store, the city came and planted a tree straight inline with his door to the road. He was a nice man and would go out and water that tree they planted in from of his door ever day without fail. But the trees kept dieing so after a few years the city stopped planting trees. The city never asked him if they could plant the tree they just did, they also put the tree right between his business door and the road so he water the tree with salt water .
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Offline NCPeavey

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Re: Calculating tree canopy
« Reply #9 on: December 22, 2016, 01:04:38 pm »
ESFted,

Thanks for the comments and resources.  In the end, simplicity is exactly what we're going for with this.  I'm building a list/chart of native trees that as part of a mitigation process, a homeowner can pick and choose how they want to meet the requirement.  For example, if a mature Live Oak is to be removed, the owner can either replant another Live Oak and be done with it, or perhaps now they want a two Eastern Red Cedars and a Dogwood which when mature, will provide the same estimated canopy coverage.  That's a hypothetical but we want to give the landowner the greatest flexibility, and at the same time, encourage some tree diversity around town. 

As the guy working on this with the rest of our Forestry Committee, I well know the frustration part.  In the end, our only goal is to maintain (or improve) our urban forest and do it in a way that is not onerous on the landowner, and is eminently easy to comply with.  We are well aware that tree ordinances can be a sensitive topic, but the town has been "burned" - for lack of a better expression - several times over the last couple of years by not having anything in place.

Regards///Scott

Offline ESFted

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Re: Calculating tree canopy
« Reply #10 on: December 22, 2016, 01:57:28 pm »
Scott,
I hope your committee doesn't get too hung up on using native plants exclusively.  While native plant enthusiasts have become very vocal, over the last several years even the hard liners have come to realize there are limitations to what can be achieved by insisting on an exclusively native palette. There are many naturalized and non invasive species that deserve a place in today's landscape.  Further complicating plant selection is the commercial availability of the species on the list.  Many native trees are not commercially grown or are available only as bare root seedlings or whips that don't meet ordinance sizes.  The committee needs to recognize this reality when crafting rules.  Good luck.
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Offline NCPeavey

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Re: Calculating tree canopy
« Reply #11 on: December 22, 2016, 03:30:48 pm »
I hear you.  Being right on the coast right now when talking about full size canopy trees, we really don't have much diversity - mainly Live Oaks.  They're beautiful but we're sensitive to the possibility of being vulnerable as a monoculture.  Back in '98-'99 kermes scale hit and there was a fear of losing them all - "fortunately" there were a couple of hurricanes that came through and gave them a good power wash that apparently saved them.

Anyway, we're working closely with the Cooperative Extension to ensure we have the right list of recommended trees for our little microclimate here.

Again,  thanks for the help!