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Author Topic: Forester tips for Surveyors estimating Tree Surveys  (Read 1983 times)

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Offline Surveyor6329

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Forester tips for Surveyors estimating Tree Surveys
« on: August 03, 2013, 03:03:15 PM »
I am a Professional Surveyor and Mapper in the State of Florida and I occasionally do what are called tree surveys. Tree surveys are basically the mapping of every single tree that meets a minimum DBH on a parcel. One of the problems that we surveyors have is estimating how long a tree survey will take to give price estimates and I am interested in learning about how Foresters (specifically Timber Cruisers) determine how many trees per acre a certain parcel may have. I am specifically interested on the function of angle gauges, wedge prisms and similar instruments and how they are used to determine how many trees per acre that there are on a given parcel.

Thanks,

Offline Clark

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #1 on: August 03, 2013, 03:34:12 PM »
Mapping every single tree on a parcel of land! That would be extremely difficult to gauge how long it would take. As you have probably guessed, foresters use instruments like angle gauges and prisms to estimate how many trees per acre are present. Statisticians would like to say we are taking a sample to estimate the total population.

There have been threads on here in the past that have gone over these exact principals.  Maybe SwampDonkey can chime in?

Clark
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Offline Texas Ranger

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #2 on: August 03, 2013, 05:56:03 PM »
I think you are looking at two different cruises.  One is not a cruise if you measure and locate every tree on a tract, some thing foresters seldom are asked to perform, it can be quite extensive.

The other is a statistical cruise that gives you diameter class volumes and numbers, but not every tree.
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Offline Rocky_Ranger

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #3 on: August 03, 2013, 07:20:06 PM »
We are testing some "whiz bang" gadgetry that sits in the cab of a hot saw or feller buncher that locates every tree that is cut, and where the skidder sorts are located.  Uses GPS and stand mapping to give operator a looksy at how the stand is being treated.  Info is downloaded every evening to master GIS file, and can be real time too if you have a link for internet.  Biggest problems are wear and tear on a fragile instrument and keep breaking the antenna off the top of the equipment.

We are also using LiDAR for veg mapping - jury still out on that one.  LiDAR is good for ground disturbance and stream erosion but can't tell the difference between species.   
RETIRED!

Offline Ron Wenrich

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #4 on: August 04, 2013, 06:54:24 AM »
Are you mapping trees in a forest or are they more in urban situations, such as a park?  Mapping would be tedious as for tying into a common point.  Maybe a GPS location would suffice.

I have used an angle gauge, which is similar to a prism.  The angle gauge is made of metal and is a lot cheaper than a prism.  It also has BAF of 5, 10, 20, and 40.  It can give you the number of trees per acre, as long as you know how to convert them over from dbh.  Its not a hard process.  I wrote an article here on the forum that may help you if you plan to do a cruise.  I'm assuming you're looking at the number of trees so you can get an idea on how to bid the job.

Here are the articles on prism cruises. 
http://www.forestryforum.com/cgi-bin/tips/tips.cgi?display:1010359123-3833.txt
http://www.forestryforum.com/cgi-bin/tips/tips.cgi?display:1010359141-3837.txt
http://www.forestryforum.com/cgi-bin/tips/tips.cgi?display:1010359154-3844.txt

Point sampling is a quick and easy way to get volume and tree estimates.  I've used them for writing management plans and for volume and value estimates before harvesting.  I find they work well if you are mapping an area as you go.  I will separate areas that have similar forest types and treat each one differently.  Your statistics hold up much better. 
Never under estimate the power of stupid people in large groups.

Offline Surveyor6329

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #5 on: August 04, 2013, 08:29:29 AM »
Ron,

Thanks for referencing your articles. They are quite helpful. A couple of questions: How do you know what BAF angle or prism to use on a cruise? and am I correct that for every tree that you would count, you would at a minimum have to measure its DBH to calculate trees per acre for each plot?

Thanks,

Offline SwampDonkey

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #6 on: August 04, 2013, 08:35:27 AM »
I am a Professional Surveyor and Mapper in the State of Florida and I occasionally do what are called tree surveys. Tree surveys are basically the mapping of every single tree that meets a minimum DBH on a parcel. One of the problems that we surveyors have is estimating how long a tree survey will take to give price estimates and I am interested in learning about how Foresters (specifically Timber Cruisers) determine how many trees per acre a certain parcel may have. I am specifically interested on the function of angle gauges, wedge prisms and similar instruments and how they are used to determine how many trees per acre that there are on a given parcel.

Thanks,

Angle gauges and wedge prisms use the same math. The difference is the point centre of an angle gauge is at the observer's eye. With the wedge prism, the prism is the centre point.  The wedge prism uses refracted light for 'in' or 'out' determination to tally trees and the gauge uses a U site. This must be kept in mind when sampling as typically a stick is poked in the ground for the point centre and every tree in the tally is based on this centre point. Can't be moving the centre point all around in the sample, it's done on pivot. Plot size of both is variable and depends on the tree diameters at breast height, and is actually called a point sample. As stated by others these tools are used to take samples of the population with randomized stratification of the point locations. You can use a GPS/Mobile GIS and add a point location layer and just walk to the points and do your circular sweeps. Either the gauge or the prism gives basal area at breast height and has a known 'basal area factor' based on trigonometry. This basal area factor says that each tree tallied represents X ft2/acre. So a gauge of factor 10 ft2/acre says each tree in the sample represents 10 ft2/acre @ breast height. However, you want density.

How many trees per acre are represented by the tallied diameters of the samples? This is called the tree factor. We need this factor for every diameter measured. It is calculated as:

tree factor=basal area factor/basal area of tree of said diameter.  The ratio of a tree's diameter to it's distance from plot centre, or radius, where it is just 'in', is the gauge constant k. With a BAF of 10, a tree of 1 foot diameter can be as much as 33 feet away to be 'in' but bordline, so K is 0.0303. The larger the diameter, the further away it can be to be tallied. Think of a triangle with a set angle at the point centre, diameter increases as distance increases between the sample point centre and the tree being observed. k is unique to each basal area factor, thus both are constants for that gauge or prism.

So a tree tallied with a diameter of 10 inches, represents:

10890 ft2/acre x k2
0.005454 ft2/in2x D2 in2/tree

10890 x 0.03032
0.005454 x 102

pi/4x144 = 0.005454

18.33 trees/acre, now multiply this by the number of trees tallied of 10 inches and divide by # of sample points. Do it for all diameters and you have total density.


This will show the distribution of diameters by abundance on the piece of forest land sampled.

Like Ron said. I was awhile making my post. ;D

If you use a large BAF prism or gauge in small wood, you will have a small count per point sample. And if your BAF is small, you will have a lot more trees tallied, especially so in big wood. A BAF of 10 would be a good fit for trees between 8-10" as a stand average. If you choose too small a BAF in big wood you will have a ton of measuring. You want something like 8-14 trees per point, as a starting reference.
Move'n on.

Offline Ron Wenrich

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #7 on: August 04, 2013, 01:07:03 PM »
A couple of thing do come into play with point sampling and BAF.  For most stands, a BAF of 10 is used.  If you're in smaller timber, than you go to a larger BAF.  If you're in really big wood, then you use a smaller one.  In Florida, I doubt you would use anything smaller than 10.

To get a fairly accurate tree count, you would have to measure the dbh.  After awhile, you get pretty good at estimating the dbh.  If you're doing a volume estimate, your accuracy on the dbh won't have as much affect as you're accuracy in usable height.  That's because as the dbh goes up, the number of trees go down.  I always try to make my dbh fairly accurate.  I use 2" diameter classes. 
Never under estimate the power of stupid people in large groups.

Offline SwampDonkey

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #8 on: August 04, 2013, 01:24:11 PM »
If you're in smaller timber, than you go to a larger BAF.  If you're in really big wood, then you use a smaller one. 

I believe you'll find the opposite to be true. ;)

In average sized mature hemlock on the BC coast we used 12.25 m2/ha. In 2-4 meter dbh sitka spruce and western red cedar we used 16 m2/ha, if we didn't the count per plot would more than double.

Think about it, large BAF, every tree counts for more area. So the tree count goes down as BAF goes up because the gauge angle is wider. Trees have to be closer to the point centre. If a BAF of 10 and 9 trees counted then 90 ft2/acre. If a larger BAF at the same point gave more tree count, then the ft2/acre jumps by leaps and bounds. Then the whole reliability of the cruise goes out the window.

I would also do 2" classes, but many jurisdictions measure down finer to the fraction of an inch. A 2" class allows you to dot tally each tree.

o o                         o-o
o o  is a count of 4   |X| is a count of 10
                              o-o
Move'n on.

Offline stavebuyer

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #9 on: August 05, 2013, 05:37:44 AM »
I have bought a lot of timber for mills that tracked the results log by log. Prism, strip, fixed radius, and 100% individually D-taped & marked. A good mix of timber cruised by myself, government foresters, and consultants. They are all estimates.  Internal defects, logging and bucking effectiveness, scaling practices of the receiving mill(s), and utilization standards all create variability that exceeds the degree of error of any of the cruising methods employed. Things tend to average out. A Biltmore stick and laying out plots/lines to get a good sampling will get you as close and sometimes closer than tree by tree.

Offline Ron Wenrich

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #10 on: August 05, 2013, 08:11:14 AM »
Not only are estimates different from forester to forester, so is recovery from logger to logger.  In this case, we're looking for number of trees, not volume. 

Swamp;  Answered it without checking my gauge, and probably not enough coffee. 
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Offline SwampDonkey

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #11 on: August 05, 2013, 02:22:29 PM »
I told this story before, but it's been awhile. One of the crews on the west coast in our company were doing some juvenile stands, cruising and aging trees and such, the whole nine yards. Well among the juvenile trees a big old ancient red cedar would be found once in awhile. Anyway, the plot spacing was 50 meters x 50 m and BAF was 9 m2/ha. Keep in mind mature was 260 + years out there. Anyway, this one old cedar was in the surrounding 4 plots of that cruise.  This was the sized cedar that would take two 7.5 meter long D-tapes to wrap around it. They were not tall like spruce, but they were massive brutes. Still way bigger than any white pine in the east ever seen. ;D That was another thing, if the BAF was too small in big wood, there were trees you could miss and never see especially in salal covered forest on the coastal plains were it was flat. There was places you could only guess heights because you couldn't see dbh with the SUUNTO unless a fellow used a paint can as a flame thrower, and we did sometimes. :D But really though, we wasn't using our heads it seems. We could have just used 0 reading for the bottom and added eye height and be close enough. Only make sure we were under 100 % for the top. And yes, we had to always be under 100 %, that was one of their coastal rules anyway.
Move'n on.

Offline banksiana

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Re: Forester tips for Surveyors estimating Tree Surveys
« Reply #12 on: August 10, 2013, 09:05:15 AM »
I would put a couple fixed radius plots in, count the trees then figure how many trees per acre from that.  Since I think you are looking for a quick and dirty method to determine how long it would take you to count all the trees on a parcel, you could even see how long it takes to count the trees in the fixed plot and base your estimate on that. 


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