Prisms

[SwampDonkey]

Beenthere, the thinner the wedge the lower the BAF. That fits with what you described so far. Now, if the prism have no markings then determine their BAF (basal area factor) as follows. ;D

We know: tan θ = 1.33 feet/44 feet = K

is equivelent to: K=sqroot(BAF/10890ft²/acre)

So find K. Take a prism and a pointed stick (in my case a garden weasel handle) and look through the prism so that the broad side of the prism is near the eye. Keep both eyes open. Walk toward or away from a tree until the image of the tree in the naked eye and that of the image seen through the prism with the other eye just touch. This is an 'in' tree, but borderline. Jab the stick in the ground directly under the prism viewpoint. Hopefully your prism was held up to your face and not arms length. ;) So once the stick is jabbed into the ground and almost perfectly straight or level, measure the distance to the centre of the tree (to it's side) at 4.5 feet, keeping the tape level. Then measure the tree diameter so the calipers are pointing toward the prism view point. Now do the math. Convert diameter in inches to feet.


tan θ = 1.33 feet/44 feet = K in this example 0.030303

and...

K=sqroot(BAF/10890ft²/acre)

so BAF = K² x 10890ft²/acre

if you want to find the angle of the wedge...

θ = arc tan (1.33/44)
   = 1.7357 degrees or (104.14 minutes)


got it?  ;)

[SwampDonkey]

Here's my figures for my metric prism

diameter of white birch 0.295 m, make sure calipers point toward point centre. ;D

distance from tree 10.4 m , measure to the centre of tree by pulling the tape to the side of the tree.

tan θ = 0.295 m/ 10.4 m = 0.02836

BAF = K² x 2500 m²/ha

       = 0.02836² x 2500 m²/ha

       = 2.0 m²/ha  rounded

θ = arc tan (0.295/10.4)

  = 1.6247 degrees (97.48 minutes)  off by 0.26 minutes :D

to convert metric to US BAF...

BAF_US = 4.356 x BAF_metric

                              = 4.356 x 2
                           
                              = 8.7 rounded

[SwampDonkey]

 

Here's what mine says:

cm

2 m


Made by Cruise-Master Prisms of Sublimity, OR.

[Ron Scott]

10 factor prism being used to determine stand basal area. 

[Rocky_Ranger]

Prisms and basal areas are just consistency standards.  Much like site index or site classes they are most useful (unless you are a timber cruiser) as giving benchmark growing stock levels in square feet per acre.  Just like doctors write prescription in Latin, if we foresters didn't have basal areas and talk prism angles, anybody could be a forester. <grin>  The statistics for variable plot cruising are the same as fixed plot cruise errors, but the variable plots coefficient of variations are affected by tree counts within your squinted eyes looking through a piece of imperfect glass.......

[OneWithWood]

Gee, Ron, I don't see a prism.  Looks to me like you are getting ready to flip a coin to decide if a particular tree is 'in' or 'out'.  :D

Of course my eyesight leaves a bit to be desired.  Went cruising my woods with my district forester yesterday to spot invasives.  He kept gazing out and saying 'There's some autumn olive, there's some Japanese honeysuckle, look there's some Japanese knot weed.  See that ailanthus?  I had to get within a few feet to see the honeysuckle and knotweed.  It is gong to be and adventure to spray the right plants when it comes time. 

I don't think a prism is in my future  :

[Ron Scott]

It's at the end of the 25 inch string.  ;) The prism needs to be kept over plot center for accuracy. I usually mark plot center with my walking stick (ski pole) and hold the prism over it and then start counting the trees starting with the first one off my right shoulder from my cruise direction.

All border line trees are measured from plot center with the tape measured distance then read off a table to dertmine if that diameter tree is "in or out".

[SwampDonkey]

Just to clarify the method used to record data we use here in NB. We use a set of standard volume tables that represent 4 site indexes for softwood and 4 for hardwood, tree taper is factored in. So in a few plots within your stand we measure a few heights and use them to estimate others in the plot. We don't measure heights at every plot, just when your uncertain of the estimates of your heights. I usually document the height per plot of the dominants, just the average for sw and hw. For suppressed trees I use a lower site index because they are overtopped trees and stunted and they get grouped into pulp. My % pulp for softwood is 30 % and for hardwood it's 60 %, but I'll adjust if the wood is really poor. That part can be kind of dodgy because you never know until you open a tree up, how much heartwood is in hard maple or how much rot on the but of a fir. You can tell if something is going on there, but for someone to say 'oh that's got 50% heart' without opening up a tree it's pure speculation. An 'inky' borer can confirm if the but has rot, but how far up the tree does it go? Your not going to bore every tree or you won't be in business long. ;) So I write a little disclaimer regarding that difficulty. Out in BC they estimate most trees by measuring some trees in every plot and record diameter and height. Sounds similar for most states. Then they use volume equations that factor in taper. Some of you folks are probably estimating the height where the last log can be bucked. The computer program they use in BC makes use of tree pathology codes to deduct for waste as well.

So Tom, if you want to use a prism I think this might help.

First, know the area of your woods and group your woods into stands of trees with similar species and ground type (swamp land , dry upland). Get yourself a good aerial photo and ground truth the scale. We can explain that later. With a grease pencil, outline the stand perimeters by texture and color on the photo. Get yourself a measuring device, such as a hip chain and a good compass with declination dial on it. Now to make the location of the points random, go a set distance and bearing to each point. Mark the cruise pattern on your photo with grease pencil and note the Azimuth changes, so you can compass your way and know with some certainty where your at. We don't want to loose ya out there in the swamp. ;D If you have a small stand of wood, say 5 acres, put at least three points in and not on the edges of the stand perimeter.

Second, take your compass and set the declination to your local area, and from a starting point and distance you choose, measure and compass to point one which you marked on the photo.  ;D After you get there adjust the compass for the path along the cruise line you drew on the photo.

Third, now that your there at point one, mark the centre with a broom handle you remembered to bring along. ;) Now to keep track of where you start tallying trees you can have a handy can of paint with you and spray a little dot on the tree you counted 'in' and measured it's diameter at 4.5 feet and height (for height measurements, that's another discussion ;) ) Make sure the dot faces the point centre so you can see it when at the point centre. ;)

If your tree is hard to see or borderline get the tape out. We will assume you have a 10 ft²/acre prism here.

To see if the tree is 'in' use.

LD = Diameter of tree x 2.75, if your measured distance is longer, then tree is 'out'

On to the next one and so one and measure each tree diameter and height (or estimate) as you count them 'in'.

If you don't have a spreadsheet program like EXCEL 2000 or something (I think OpenOffice has a freebie), be prepared for long hand calculations for the next steps. ;D



Here is a long hand calculation of your tally to find density and basal area. Well the basal area part can be done in your head by adding all the tally up, multiply by Basal Area Factor (10 ft²/acre) and divide by # points tallied. And density can be sped up by making up a table of tree factors for each diameter class of that BAF. This is different for prisms of different BAF's. ;)


BAF                                      diameter
+++++++++++++++++++++++++++++++++++++++++++++++
                 +     10     +    12     +    13     +   14   +   15
+++++++++++++++++++++++++++++++++++++++++++++++
      10           18.3352 + 12.7328 + 10.8492 + 9.3547+ 8.1490

TF = BAF / (0.005454 x Diameter²)


To do your volumes it's more work unless you use an average height of that diameter in that particular stand (site). I would group the suppressed ones from the upper canopy trees and have two, maybe three if you group codoms from dominants, volume calculations per diameter and species per stand (site). Maybe when your tallying you can have a code for suppressed (1), Co-dominant (2), Dominant (3) and have average height for each group in that stand (site). Something similar to this...



Well, anyway this is the not so pretty way because it's all manual calculations.  Better find some wide paper and a big table. : Hope the wife don't chase ya off the dining room table.  :D :D :D

[SwampDonkey]

Sample cruise photo:



Ground truthing reveals that the photo has a scale of 1:10000. So for a rough idea of stand area, we can use a transparency with dots spaced 1 inch apart. Drop the transparency onto the photo at random, count the dots inside each unique stand number and some math

Ground Area = # dots x (10000² in² x ft² x acres)/(12² in² x 43560 ft²)

or

Ground Area = # dots x 15.94 (round to 16) acres.

If you find the plot centres are a lot closer than the dot grid spacing, reduce the dot grid spacing to get more accurate area estimates.

If any dots land on the perimeter, count every other dot on the perimeter.

Example:

Drop the spacing down to 1/4"

so.........

Ground Area = # dots x (10000² in² x ft² x acres)/(12² in² x 4²x 43560 ft²)

Ground Area = # dots x 0.996 (rounded to 1) acres

;D

[SwampDonkey]

Typical Area Dot Grid



The dots in this case are actually spaced at 0.8 cm apart. (reciprocal of 1.25 cm) That way, each dot represents a hectare. ;)

[WDH]

SD, that is the old fashioned way ;).   You are dating yourself ;D.

[SwampDonkey]

Yeah I know, but does Joe land owner have all the fancy GPS/GIS and equipment? ;D


I think if Tom and Dang got together as a cruising team and cruised their ground and survived the ordeal with all this math and paperwork, in this blistering heat, it would definitely be worth more than a shared bottle of beer wouldn't it? ;)

[WDH]

DanG right it wood ;D.  We used to measure our productivity in acres cruised/day or in plots/day.  With those two, it would be acres cruised/mint julep :D.  By the way, the heat here was brutal today............. :-\.   

As I read your post about the cruise methodology, I got tired just thinking back about doing that so many times ;).  With all the fancy GIS/GPS tools and spreadsheets and such, it is much easier than it used to be.  However, many of the young foresters today might have difficulty doing things the old way.  Using the compass and your pace to do a type map is probably not taught these days.  Just find the satellite photo on the internet and point and click to outline the boundaries to get the acres magically from the computer.  Getting the accurate acres (hectares  :) used to be quite a lot of hard field work .

[SwampDonkey]

I wonder if someone has written a JAVA GIS program for the Terraserver website? ;D Most of these programs I think are commercial products, ARCIMS by ESRI comes to mind. That means something else to learn. Give me my map and dot grid. Through them up in the air, where they land, count the dots. Try that with the computer.  ;D :D

When we cruised the west coast an 8 point day was very good, a 12 point day was rare and made DNR suspicious about quality, 6 was a minimum target. Takes anywhere from 40 mins to 1 hr 25 minutes per point with all the tight chaining for horizontal distance, reference tree and centre stake marking, pathology and measuring, sometimes even clearing of salal vines.  ;)

[Texas Ranger]

Cruising for Champion was interesting in light of the daily achievement.  We would try for 20 (flat land and plantations), but usually got just over 10, with travel time, and cutting our way through to the points.

[Pullinchips]

In relitively open older stands i can get 20-30 day.  Tom your string idea is what plot cruising is that 37.2 foot string is your 1/10 acre!  It is confusing that is why there is an entire class devoted to the subject of cruising.

-Nate

[Texas Ranger]

In open stands, yes, 20-30 a day, but, been to South Carolina, and you don't have NEAR the brush we do in Texas.  On some plantations we had a machete man in front of the compass man.  On a two man crew.  To DanG old to go in the woods by myself and let the buzzards be the ones that find me.

[Pullinchips]

Thats why i put the little disclaimer "older open stands".  We have a coastal plain that has the growth of bushed and vines so thick that you cant see, just like your talking about. I have not been in these relly bad first thin stands but i have been in some upper coastal plain stands where i could only get arount 10 a day.

-Nate

[Texas Ranger]

Same ol' same ol', far as I can tell.  I cruised a 22 year old plantation a couple of months ago, like walking in a park.  Right next to it a 15 year old unthinned, you can lose your religion in one of those.

I have decided some cruising is a young mans sport, but still love it.

[Greg]

This gets my vote to belong in the top 10 most informative FF threads!

I'd guess the postings here pretty well cover the same if not more, crucial real world information covered in a 10 week undergrand forestry course...

Thanks for sharing,
Greg

[OneWithWood]

That's for sure, Greg.  Ole Tom sure knows how to stir up a learnin' fest  8)

[SwampDonkey]

Like Tom, and others, and probably most of us.... If there is something that draws our interest we like to pull it apart and take the mystery out of it.  ;D 8)

[SwampDonkey]

Hmmm, the GIS statistics of the aqua colored perimeter............using metric




And by dot grid?............ count the dots inside the black perimeter.



Some more random drops of the dot grid come up with the following counts.

4 inside, 4 on perimeter = 6 (count every 2 perimeter dots)
5 inside and 3 perimeter = 6.5
5 inside and 2 perimeter = 6
5 inside and 1 perimeter = 5.5
6 inside and 2 perimeter = 7
5 inside and 1 perimeter = 5.5
6 inside and 1 perimeter = 6.5
5 inside and 1 perimeter = 5.5
4 inside and 3 perimeter = 5.5
4 inside and 4 perimeter = 6
4 inside and 2 perimeter = 5
6 inside ....................  = 6
=====================
5.91 (average)  ;D  :D :D :D

[WDH]

I got broke in on a dot grid.  I bet most of the new generation of foresters have never used one.  SD, we are archaic.

[Ron Scott]

I still use one. Very reliable. ;)