I am still trying to get some discussion going on veg. sampling - Thank you Tommy. Is anyone else able to offer some guidance?

Here is what we have so far

quote:

A while back there was some discussion on vegetation sampling and my question which perhaps was to far into the thread for anyone to notice was this: For woody material in the tree and shrub stratums, basal area has been used as a sample method in addition to aerial cover. I have noticed a shift towards using mostly aerial cover in recent years (admittedly, basal area is more work). What I am wondering is if folks are mostly using percent aerial cover and, are you using the cover of the stems or cover of the canopy? Obviously, the canopy will provide a much higher cover value than the stems and I think this is an area where there is much subjectivity and variation.

Tommy Dye suggests a spherical densiometer

quote:

Interesting. Can you explain how the instrument is used in terms of plot size and what it samples. And. how does it differ in winter?
Thanks

I have an instruction sheet somewhere, but can give you the basics.

A Spherical Crown Densiometer consists of a small mirrored hemisphere (either convex or concave) that has a grid scribed on it set in a small wooden box with a lid.

Hold the device at waist height then mentally subdivide each grid square into 4 smaller squares (this is where the subjectivity comes in) all of the subdivisions that are more than 50% obscured are considered cover, the subdivisions are then counted up to get the % aerial cover.

I cannot remember the exact size of the plot area reflected in the densiometer, but will look it up and post it later.

Thank you Tommy.
I have read up on it and it sounds pretty helpful for what we do. But I did not find the plot size it represents, which of course is important, so ant info. you have would be helpful.

The exact overhead area reflected in the device is not stated in the instructions, so I would assume that it is supposed to be for point sampling within a plot area of whatever size you want. Next time I take it in the field I will do some plot size experiments to see what kind of coverage it produces

This is a photo of the instrument in operation.
http://mississippiwetlands.blogspot.com/

References listed in the instructions

Lemon, Paul E. 1956, A Spherical Densiometer For
Estimating Forest Overstory Density. Forest Science 2(4):314-320

Lemon, Paul E., 1957, A new instrument for measuring forest overstory density; Journel of Forestry 55 (9) 667-668. 236501 LET

The Cemml page has a good reference document for different vegetation measurement methods.

http://www.cemml.colostate.edu/methods/methods.htm

Brian,
Why use a method not recognised by the '87 Manual? While the Densiometer is probably very quick method, you would have to redo any plot data with trunk diameter measuremnt that are submitted to the Corps or other regulatory agencies, right?

That's exactly what I am trying to get at! My original point was that while the 87 manual cites basal area of stems as the preferred method, almost every consultant I know is using estimated canopy cover because it is easier. So, do you only use basal area for trunks/stems and do you fell that it is the only acceptable method? If so, do you actually measure dbh for each plot?
Now we are getting some good discussion.....!

Measuuring Diameter at breast Height (DBH) enables additional understanding of the forest because you can get density and frequency of trees as well as DBH.

Excellent and simple methods for DBH include two plotless methods:
Point quarter method and random pairs method.

Also foresters use a prism method whereby it is not necessary to walk to every tree to measure its diameter.

These methods are readily available in the forestry literature for the prism method and the plant ecology literature for the plotless methods.

An extremely simple method for the aerial cover is the plotless method of point sampling. With a strong laser pointer shine the light into the canopy and if it encounters a leaf count cover - no leaf encountered no cover. The percent of points encountering leaves is the percent cover. This technique underestimates cover as compared to other methods and is not very useful when their is very much wind.

Gary Pierce
froghome@voyager.net

Gary,

If you want to measure DBH, measure DBH.

The point-centered quarter and randon pair methods will define the density of a stand, but give no information on DBH. Using a prism to cruise a stand results in a basal area for stocking, but gives no information about individual DBH. None of the techniques would routinely identify species, although that could be recorded for future manipulation of the measured values.

Gary, how does the prism method work for measuring DBH?
When I am doing plots for submission to the Corps, I measure DBH directly. I walk around to every tree and record species and diameter. If the corps will accept another method, lets hear about it! While timber cruising methods might even be better than the '87 manual method, if the Prism method or Laser shining methods are not recognized by the corps, than they cannot be used in formal wetland delineation.
On the other hand, I do use aerial coverage when not submitting to the Corps because it is easier than measuring DBH.

All of the sampling methods I mentioned above are capable of incorporating DBH, but of course it has to be measured and recorded for each individual tree in the sample. An example of detailed method is given at http://el.erdc.usace.army.mil/elpubs/pdf/EL95_24.pdf.