Rick/Ecolog:
I think you are absolutely right to question these procedures; in fact your
post set off so many bells in what's left of my mind that it looked like the
Fourth of July and New Year's combined! I hesitate to make any remarks at
all unless there is enough interest to get into a lot of specifics, and I'm
sure there would be a lot of disagreement amongst subscribers, as "sampling"
procedures are the Holy Grail for a lot of people.
You do not want comments on anything but density, and I think you are right
on this too, but I again hesitate to comment because it would take a long
time and exchange of emails to resolve the sticky issues that will arise.
Suffice it to say that a lot of "protocols" have, if any, foundations that
are highly suspect to me; hence, I share your instincts (which, I suspect,
are only a sample of the entire thicket of stickery issues.
I believe that it is simply lazy, if not downright fraudulent, to leave
"minor" (grasses, cryptobiotic communities and species) out of most
studies--unless the purposes of the study are stated up front to be looking
only for data on a limited fragment of the ecosystem. Apart from that, I
believe that there is often little value to any survey data without
long-term replication that would reveal at least interesting changes and
trends, but how many actually do that. And when they do, what is actually
DONE with the data? All too often it seems to me to be in the realm of
"employment act" stuff . . .
I will say only this for now: RELEVANCE, RELEVANCE, RELEVANCE!
WT
PS: I ran many, many miles of transects during my brief Farce Service
"career" back in the last century, and I think we produced some very good
data and mapping, with little relevant "error." I re-visited my old stomping
grounds a few years ago, and was kindly allowed to poke around in the
storeroom of the Supervisor's Office, where I found our old field notes and
maps (apparently undisturbed, and probably un-analyzed).
As to density--like "cover," I don't think it reveals much except when done
over time like your case, it might provide interesting data on the maximum
productive (carrying) capacity potential for the vegetation being studied,
as well as recovery times following perturbations like fire and logging.
----- Original Message -----
From: "Rheinhardt, Rick" <rheinhar...@ecu.edu>
To: <ECOLOG-L@LISTSERV.UMD.EDU>
Sent: Saturday, June 01, 2013 4:43 PM
Subject: [ECOLOG-L] plot sampling for density
I recently started re-sampling vegetation in fixed plots on a U.S. Army
base. This base, and I presume many others in the U.S., use a standard
protocol for collecting vegetation data. There are many plots on this base
that are marked with benchmarks so that they can be re-sampled at intervals
of years to decades. I presume that the data obtained from these plots will
be used to monitor vegetation changes (structure and composition) through
time. One aspect of the sampling protocol is a straightforward
line-intercept method: a 100-m tape line is laid out in a straight line and
the height and species of all plants that touch a vertical rod are recorded
at 1-m intervals along the line. This method provides a fairly objective
measure for cover but cannot provide any information on density. A second
aspect of the protocol is designed to obtain density data for woody species
> 1-m tall. This protocol essentially involves delimiting a 100-m-long plot
using a range pole to determine the width of the plot, walking along the
100-m tape line from one end to the other, and recording woody plants, by
height category and species, within the pre-determined horizontal distance
delineated using the range pole. Usually, the predetermined distance (plot
width) is 6 m, which delineates a 600-m2 plot (6 m x 100 m). Horizontal
distance can be altered, based on perceived stem density.
The question I would like to submit to LISTSERV subscribers concerns the
methods used to apply the density sampling protocol. In all the plot work I
have done, I have always recorded only woody plants (stems in the vegetation
ecology vernacular) that are rooted within (or mostly within) the fixed plot
of interest. That is, plants rooted outside the plot, but with canopy
overhanging the plot boundaries, are not counted. However, the protocol we
have been asked to apply involves also recording plants whose canopies
overtop the plot even though they are rooted outside the plot. I believe
that counting plants rooted outside the plots severely compromises both the
accuracy and precision of the data, i.e., accuracy is compromised in that
the plots are no longer of a fixed size, and precision is compromised in
that there is much room for observer error when determining whether canopies
from large far off trees are overhanging the plot (because the observer has
to be in the middle of the plot to hold the ranging pole in place).
If we were measuring cover, then it would be immaterial whether a plant were
rooted inside or outside of a plot, since canopy overtopping the plots would
be the parameter of interest. Part of the confusion may be due to the
terminology used in explaining the protocol. The protocol says that woody
"stems" are to be recorded in the plot. To me, the term "stem" refers to the
main stem (trunk for a tree) that directly attaches to the roots, but I
think the term may have been misinterpreted to include branches and
secondary branches of plants.
My concern that the density data we collect will be a nightmare to
interpret, and worse, will not measure what it is intended to measure.
Unfortunately, in searching the web, searching papers, and even looking
through plant ecology texts, I have not found any guidance concerning what
plants should be counted in plot work (plants rooted outside vs. insides of
plots). Is this because protocol writers assume that everyone knows how to
do it? Could there be there a potential problem with density data in the
peer-review and/or gray literature? How much of a problem could misapplied
protocols be having on data collected by natural resource programs? Should
the word "stem" be defined every time it is used in describing a protocol?
Rick Rheinhardt
ECU
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