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
