Tree Form Analysis Edward Frank Jan 22, 2005 12:30 PST
 ENTS, I have been thinking about this problem: How to calculate what the average dimensions of a typical tree would be in order to determine the weighing factors? The other question is how does the shape of the tree change over time as the tree grows taller and matures? We can't simply average the crown spread, height, and girth of the trees in our dataset (this is something I ask Bob about), because our trees measurements are dominated by lots of some trees - white pine - and few examples of many others. So averaging the numbers would produce a value, but that value would produce something closer to the typical white pine shape than the shape of an average tree. The other consideration is how the shape changes as the trees grow larger. We are generally looking at the tallest trees when me measure them, so if the form varies, we should calibrate our weighting numbers for the larger trees. It is like calibrating a pH meter. If you are measuring acid solutions you calibrate using a pH 4 buffer, so that the measurements will be most accurate in the range you are measuring. If we were looking at the shape of saplings, or young trees, we would need to calibrate to determine appropriate weighing parameters for trees in that size range. It occurs to me that using a given set of weighing factors, you could plot a large number of tree of the same species representing different ages and sizes and see if there is a consistent pattern of shape change over time as the tree matures.   You would need to compare forest grown with forest grown instead of mixing open and forest grown on one plot for this purpose. How to determine a good weighting factor to characterize an "average" tree shape. One possibility would be to take say three to five examples per species of a wide variety of trees, including both forest grown and open grown if possible, and averaging them together. This would offset sampling bias caused by one species being sampled more often than another. It doesn't really matter if a particular tree is larger or smaller than the average, the same weighting factor would be applied to each parameter, and the result calculated as a percentile of the total. Distinct shape differences should be seen between species, between open grown and forest trees, or between trees of different ages. This is a way to characterize tree shape in a mathematical way, rather than simple description. Does anyone know how to do a ternary diagram with excel? Ed Frank TernPlot - Excel Ternary Diagram Spreadsheet  ternplot.xls