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Data Set #076





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Many questions can be asked about the student's sample of Douglas fir trees (or whatever tree is convenient for your students). Is the sample biased or unbiased? Is the sample stratified or unstratified? Is this a sample of convenience? How representative of the population of Douglas firs (along the White River valley) is this sample? The Douglas firs show a typical growth pattern. Students can try curve fitting using a graphing calculator or Excel; what kind of functional model best describes Douglas fir growth? Growth sequences can have all sorts of utility. For example, to determine the total amount of lumber in a particular stand of second growth Douglas fir, it is not necessary to measure the height of the trees, which is time consuming and difficult in thick forest. Instead, the diameters can be quickly measured, and using the growth sequence already established for this specie, the height can be read off the graph or calculated from the bestfit empirical formula. The volume of lumber can then be determined. The influence of growing parameters such as soil type, elevation or microclimate can be quantified by determining growth curves for trees in different areas. 
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