A NOTE ON THE GROSS ESTIMATE OF FOREST INSECT DAMAGE IN CANADA

I N RECENT years, workers in forest entomology have become increasingly cautious in advancing any quantitative estimates on the amount of damage caused by insects.As a result, we have had nothmg concrete to give us a picture of the relative importance of present destructive forest insect outbreaks.The main reasons advanced for not attempting to give any figure are: 1.The virtual impossibility of obtaining such a figure in cases where very extensive areas are involved.2. The inaccuracy of the figure, if obtained.3. The inadequacy of a mere figure for damage, whether in cords or in dollars, to evaluate its relative importance in other respects; if in cords, with regard to accessibility and merchantability; and whether in cords or dol.lars, with regard to fire hazard, site deterioration, ecological succession, amenity value and the like.In this paper, an attempt will be made to answer the three points enum.erated above : 1. Figures dealing with insect damage even over extensive areas are not im.possible of attainment.It is not necessary, as seems to be the impression in some circles, to make a detailed cruise acre by acre.Application of the sampling method, combined with a sense of proportion and an idea of the probable error, will tell us what we want to know.2. The claim of the inaccuracy of such a figure may be countered by the simple question: What is understood by the usual terms "heavy," "mod* erate" and "light" to describe the degree of infestation?These are mere terms of quality, and any quantitative figure, within a reasonable limit of error, is more definite and, therefore, generally more satisfactory.3. The inadequacy of a figure to take care of certain important factors.T h s paper recognizes that fact, and adduces figures only to take their place along with the other values to be considered.The straw man having been set up and appropriately demolished, one may now turn to derive and advance a set of figures for damage,-good round figures that are an approximation, and are only correct (but at least correct) as to the placing of the thousand comma.Although there are many possible methods of derivation, depending on local conditions and on the basic data available, the underlying principles for calculation of gross estimates are the same in all cases.The essentials required to obtain an approximate estimate are: 1. Maps showing the extent and intensity of the infestation.For convenience, intensity may be divided into three classes,-heavy, medium and light.As