. The Canadian field-naturalist. Natural history; Sciences naturelles. 2005 Pruitt: Why and How to Study a Snowcover 123 ferentiate hardnesses of, for example, six layers in a given profile instead of only four layers with the cir- cular discs alone. Start measuring hardness by using the medium range gauge and attaching to it the largest disc that will fit the topmost layer of the api exposed on the vertical cut face. Push the gauge and disc, horizontally, slowly and steadily against the cut face. Be sure to engage the disc and the cut face with a horizontal motion otherwise error will be prod
. The Canadian field-naturalist. Natural history; Sciences naturelles. 2005 Pruitt: Why and How to Study a Snowcover 123 ferentiate hardnesses of, for example, six layers in a given profile instead of only four layers with the cir- cular discs alone. Start measuring hardness by using the medium range gauge and attaching to it the largest disc that will fit the topmost layer of the api exposed on the vertical cut face. Push the gauge and disc, horizontally, slowly and steadily against the cut face. Be sure to engage the disc and the cut face with a horizontal motion otherwise error will be produced ( Brown and Theberge 1990). At first, there will be a bit of surface crumbling. Con- tinue pushing until the crystalline structure suddenly collapses. The ratchet on the push-rod keeps the calibra- tions in view so that the maximum force needed can be read and recorded. Repeat the procedure several times, each in an adja- cent, fresh spot of the layer. Continue the procedure for each layer of the api. Undoubtedly you will have to use several combinations of gauges and discs to get combi- nations that will fit each layer and its hardness. Consid- erable practice is necessary in order to achieve consis- tently-reproducible results. A characteristic of the snowcover which I have found useful when considering supranivean animals is vertical hardness (VH). Use the proper combination of gauges and discs and bring them vertically down onto the sur- face until the crystal structure of the surface layer col- lapses. Horizontally cannot be substituted for vertically in this measurement (Pruitt 1990). A useful variant of VH is vertical hardness to track depth (VHT). Choose a disc approximating the animal track in area and push it vertically down to the same depth below the surface of the snowcover that the track reaches. The Swiss "ramsonde," because of its total mass, cannot be used on soft taiga api. Density Density is a function of the complex history of a snowcover,
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