| The clearing: |
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This big opening was cleared to accommodate a climate station (the photo on the left is actually of the clearing in Watershed 1, but you get the idea). We commonly refer to it as a "rain gauge clearing". Most of the delineated watersheds at Hubbard Brook have two or three rain gauge clearings set up at different elevations within or alongside the watershed, and each clearing has a unique number assigned in the order it was established. In the aerial photo above, the W6 clearings are labeled as RG 11, RG 10, and RG 9 (click on the photo for a closer view). Other clearings alongside Watershed 4 can also be seen as circular patches. The climate stations are located in the middle of the clearing and consist of at least one standard rain gauge, and in some cases a weighing gauge and/or a hygrothermograph.
The clearing itself, although it may look like a somewhat unkempt field of weeds at times, is actually carefully designed to insure the accurate measurement of precipitation. Since precipitation measurements from a standard rain gauge assume that all rain falls straight down into the can, wind effects that would blow rain sideways must be kept to a minimum. To achieve this, the gauge is placed in a location free of tall objects that would cause eddies and erratic wind patterns. The general rule is that any obstruction must be no closer to the gauge than four times its height above the top of the can. Therefore the gauges are placed a little bit downhill of center in the clearing, with the open top of the can in a horizontal plane perpendicular to gravity. Whenever a tree on the perimeter of the clearing grows to be taller than four times its height above the can, it is cut down. The vegetation in the clearing, mostly fern and blackberry, is cut back every three to five years when it becomes too tall.
Since the climate stations are visited once a week, a trail network was established throughout the watersheds to facilitate frequent travel to the stations. The trail we will use up to the top of W6 is part of that network, and is in fact one of the larger trails within the watersheds. We call it the "Weasel trail", because in the old days, Forest Service personnel traveled this trail in winter with a military vehicle know as a Weasel. Today they use snowmobiles.
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