Looking for information about the large circles free of snow that form in the spring around the trunks of large trees?
We have often used the large snow free circles that form in the spring around the trunks of large trees as camping spots. Even in an area blanketed with deep snow, there will be such bare, dry ground to camp on, although one may have a steep climb into or out of such a spot. They are like dry wells.
First, what are such bare-ground wells called?
I assume that the dark tree trunk absorbs heat and then acts as a heater to speed up melting around the trunk. Moreover, the snow was probably shallower around the trunk because of the tree branches. We observed these circles under evergreens.
Second, does this accelerated melting happen only when daytime temperatures go above freezing, or does it start earlier?
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1 answer
Much of it is due to conifers -- especially spruce and fir shedding snow away from the trunk. I routinely see trees with 1/3 of the snow under their branches as in the open.
A spruce in winter appears nearly black. Sunlight enters, and bounces around a lot before escaping. Most is absorbed during a bounce.
So the crown of the tree is warmer than the surrounding air. There is some warm radiation between the lower branches and the ground.
The space under the tree cannot radiate readily on a clear night into space. So the temps at night aren't as cold.
My experience is that wells down to bare earth don't start to form until late winter or early spring. I don't think that temps have to be above freezing for them to form, but likely start when temps are near freezing.
The wiki article https://en.wikipedia.org/wiki/Tree_well describes the formation of much larger ones than I've seen. (We rarely get snow deeper than 2-3 feet here)
Here, in spring, the effect of a row of spruce is strong enough that a band of bare ground 20-30 feet wide forms on the south side of the trees, while snow is still a foot or more deep in the general open area.
I've not noticed tree wells around any type of tree besides spruce or fir. Pines generally don't shed snow outward. Cedar and hemlock may support tree wells. I don't have them here.
This post was sourced from https://outdoors.stackexchange.com/a/24609. It is licensed under CC BY-SA 4.0.
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