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Is the temperature (even a bit) warmer in a forest?

For example, there no frost on the ground in a forest when there is some in a field just outside the forest. Is it because the temperature is a bit warmer? Or simply because there is no dew on the ground in a forest?

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  • $\begingroup$ it's because the effective surface is the canopy top... below the canopy provides some insulation and so the forest floor has less exposure to frost. $\endgroup$ – farrenthorpe Jan 1 '15 at 2:34
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    $\begingroup$ Here's a schematic of what housing insulation does to the daily temperature cycle - ignoring evapotranspiration, the insulating properties of a forest would have a similar, but probably less pronounced effect - less extreme minimum and maximum temperatures. $\endgroup$ – naught101 Jan 2 '15 at 6:07
  • $\begingroup$ @naught101 - That's exactly what I notice when I walk my dogs through a nearby woods. Cooler in summer, warmer in winter. The extremes aren't quite as extreme in the woods. $\endgroup$ – David Hammen Jan 3 '15 at 10:36
  • $\begingroup$ have you considered the albedo effect? $\endgroup$ – user4955 Dec 8 '15 at 16:07
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It will depend on the time of year and the time of day. As you noted, you often see more frost in an open field than in a forest. A comment indicated the forest insulated the surface but I believe it will also reduce radiant heat loss at night, compared to the open field. During the day, the ground surface is more shaded and the trees reduce the advective movement of warmer air into the forest floor so the forest will often be cooler than the open field.

Another factor is evapotranspiration. Forests will tend to be cooler in drier summer conditions because, in general, you get more evapotranspiration from trees than from shallow-rooted vegetation and annual grasses die off in summer. The evapotranspiration cools the area.

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  • $\begingroup$ I didn't know about evapotranspiration and I didn't think about radiant heat loss too. Thanks for your insights! $\endgroup$ – MagTun Jan 3 '15 at 10:23
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Don't forget the protection from wind in colder seasons as well. Basic survival skill is to always make shelters under cover (as in a forest) rather than in an open meadow. On a cold day it may not feel much warmer in still air but getting out of the wind does make a significant difference.

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  • $\begingroup$ You're right, for the wind, but does it also count for the soil. For example at the same (below zero) temperature, does a windy field will freeze faster than a non-windy one? $\endgroup$ – MagTun Jan 3 '15 at 10:26
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    $\begingroup$ You don't have to get very deep for it not to make too much difference. But at the surface, yes - you can definitely have frost in fields with very little or none in adjacent forest. Another example of this is black ice on roads where they are exposed to wind. $\endgroup$ – geogaffer Jan 3 '15 at 20:05
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    $\begingroup$ This is a good point. Rate of cooling isn't the same as temperature but it is important in frost development and frost damage. But wind turbulence can also prevent frost development by preventing the formation of a stagnant cold air layer. $\endgroup$ – haresfur Jan 3 '15 at 22:42

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