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Assuming two trees have similar shape and leaf coverage, could differences in the biological processes among them lead to differences in the temperature of the shadow they cast?

What biological processes occurring in plants could affect this? I was thinking that transpiration will cause heat loss, and photosynthesis also absorbs energy, so these would contribute. What other processes that occur in a tree could affect the dissipation of heat causing cooler shade?

Has there been any studies specific to rates of transpiration and photosynthesis, and the effect on shade temperature?

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    $\begingroup$ please specify what you mean by quality of shade. also, probably, number of leaves in $m^3$ is not good enough: something like total surface of leaves in $m^3$ should be more useful $\endgroup$ – aaaaa says reinstate Monica Jun 22 '15 at 17:26
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    $\begingroup$ By quality of shade, do you mean something like $ΔT = T_{unshaded} - T_{shaded}$, the difference in temperature between a shaded and unshaded area? $\endgroup$ – Luigi Jun 22 '15 at 18:18
  • $\begingroup$ From personal experience (I don't know that anyone has actually studied this), much depends on the air, not on the tree itself. In humid lowland climes, shade may not be all that much cooler. In a dry, high-altitude clime (like the Sierra Nevada, where I live), you can be hot in the sun, but want to put on a sweater when you move into the shade. $\endgroup$ – jamesqf Jun 22 '15 at 18:36
  • $\begingroup$ Density of leaves, humidity, general temperature, time of day/sun angle... various differences in human experience $\endgroup$ – SolarLunix Jun 22 '15 at 21:41
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    $\begingroup$ @WYSIWYG I thought transpiration has a major role in regulating temperature around trees $\endgroup$ – One Face Jun 23 '15 at 7:05
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The short answer is NO. A shadow is strictly due to the blocking of sunlight, so the shadow of 2 equally non-transparent (i.e., same density of leaves, both have similar trunk diameter, etc.) trees on the same hillside in the same weather conditions would not have different temperature shadows.

A plant's metabolism can and will affect the temperature surrounding the tree, but this affect is lost almost immediately as you move away from a tree. For example, in a study I did a few years ago measuring spruce tree temperatures (unpublished), we found that even within 5-10cm from the tree, the rise in ambient temperature was no longer measurable.

You're correct that the leaves of plants will absorb sunlight and as a result will increase in temperature. Walter Loomis's (1965) paper, Absorption of radiant energy by leaves (found here), suggests that leaf temperatures can raise to 30 $^\circ$C or more. However, he notes that their study found that even wind speeds of 5mph instantly cooled the leaves via conductive heat transfer. Our study with spruce trees also found this to be true. Transpiration will further help the tree rid itself of that increased temperature fairly quickly. Regardless of these facts, radiant energy from leaves in the canopy will not be felt how-ever many meters below within its shadow.

Finally, yes, transpiration can affect local climate, but this is only on the scale of whole forests. The transpiration of a single tree will likely not impact the ambient temperature around itself in any measurable way, especially at any distance greater than that I've already mentioned.

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