That's an interesting question! It does seem like different trees will let through dappled light, very little light, etc. You might get an idea of how much light (i.e. shade) by the plants that grow under various trees. Some ferns will grow under dense leaves of a perennial pine or redwood, and some fruit bushes prefer the dappled shade of an oak tree. You might also check which molds grow under/on certain trees, because they will only grow at certain temperatures. Redwood trees, for instance, let through very little light, create dark cool shade, and there is a very specific mold that grows under redwood trees. And, of course, breezes and winds will affect temperatures, but that may be location dependent.
I followed up with an arborist and chased a Professor called Dr Greg Moore. Google him for a bit. The place that may have some information is https://www.treenet.com.au/
There is a temperature compare of inner urban Adelaide but its not what you are after. This was in the latest symposium. It will be somewhere.
A great BD farmer in the Hunter Valley, John Priestly, tells of the ability of mulberry to create a breeze by rotating their leaves and wasps and other good guys can often be seen sheltering in a mulberry on hot days. Under our tree is always cool on hot days and the chooks under there seem to thrive too. Though they often get sick of eating the mulberries.
Hi Andrew, although it doesn't drill down into details for specific trees, you might find this basic summary and link to a solid scientific paper interesting on the temperature and water cycle effects of vegetation: Catch water and grow plants: how to "seed the rain" and cool the climate The dappled shade of Gleditsia and Robinia will obviously allow more sunlight, and hence heat though, and trap and cycle a bit less moisture below the canopy, but that can be outweighed by the lush C3 grasses that love those conditions of course.
This paper by the FAO is pretty good too on microclimate effects: https://www.fao.org/docrep/005/X3940E/X3940E05.htm In savannah conditions in Africa, soil temperature was 10 degrees cooler and air temperature 6 degrees cooler under trees compared with out in the open, and that was with fairly sparse canopies.
That's why they cut the last tree in their paddock down, stops the sheep from siding with your theory every time the sun's shining. Even huddled together they're still cooler there.
Sydney morning herald weekend edition published the /an answer on p13 (talking bout canopy cover in suberbia) Apparantly 1 tree cools like 10 air conditioners running continuosly
Using the trusty old "TEZZA" method of shadows under trees or in bare area's.Every tree is different but the difference by using shade/sun outdoor thermometers and 3 years of on/off checking The difference is between 7 and 15 degrees C.... it might not seem much but its a lot on a hot day Cold weather temps proportionally cooler but degree differences arnt as great.. A shady tree is better then a hot house any day, and better then a/c also. Tezza
In the PDM it states: Deep Shade, -10f to -15f degree difference Normal Shade, -5 to -10f degree difference Partial Shade , -1 to -5f degree difference When walking around my property given its heavily wooded nature combined with benches and teirs, I can confirm the PDM estimates.