I would just like to start collecting numbers. Good ole anecdotal information. On a hot day, just put a thermometer in the sun and another thermometer under a tree. What are the temperatures?
Further, I would like to hear about REALLY BIG TREES.
There was one time I was standing in the sun and it felt like it was 90. And then when I went under a really huge tree, I guessed it might be 18 to 20 degrees cooler. I'm hoping that some people with really giant trees might measure this. Or maybe go to a park and measure this. Maybe even send in a picture of the giant tree.
I remember as kids, one of our favorite mid-summer hangouts was under a giant weeping willow.
It was huge - drip line was probably a 20+ foot radius.
The creek was usually dry by that time of year, but it was like going into an air-conditioned building.
The ground [and maybe even the mass of the trunk of the tree] is cooler because the shade is more intense for a longer time during the day. So the temperature of the shaded 'microsite' will be lower. You could determine this by measuring the soil temperature or laying in the grass on a hot day and measuring nap length, relative to ambient temperature Ground cover plants and soil moisture will matter too. btw soil temp means everything to lots of plants.
I've heard that a large shade tree cools as much air as forty window air conditioners. The trouble is that if you have high humidity like we get here in Missouri then the effect is minimized a bunch. Even the air misters end up just making you more miserable.
it doesn't get hot enough here or we sometimes get a heat wave for a few days. if that happens I will go looking for good trees to use for this experiment but mostly i am in a fairly dense forest it is hard to find trees that are not close to other trees.
There is a huge copper beech just around the corner from my small urban site. I will take a tape measure, too, and measure the girth of this gigantic tree. I wouldn't know how to get the whole thing into one frame, but I'll try. Trees are marvelous creatures and are to be nurtured. Without them we would be gone. Ever read the Easter Island story in Jared Diamond's Collapse? Here he is in a 2003 TED talk where in addition to trees, he even mentions Montana. http://www.ted.com/talks/jared_diamond_on_why_societies_collapse
Furthering Permaculture next to Lake Ontario.
I will have to get some actual numbers to prove it but I know that the "grove" of 4 pecan trees (the largest is easily 50-60 ft tall) plus a few dogwoods, a camellia, and some bushes produce an ambient temperature easily 10F lower than outside the grove...even in high humidity. I live on the southeast coast of NC and I have small livestock, including rabbits which are very temperature sensitive. Last year, when the first over 90 day hit, I was not forewarned that it was going to get that hot. When I learned it was 90+ outside, I rushed home to check the rabbits. As soon as I got there and stepped into the shade of the pecans...I knew I need not have worried. It was nice and a nice breeze was blowing that I had not noticed outside the shade.
I am planning to plant a good many more trees, and understory trees to further this effect to the rest of my half-acre property.
Yep, it would be very interesting to see the actually temperature and humidity readings between the grove and outside the grove...
http://notquitethereyethomestead.blogspot.com/ --On the highway going from here to there the question is oft asked "are we there yet". The oft given answer is "not quite yet". So it goes with life and with my little piece of it. This is my story. I get to tell it my way. I hope you enjoy it.
I did some measurements. I can do more measurements if you would like. just let me know.
on 5/28 at 6pm the air temperature in a place with no shade in east texas was 86F and the soil temperature was 80F
Under a small tree the air temperature was 81F and the soil was 70F
under a fairly large tree the air temperature was 83F and the soil temp was 70F
Under a very large tree the air temperature was 80F and the soil temperature was 72F
In a mulched garden the air temp was 84F and the soil temperature was 70F
By a pond the air temperature was 84F and the soil temperature was 80F and the water temperature was 85F
This made me wonder how a pond affects temperature during the winter months, especially soil temperature.
I have just deployed 3 Thermocron data logging thermometers on the farm. One is in full sun at about the same elevation up the slope as a medium size maple tree. The second logger is under the maple at the base, on the west side of the tree. The third thermometer is up the slope a bit under an apple tree at the edge of a wood. These three thermometers will log the temperature every ten minutes 24 hrs a day until I collect the data. They are all synced to the same clock so should be 99.9% close. I have placed them in positions that are out of the wind and away from any late season rolling frost we might yet get. I put them out in the cool of the evening.
I'll leave them go for a week or so and see what sort of results we get. I can post a graph of each thermometer and also a list of temps and the number of times a certain range was hit. I set limits at 32deg and 115deg as outside marks. I doubt either of those temps will be reached, but the thermocron in full sun might get the high temp.
I'm in costal Maine and were finally getting our first real spring days of the year. The high today around here was probably 68 while inland 70 miles it hit 80deg. It's looking to be cool for the next 2 days and then heating up for a high of 75 here on the weekend. I'll check these next week and then re-deploy. They can log for years, as i found out when I forgot about them in an orchard I was studying.......
First weeks results are in and they are interesting.... Not at all what I expected to see.
You'll see in the attached file that the thermochron thermometer in the open recorded temps in the range of 42 to 96 degrees, with 33 temps logged at over 86 degrees.
The thermochron under the maple tree had a range of 42 to 85 degrees with 29 temps 82 to 89 degrees, but none hotter. The really interesting thing is that it was also warmer under the maple during the cooler parts of the day.
A little further up the slope and deeper in the shade of an apple tree, wooded polyculture the temp range is 42 to 81.5--so cooler still. With only 50 temps at the upper range and 211 recorded between 53 & 56--which is 30 more logged than under the maple tree and 35 more then out in the open. And it was slightly warmer in the morning and evening.
So, from this it seems that a tree out in the open or on an edge had a moderating effect of possibly keeping it warmer during cooler periods and cooler during warmer times.
I have re-missioned the data loggers and set them back out. I'll let them go for a longer time to verify these results now that we are finally getting into some hotter weather.