Is my Tree an Air-conditioner?


Yes! Every plant acts as a conditioner of the air surrounding that plant. You might think trees cool you off when you stand in their shade, because they block the direct sun.  You’d be right, of course. Scientifically, that is the tree acting as a big umbrella.

But another significant benefit of the tree in your yard or by your sidewalk is through evapotranspiration (ET). To scientists, evapotranspiration is the sum of evaporation and plant transpiration from the Earth’s land surface to atmosphere.

To the rest of us, ET means that our tree’s breathing is constantly pumping moisture into the air through its leaves.  As it evaporates, this water cools the air.

Depending on many factors, research on green roofs suggests that energy use for cooling in suburban and urban buildings and neighborhoods can be reduced by 10-25% or more if the area has relatively abundant trees.

“The benefits of evapotranspiration are huge!” says Simon Gruber, “Trees lower the air temperature all around them.  Your neighborhood’s trees help you whether or not their shade ever touches your property.”

ET is the reason that the air in the shade of a big market umbrella–while cooler than without the umbrella–will generally be warmer than the shade under a tree of the same diameter.

Gruber works on studying and developing green infrastructure here in the Hudson Valley, with a long time focus on the links to water quality.

“The shading value of trees is widely known, but many people don’t understand the additional cooling benefits they provide from evapotranspiration,” notes Gruber, “and well-placed, healthy trees can capture large amounts of rain during storms, reducing stormwater run-off  as well.  In addition to keeping streams healthy and protecting water quality, this reduces energy used when runoff flows to wastewater plants that have to process it.”

Now that the trees are leafing out in our neighborhood, I took a quick walk around to test out LeafSnap, one of my favorite phone apps.


Do you want to know what specific kind of trees you see that have those beautiful flowers or leaves? Take a photo of one leaf, and LeafSnap serves up all the possible species that leaf’s shape might be.

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