Stepping into the shade under a large tree can bring instant relief from the blistering rays of the summer sun. The actual air temperature in the shade may be only marginally lower than in sun, but because the leafy canopy blocks solar radiation your skin is spared that broiled feeling. The interior of your car is also affected by radiational heating in direct sun, which certainly explains why drivers flock to those rare shady spots under trees when parking on streets and in parking lots.
Mature shade trees are both beautiful and useful. Before modern air conditioning was widely available, street trees [pdf] provided some of the only cooling capacity available, especially in urban areas, and trees continue to be valuable for reducing the urban heat island effect and for improving the mental well-being of residents.
Many large tree species make excellent shade trees. With its broad, vase-shaped canopy, American elm [pdf] (Ulmus americana) was once the gold standard, but unfortunately Dutch elm disease wiped out many of these majestic trees. Several disease resistant American elm and hybrid elm cultivars [pdf] have been introduced and elm research continues. Japanese zelkova (Zelkova serrata) is smaller than American elm but has a somewhat similar vase shape and adapts well to a range of growing conditions. Many oaks (Quercus) [pdf], maples (Acer) [pdf], lindens (Tilia), and honeylocusts (Gleditsia) also make excellent shade trees. Shade-seeking visitors [pdf] to the Arboretum will find many magnificent specimens of these and other shade trees.
Whether you live in the city, suburbs, or countryside, do yourself and future generations a favor by planting trees whose shade will be appreciated for decades to come.