Our lives are going to become more local. Perhaps we should start to pay attention to what "here" looks like, feels like, and can provide; pay attention to whether the places we live are places worth living. Trees help cool an area, cut electricity use and cost, and soothe the eye - all while providing the benefits mentioned above.
One of the easily anticipated effects of an unraveling economy and a declining supply of oil is a need for cheaper modes of transportation, namely biking and walking. If we are to transform our urban areas to be walkable and bikeable, we will need to make them more pleasant than the baked scrubby Bermuda strips that now predominate (in Oklahoma City, anyway). A helpful, but perhaps overlooked, way to encourage pedestrian transport is to plant trees.
Trees not only provide shade, but in groups and clusters, they cool an area down. The difference between walking down a shadeless street vs. a shady street in 100+ degree heat can be more than 10 degrees - the difference between walking and staying at home, in my experience. Various sources estimate that trees shading a home can cut air-conditioning costs by 30-50%, which will also decrease the strain on our aging electrical grid.
When air-conditioning becomes unaffordable (or electricity becomes unreliable), shade from trees could make a place bearable. And shade is not just a matter of comfort, as many people (elderly, infants, people with health issues) can suffer from heat distress, and even death from heat stroke in extreme cases.
Not only are trees useful, but they are beautiful. Their green soothes the eye. Their spring blossoms remind us that winter's harsh reign is almost ended, and their multi-colored fall leaves remind us that the baking heat of summer is over. We will need beautiful places to live once we can't escape to info-tainment all day long and a seaside/mountainside/forested vacation several times a year.
Any one of these reasons should be enough, but all of them together make planting urban trees, food forests, and managed woodlots an important part of any resiliency effort. Trees aren't a cliche - they are a keystone of the environment, and therefore, our future. Since trees take many years to reach maturity, we need to plant a variety of fruit, nut, and shade trees now, wherever we can feasibly and safely do so. For food security, for heat in the winter and shade in the summer, for income, taste and nutrition, for a place worth living, plant a tree this fall.