Having the shade of a canopy tree is greatly appreciated on a sunny day. How often do we think about how long it took that tree to get large enough to provide us with that shade? How long will it continue to live and provide us with shade? While many trees can live to be hundreds of years old, it is not the norm. Think about how many acorns each oak tree produces each fall. Consider how many of those spiny balls fall off each sweet gum tree; those each contained a few dozen seeds. Now think about how many hundred-year-old trees there are where you see those acorns and sweet gum balls. Not very many of those babies make it to old age.
Many of the largest, oldest trees in Charlotte were planted about a hundred years ago. It is not unheard of for trees to live to be a few hundred years old; some trees have been alive for more than a thousand years. But trees growing in an urban, or even suburban, environment have to put up with numerous stressors they would not have in a forest. They are subjected to significant air pollution, light pollution, soil compaction, and reduced water availability. The soil is nothing like what would be found in a forest.
I have two tulip poplar trees in my front yard that are probably around 70 years old. This is relatively old for urban trees. They provide ample and greatly appreciated shade to the house and yard. They’re healthy now, but if I want to maintain a shady house and yard, I need to plan for their replacements now. One might argue that there’s not room in my front yard for more than two large, mature trees. That’s true. But my planning now for the demise of the two current residents doesn’t mean I am going to plant two large trees now. It means I will plant small trees now. Those small trees will grow very slowly for the next decade or two, in the shade of the large poplars which have deep roots, drawing nutrients and water from depths unavailable to the small trees. Then, in a decade or two or three, when the tulip poplars are no longer healthy and come down, I will have a couple of sub-canopy trees that will then be able to quickly take advantage of the extra water, nutrients, and light available to become good shade trees in a handful of years as opposed to my having to wait another 40 years for newly planted trees to grow.