The act of planting a tree comes freighted with symbolism, often equated with any up-against-the-odds endeavour for the common good. It’s also commonly the focus of educational programs meant to reconnect children with the natural world, or community initiatives for improving neighbourhood aesthetics. But planting trees also impacts “livability” in the broader ecological sense.
Collectively, trees around the globe absorb massive amounts of carbon dioxide from the atmosphere to drive their photosynthetic engines. Recent research suggests they constitute a major “carbon sink,” all the more critical as anthropogenic activities add more of this greenhouse gas to the atmosphere. Urban “forests” of planted trees certainly do their part, and are particularly important where native vegetation communities have been decimated. Whatever the specific numbers generated by complex carbon-footprint equations, trees planted in developed areas can be thought of as at least some mitigation for the human-sourced emissions inherent in such a place.
Trees can also help anchor the soil, reducing the ravages of erosion. Bare earth—as exposed by construction work, poor land-use practices, landslides, or other disturbances—is prone to gullying from precipitation and runoff alike. The roots of a planted tree lend some stability to the soil layers, which can be enhanced by any shade-tolerant grasses, herbs, or shrubs propagated, naturally or otherwise, under the canopy. Not only does such vegetation secure soil, but it also buffers the ground from hard-falling precipitation and slows runoff. Planting native shrubs and trees along riparian corridors—the shoulders of streams and rivers—is a particularly excellent way to begin restoring degraded drainages.
In addition, trees impact the immediate microclimate in their vicinity, affecting variables like temperature, precipitation, and wind speed. The shade cast by their canopy can encourage the proliferation of groundcover and understory plants that could not survive in full sun; this promotes greater habitat diversity. A small grove of trees can greatly moderate temperatures near and within its shelter, offering refuge from extremes of blazing summer heat and punishing winter cold. On a plot of land, such a stand might serve as crucial thermal shelter for deer during winter, for example. With its shade and also through fog-drip—the condensation of water vapor upon leaves and twigs—a tree can also increase moisture beneath its crown. Mingled canopies can also reduce and reroute breezes, providing shelter in wind tunnels formed by topography or the layout of city buildings.
A tree functions as habitat for a host of organisms, from bark-living insects to nesting songbirds. Thus a stretch of median or sidewalk strip formerly deficient in wildlife might, with the addition of a few saplings, begin attracting all manner of associated creatures. Using native trees acutely targets fauna indigenous to the region; certain butterflies and moths, for example, depend on specific species of tree in their larval stage. The complexities of the food web ensure, too, that tree-dependent organisms can attract their predators to the area, thereby enriching the local ecology. Even in dense cities, a Cooper’s hawk or peregrine falcon might use the summit of a planted tree as a vantage from which to survey for prey.
In short, the simple effort of planting a tree can dramatically impact your local environment. Keep in mind that using species native to your area—those that evolved in the regional ecosystem over many millennia—tend to provide the most net benefit: They are accustomed to the particular vagaries of the climate (in a semi-arid location, for example, an indigenous tree will likely do just fine, whereas an exotic type might require extensive watering or other energy-intensive management), and come associated with a community of native organisms.