Prune pavements; protect and plant trees
by Mark von Wodtke, FASLA
Prolonged heat waves and more intense rainstorms are likely consequences of climate change.
Our children and grandchildren will find it strange that, faced with climate change, we not only continue using fossil fuels, but also spend billions on asphaltic pavements that need re-topping or slurry sealing every 7 years.
Pavement intensifies urban heat island effects accentuated by climate change. We could mitigate heat islands, and avoid emissions from sealers, by pruning asphaltic pavement and providing more shade trees. Trees, shrubs, green ground covers and healthy soil micro-organisms absorb carbon dioxide, and release oxygen, as well as filter dust. They also absorb and filter runoff from pavements helping to sustain clean groundwater supplies. Instead of nurturing nature and its beneficial services, we typically protect pavements and prune tree roots.
We have it backwards and should rethink paving policies, while protecting and planting trees, as an integral part of sustaining and enhancing our urban forests. Not only will pruning pavements improve the livability of communities, it will also help balance budgets in the long term.
Although asphaltic pavements seem cheap, they are actually expensive over their lifecycle and are becoming increasingly more expensive as the cost of petroleum products increases. Unlike pavers and other permeable pavements, asphaltic pavements need to be continually topped and sealed. Why are we even using the byproducts of tar sands, as well as other low-grade petroleum products, and coal residues? How strange that we slather this slurry throughout our communities—even on school playgrounds. We then breathe the toxins that evaporate. Some toxins also run off into streams and the ocean, and even get into ground water we drink.
In effect, we are creating mini tar sand spills in our communities and paying for it in many ways. We should be divesting from petroleum and coal and not encouraging more of it to be extracted at great cost to the environment.
A better approach, in the long-term, would be to use less pavement—as the Claremont Environmental Design Group (CEDG) did more than 25 years ago when we designed the Meadowood development in Claremont. Only the traffic lanes have asphaltic pavements and, if done today, even those could be permeable pavements with non-asphaltic binders. The parking areas were intended to have concrete pavers, but the developer put in stamped concrete instead. At least concrete doesn’t need slurry seal.
As you can see in the picture, we also created ample planting areas for street trees. In areas where there is insufficient area for street trees, it would make sense to remove pavement around larger established trees. These planters could have irrigation bubblers attached to perforated pipes imbedded vertically into the ground so the trees are watered deeply, decreasing surface roots that conflict with pavement.
Interlocking pavers can be adjusted if there is root uplift or settlement. They can also be taken up and reused if there is a need to access public infrastructure beneath the pavement. Permeable pavements also reduce runoff, allowing more water to percolate into the ground.
Many charming towns in Europe have been using and reusing stone pavers for centuries. New towns in Holland make extensive use of concrete pavers—with attractive colors and textures—for walks, bike paths, parking lots and streets. This is cost-effective, on a lifecycle basis, and doesn’t have hidden environmental costs.
For Claremont to live up to its reputation as being “the City of Trees and PhD’s”—and meet the challenges of climate change—we need to change paving policies. Many communities around the world can do this. It takes local leadership and political will.
Acting locally we can reduce emissions and mitigate some effects of climate change.
Mark von Wodtke is a Fellow of the American Society of Landscape Architects. He is also a Professor Emeritus of Landscape Architecture at Cal Poly Pomona.