Trees fight flooding. Houston needs a lot more.

When cities have healthy trees, they have healthy people.

The universal need for nature is evidenced across all cultures and demographics. Study after study demonstrates the positive effect of trees on every aspect of human emotional and physical health, including obesity and asthma.

One can, and should, think of our city's trees as forest therapy.

As much as trees do for our health, they make just as much sense when thought of as living infrastructure. They act as sound walls, water and air filters, and shade structures. They reduce cooling bills, slow down floodwater, fight erosion, make our summer streets more walkable and increase our property values.

That's why every city should look to plant as many trees as they can – and that is especially true in Houston.

Because, as living infrastructure, trees also positively impact the severity of flooding. How? Though most of us know that soil stores stormwater, the soil surrounding trees tends to be more permeable, soaking up and holding even more water.

Other studies have shown that a decrease of up to 20 percent in maximum flood levels can be achieved by foresting 30 percent of retention space, or catchments.

In other words, if you turn a third of the grass of the catchment into a forest, your flood becomes 20 percent less severe.

In this scenario, Buffalo Bayou Park, which saw a peak flood of about 38 feet, would have crested at about 30 feet – that eight-foot difference could have saved hundreds of homes from flood damage.

LIVING INFRASTRUCTURE: What wildflowers do for our cities

Additionally, the canopies of mature trees act as umbrellas. Every large shade tree will deflect and slow down thousands of gallons of water during a rain event, delaying water from entering catchments.

Multiplied by the millions of trees in the Houston area, interception can play a significant role in stormwater management.

Deflecting and slowing the flow of water greatly reduces the amount of sediment. Less sediment and debris means our main bayous and creeks can be more efficient and will require less maintenance over time. Finally, excess floodwaters are slowed by the forest in this process, allowing for more time in which the bayous, creeks and catchments can process the flood event.

The picture is clear: Trees make sound economic sense as affordable, sustainable infrastructure choices, not just pretty amendments.

Trees, in a wild or natural setting, will by and large take care of themselves. In the city, however – even in our greenspaces – trees don't readily reproduce in a healthy, balanced manner.

Street trees in particular face many challenges that their wild cousins in greenspaces do not. Poor soils, higher ambient temperatures, toxic runoff and airborne pollutants all take a much larger toll on them, which often require different species and planting techniques.

STORMWATER MANAGEMENT: Twelve steps Houston can take to address our flooding problem

Trees For Houston, the organization for which I am executive director, works with a wide variety of groups across the area, including the City of Houston and the Houston Parks Board, to plant about 20,000 trees every year in the greater Houston area. But we'd need to plant another 80,000 or so every single year just to keep up with the estimated annual loss from both natural and manmade causes. And we need to.

We want to.

It's clear that trees matter and matter greatly. From beautifying our environment to mitigating stormwater, trees are important, especially in an ever-developing urban landscape.

They don't simply line our streets; they line the road to our sense of place. Our neighborhoods, streets and parks are folded into us as part of our identity, and when our streets are barren and parks denuded, the quality of all of our lives goes down.

Barry Ward is the executive director of Trees for Houston.

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