Environmental Insight With a Touch of Real Science
by Don Flora (a real scientist)
Last month’s poem by Alice Wentworth, about lawns, raises questions. Can grass really serve better than shrubs and trees in our buffered places?
In particular (and bearing in mind that landscaped yards and mandated buffers can be complex natural systems):
Does grass deal better with storm water? Yes. Tree trunks and shrubs’ stems don’t stop surface water. Leaf liter helps but doesn’t match grass; grass slows and may even stop storm water.
Do lawns corral erosion? Yes. By slowing storm water and keeping it from forming rills, which merge to erode and carry sediments.
Is grass better at stopping pollutants? Yes. By slowing storm water it limits transport of dissolved pollutants as well as those that cling to sediments. Water-restraining groundcover is scant in clumps of salal, salmonberry, and other shrubs and trees.
What about plant-unfriendly chemicals? This is a “maybe”. No vegetation likes harmful chemicals, Grass, shrubs, and trees have limited capacity for even organic chemistry. In all environments the trick is to use chemicals sparingly, and choose those with short half-lives.
Does grass recharge aquifers better than other buffers? Yes, assuming the soils are identical. The aim here is to slow storm water long enough to infiltrate the soil. This can be a long time in our hardpan (glacial till) areas. Grass works best relative to other vegetation.
Does grass really qualify as “Native vegetation”? For some popular species, yes indeed. Wentworth is right.
Can grass get along with less summer water than trees? Yes, at least in our climate. Perhaps half as much, depending of course on the trees’ size and density. Trees are immense users of water, and unlike lawn watering, you can’t turn off the sylvan spigot.
In summer, does grass sustain stream flows and wetlands better than trees? Yes, because grass holds storm water in place while it soaks in, to gradually work its way down hill to needful waters. Three roots soak up the water, sending it through those massive conduits to the sky. (as water vapor – ed.)
Is there some reason to favor grass in suburban drain fields? Yes. Grass roots behave themselves, while helping to aerate the drain field’s soil. That’s critical for “processing” septic nutrients.
Is grass more fun? Well, trees are great to climb and support tree houses. However, families come here looking forward to an outdoor place for children that offers many options -– swing sets, sand boxes, Radio Flyer wagons, croquet layouts, tent pitches, hoops, nets, hopscotch, et. al. Sadly, in land use planning a children’s place is becoming an after thought.