Wednesday, September 9, 2015


Swales are surface water detention "ponds".   They are usually on the downhill side of an expanse of parking lot.  The main purpose of these "ponds" is to buffer natural surface water from the shock of hot, polluted water streaming off hot asphalt directly into the nearest stream.

In many cases these swales are dry except for when a significant rain occurs.

Willows at the bottom.  Brome grass up the side.  One indicative of standing water, the other of drought stress.
Typically, swales are fenced because they are steep sided and constitute an "attractive nuisance".
This is a photo looking diagonally across the bottom of a swale.  The bottom of this one is normally dry.
This one has a wet bottom.
The steepness of the sides offers an opportunity.

From May Theilgaard Watts, Reading the Landscape of America.  Changes in moisture retention and the thinning surface duff causes a change in the climax community as one approaches the lip of a canyon.
The south-facing side of a steep canyon (the north side) will receive much more sun exposure than the north-facing side.  The south-facing side will have vegetation similar to Arkansas while the north-facing side will have vegetation communities similar to Ontario.
In a similar way, the west-facing side will be more exposed to the drying action of the wind and the higher ambient temperatures of the blasting, afternoon sun.  It will have vegetation communities that are similar to those found 400 miles west of the site. 

The east-facing slopes will be sheltered from the direct wind and will be kissed by the gentle morning sun.  They will have plant communities reminiscent of places 400 miles to the East.

So it is with swales:  An opportunity to create four unique ecosystems that are disjunct communities that encompass +/- 400 miles in any direction....all within a few hundred yards of each other.

But that is not all

One consequence of habitat fragmentation is increased risk of inbreeding depression.  It might make sense to have swales specialize.  For example, instead of planting twenty species of trees, plant three species but ensure that the seed sources were far enough away to minimize the risk of inbreeding depression.  (this photo was taken on the grounds of the VFW National Home).

Depending on the bottom, it may be a great way to create islands of genetic diversity of less common floodplain plants.
Artwork by Robert Bateman, a phenomenal artist whose paintings are better than photos. for more information.  Image from HERE 
Swales can also harbor extremely persistent fruited plant species that can feed birds on their northward migration.  Examples include Highbush Cranberry, Bittersweet, Ilex verticillata and some crabapples like White Angel crab....the kind planted at the top of the Northwestern Elementary sledding hill.


  1. Replies
    1. Hello Lucas Machias:

      Thanks for reading. And thanks for taking the time to comment.

  2. Never thought of it that way... Thanks for the education!

  3. Never thought of it that way... Thanks for the education!