Friday, November 9, 2012

It's the drip line, people!

A few weeks ago a wrote about how heartened I was to see more and more construction projects with protective fences set up around the drip line of oak trees in order to protect the root zones from soil compaction and grade changes.

Well, the last few construction sites I have seen... not so much.

(Click to enlarge)

Above: Mid-state Fairgrounds, Paso Robles, CA.  Below: Hwy 46 east of Paso Robles.  In both cases California white oak (Quercus lobata) - also called valley oak.

Granted there are mitigating circumstances and the construction crews might be doing the best they can under limiting circumstances.  The tree above is located in a roughly paved parking area and the fence marks the perimeter of the area of bare soil around the tree.  Despite the tough growing conditions this is obviously one heck of a healthy tree.  To some degree the pavement is probably serving the same function as mulch film - holding moisture in the soil.  Rip up the pavement and I guarantee you find a ton of feeder roots immediately beneath it.  So my fear is they are going to do just that:  Rip up the pavement and the feeder roots beneath, the compact the soil in the process of re-paving the area.  I hope I'm wrong.

No matter what, why wouldn't they have put the construction fence at the drip line or beyond?  Answer: Because the Mid-state Fair is in August when it's hot as Hades in Paso Robles and everyone wants to park in the shade.

In the lower photo the tree is on the shoulder of a soon-to-be-widened highway, and a fence, private property and a vineyard lane on the other side.  This photo is taken looking east.  No way you can fence out to the drip line to the north (road) or south (fence/vineyard lane).  And you don't really have to, since the road shoulder and the vineyard lane have probably limited root growth in those directions for years.

But you could, in order to compensate, extend the fenced area east and west to the drip line - or even far beyond the drip line.  There's no law (although sadly there's probably a CalTrans spec) that says tree protection fencing needs to be erected in a circle.  Most of the root growth of this great tree has been going out from the tree to the east and west.  Why not protect those roots from construction damage?

I keep a mental catalog of at-risk construction site oaks and follow them for years to see how they fare post construction.  I'll keep watching these in the years ahead.

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