From the earliest chapter of his career as an urban forester
in the northern Kentucky community of Anchorage, Jack Rowe still recalls the earnest
older couple who chose a patch of land under the bountiful shade of two stately
white oaks to build their dream home.
Within only a few years, those stately oaks were dead. The culprit? A water line that the
contracting plumber had chosen to run between the trees during the home’s
For Rowe, an Alabama Cooperative Extension System community
forestry agent, and his colleague, Extension forestry agent Beau Brodbeck, it
is one of the hard lessons of their profession: building construction and trees
often don’t mix well. And, literally
speaking, there is a root cause behind all of this, namely tree roots.
As one of the great sages of urban forestry, Allan Siewart
once stressed: “As go the roots, so go the trees.”
By their nature, roots aren't fragile, Rowe says. But they are
intimately bound up with the soil. And if
the soil becomes poisoned or compacted, roots may suffer, sometimes terribly.
“Trees can take a lot, but if you take away the roots,
things begin to happen,” Rowe says, adding that if the root system isn’t up to
the task of servicing the tree with adequate moisture and nutrients, the tree ultimately
Unfortunately for trees — and the growing number of aspiring
homeowners who are choosing to build under lush tree canopies — there is a
powerful countervailing force working against all of this: human nature.
On sweltering hot days common in the South, shade trees function
like magnets to construction workers — small wonder why, considering that
canopies not only provide cooler places to work but also to park construction
vehicles and equipment.
Three years ago, Rowe and Brodbeck determined get to the —
well, the root of this problem both literally and figuratively.
Virtually every community forester can attest to potentially
harmful effects of construction on trees, but until now, there has been little hard
data to support this, only anecdotal accounts — the sorts Rowe and Brodbeck
have collected through years of experience.
The last study to assess the effects of construction-related
compaction on trees was conducted by the University of California-Davis way
back in 1986. And, as Brodbeck stresses,
this study focused on soil types that are not prevalent in the Deep South.
With funding from the Alabama Urban Forestry Association,
the two foresters not only set out to determine how heavy equipment affected
trees but also the most effective ways to mitigate it. They enlisted the help of researcher Dr.
Francisco Arriaga at the U.S. Department of Agriculture’s National SoilDynamics Lab at Auburn University.
Working closely with Arriaga, the two foresters gauged the different
effects of soil compaction on roots using a large flat-bed truck bearing various
weights. They also investigated
materials that could be used to mitigate the effects of compaction.
The results of the study surprised both of them.
“We learned that just using mulch piled 8 inches deep and
covered with 3/4-inch plywood does wonders in helping distribute the weight of
the vehicle,” Brodbeck says.
The two foresters and Arriaga compiled the results of the
study in a new Alabama Extension publication titled “Raising Trees: Guide toPreventing Soil Compaction during Construction.”
The new publication essentially is grounded on the premise
that “an ounce of prevention is worth a pound of cure.”
“If you really want to protect your trees, it’s important to
start from the beginning by fencing off the critical root zones, or, in cases where
this is not possible, providing effective protection,” Brodbeck says.
“Without this sort of advanced planning, you’re essentially playing
Russian roulette with your trees — and always remember that prevention is a lot
less expensive than mitigating roots that already have been damaged.”
Only a few passes of heavy equipment over a tree’s root
system brings immense stress to the tree.
In fact, it only takes about three passes for considerable
soil compaction to occur — enough to prevent sufficient amounts of air and water
from reaching the root system, says Rowe, adding that even one pass of heavy
equipment has the potential to cause considerable compaction.
With more prospective home buyers gravitating toward shaded
lots for a number of reasons, aesthetics and energy savings, to name only a
couple, the stakes have never been higher for buyer and home builder alike.
Rowe and Brodbeck hope the results of the study will aid
them in their ongoing training efforts to help architects and building
contractors gain a better appreciation for what can be done to mitigate the
effects of construction on trees.
“I’ve never known any builder who sets out to mistreat
trees,” Rowe says. “All of them want to build cool neighborhoods with trees
serving as an integral part in them.”
“But the more they know in advance about reducing the risk
of root damage, the better for them and for the homeowner, who is typically
left to pay the bill after these trees begin exhibiting stress months or even
years down the road.”