"They Said It Couldn't Be Done" Tree Matrix Helps Plot Course to Save 5 Trees

A large open lot in upper NW Washington, DC was developed to add three large homes where only one home had existed previously.   Large trees remained from the original estate home, most of which were close to 100 years old, or more.  Neighbors rallied against the development saying that all the trees would die.  Other arborists hired by the neighbor’s said that this couldn’t be done.

It is difficult to build large homes near big trees, but Tree Matrix provides the tool to make these difficult situations easier.

The owner/developer was committed to saving these heritage trees.   With the coordination of all subcontractors, and using the Tree Matrix software, most all of the larger trees are alive today roughly 5 years after the initial root pruning.  Only one tree has died and that was only because a landscape contractor cut several support roots near the base during the installation of large screening trees.  This was too much stress for this oak.  Ambrosia beetle overwhelmed it shortly after this damage.

University Terrace Tree 1

Common Catalpa

(Catalpa bignonioides), 54” dbh

This is a beautiful specimen of this tree type. Boundaries to root growth were identified on two sides including a residential driveway to the north and a city road to the east. Root growth was not assumed to be under the driveway to any significant degree because of the ample and good rooting environment in the interior of the lot.

To reduce root loss, the driveway to the new house was ‘floated’ on grade, using piers. The utilities were directional bored into the home so that no trenching was used. Sheeting and shoring was done to reduce foundation footpring.  This greatly minimized root loss.

The survival potential shown by Tree Matrix was 81%. This score suggests a high percentage chance of tree survival and with little post-construction treatments required. The tree is unchanged in condition approximately 5 years after the initial root pruning for the house footprint.

Tree Matrix Score For 54" Catalpa

Street View of 54" Catalpa

University Terrace Tree 6

36" Black Oak

(Quercus velutina), 36” dbh

The structural root zone was bisected by the footprint for the new house. A super-sonic air tool was used to explore for structural roots in this area. No larger roots were found, so sheeting and shoring excavation was conducted. Utilities were added by directional boring versus trenching to reduce root loss.

Unforeseen Impacts to Root System

This tree was doing fine until a landscape contractor cut several large structural roots while installing large screening plants. Excessive new irrigation was also applied. Quite soon afterwards, ambrosia beetles attacked this tree and it died within a month of the invasion. With a survival score of 78%, it was quite likely to have survived if it were not for the additional root loss and excessive irrigation.

Tree Matrix Score For 36" Black Oak

University Terrace Tree 20

38" Tulip Poplar

(Liriodendron tulipifera), 38” dbh

This tree was in Good-Fair condition at the time of root pruning. Root pruning was conducted during the dormant season. The survival score was 68%, which suggests ‘caution’ and that supplemental efforts will be required. For this reason, additional tree care measures were instituted including two applications of a tree growth regulator and three years of insect control. The proposed pool was taken out of the construction package due to the potential for impact. The storm water management feature was also moved to be outside of the critical root zone.

Tree Matrix Score: 68% Indicates Caution

The survival score is 68%, which is in the ‘caution’ range of the tree matrix analytics engine. This is why the additional tree care measures were instituted. The proposed pool was taken out of the construction package due to the potential for impact. The storm water management feature was also moved to be outside of the critical root zone.

Outcome: 5 Years Later

This tree is still alive and doing well, at least 5 years after the initial root pruning.

Tree Matrix Score For 38" Poplar

University Terrace Trees 83 & 84

Eastern white pine

(Pinus strobus), both 24” dbh

This pair of white pines were positioned perfectly to frame the front of this new home. With Tree Matrix, we were able to site the house so that the sheeting and shoring along the front of the home would be just outside of any anticipated structural root zone. Both trees were only in fair condition, so we had to be extra careful when working around them.

Floating Driveway and Walkway

The walkway and driveway were both ‘floated’ above grade, with excavation only into the organic layer, to minimize root loss. A layer of protective and insulating wood chip mulch was added under both, and a pine bark beetle protection program was initiated. Super silt fencing installed above grade (no excavation) was used as tree protection fencing. Approximately 5 years past the initial root pruning, both of these trees are in better condition than when we started. It looks as though this house has been there for 30 years, not just 5!

Tree Matrix Score For 24" Pines

Outcome: 5 Years Later

Survival scores of 72% and 67% respectively were encouraging. Some concern existed with tree #84, but with constant attention to irrigation needs and insect control, both trees survived quite well. Another accurate call by Tree Matrix.

University Terrace Tree 34

43" Black Walnut

This tree was under considerable pressure from the building of two large homes to the west. The Tree Matrix review indicated that large structural roots may be present in the area of the proposed garage. Exploration with a super-sonic air tool did not reveal structural roots in that area. Therefore, construction moved forward as designed. Sheeting and shoring techniques were used to build the garage and the walls of the homes within the critical root zones (shown as the lighter green outer ring).

Floating Driveway and Walkway

The driveway on the lot to the north was floated over grade on pier footings and all utilities were installed using directional boring instead of trenching. Grading was also not allowed within the root save area along the road.

A Tree Matrix survival score of 68% for winter pruning was high enough to justify proceeding with this design. However, because it is in the ‘caution’ zone, a tree growth regulator was applied twice since root pruning occurred, and the tree was regularly treated to control the infestation of wood boring insects. It was also regularly inspected during the critical 3-5 period after root pruning.

Tree Matrix Score For 43" Black Oak

Outcome: 5 Years Later

The tree remains in good condition, at least 5 years following the root pruning. The homeowners are not crazy about the large walnuts hitting their roof, but they love having this tree framing their home!

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