Attachment_11,_Shaw_-_Tree_Protection_Report_11.27.18.pdf

Site-Specific Tree Protection Plan for Shaw Memorial Restoration Project.

Normand Helie 11.27.18

Historical Significance

The English elm trees at the Shaw memorial on the Boston Common are old. These old trees had retrenchment pruning done in 2013. The final cross cut section taken 40 feet in height, from this 2013 pruning, shows the annual ring count. The age, of this cut, is estimated at 200 years old. Each pushpin represents ten years of growth from the center of the tree to the bark.

These trees can survive another 200 years or more. Care for these old trees is essential for their survival during and after construction. However, one caveat is that the growth and development of old trees is poorly understood. There is little research done on old trees. It is rare for trees to reach this age in an urban environment. Old trees are very rare even in our New England forests. Site improvement disturbance prematurely kills most old trees.

These mature trees were connected to the sculpture by the artist. This gives these trees great historical significance in this setting even at this time. The annual rings, shown above, of these Shaw Elms are historical records, records directly tied to the Memorial itself.

Care for these trees

The plan includes pre-construction and post-construction health improvements. These trees have been treated for nutritional deficiencies and at the same time treated for biotic root and trunk stresses. The treatments have been done every 30 days during the growing season this year. This is a pre-construction strategy to treat roots preventively against biotic root stresses.

Care for the tree’s canopy has also initiated modified pollarding techniques to reduce branch decay and at the same time maximize energy captured from the sun. The trees are monitored every other day. The modified pollard pruning cuts promotes both callus and more efficient photosynthetic material.

At this time, the trees’ nutritional status is optimal. Foliar nutrient analysis indicates nourishment in the optimum range for trees (See tissue analysis below). It is only this past year that the tree’s foliage was damaged due to excessive salt used during the winter months.

However, this sodium salt damage occurred during a hand irrigation event in August. The sodium salt resides between the bricks of the monument in the standing area. Care must be taken to prevent this salt material from contaminating the soil below. The demolition of the walk should be done only during dry periods. The soil surface below should be vacuumed during this process. A commercial wet dry vacuum shall be used to retrieve all surface contamination from daily operations.

It is well documented that organic matter will bind most organic and inorganic toxic materials that are generated during this demolition and the restoration process. Once the demolition work is done, the old pre-existing mulch layer should be removed. A new layer of compost shall be installed over the entire root zone of these trees. This mulch will be here for the remaining time of the restoration project. If the mulch becomes contaminated then portions or whole mulch replacement shall be done. If only the surface becomes contaminated then the surface should be vacuumed and replaced with a fresh compost layer. At the end of the project remove and replace all of this compost mulch.

Additionally, the present band is constricting growth of these old trees. Placement of new metal rings to surround these trees at the brick surface, leaving 3 to 4 inches of air space around the entire tree trunk will be required.

Excavation and Soil Disturbance

The soil volume and surface area exposed to the atmosphere for these trees are extremely limited. The roots growing in this soil are highly susceptible to damage from all excavation.

Even small excavations can damage roots that support water and mineral movement up into the tree. Old trees have large roots but, rely more heavily on fine absorbing root systems for nourishment. These fine roots are very important for the tree’s survival. An arborist shall be present for all excavation and soil disturbance work. All excavations shall be hand dug carefully with minimal soil disturbance. A vacuum shall be used to aid in loose soil removal.

During all ground work soil mats should cover the mulched surface. These mats will prevent soil compaction from foot traffic during the renovation. The mats should be cleaned with a vacuum prior to their removal.

If large roots are encountered the arborist shall stop the project and document the root health and condition. If a root obstructs an essential construction step, it can be pruned to accommodate the work with the same tools and technique for pruning branches. This root pruning should be documented. Notes on health, size, and proximity to tree are important.

It is important to stress the significance of fine root development of old trees. Old trees do not produce large volumes of secondary growth from the vascular meristem. Instead, the meristem production of secondary growth in large roots is almost negligible. They use and reuse older roots in water and mineral movement. The central core of the primary root is functioning physiologically in old roots. Larger roots are supported by a well develop fine root system. In this restricted rooting zone all roots, big or small are critical. Careful soil excavation and disturbance is essential. For old trees this is hallowed ground.

Disease and Insect Management

Root stress treatments will continue every thirty days. In addition, these trees shall be treated for insects and borers this coming year with applications done in mid-July. This single insect prevention treatment is sufficient for the time of the restoration project and the overlapping time (August) of primary insect attack. Long term goals include treating these trees for cambium dwelling pests every other year.

Soils and Water Management

The restrictive soil surface and volume has unique but, somewhat hidden features of soil physics, chemistry, and biology. It is believed to be a protective vault that has adequate water permeability and drainage.

This soil is a textural sand and silt mixture which has a low cation exchange capacity. Under natural conditions, sands and silts do not contribute to water and nourishment that big shade trees need to grow. However, in the case of these Shaw Elms, nourishment found in the foliage today is due to repetitive, site specific treatments combined with anti-fungal treatments. (See attached foliar analysis reports) No further fertilization is advised for these trees because the surface applied compost is sufficient.

To help these trees during extreme dry conditions in July and August the soil should be treated with sufficient water and natural wetting agents. These treatments should be done as needed during the restoration process.

Although the original biotic life of this soil is unknown, beneficial bacteria and fungi have been introduced over the past three years. The compost applied during the final stages of restoration will provide habitat and nourishment for their survival.

In Conclusion

It cannot be stressed enough the importance, the historic value, these trees have in relation to the Shaw 54th Memorial. All work must proceed in a manner suited to the understanding of the value in the protection of these trees during construction.