Arborists are faced with many challenges in their everyday work. Wild storms are a part of it. This month Guy Meilleur takes us to Puerto Rico to have a look into tropical tree care and landscape restoration in the aftermath of hurricanes Irma and Maria.
WORDS AND IMAGES | GUY MEILLEUR
September 5, 2017: Hurricane Irma, packing winds of 185 miles an hour, blasted the peaceful island of Puerto Rico. The stunned staff at the Dona Ines Arboretum at the Luis Munoz Marin Foundation in San Juan pulled the fallen trees back up and staked them. With their garden stabilised, the arborists boarded a boat and delivered 2,000kg of supplies to colleagues 75 miles away in the Virgin Islands. Then they heard the weather forecast, and steamed back home in a hurry. September 20, 2017: Hurricane Maria, a Category 4 storm packing sustained winds of 155 miles an hour, hit the southeastern tip of Puerto Rico. Over the next day and a half, it crawled across the island. This slow storm tore up the repairs from Irma’s damage, and destroyed a whole lot more. These tag-teaming sisters devastated the green infrastructure in Puerto Rico as well as the gray. This article will describe some of the challenges and opportunities faced by Tropical Tree Experts LLC during three weeks of restoration work at the prime collection of native and regionally adapted trees in Puerto Rico. The governing board at the Arboretum did not want a total clean-up of all damaged material. Instead we were asked to retain as much of the natural ecology as possible, and restore as much tree value as we could. To meet this objective, we had to get beyond the shock and awe of the devastation. Based on our experience after other storms, we followed an asset-based systematic process for triage, salvage, repair, and restoration of the landscape. From roots to trunks to branches and back to roots, this process involved arboriculture not often practiced in formal gardens.
Salvaging some of the beautiful wood in the totally uprooted trees for timber came first. Some of the upturned stumps were integrated into the landscape, and used for supporting newly planted trees. Partially uprooted trees were pruned and propped, where practical. If there was still life in the roots and trunk, the tree was reduced back to healthy tissue. Reducing back to ground level and managing the sprouts (coppicing) was a last resort.
In all cases, we tried to remove competing growth out to the dripline, and apply up to 6” of the coarse woody debris that covered this once-pristine public garden. Sections of fallen trunks and branches were used to control erosion and rebuild the soil resource. They were placed in contact with the ground where possible, to speed nutrient recycling in the humid tropical climate.
“From roots to trunks to branches and back to roots, this process involved arboriculture not often practiced in formal gardens.
The branches of some partially uprooted trees were also pressed to the earth, but with a very different objective. One large tree near a sidewalk was blown over, but most of its roots remained intact. It had branches laying on the other side, so we tried “layering” – forcing the branches to grow new roots. Typically, the bark is scraped off first, so the pluripotent “stem cells” in the cambium are provided with the right conditions to sprout roots. Then the areas were covered with more of the copious coarse woody debris as mulch. This root growth will sustain an archway that provides visitors welcome shade, and a compelling feature to enjoy in the years to come.
Bending branches is more successful with Ficus sp. than other species. Too much torque constricts circulation. Some bending can be tolerated, and branches can be pinned to the ground. Landscape staples work for smaller branches, while rocks were used to stabilise bigger limbs. Extended branches were pruned to allow pedestrian clearance and lessen sway, and further stabilised with props cut from fallen branches. Creating archways out of fallen trees was one way to add valuable features to the landscape, but other strategies were employed to conserve tree value.
After the timber salvage, 1”-2” diameter branches with suitable forks were cut into lengths for props. Branches that size with special character were fashioned into walking sticks. Other ideas for salvaging assets from debris are still being developed. 4”-6” diameter limbs with attractive colour and grain patterns were sliced 1” thick, for sale as coasters to hold drinks like “mojito”, the popular rum-limemint concoction. Conservation activities in Puerto Rico are funded by a tax on rum, another worthy reason to imbibe!
Props “are rigid structures installed between the ground and a branch or trunk to provide support from below.” We used props to maintain clearance for pedestrians, and reduce the potential for further tree failure. Propping is much more common in Asia than in “western” cultures – which includes Australia! It may be an aesthetic mindset, to want to see a tree stand on its own. When propping is not considered, it’s a missed opportunity to create something special. As AS4373 is revised (it has been over ten years after all), a section on support and propping should be included.
Standing trees sustained branch losses ranging from major to extreme. Triage on the tree crowns was possible by focusing not on what remained, but on what was gone. Artificial (and unsupported) guidelines like “Consider removal if 50 per cent or more of the branches are broken”, or “Avoid heading cuts” would have made our work impossible. Instead, we applied lessons learned after ice storms, and from Dr. Alex Shigo: “…proper crown reduction is done at nodes… a node (has) buds”.
Avoiding decay is another good reason for nodal pruning. Large wounds on trunks are motorways for decay-causing fungi and bacteria racing into the heart of the tree. Many nodes contain dormant buds that have waited in the cambium as the tree grew. Endocormic growth from these buds is well nourished, and unlike epicormic growth, well anchored. Nodes are indicated by wrinkles and bulges. Wrinkles on some branches resemble collars, indicating branch protection zones. Cuts just beyond bulges left smaller wounds, and retained more symmetry and structure. We lightly reduced some of the load from the undamaged limbs, so they experienced less stress and strain.
Sprouting is a natural response when storms upset the balance between roots and canopy. The more the tree loses, the greater the imbalance and the greater the sprouting. No follow up pruning is needed until the sprouting slows. Over time, the dominant sprouts can be trained to become permanent branches, by removing branch sections that have failed to sprout well, or with rapidly advancing decay, codominants with included bark, and sprouts that are not forming a buttress, or are declining or dead. Branches reduced to buds after Hurricane Fran in 1996 were loudly criticised as “stubs”, but they now have not one, but two or three strongly attached branch ends to carry on. What at first looked ugly grew into attractive, safe, and symmetrical portions of valuable tree canopy. It’s high time for the anti-topping passion to chill, so we can Give Trees a Chance.
Interpreting these strategies with signage, video, and other media is underway, so visitors can appreciate not only the devastation from nature, but the renewal that happens when people work with nature. We are still learning about arboricultural treatments that repair landscapes, and prepare them for the next, inevitable storm.
Please write to The Australian Arbor Age and/or contact the Tropical Tree Experts Facebook page with feedbacks and any suggestions that you might have.