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An Inside Look at Zoo Arboriculture

By Michelle Sutton

 

Whether they’re in-house or contracted, arborists who work in zoos have to be high-level communicators, coordinating work hour by hour with zookeepers. The tree work has to be done safely and without stressing the animals — yet efficiently, so that the animals are not removed from public view any longer than necessary.

The 43-acre Naples Zoo at Caribbean Gardens in Naples, Florida contracts Davey Tree. Danielle Green, director of gardens and grounds, said, “Scheduling work in a zoo can be very tricky; it requires coordination with nearly every department of the zoo, including guest services, the animal and horticulture departments, and even food service to ensure work can be completed in a timely manner with the least amount of guest and animal disruption. Davey has always been accommodating, even if it means workdays are shortened, lengthened or rescheduled.”

Davey Naples Branch Manager Dan Powell said, “At most job sites, the client clears the way for the arborist. But at the zoo, the arborist’s movements are dictated by the zookeepers in relation to each individual animal.”

Over time, the Davey team has learned a great deal about the animals at Naples Zoo. For example, Powell said that when the crew initially pruned ficus trees away from the giraffe exhibit/habitat perimeter, they thought 24-inch clearance was adequate to keep the giraffes from eating the branches. “But when the zookeepers told us that the giraffes have tongues that are 8 to 10 inches long, we had an ‘a-ha’ moment that we had to cut further back,” he said.

 

Safe and calm  

It can be hard to predict the many ways the animals will interact with the trees in and out of their exhibits. Former longtime Jungle Island (Miami, Fla.) Director of Horticulture Jeff Shimonski recounts when a female orangutan climbed to the top of a structure within her space in an attempt to reach the fronds of an out-of-exhibit palm tree on a very windy day. She stood on the top of a 10-inch-wide pole about 25 feet off the ground and kept trying to grab one of the palm fronds blowing in the wind, and finally, she was successful at pulling in the frond.

“She suddenly shot out of the enclosure like a rocket while fortunately maintaining her grip on the palm,” said Shimonski. “It would have been pretty funny except for the fact that a 10-year-old orangutan was now outside of her exhibit. She seemed scared to death and remained clinging to the palm while those of us below figured out what to do. We finally had to dart her and catch her on a blanket, fireman-style, when she fell from her perch. She was not injured, but I had to cut down two of the palms immediately so she would not escape that way again.”

A lot of things that arborists in the larger world take for granted — such as the ability to run a chain saw — are things zoo arborists must reconsider. Davey Naples Arborist Derek Harris said, “We use hand saws when in the vicinity of the giraffes and around impalas and anteaters, all of whom tend to be nervous.” To avoid using loud trucks to remove pruned branches and other debris from job sites, the Davey team uses the zoo’s quiet golf carts to haul out the bio matter in small batches, and they seldom use noisy chippers. (The downside of this: it takes much longer to extract debris.)

Another consideration is the arborist’s safety — for example, when working in the alligator exhibit, where objects that fall in the water can be considered food by captive gators. Powell said that the use of a 45-foot articulating lift gives them access to trees and shrubs while protecting arborists from carnivorous animals or aggressive animals such as honey badgers. “We do very little manual climbing at the zoo,” said Powell.

Harris has been working at the zoo for seven years, and has found that with repeat visits, he and his cohorts develop respect and fondness for the animals. “I got attached to the big, old male lion who died in late 2014 — even though he didn’t like me much,” said Harris. “He perceived me as a rival dominant male and would pee as close to me as possible to mark his territory.”

 

Creative protection

Green said that the life of a tree in the zoo environment can be tough. “Our trees at the zoo serve many functions: beauty, shade for animals and guests, food for the animals to browse, perching sites for birds, scratching posts for tigers, and ‘furniture’ that encourages animals to explore and be active,” she said. One of the biggest challenges for trees in the zoo is soil compaction from the foot traffic of guests, staff and/or animals, and from construction. “We have used an air-powered excavator at the zoo to reverse soil compaction issues and get fertilization to the root system,” said Green.

In his 40 years at Jungle Island, Shimonski found that when space is limited, as it is in the majority of zoo situations, animals tend to destroy the trees in their exhibits. Assistant Curator of Horticulture for the Toledo, Ohio Zoo Alan Donges said that large animals can damage trees in several ways: by climbing, chewing or rubbing the foliage, bark or limbs (They can also make dens in the root systems).

“We use a number of protective measures to ensure the integrity of our trees based on the animals in the exhibit and the type of damage they are likely to do,” said Donges. “With animals such as gorillas that may climb, break limbs, or feed on foliage, our objective is to keep them at a sufficient distance from the tree to avoid such damage. For this we use a type of electrified wire called ‘hot grass,’ which is more naturalistic in appearance than a standard two-wire electric fence and can be spaced to provide continuous protection.”

Another type of tree protection Donges has used in an exhibit of mixed African hoof stock is chain link fencing. “This was particularly useful for a stand of existing sweet gum trees we left in the exhibit to provide shade to the animals,” he said. To protect the sweet gum trunks, Donges and staff wrapped them with black vinyl-coated chain link to a height of about 8 feet and joined the ends using heavy-duty cable ties. Each year they adjusted the chain link as the trunks grew. These worked well, and over time they were able to remove or reduce the amount of chain link on the trees because the animals came to ignore the trunks of the trees altogether.

Adam Alves is the arborist for the 28-acre Henry Vilas Zoo in Madison, Wis. “We have American bison that love rubbing up against, and trampling, the honey locust trees in their enclosure,” he said. “For the trees that were damaged beyond saving, we removed their crowns to limit any hazard, leaving trunks to provide an opportunity for animal enrichment. The remaining honey locusts had a natural, aesthetically pleasing boulder wall built around them to separate them from the animals.”

Alves said that with the large cats they need to be mindful of their climbing abilities so they don’t get up and out of their enclosures. “We keep trees limbed up high and away from the perimeter of the enclosure,” he said. Alves checks in regularly with zookeepers to understand the abilities of the animals so he can make sure to maintain enough clearance. “We also have to prune trees outside the enclosures to ensure no humans enter the exhibits by climbing trees!”

The Henry Vilas Zoo has a greenhouse/aviary with trees needing intensive pruning at least once a year. “Among them are Norfolk island pines, avocado, ficus trees, and palms — presenting a learning curve for arborists trained in the frozen tundra that is Wisconsin,” said Alves. In the aviary he has to be mindful not to disturb any nesting that may be going on in the trees or underbrush.

Aviary Henry Vilas Zoo

An arborist prunes a tree in the Henry Vilas Zoo aviary. Photo by Adam Alves

“The aviary also presents some operational difficulties, as there are very few drop zones and a number of the trees have limited rooting zones, making some unsafe to climb,” said Alves. “Currently we use scaffolding and ladders where necessary; however, for greater efficiency and safety we are in the process of looking at putting a fall-arrest system into the ceiling to provide extra tie-in points.”

One of the gratifying things for Alves is seeing how what would normally be considered waste wood is used for animal enrichment. He said, “We provide large chunks of oak logs for the rhinos to interact with, platforms for the goats to stand on, hollow logs for the porcupines to traverse, and branches for parrots to perch on. We even save the invasive mulberry brush cut from throughout the County parks as a dietary additive for the giraffes. The animal keepers are extremely imaginative in their applications for reusing all parts of a tree.”

 

Michelle Sutton (michellejudysutton.com) is a horticulturist, writer, and editor.

Main photo (above): Deadwood pruning on Ficus microcarpa between event space, python and panther exhibit, and public pathway at the Naples Zoo at Caribbean Gardens.
Photo by Danielle Green

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