Arborist recommends planting less trees...but make the ones that are planted BIGGER!
Posted on Nov. 1, 2023 / Arboriculture / Subscribe 0
By: Steve Nimz and Ilana Nimz
In the late 1800s to early 1900s, there seemed to be a fascination with planting varieties of large trees in Hawaii. In the 1850s, Prussian physicist Dr. Hillebrand planted what we know today as Foster Botanical Garden, which hosts world-class large-canopy specimen trees. He introduced the Weeping Fig (Ficus benjamina) to Hawaii, which has become a popular wide-canopy tree found across the islands. Jared Smith, former director of the Department of Agriculture Experiment Station, planted the iconic Indian Banyan (Ficus benghalensis) at the Moana Surfrider in 1904. It is hard to imagine that from a seven-foot-tall sapling, he was able to foresee what it would become in over 100 years. The massive baobab tree at the University of Hawaii was planted in the early 1900s by botanist Joseph Rock, and the art building was designed around it. Rock contributed greatly to the greenery of the University’s accredited arboretum, which now hosts many interesting large specimens including sausage trees, Indian Beech, Teak, Bayur, Kou, and Blue Marble. ‘Iolani palace also has a wonderful collection of large-canopy trees, including Kapok. This gorgeous species tree is found at the Department of Agriculture and at Queen’s Hospital as well.
Figure 1. Weeping Fig (Ficus benjamina).
Figure 2. Sausage tree (Kigelia africana).
Figure 3. Kapok tree (Ceiba pentandra).
During this time, a wide variety of large-canopy trees were planted across the Hawaiian Islands. We commonly see large trees like Moreton Bay figs, Chinese banyan, mahogany trees, monkeypods, and earpods throughout the urban environment. Several of these historic trees are now on the Exceptional Tree List of the county in which they are planted. The Exceptional Tree List recognizes the unique characteristics of each tree or grove of trees, such as their size, historic status, and aesthetic qualities. County ordinance protects trees on the Exceptional Tree List from damage and removal. Not all large or interesting trees are deemed Exceptional. Each tree is reviewed by the Mayor’s Arborist Advisory Committee and voted on before being submitted to the City Council for acceptance into the protection ordinance.
Figure 4. Moreton Bay Fig (Ficus macrophylla).
Figure 5. Mahogany tree (Swietenia sp.)
Nowadays, except for monkeypods, a diversity of large-canopy trees is not commonly planted. While monkeypod trees are aesthetically beautiful, planting only this species leads to a monoculture of large-canopy trees. There is a history of concerns over monoculture across the world and within Hawaii. Locally, the Erythrina gall wasp (Quadrastichus erythrinae) caused devastating losses of coral tree species before a natural enemy wasp (Eurytoma erythrinae) was introduced. The Erythrina trees, including the native wiliwili are still negatively impacted by the gall wasp. The Ficus stem gall wasp, which lays eggs in the stems of Chinese Banyan trees, is presently causing the significant decline and loss of many of these large and impressive trees. Coconut rhinoceros beetle is impacting many varieties of palm trees. As of now, coconut, royal, and loulu palms are apparently impacted more than other species. Monkeypod trees are presently considered to be hardy and tolerant trees, with minimal insect problems, but Hawaii is only one pest introduction away from losing its dominant large-canopy trees. Relying on one species of large canopy tree is not a suitable plan for the future treescape of Hawaii.
One large canopy tree (i.e. monkeypod, earpod or ficus) is approximate to the canopy cover of 15-30 medium-sized trees (i.e. shower, tabebuia, or hong-kong orchid trees). Instead of planting more trees, consider a single, well-placed canopy tree in the landscape. The benefits of a large canopy tree are numerous.
I. Environmental Benefits
A well-placed large-canopy tree can help cool an area drastically, which is beneficial in an urban setting. This contributes to energy savings for adjacent buildings, shade for parking lots, reduction of storm-water runoff, and atmospheric carbon reduction.
II. Maintenance
Planting a large-canopy tree can have maintenance benefits as well. Only one sufficient planting space is required, rather than up to 30. This means fewer trees to maintain and lower maintenance costs for pruning, irrigation, and leaf litter management while receiving the benefits of many trees. Planting one tree also reduces the extent of infrastructure damage from roots by concentrating it in one area.
III. Social & Economic
Large trees are providers of economic benefits as well. Large trees can increase property values and aesthetics. They also create gathering areas that benefit nearby businesses and facilitate communities. Large trees are also muses, inspiring awe, and creativity.
While there is still a place for smaller canopy trees in the landscape, and smaller trees should still be integrated into landscape plans, a diverse array of large trees are so much more valuable and necessary. Developers and designers should plan for large-canopy trees in each new development, by designing a sufficient space for a large-canopy tree to reach its full size and provide numerous benefits. Increasing the diversity of species available would help to incentivize new projects to include these large trees into landscape designs. There are many native and Polynesian Introduced trees that could be candidates for large urban trees, including Kou, Manele, Kamani, Ulu and Koa. Our local botanical garden and arboretum specimen trees are also a good place to start with understanding which introduced trees would work well in Hawaii. Additionally, looking at landscape trees in tropical America and Asia can help diversify the planting pallet. Trees that are salt-tolerant, drought-tolerant, and non-invasive are good characteristics to consider, as climate change will surely impact our treescape.
Now is the time to plant the Exceptional Trees of the future and provide for large trees in our future urban tree canopy.
Steve Nimz and Ilana Nimz are a father-daughter team at Tree Solutions Hawaii, a consulting arborist company.
0 Comments