Turns out the trees of Maui are taller than previously thought.
In fact, a new effort to map the height of the island’s forests reveals that a stretch of midlevel trees, covering about 1,000 acres in windward East Maui, are twice as tall as they were previously thought to be. That puts the height of the forest in those areas soaring up to 130 feet.
Overall, Maui forest trees previously thought to range in size from 33 to 66 feet were found to be 3 to 16 feet taller on average.
The information comes from the newly published 30-meter Maui Forest Height Map by a research team led by Qi Chen, a University of Hawaii at Manoa geography professor in the College of Social Sciences.
The fact that Maui’s trees are taller challenges past assumptions about the island’s forests and suggests they may be more resilient in the face of climate change.
Their greater stature, Chen said, also could demand a reexamination of environmental resource management across the island.
Chen’s groundbreaking work utilized remote sensing technology (airborne lidar) as reference data to train models based on satellite imagery, surpassing the accuracy of traditional mapping methods.
Then, like doctors examining an X-ray, the researchers analyzed the colors and values of each pixel in satellite and lidar imagery to estimate the height of trees at various locations.
Calculating the horizontal spread of forests is relatively simple, but determining their vertical height has been an ongoing challenge.
“It’s hard to measure every single tree in any forest,” Chen said.
A handful of federal agencies joined the Nature Conservancy in hiring a firm to measure the height of Hawaii’s forests about 10 years ago, but technology that required cloudless days forced the effort to be abandoned after a few months, leaving a knowledge gap about the forest, he said.
Chen, an expert on remote sensing who joined the UH faculty in 2007, said the latest height estimates for Maui’s forests have significant implications for determining the impact of the forest on the environment.
“The revised height estimates for Maui forests will help enhance the accuracy of calculations for factors like evapotranspiration, wind speed and carbon sequestration rates,” Chen said, adding that it also will help in the development of more precise ecological models.
Accurate information about forest height is important for a number of reasons.
Taller trees, in general, offer greater ecosystem services, affecting everything from water yield to carbon sequestration and wildlife habitat, Chen said.
Taller trees capture more water from the clouds. That fact, he said, could offer additional data to accurately evaluate the upstream freshwater yield, which is a crucial consideration for town planning in watersheds like Lahaina.
Forests with diverse heights also tend to support more biodiversity and are thus healthier and more resilient.
“Smaller trees don’t host as many insects and animals,” he said.
Larger trees also can capture more carbon in the atmosphere and are better at combating climate change.
The Maui Forest Height Map is an extension of a similar map developed for Oahu and released in 2021. The research team plans to expand its efforts, with maps of Kauai and Hawaii island expected in 2024 and 2025, respectively.
The project has received funding of $119,500 since 2019, with $23,500 allocated for the Maui Forest Height Map, from the U.S. Geological Survey through AmericaView.
The Maui Forest Height Map can be found online at hawaiiview.org/data/l2fhm-maui.
