On most weekdays, on the slopes and gulches above and below the Hāna Highway, a crew is hacking its way through the forest, spread out in a sweep line. They make slow progress through a mix of non-native and invasive plants: bamboo, inkberry, guava, and white ginger proliferate in this low-elevation forest. Somewhere in the midst of these forests is miconia, another non-native invader. The Hāna-based crew from the Maui Invasive Species Committee is here to find miconia and pull it from the ground.
Miconia may be found across a broad swath of the East Maui Watershed, from Kīpahulu to Huelo, but not as a continuous infestation. Dense pockets occur, especially in the area above Hāna town and in parts of Nāhiku, but elsewhere it’s patchy, thanks to decades of work to suppress and contain the infestation.
Miconia should be an understory plant, as it is in the dark subcanopy of South Central American jungles of its native range. But in Hawaiʻi, open-canopy forests and the absence of significant “natural enemies” allow miconia to become the dominant plant. Invasive plants don’t just crowd out native plants and diminish habitat for native animals; they also can alter the landscape and ecosystem processes. A 2013 study on Hawaiʻi Island, by Kazuki Nanko of the Forestry and Forest Products Research Institute in Japan and University of Hawaiʻi professor Thomas Giambelluca, set out to dig a bit deeper into how miconia affects the ‘aina.
The team examined what happens on the forest floor when miconia takes over. Miconia’s leaves are huge – up to three feet long by two feet wide. These monstrous botanical solar panels help collect light in a dark understory in South America, but in Hawaiʻi they cast a deep shade, reducing the ability of native plants to capture the energy they need to thrive. Their study revealed that the amount of sunlight that reaches the forest floor is consistently lower in a monotypic miconia-invaded forest when compared to a native ʻōhiʻa-dominated forest, or forests invaded by a diverse mixture of plants. Additionally, miconia leaves decompose quickly, reducing the amount of leaf litter.
This study also investigated what happens to raindrops as they hit the forest canopy all the way down to the forest floor.
The giant leaves act like a tarp: water puddles before falling to the ground.
Miconia produces some of the largest leaf throughfall drops ever measured, with cascading impacts.
Unlike our multi-layered ʻōhiʻa forests, with their carpets of ferns and mid-canopy plants, miconia can develop into a one- layer stand. Larger raindrops, unimpeded by understory or leaf litter, gain speed, hitting the ground with greater kinetic energy than rain falling from the sky. Giant raindrops pound and compact bare soil, causing water to travel along the surface instead of filtering into the ground to recharge our aquifers. In some areas of miconia-invaded forest, bare roots and other signs of erosion tell the tale of how miconia is washing away our forest floor.
The scale of the East Maui miconia infestation has demonstrated that this plant is a formidable foe. Current efforts focus on keeping it out of upper elevation forest and preventing it from spreading farther west. Research and testing continue to find safe and effective natural enemies of miconia. Help us keep the raindrops in our forests. If you find a miconia plant on Maui, recognizable by its large green and purple leaves, report it to 643pest.org.
Lissa Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. Kia’i Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy, and quality of life.
This article was originally published in the Maui News on September 12, 2020 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.
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