Endangered Plants and Hawaiian Forest Evolution
Although Hawai`i is home to many diverse species of plants, it is also known as the endangered species capital of the world (Rare Plant Program, n.d). “Hawai`i has 272 plants considered endangered under the U.S. Endangered Species Act [...]” (Hawaiian Plants, 2023). When the islands were first formed, plants were brought over by birds, wind, and ocean currents. Although they originated elsewhere, those plants are considered native since they came to Hawai`i before people arrived. Many of the native plants are classified as endemic, meaning that they are found only in Hawai`i (Hawaiian Plants, 2023). “This means that after their arrival, as these plants adapted to their new environment, they changed so much from their original ancestors that they transformed into a new species” (Hawaiian Plants, 2023). Because of this, they are sensitive to changes in their environments. Human activity, land development, climate change, and non-native plants and animals have all chipped away at Hawai`i’s ecosystems. But how exactly has the flora and fauna of the islands changed over the years? This article aims to provide an introduction to endangered Hawaiian plants by examining the evolution of Hawaiian forests.
The extreme isolation and unique environment of the Hawaiian islands have fascinated biologists for years. “Hawaiian forests are among the most threatened in the world, largely because of the direct (competition, disease) and indirect (altered nutrient or disturbance regimes) effects of non-native species [...]” (Potter et al., 2023). Like all forests, they remain vulnerable to fragmentation. Fragmentation is when parts of a habitat are destroyed, negatively impacting wildlife (Trust, 2018). This has occurred naturally in Hawai`i due to active volcanoes, hurricanes, and other extreme weather. However, human activity also results in the loss of habitats.
Data shows that Hawaiian forests have gone through various states of stable transition due to the arrival of new species brought over by humans. For example, the Polynesian arrival introduced the forests to the Pacific rat, which led to the collapse of lowland forests (Barton et al., 2021). Although this affected other species that had lived in the lowland forests, forests continued to be dominated by native species for centuries. Polynesian settlers also brought food crops and other plants when they came to Hawai`i, which was necessary for survival as they developed farming practices (Hawaiian Plants, 2023). While ecological changes initially began with the arrival of Indigenous peoples to the islands, the forests remained stable due to their management practices, which promoted connectivity across all species (Barton et al., 2021).
Wao is the term used for inland regions that were often forest areas. These were the regions where most people lived and worked, and there were regions high in the mountains called wao akua. The wao akua was believed to be the realm of the gods and, as such, was highly revered and respected. Since there was limited human activity in these areas, these cloud forest zones provided a refuge for endemic plants to thrive (Barton et al., 2021).
In ancient Hawai`i, the islands were divided into regions called ahupua`a. “The ahupua`a consisted most frequently of a slice of an island that went from the top of the local mountain (volcano) to the shore, often following the boundary of a stream drainage” (Nation of Hawai’i, 2022). These ahupua`a varied in size, and each had their local chief who was in charge of ruling their community. They believed in the interconnectedness of all life, from the sea to the mountains to the clouds, and sought to keep the balance between all things (Nation of Hawai’i, 2022). Each community further divided their land into smaller sections and plots of land, which were used to manage resources. Their agricultural methods consisted of irrigated and rain-fed systems. “In the irrigated systems, the Hawaiians grew mostly taro (kalo), and in the rain-fed systems, they grew mostly `uala (sweet potatoes), yams, and dryland taro in addition to other small crops” (Nation of Hawai’i, 2022). In this way, the Hawaiian people could maintain the resources necessary for a thriving community. However, this way of life began to break down after European influence.
European arrival introduced many diseases and new plant and animal species, triggering declines in native forest species at all elevations. European influence led to the abandonment of Hawaiian farming practices, which, in addition to increasing large-scale agriculture, “[...] led to the rapid loss and degradation of native ecosystems through increasing dominance by non-native plants” (Barton et al., 2021). This process of non-native plants outnumbering native ones continues today.
A comprehensive study was done to assess the trees in Hawaiian forests, and it was found that 56% of Hawai`i’s forests are made up of non-native trees, and 44% are native (Potter et al., 2023). One problem that contributes to this is the lack of native species regeneration. In addition to this, non-native and invasive plants grow much faster than native species. “Native seedlings and saplings, therefore, are likely to be displaced by non-native species, preventing them from replacing native trees in the canopy when these trees eventually die” (Potter et al., 2023). Invasive species in forests often grow aggressively, with some even injecting toxins into the ground to kill nearby plants. Certain trees, such as Miconia, grow tall and form a canopy that overshadows native plants, preventing them from receiving sufficient sunlight (Pono Pacific | Invasive Species, n.d.). Some examples of invasive plants are Albizia trees, miconia, strawberry guava, and fireweed (Hawaii’s Top Ten Invasive, n.d.). Invasive animals also negatively affect the islands by uprooting native plants and spreading diseases through mosquitoes that kill native animals. This, in turn, hurts the forests, as animal and plant life affect each other. However, it is not just invasive species that are dangerous for Hawaiian forests. Rapid ʻŌhiʻa Death (ROD) is a fungal disease that targets ʻōhiʻa trees and kills them by depriving the trees of water. “ʻŌhiʻa is the keystone species in Hawaiian forests, and ROD has the potential to cause major ecosystem disturbances that will negatively impact watersheds, cultural traditions, natural resources, and quality of life” (Rapid ‘Ōhi‘A Death, n.d.).
Hawai`i’s forests have changed drastically over the years, with the islands now containing about 44% of all the endangered plants found throughout the United States (Rare Plant Program, n.d). Ever since the Hawaiian islands were first discovered, they have been remembered for the lush tropical plants that flourish there. Today, the islands are still known for their greenery, though many of the original native species are dying or already extinct. Education programs and restoration initiatives are being carried out in the efforts to combat invasive species. Some solutions currently being worked on are the removal of invasive species and keeping uninvaded native areas protected by preventing the introduction of new species. Unfortunately, it is expensive to remove invasive trees, making it very difficult to accomplish. One suggestion is “using non-invasive naturalized or Polynesian introduced species on degraded sites where they can provide such ecosystem functions as soil and water quality protection, habitat for rare animals, and shelter for threatened and endangered plant species” (Potter et al., 2023). Some local groups target specific invasive species to remove them. While much work is being done to spread awareness of the islands’ environmental degradation, much more is needed to protect and improve the Hawaiian forests.
Works Cited
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Hawaiian Plants • Manoa Heritage Center. (2023, February 22). Manoa Heritage Center. https://www.manoaheritagecenter.org/moolelo/hawaiian-plants/
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Li, Y. (2020). Impacts of invasive species on agriculture in Hawaii. Agricultural Research & Technology Open Access Journal, 24(1). https://doi.org/10.19080/artoaj.2020.22.556253
Nation of Hawai’i. (2022, March 22). Ahupuaʻa system » Independent & Sovereign nation state of Hawaii. Independent & Sovereign Nation State of Hawaii » the Official Nation of Hawai‘I Digital Platform. https://www.nationofhawaii.org/ahupuaa/
Pono Pacific | Invasive species. (n.d.). https://www.ponopacific.com/invasive-animals/
Potter, K. M., Giardina, C., Hughes, R. F., Cordell, S., Kuegler, O., Koch, A., & Yuen, E. (2023). How invaded are Hawaiian forests? Non-native understory tree dominance signals potential canopy replacement. Landscape Ecology, 38(12), 3903–3923. https://doi.org/10.1007/s10980-023-01662-6
Rapid ‘Ōhi‘a Death - Hawaiʻi Volcanoes National Park (U.S. National Park Service). (n.d.). https://www.nps.gov/havo/learn/nature/rapid-ohia-death.htm
Rare Plant program. (n.d.). https://dlnr.hawaii.gov/ecosystems/rare-plants/
THE TARGET: Albizia (Falcataria moluccana). (n.d.). https://dlnr.hawaii.gov/hisc/info/biocontrol/latest-biocontrol/falcataria-moluccana/
Trust, W. (2018, August 16). What is habitat fragmentation and what does it mean for wildlife? Woodland Trust. https://www.woodlandtrust.org.uk/blog/2018/08/what-is-habitat-fragmentation-and-what-does-it-mean-for-our-wildlife/
