User:Ajvillalta/Mangrove trees in Hawaii

Mangrove trees in Hawaii

The red mangrove, Rhizophora mangle, and Oriental mangrove, Bruguiera sexangula, are non-native, invasive plant species that can be found along many of the coasts of the Hawaiian Islands.

History

Mangrove trees were brought to Hawaii in 1902 by the Hawai'i Sugar Planters Association in hopes that they would help to keep the sediment from running-off into the water due to heavy rains and agriculture making the land barren. It was later planted in Kalihi fishpond, then in 1922 it was planted in He'eia marsh, and it was brought to Kealia Pond, Maui in 1960. A third of the estuary habitat was reported to be made up of mangrove trees by 1977. By 1980 removal actions began to take place. The trees took, and spread much more easily than they had in other places, destroying much of the native wildlife, which has led to the more recent removal efforts.

Effects

When an alien species is introduced, such as the mangroves in Hawaii, the positive and negative impacts it has on the environment need to be weighed. This includes how it effects the existing native wildlife, changes in the ecosystem, agricultural, infrastructure, and any aesthetic impacts.

Positive Effects

Mangroves are known for helping to keep soil and sediment, reducing erosion in coastal environments, due to their unique roots. The trees are said to provide a habitat for fish, birds, and other fauna, while also keeping the land safe from storm surges, and stopping runoff. They provide shade for native flora and fauna, protecting them from the harsh sun. The coral reef under the water is also shaded and protected from the harsh sun. The trees have flourished in Hawaii so well that they provide incredible research opportunities to observe their true role in coastal ecosystems as well as how they interact with different species. Another important local impact is that the bruguiera gymnorhiza flowers are used in the making of leis. They are also used in the making of charcoal, their bark is used in medicine, provide fruit, produce dyes, and their roots have been used in cosmetics.

Negative Effects

The trees drain nutrients from the area that other native plant species need, killing them off, destroying the habitat of native fauna, including all 4 native Hawaiian shorebirds. Mangrove trees are known to help with such things (sediment) in other areas where they are found, but they have not demonstrated this quality in Hawaii, even showing the opposite effect in some cases. The Hawaiian stilt was pushed out of its habitat, along with monk seals, native fish species, and a native, endangered beach grass. The only thing keeping the trees in check are conservation efforts. The periodic chopping and burning of the trees by humans is the sole reason they have not taken over completely. Often times they are on top of ancient ruins, and the roots pierce through and break apart any and everything in their path, destroying this ancient culture and heritage. The forests have been said to smell bad, be displeasing to look at, and impede on much needed farmland. This is costing the community a lot of money, because they drive down housing prices near them, drive away business, and since they grow so fast and well, farmers need to constantly pay to have them cut down, while also not having full access to necessary land in order to expand their farms. The mangroves also release large amounts of their biomass into the surrounding marine environment, lowering the water quality, driving out native aquatic life, and destroying their habitats. They take very well to the Hawaiian coasts, and will beat out the other wildlife there, and their roots will often destroy coral reefs. Turning once beautiful, unique to Hawaii coral gardens filled with native wildlife to mangrove swamps. The trees have been found to drop, "large amounts of organic matter, resulting in nutrient loading and anoxia, sedimentation, and hypersalinization, conditions favoring alien fish and excluding coral and associated organisms."

Removal and Aftermath

There have been many efforts in recent years to remove the trees, but none large-scale enough to eradicate them from the islands entirely.

Removal

In Wai ‘Opae in Puna, Hawai‘i, though, a project is making headway towards eradicating mangroves from the islands entirely and hope to achieve this. They are injecting various herbicides, mainly Habitat herbicide, directly into the trees and then replacing them with native ones, which has proven extremely effective. In places where it is particularly bad, they will also have volunteers cut and remove the trees. In He'eia, Oahu they are removing the trees by burning the tops and bottoms, and saving the middle to be cut and sold later on. The mangroves have also been found to be especially weak to Garlon 4.

Aftermath

After removing the mangroves, taro, other native wetland shrubs, and other native trees like hala, naupaka, and kou are being planted to help restore the environment to its traditional ways in hopes that the fauna return, as well as providing a source of food for the community. in other cases they are simply removing the mangrove trees and letting nature take its course, which has led to the water quality increasing and the native flora and fauna to return on its own. By removing the trees, the Hawaiian stilt, native fish, and monk seals returned to their previous habitats. Invasive plant species as a whole have been associated with economic growth in Hawaii for a while now, so a big hurdle is getting the entire community on board for restoring their traditional, native ecosystems.