Large-scale Habitat Degradation

Habitat Loss, Ungulates, and Invasive Plants
Habitat Loss

The main Hawaiian Islands were primarily covered in forest prior to the arrival of humans. An incredible diversity of plants and animals lived throughout the islands free of disturbance. On Maui, a host of flightless ducks, geese, ibis, and rails ran around in the understory while dozens of songbird species darted around the treetops. When the first humans arrived in Hawai‘i, they cleared much of the lowland, dry and mesic forest for agriculture and other activities. This drastic habitat alteration led to a wave of extinctions in plants and animals, particularly those specializing on these lowland habitats. Following this first wave of destruction, however, Hawaiians left much of the upper elevation forests alone choosing only to enter the wao akua for specific ceremonial purposes.

A second wave of habitat loss and extinctions came following the arrival of Europeans and the introduction of domestic ungulates (hoofed mammals). In addition to habitat destruction done by ungulates, ranching and logging has also taken its toll on native forests. It is now estimated that only 40% of Hawai‘i is dominated by native vegetation and a smaller fraction is unaffected by invasive plants and animals. Although we still have native forest in some areas, much of this is a single habitat type, wet montane forest. Less than 10% of mesic forest and 3% of dry forest remains. With the loss of these habitats, the organisms dependent on these environments also disappeared. We only know of the existence of many species from subfossil remains found in lava tubes and sand dunes. Although a lot of effort has been put into protecting the remaining native forest, protecting these areas will require continued efforts to remove invasive plants and animals.

Past Ecosystems Across Maui

Copyright Sam Gon, The Nature Conservancy Hawaii

Ecosystem Cover Across Maui Today

Copyright Sam Gon, The Nature Conservancy Hawaii

Ungulates

During their first voyage to Hawai‘i in 1778, Captain Cook presented goats and pigs as gifts to native Hawaiians. In 1793, Captain George Vancouver gave a few cows to Kamehameha I as a gift. To foster the burgeoning cattle population, Kamehameha I instituted a kapu on killing cows. This kapu was in place until 1830 when the population had grown so large as to become a nuisance. Huge swaths of mesic forest on the leeward slopes (west- and south-facing) were cleared to harvest forest products and for ranching activities in the mid- to late 1800s. By 1900, large herds of wild cattle were present on the south slope of HaleakalA and territorial foresters commented on the devastating effects these animals were having to the remaining forest. Control of feral cattle began in 1830 through hunting, round-ups, and fencing. However, ranching activities and feral ungulates continued to erode the forest throughout most of the 20th century.

The long-term protection and restoration of many native forests is contingent on the removal and/or control of feral ungulates. Believe it or not, the descendants of the cows given to Kamehameha still live wild in the Kahikinui region of Maui. We call these animals “feral” but given the number of generations since captivity, these animals are truly wild and can be quite dangerous to humans. Massive herds of goats roam these slopes throughout the forest. In 1959, a few axis deer were introduced to Maui and their populations have skyrocketed, now numbering > 50,000, and are spreading into upper elevation forests. However, these animal’s days of munching the native forest unabated are numbered. Significant control measures for all ungulates began in earnest in the mid- to late 1900s and hundreds of miles of fences have been installed to protect remaining native forest. These efforts continue today and new fences go up every year. In the next few years the vast majority of the remaining leeward forest band in Kahikinui and Nu‘u, including Nakula NAR, will be fenced and can finally begin to recover from over a century of damage.

Invasive Plants

Introduced and invasive plant species have contributed to habitat degradation and the loss of suitable native forest bird habitat across Hawai’i. Invasive species are non-native or alien species (plant, animal, or microbe) transported by humans to a location outside its native range and whose introduction does or is likely to cause economic or environmental harm and/or harm to human health (U.S. Presidential Executive Order 13112). Non-native species make their way to Hawai’i every day through imported plants, people, and ships.

Invasive plants create dense growths and crowd out native plants, which decreases biological diversity. Additionally, many of these invasive plants use more water than native plants, thus decreasing the availability of water within the forest and the watershed. Most native birds will not feed off of non-native plants as they are not adapted to recognize them as a food source. There are organizations on island like the Maui Invasive Species Committee whose mission is to prevent invasive species from becoming established and limiting the most harmful ones.

MFBRP works in some of the most pristine areas of Maui, where much of the forest is native. Some of the top invasive plants of concern in The Nature Conservancy’s (TNC) Waikamoi Preserve include: Gorse (Ulex europaeus), Kahili Ginger (Hedychium gardnerianum), Blackberry (Rubus argutus), Pines (Pinusspp.), Blackwood Acacia (Acacia melanoylon), Tropical Ash (Fraxinus uhdei), and Eucalyptus (Eucalyptus spp.). At Nakula Natural Area Reserve, where MFBRP also works on forest restoration, there are many invasive plants such as Kikuyu grass (Pennisetum clandestinum), Velvet grass (Holcus lanatus), and Tree Poppy (Bocconia frutescens). We are also on the lookout for Koster’s Curse (Clidemia hirta) and Australian Tree Fern (Cyathea cooperi). Introduction of non-native plants to these areas could be caused by humans, pigs, or bird dispersal.

To prevent the introduction and spread of weed species, MFBRP takes precautions by making sure all gear is clean before entering any field sites- this includes cleaning clothing, backpacks, tents, boots, and raingear. Before each field trip, all gear is thoroughly inspected and cleaned. All dirt, seeds, and insects are carefully removed. MFBRP uses GPS to mark locations of non-native plants and may remove them to limit and prevent their spread. In Waikamoi, TNC is also notified of invasive plants as they have an intensive invasive species management program. Control efforts are focused on ecosystem modifying species and incipient populations that can be controlled through minimal effort. Because invasive plants are often very difficult to control once they have entered an area, prevention of new introductions is crucial.

Rapid ʻŌhiʻa Death is a new fungal disease that is currently killing native ʻōhiʻa (Metrosideros polymorpha) trees. As of 2016, Hawai’i Island is the only place this disease has been found, but hundreds of thousands of ʻōhiʻa have already died. It is important to prevent the spread of this disease to other islands and other forests on Hawai’i Island. Please read more about this alarming invasive disease here.

You can do your part by becoming aware of invasive plants (Hawai’i State-listed Noxious Weeds) and making sure not to spread them. Clean your camping and hiking gear and do not support more introductions. For more reading go to: What You Can Do to Help Stop the Silent Invasion.

Report a Pest Here.

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