Hawaii photograph

Wild Pigs & Goats Destroy Native Hawaiian Forests

Wild pigs and goats destroy the native forests of Hawai’i. They dig holes in the ground, roto-till the earth, and strip the mountain-sides of vegetation. So when the rain falls, nothing holds the soil and rocks from washing down the streams into the sea.


Muddy Seas

Mud & freshwater washes into the ocean and kills reef

Pigs, goats, and other grazing animals are not native to Hawai’i—they were brought to the Hawaiian Islands by humans. For millions of years prior to human contact, the native plants and animals found it unnecessary to produce thorns, toxins, strong odors, and other protective mechanisms against these animals. Most of the endemic species evolved to lose whatever defenses they originally had.

When goats, sheep, cattle and other grazing animals where introduced to Hawai’i upon Western contact in 1778, they found the vegetation lush, inviting, and virtually defenseless.

Invasive Pig

Pigs roto-till the earth killing the vegetation

Pigs and goats inflict severe damage on native ecosystems by devouring the vegetation, trampling the undergrowth, compacting the soil, and uprooting the tender shoots of growing plants. Pigs roto-till the soil in search of food and destroy the soil structure. Pigs routinely decimate once pristine stands of native forest and create places for standing water to collect enabling mosquitoes to breed. Mosquitoes spread avian malaria and pox that kill rare and endangered native forest birds that can only be found in Hawai’i.

Other grazing animals like goats and sheep cause extensive damage because they don’t stop eating a plant when they reach the ground—they devour its roots as well. As a result, the vegetation cannot regenerate and the land loses its cover. When the mountain slopes are devoid of vegetation, they cannot withstand the onslaught of rain. Large scale erosion of the land and destruction of coral reefs is the inevitable result.



Goats denude mountain side of vegetation

Native forests are particularly good at protecting mountain slopes from erosion by allowing the land to retain the rainfall during heavy rains. Native forests soak-up water like a sponge and slowly release that moisture over the following days, weeks, months, and years. Rain runs down the branches of trees, becomes soaked into the mosses, lichens and ferns growing on trees. Additionally, the moisture is protected from evaporation when the water trickles into the leaf litter at the base of trees. In places where native forests are intact a considerable proportion of the rain seeps into the ground by following the roots of trees into the soil and percolating deep into the earth to recharge the aquifer.


Muddy Torrent

Muddy torrent washes tons of soil into the streams

When the land is denuded of vegetation, heavy rains pelt the earth. Nothing prevents the water from rushing down steep mountain slopes washing tons of nutrient-rich, top-soil into the streams. Muddy torrents sweep down the mountains and wreck havoc on native stream ecosystems. The destruction continues when the muddy torrent reaches the ocean. Tons of soil settle on the sea floor and smother everything that lives there. Entire reef systems can be killed from the silt and freshwater that washes down from denuded mountain slopes.

Once pigs and goats start browsing the native forests, they create openings for invasive alien plants such as strawberry guava, ginger, Miconia, and other fast growing alien plants to take root. Many plants from elsewhere in the world have no natural enemies or pathogens in Hawai’i to keep them in check. As a result, they can spread rapidly in areas cleared by pigs and goats. Once invasive alien plants become established, they spread rapidly, and choke out the native species, resulting in wholesale replacement of the native forests with alien weeds.

Erosion Scar

Top soil being washed away leaving boulders behind

The damage caused by pigs and goats in formerly pristine native areas has contributed greatly to Hawai’i having the highest number of endangered species in the U.S. Hawai’i has nearly 75% of the nation’s documented extinctions and 35% of all endangered species in the country. Unless steps are taken to stop and repair the damage caused by these animals, unique species found only in Hawai’i will become extinct within the next few generations. In order to perpetuate these biological treasures for future generations, sustained efforts must be made to protect and enhance native ecosystems. Relatively pristine areas must be surrounded by fences and the animals and plants that threaten the native ecology must be removed. Only by supporting such conservation efforts can the endemic species that are truly unique to the Hawaiian Islands be protected for posterity.