Invasive species pose significant threats to global agriculture, according to a study on impacts of 1300 invasive species on agriculture in 124 countries . Invasive species dramatically decreased crop production and can be a major factor affecting food security . In the United States alone, the losses in agricultural and forest production from invasive insects and pathogens have been estimated about $40 billion per year . The United States as one of the four large agricultural producers in the world could experience a serious cost from further species invasion. The state of Hawaii makes up less than one percent of the United States land area but over 40 percent of the country’s threatened and endangered plant species are found in Hawaii. Hawaii is known as the endangered species capital of the world, with 90 percent of the 1,400 Hawaiian endemic plant species are found nowhere else in the world according to the Hawaii State Department of Land and Natural Resources.
As one of the most isolated archipelagos in the world, Hawaii islands are vulnerable to invasive species. The entire island chain of Hawaii has been devastated by invasive insects, plants, hoofed animals and other pests in almost all agricultural and forest ecosystems [4,5]. Among at least 5300 alien species already established in Hawaii approximately 300-500 species are estimated to be invasive [6,7]. In addition, the introduction of exotic species to the islands increased exponentially over the past several decades [7,8]. With the alarming rate of exotic species introduction, the numbers of invasive species naturalized to the islands are predicted to increase remarkably though only a small percent of introduced species ever become invasive. The growing invasive species crisis poses significant risks to Hawaii’s tourism and agriculture-based economy.
For hundreds of years before the arrival of Europeans led by British explorer James Cook, Hawaiians have been associated with ecological agriculture since their settlement. They followed the land divisions, called ahupua’a. Each ahupua’a was an area of land running from the uplands to the sea, following the natural
boundaries of the watershed created pie-shaped slices of land. The Hawaiian Islands are suitable for agriculture under a mild climate allowing a year-round growing season with the average high temperature of 25°C in July and the low temperature of 21°C in January. The native Hawaiians produced a wide array of agricultural products, including banana, taro, sweet potatoes, ginger, sugar, coconut, and some uniquely Polynesian crops. From 1840s to 1980s, Sugar Cane and Pineapple plantations were the largest employers in Hawaii and the most valuable agricultural industry. Due to the shifting political alliances on food market, increasing labor cost and thriving tourism industry, land used for agriculture has declined by 68 percent from 1980 to 2017 according to a report by The Washington Post.
After the abandoned sugar cane and pineapple plantations, how to keep Hawaii’s extraordinary lands in active agriculture is a great challenge. Besides the high cost of land, irrigation, workers and transportation, a significant modern challenge to farming on the land in Hawaii is the rapidly expanding invasive species which exert severe negative impacts on agriculture . The following are the major problems caused by invasive species in almost all branches of agriculture in Hawaii.
Habitat loss The Hawaiian Islands possesses a wide range of habitats, from wet forests to extremely dry coastal grasslands. The habitats are characterized by high levels of endemism in both native animals and plants, with over 10,000 species found nowhere else in the world. Native biodiversity is not only important to natural ecosystems but also to agricultural practices. Hawaii’s native wildlife and their associated ecosystems provide essential goods and services to residents such as water quality, soil conservation, carbon storage, and climate regulation [10,11]. With the introduction of invasive species and more recently development, many of native habitats have been fragmented or completely lost. For example, 90 percent of Hawaii’s dryland habitat, 61 percent of the mesic habitat, and 42 percent of wetlands have been estimated to be lost since the late 18th century .
Today, native vegetation occurs over less than 40 percent of
the land area of Hawaii. With only 0.2 percent of the country’s total
landmass, Hawaii has the highest number of endangered species
in the United States accounting for more than 30 percent of the
total species listed as endangered in the country . Almost
all the native bird or plant species in Hawaii have no defense
mechanisms due to the lack of predators or large herbivores
during their evolutionary processes and ecological interactions.
Invasive predators such as rats, mongoose, and feral cats’ prey on
native birds. At higher elevations, feral cats are the most important
predators of endangered Hawaiian birds including groundnesting
waterfowl  and tree-nesting passerines . The
mongooses are native to India and were intentionally introduced
to Hawaii in 1883 to control rats in sugarcane fields. Mongoose
and rats consume a wide variety of food types including seabird,
water bird, bird eggs, chicks, and even adults, sea turtle eggs and
hatchlings. Invasive ants in Hawaii can also have great impacts on
habitat of native invertebrates and birds, especially seabirds. Ant
colonies can reach incredibly high densities on the islands and
reduce native insect food available for birds and exclude native
plant and crop pollinators from nectar sources, especially native
bees and moths [15,16].
Alteration of Hawaiian ecosystems Invasive species can change
abiotic and abiotic components of an environment in many ways
based on how they interact with their new surroundings. These
interactions can reduce the amount of resources for native
species, directly or indirectly affect food-web structures, and thus
alter the balanced ecosystems. Some invasive species in Hawaii
play a significant role in altering entire ecosystems. For example,
strawberry guava and albizzia destroys native forest habitats,
reduces the abundance of native plants, and diminishes food
resources for native birds. The lack of a diverse understory in
dense strawberry guava forests greatly enhances soil erosion and
damages watersheds [17,18].
Hybridization of native species with introduced related
species can have a large effect on the genetic structure of native
species populations. Genetic extinction occurs when population
sizes differ immensely . An example of this phenomenon
is the hybridization of Hawaii’s native duck with introduced
mallards. Ungulates such as feral pigs, goats, sheep, and cattle
Ungulate populations have played a destructive role in the
fragile agricultural ecosystems of Hawaiian Islands. Grazing and
rooting damage native vegetation and cause soil erosion and
sediment run-off. In addition, invasive mammals together with
invasive plants alter island nutrient cycles . Researchers
from the Savannah River Ecology Laboratory at the University of
Georgia reported that invasive mammals in Hawaii altered island
ecosystem nutrient cycles which poses significant impacts on
farming and animal husbandry.
Insects & diseases Introduced diseases and insects can
dramatically reduce the production of agricultural crops and
tree plantations. For example, the Small Hive Beetle (SHB),
Native to sub-Saharan Africa and found in Hawaii in 2010, may
cause rapid decline of the populations of honeybees, a critically
important pollinator of agricultural crops in Hawaii. Invasive
species often carry new diseases for crops and native plants and
animals. For example, the introduction of mosquitoes to Hawaii
has resulted in the spread of avian malaria, a major contributor to
population declines and extinctions for many endemic Hawaiian
honeycreepers . A new fungal pathogen referred to as “Rapid
Ohia Death” (ROD) was identified on Hawaii Island in 2014.
ROD is comprised of two pathogens, Ceratocystis lukuohia and
Ceratocystis huliohia, and currently attack and kill Ohia on Hawaii
Island. Ohia (Metrosideros polymorpha) is the most abundant
native tree in Hawaii islands and Ohia forests provide habitat for
countless plants, animals and invertebrates. A significant amount
of agriculture and drinking water is from Ohia forests. ROD poses
a very serious threat to Hawaii agriculture, forests and natural
Some 90 percent of food in Hawaii is still imported and it
deadly needed to revitalize its agriculture to produce agricultural
products for the local market efficiently enough to replace most
imports. To reach this goal Hawaii Department of Agriculture
(HDOA) provides facilitative leadership to both the public
and private sectors to develop regenerative and sustainable
First, prevention and control of invasive species. Hawaii, the
capital of endangered species in the world, is vulnerable to species
invasion. Currently Hawaii’s agriculture is greatly threatened by
increasing invasive species, such pollinator risk and various
crop diseases and pathogens. To revitalize its agriculture, local
communities, nonprofit organizations, county agencies and
educational institutions should work collaboratively to enhance
prevention and control of invasive species.
Second, developing sustainable agriculture. The future
agricultural systems must be resource conserving, socially
supportive, commercially competitive, and environmentally
friendly. To develop sustainable agriculture and communities,
producing local foods, such as breadfruits, cacao and avocado, and
restoring ahupua’a-like management of the land are essential to
creating high-value products and protecting the land.
Third, application of high agricultural technology. RBC’s
Farm 4.0 indicates that coming skill revolution can transform
agriculture and the fourth agricultural revolution is underway.
For example, advanced technology like autonomous tractors and
drone-mounted sensors can transform the traditional way we
produce food. Only if applying new technology skills can Hawaii’s
agriculture develop sustainably by reducing the labor cost which
is one of the major buriers of agriculture in Hawaii.
Finally, agritourism. Travel associated with farming is a
growing phenomenon. Agritourism includes farm stays, walking tours, livestock operations, restaurants serving regional cuisine,
agricultural fairs and festivals, etc. Agritourism generates
supplemental income and it helps to farm stabilization. Good
examples for agritourism in Hawaii are Kona’s Uchida Coffee farm
and Mauna Loa Macadamia farm.