Hawai'i: The Physical Environment

Over the course of the past two centuries, the Hawaiian Islands have been transformed from a rural tropical archipelago to a highly developed and urbanized US state. Development, however, has not affected each of the eight islands equally.  The island of Hawai‘I (also known as the Big Island), remains mostly rural, while O‘ahu, as the site of the state capital of Honolulu, has been most heavily developed. These two contrasting islands each face imminent environmental issues, but their respective issues vary because of different human development patterns. In contrast to the Big Island, it is impossible to describe O‘ahu’s geological, biological and oceanographic features without acknowledging human impact. Urbanization has created permanent changes in the landscape in the forms of erosion, species introductions and extinctions, and dramatic shifts in the marine ecosystem.  While erosion is O‘ahu’s most looming threat, even the less-developed Big Island is threatened by the introduction of non-native species.

Urbanization has increased erosion and created dangerous potential for landslides on O'ahu that are difficult to mitigate. According to Sanjit K. Deb of the University of Hawaii at Manoa, O‘ahu’s combination of steep hillsides with loosely packed sediment, heavy rainfall, and residential development makes it especially vulnerable to debris flows and landslides [1].  O‘ahu is one of the oldest islands of the archipelago; two dormant volcanic mountain ranges, Wai‘anae and Ko‘olau, dominate the landscape and erosion has had a significant effect on their easily-weathered basalt slopes, creating steep, unstable hills. The tropical climate’s 25-30 inches of rain per year, and the frequent storms that occur during the winter months[2] can trigger small landslides and debris flows, sending a rapid flow of soil, vegetation, and loose sediment down hillsides[3]. As climate disruption increases both the frequency and intensity of extreme weather events, erosion is likely to accelerate.

Even more alarming, “attempts at stabilizing slow landslides in ‘Aina Haina and Palolo Valley have been unsuccessful” [4], according to Deb, suggesting that Honolulu’s increasing urban development is in danger. This is especially true because current demographic trends show a young population forming families, which has increased demand for single-family suburban dwellings[5]. Because housing stock in Honolulu is in short supply, developments that were previously confined to lowland areas must necessarily move further up hillsides. According to Ferguson and Khan, “the urban district on O‘ahu currently occupies nearly 100,000 acres or one-quarter of the island,” while “mountainous and upland regions [comprise] about 40% of the total area”[6]. With a good deal of the land covered by steep slopes vulnerable to landslide, and much of the rest already developed, any expansion of the city places both residents and the island landscape in danger. Because construction displaces the natural ground cover and replaces porous soil with concrete, runoff from storms is more likely to concentrate in valleys and flood them, while dwellings built on unstable land are vulnerable to collapse.

As an illustration of the hazards posed by erosion, a recent rainstorm eroded the ground cover of Waimanalo Gulch Landfill, a public facility owned by the City of Honolulu. According to Brooks Baehr’s Jan 14, 2011 report on Hawaii News Now,an exceptionally heavy rainfall damaged O‘ahu’s largest landfill to the extent that garbage was exposed and flowed into the ocean and surrounding streams. Most of the trash was medical waste, leading residents and authorities alike to speculate that it may be biologically or chemically contaminated. The storm generated 11 inches of rain, close to the 12-15 usually accumulated in a year. According to Waste Management, Inc.(WM), which operates the landfill, 400,000 tons of garbage are brought to Waimanalo Gulch each year. The facility was unable to withstand the rain, despite a $2 million investment in a new berm to reduce surface runoff in 2005, which WM described as an “additional safety factor to guard against catastrophic events.” The rather alarming incident is a demonstrative example of the impact dense population has on O‘ahu’s fragile landscape.

Biologically, the extinction of many native species and the introduction of large numbers of invasives have permanently changed the ecosystem. Because of the archipelago’s remoteness, up to 95% of Hawaiian species are endemic[7]. As asserted by BioScience’s Laura Tangley, “Hawaii is considered one of the world’s prime showcases for examples of adaptive radiation”[8] because the island chain’s location allows for extreme speciation and the development of unique adaptations. Both deforestation and the introduction of invasive species threaten this ecosystem. Tangley further notes that “virtually all of Hawaii’s lowland tropical forests already have been converted to agricultural and other uses” [9], emphasizing the degree to which the island has been converted for human use. Because of the intricacy of the tropical rainforest ecosystem, even if allowed to grow wild, rainforests would take decades to recover from such disturbance. In addition to urban developments, agriculture is a major land use in O‘ahu and has been a major source of ecosystem loss since humans first settled on O‘ahu around 500-800 AD. However, the introduction of new species poses an equally significant threat, despite the fact that the majority of introduction is intentional and its effects predictable. According to a 2000 study published by the International Association for Ecology, spcies introduced intentionally for purposes such as weed control are highly likely to damage closely related native plants[10].

Human-induced nutrient supply changes in the ocean have provided extreme enough stress to cause ecosystem-level feeding and composition changes. O‘ahu is a very densely populated island, and the magnitude of human waste produced, both biological and commercial, is great enough to cause significant changes in the seawater chemistry. Anthony R. Russo of the Water Resources Research Center at the University of Hawaii at Manoa conducted an examination of marine ecosystems’ response to sewage outfalls showing that eutrophication from increased nitrogen and phosphate input fundamentally changed some communities’ trophic structure. Russo’s study of Kaneohe Bay describes a scarcity of fish at two of his observation sites, before the outfall; however, “six months after the outfall operation began there was a large increase in total fish at the outfall site, especially over the large rocks covering the outfall pipe”[11]. This is especially striking since ecosystem changes of observable magnitude typically take place over thousands of years, and yet this researcher noticed significant population changes in a matter of months. Additional changes observed at the outfall sites include replacement of herbivores and filter feeders with carnivores and “large amountsof the filamentous blue-green alga Lyngbya, a species of cyanobacteria, on rocks near the outfall pipe[12]. Russo makes several observations that help explain these changes, including increased available substrate for benthic organisms and higher levels of nitrogen and phosphate present in the environment [13]. While these chemical changes can occur naturally, Russo makes it clear that “communities would only be expected to change their species composition and relative abundance under extreme stress – for example, depletion of food supply, destruction of habitat space, or change in the physicochemical environment” [14].  Kaneohe Bay provides a case study of human impact on O‘ahu’s shoreline, and therefore a study of the island’s human-induced chemical changes in Oahu’s coastal seawatershave led to major changes in its ecosystem, and therefore a study of the surrounding waters is inseparable from human development.

Whereas O‘ahu’s physical environment has been at the mercy of human development for the past century, the Island of Hawai‘i’s physical environment is still dominated by the volcanoes that created it. The Island of Hawai‘i, commonly known as the Big Island, is the largest and youngest of the Hawaiian Islands. It has almost twice as much land as the other seven islands combined.[15] Like all of the other islands in the chain, the Big Island was formed by the Hawaiian hot spot. The center of the hotspot now lies just off the Big Island’s southwest coast, where it is forming the newest Hawaiian island, Lo‘ihi, which will break the water’s surface about 10,000 years from now.[16] The Big Island is made up of five major volcanoes: Kohala, Kilauea, Hualalai, Mauna Loa, and Mauna Kea.[17] Kohala, Hualalai, and Mauna Kea are considered dormant, while Mauna Loa and Kilauea are considered active. Mauna Loa has not erupted since 1984, but Kilauea is currently one of the most active volcanoes in the world, and has been erupting continuously since January 3, 1983.[18] This continuous eruption has created over 500 acres of new land on the Big Island since 1983.[19]

HawaiiAlanaPicture.jpg

Photo by Genny Anderson

http://www.marinebio.net/marinescience/02ocean/hwimg/crst16bno[1].jpg

The Hawaiian Islands are situated in the middle of the Pacific Ocean, and are formed of oceanic crust. Oceanic crust is mostly basaltic rock, as opposed to the silicate rock that forms continents. The basaltic, or mafic rock that flows from the volcanoes is extremely mineral-rich, and quickly erodes into fertile soil. The first seeds were transported to Hawai‘i by winds, currents, and birds. The first animals that made it to the islands were probably birds and flying insects. Other animals probably got to Hawai‘i on floating logs or vegetation.[20]

The Big Island has eleven of the planet’s thirteen Koppen climate zones, making it an especially unique place. Zones found on the Big Island include: tropical wet, tropical monsoon, savanna, dry semiarid, humid subtropical, Mediterranean, marine, dry winters, dry summers, wet all seasons, and polar tundra.[21] The existence of this many climatic regions in such a small area means that the island is rich in both ecosystems and biodiversity. The island supports ecosystems like fresh water streams, tropical rain forest, savanna regions, upland forest, grass plains, and tundra regions. Alpine environments occur on Mauna Kea, Mauna Loa, and Hualalai. However, introduced sheep and goats have left the environment significantly altered, and the vegetation is much sparser than it must have been in the years before European contact.[22] The Big Island also has coral reef ecosystems, but due to the island’s young age, only small patch reefs along the western coastline have had a chance to form as of yet.[23]

Endemic species are present on all of the Hawaiian Islands, and many of their populations have been decimated by human activity and the introduction of invasive species. A conservative count of endemic species known to exist, now or in the past, counts 10,000 insects, 1,061 mollusks, 100 birds, 1,394 seed plants, and 119 ferns. This does not take into account the various unknown species that must have perished when the first humans arrived in Hawai‘i.[24] The Big Island alone supports 248 species of endemic flowering plants, 25 of which are endemic specifically to the island.[25] Hawai‘i is also famous for its finches and honeycreepers, which are a classic example of adaptive radiation. Many of these birds are now extinct or endangered. One example of this is the palila. The palila only lives on the slopes of Mauna Kea, and currently occupies only 10% of its historical range, and its population has decreased by 75% since 2003.[26] The species is at an extreme disadvantage because sheep and goats have been destroying the palila’s mamane tree habitat for many years, and feral cats have been known to kill the birds[xiii]. These are just some examples of the severe issues introduced species pose for endemic flora and fauna, and these issues are often linked to human activities as well.

Invasive species have been an issue since the beginning of mass transportation to the islands. There are no large predators native to Hawai‘i, so any critters that were accidental stowaways on ships found a comfortable home in the islands, but seriously disrupted the ecosystems for the native plants and animals. Some invasive species on the Big Island are Salvinia molesta, which was accidentally introduced; alien species of algae[27]; Miconia calvescens, which blankets the native forest, and essentially chokes it to death. Miconia is a problem on the Big Island, Maui, O‘ahu, Kaua‘i, and even Tahiti.[28] The coqui frog is the most famous unwanted species on the Big Island. It is a native to Puerto Rico. The frogs are extremely loud, and can reach densities of 10,000 per acre. They eat insects, however they do not eat mosquitos, and often end up eating the native insects.[29] Invasive species cost Hawai‘i hundreds of millions of dollars each year.[30] Some people introduce them purposefully for aquaculture, the pet trade, botanical gardens, the horticulture trade, or experiments, and they arrive through the mail, luggage, ship hulls, ballast water, and air cargo. The costs of invasive species are multifaceted. Not only do they cost the state a large sum of money each year, but they also reduce the productivity of watersheds, and increase erosion.[31]

The detrimental effects of human activity are perhaps most notable on O‘ahu, where the vast majority of people in Hawai‘i live. While O‘ahu is aging and suffers from erosion, the Big Island is still forming new land; while landslides constantly threaten a human population that is claiming more and more land for development on O‘ahu, the Big Island is home to relatively well-preserved, unique ecosystems whose primary threat is from invasive species rather than development. On O‘ahu, humans are a threat to themselves, but on the Big Island people must be wary of their environment and the volcanism that still occurs there. Both islands have been significantly impacted by development and urbanization, but they contrast in the level of human settlement, creating an inequality in what ecosystems and species are preserved, and which are not.

Alana Bryant, George Washington University
Allison Gramolini, Colgate University
2011 

 

NOTES

[1]  Deb, Sanjit K and Aly I. El-Kadi. “Susceptibility assessment of shallow landslides in O‘ahu, Hawaii under extreme-rainfall events.” Geomorphology 108 (2009): 219-233.

[2]  Deb, 219

[3]  Deb, 220

[4]  Ferguson, Carol A and M. Akram Khan. “Protecting farm land near cities: trade offs with affordable housing in Hawaii.” Land Use Policy (1992): 259-271.

[5]  Ferguson, 261

[6]  Tangley, Laura. “Fighting deforestation at home.” BioScience 38.4 (1988): 220-224.

[7]  Tangley, 220

[8]  Tangley, 221

[9]   Pemberton, Robert W. “Predictable risk to native plants in weed biological control.” Oecologia125.4 (2000): 489-494.

[10]  Russo, Anthony R. “Temporal changes in fish community structure near a sweage ocean outfall, Mokapu, O‘ahu, Hawaii.” Marine Environmental Research 6 (1982): 83-98.

[11]  Russo, 93

[12]  Russo, 95

[13]  Russo, 93

[14]  Kirch, Patrick. Feathered Gods and Fishooks: an Introduction to Hawaiian Archaeology and Prehistory. Paperback ed. Honolulu, HI: University of Hawaii Press, 1997. 22-33. Print.

[15]  Anderson, Genny. "Hawaii: Geology, Plate Tectonics/Hot Spot." Marine Science. N.p., 29 Aug 2010. Web. 26 Jan 2011. <http://www.marinebio.net/marinescience/02ocean/hwgeo.htm>.

[16]  Anderson, et al.

[17]  "Kilauea." USGS- Hawaiian Volcano Observatory. US Geological Survey, 7 May 2009. Web. 27 Jan 2011. <http://hvo.wr.usgs.gov/kilauea/>.

[18]  "Beware Kilauea's new land-- not exactly terra firma?."USGS- Hawaiian Volcano Observatory. US Geological Survey, 12 Aug 1999. Web. 27 Jan 2011. <http://hvo.wr.usgs.gov/volcanowatch/1999/99_08_12.html>.

[19]   Anderson, Genny. "Hawaii: Introduction/History." Marine Science. N.p., 3 Jan 2008. Web. 26 Jan 2011.<http://www.marinebio.net/marinescience/02ocean/hwintro.htm>.

[20]  Pidwirny, Michael. "Climate Classification and Climatic Regions of the World." Fundamentals of Physical Geography. University of British Columbia, 2006. Web. 28 Jan 2011. <http://www.physicalgeography.net/fundamentals/7v.html>.

[21]  Kirch, Patrick. Feathered Gods and Fishooks: an Introduction to Hawaiian Archaeology and Prehistory. Paperback ed. Honolulu, HI: University of Hawaii Press, 1997. 22-33. Print.

[22]  Kirch. 

[23]  Kirch.

[24]  Gon, Sam. "Hawaii Island Conservation Area Profiles." Hawaii High Island Ecoregion. The Nature Conservancy, 8 Sept 2006. Web. 28 Jan 2011. <http://www.hawaiiecoregionplan.info/CAHA.html>

[25]  "Hawaii's endangered palila bird numbers dropping. "Honolulu Star Advertiser 14 Sept 2010: Web. 28 Jan 2011. <http://www.staradvertiser.com/news/breaking/102911719.html>.

[26]  "Hawaii's endangered palila bird."

[27]  Howard , V. "Salvinia Molesta." NAS-- Non-Indigenous Aquatic Species. USGS, 12 Feb 2008. Web. 29 Mar 2011. <http://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=298>.

[28]  "Alien Species: Miconia calvescens." Department of Land and Natural Resources, State of Hawaii. DLNR, n.d. Web. 29 Mar 2011. <http://www.state.hi.us/dlnr/Miconia.html>.

[29]  "Why are Coqui Frogs a Problem in Hawai'i?." Control of Coqui Frogs in Hawai'i. College of Tropical Agriculture and Human Resources, University of Hawai'i at Manoa, n.d. Web. 29 Mar 2011. <http://www.ctahr.hawaii.edu/coqui/background.asp>.

[30]  Wilson, Christie. "Fighting invasive species in Hawai'i." Honolulu Advertiser 14 Jan 2008. Web. 29 Mar 2011. <http://the.honoluluadvertiser.com/article/2008/Jan/14/ln/hawaii801140359.html>.

[31] Wilson, Christie. "Fighting invasive species in Hawai'i." Honolulu Advertiser 14 Jan 2008. Web. 29 Mar 2011. <http://the.honoluluadvertiser.com/article/2008/Jan/14/ln/hawaii801140359.html>.