Introduction to Tongan Tropical Moist Forests

A Biodiversity Hotspot:

The World Wildlife Fund, as a part of it's mission to save biodiversity and reduce human impact on natural ecosystems, identifies 238 different ecoregions throughout the world. An ecoregion, as defined by the WWF, is:

"a large unit of land or water containing a geographically distinct assemblage of species, natural communities, and environmental conditions".

Tongan Tropical Moist Forest, the subject of this blog, is one of these WWF ecoregions and is considered a rare forest among WWF’s network of 142 terrestrial ecoregions, 53 freshwater ecoregions, and 43 coastal ecoregions. The forest is found on islands in the South Pacific Ocean, and is restricted to the island of Niue and the islands of the Kingdom of Tonga.

Tonga: The Friendly Islands

Tonga is an island nation in the South Pacific. Tonga is located between Fiji and Samoa. Tonga is made up of 170 islands between 15 and 23 degrees south latitude and 173 to 177 degrees west longitude. The island chain covers approximately 276 square miles of land area and spans over 270,000 square miles of total area. The total population of Tonga is 102,000. Only 36 islands are inhabited of the 170 islands. The archipelago of Tonga is made up of the following areas:

1. Tongatapu in the South, area: 256 sq.km., low-lying coral limestone islands.

2. Vava’u in the North, area: 143 sq. km.,volcanic island.

3. Ha’apai in the center, area: 119 sq. km.,coral limestone and volcanic islands.

The archipelago of Tonga, which is comprised of 176 islands, is divided into three main groups: Vava'u, Ha'apai, and Tongatapu. Within these divisions, the three major islands are Vava'u, Eau, and Tongatapu, on which the capital city Nuku'alofa is located. There are 33 smaller islands that are also inhabited by humans.

Niue: The Rock of Polynesia
Niue is situated in a triangle between Tonga, Samoa and the Cook Islands. It covers approximately 100 square miles in area. Niue lies to the southeast of Tonga, approximately 376 miles away. Tonga is made up of coral reef and volcanic islands. Niue is one of the world’s largest coral reef islands. It has an estimated population of 1,400. An interesting fact is that in 2003 it became the first nation to have free access to Wi-Fi throughout the country.

Regional Biodiversity

The following chart breaks breaks down the different types of species in Tonga. According to the 2008 Red List of IUCN, Tonga supports 2264 species of fauna and flora:

5.6% of Tonga is forested. Tonga supports 419 known plant species, 3% endemic. Tonga lacks herpeterofauna diversity, as there are only 19 known species. The Banded Iguana, found on Tonga and Fiji, is endangered. The Tongan Skink, found on Tonga, is considered extinct. Tonga and Niue support a number of avian species endemic to the area. The regions consist of only one restricted-range bird species. Restricted-range endemism refers to a range less than 50,000 km (approximately31,000 miles) and thus considered a secondary endemic bird areas by Birdlife International. Tonga supports 20 bird species. Niue supports 18 bird species.

Threats toBiodiversity

Only 36 of Tonga’s islands are inhabited; however, the population is rapidly growing. Population growth is expected to increase the rate of forest clearing for agriculture and settlement. This inherently alters the landscape and results in habitat destruction for the fragile ecosystem.This leads to massive deforestation. Other threats include invasive species and removal of native species. For example, the introduced Black Rats and Norway Rats carry diseases that pose a threat to bird species. Bird species native to the islands are further threatened by poaching and rat predation.

Figure 6

On Tongatapu and Vava’u onshore mudflats, depauperate mangrove swamp vegetation is dominated by the mangroves Bruguiera gymnorrhiza, Rhizophora samoensis and Rhizophora stylosa. On the empty regionsinland, Paspalum vaginatum often forms a dominant grass.

However, the mangrove ecosystems in Tonga are currently threatened by the fishing and crab collecting traditions. As well, mangrove timber is used for firewood and building houses and boats, further contributing to the decline of the mangrove forest biodiversity.

Figure 7

However, the threats to Tongan forests do not stop at mangrove swamps. The entire forest ecosystem is currently endangered, due to human disturbances. As the summary of table below shows, there have been remarkable declines in certain forest types throughout the whole of Tongan islands. Within five years, woodland declined to 9.4% from 11.5% of total forest areas while mangrove and wetland areas were almost halved.

Figure 8

(Kingdom of Tonga Fourth Report, 26)

Over-exploitation of natural resources and land use change for agricultural purposes have led to massive deforestation in Tonga. Agriculture and forestry are the main industries of Tonga; they provide jobs in tree nurseries, plantations, and sawmills. Sawmills, which constitute 10% of the manufacturing sector, represent 5% of the total GDP of Tonga, signaling how important wood products are for the national economy of Tonga. As Tongan population increases, land use changes resulting in change from primary or secondary forest to agricultural areas have led to increased deforestation,which, due to fragmentation and the edge effects of habitats, has led to habitat loss and threats to the biodiversity of Tongan tropical moist forests. As well, inadequate infrastructure and the spread of pollution resulted in diseases that worsened the state of the Tongan forests and overall ecosystem. Moreover, the use of trees for medical or cultural reasons contributes to the rate of deforestation in Tonga. Out of 60 species identified in the 2006 IUCN Red List of Threatened Species, 55% are used for medicine, 38% for cultural purposes and 33% for timber purposes. Twenty-five species were identified as endangered species.

Sources

BirdlifeInternational. 2011. Endemic Bird Areas. Retrieved May 2011 from http://www.birdlife.org/action/science/endemic_bird_areas/index.html.

Columbia Gazetter. 2011. Tonga. Columbia University Press. Retrieved May 2011 from"http://www.columbiagazetteer.org/main/ViewPlace/144783"http://www.columbiagazetteer.org/main/ViewPlace/144783.

Kingdom of Tonga. 2010. Fourth Report Review of Tonga National Biodiversity Strategy and Action Plan. Retrieved May 2011 from http://www.cbd.int/doc/world/to/to-nr-04-en.pdf

Rinke, D.1986. Status of Wildlife in Tonga. Retrieved May 2011 from http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=4958652

Tonga Meteorological Services. 2011. Climate Summary. Retrieved May 2011 from http://www.met.gov.to/index_files/climate_summary_tonga.pdf.

United States Central Intelligence Agency. 2011. CIA World Factbook. Retrieved May2011 from CIA worldfactbook: https://www.cia.gov/library/publications/the-world-factbook/geos/tn.html.

World Wildlife Fund. 2011. Terrestrial Ecoregions: Tongan Tropical Moist Forests. Retrieved May 2011 from http://www.worldwildlife.org/wildworld/profiles/terrestrial/oc/oc0114_full.html.

Wikipedia. 2011 May. Retrieved May 2011 from www.wikipedia.com.