Bermuda subtropical conifer forests

Content Partner: World Wildlife Fund (other articles)

Article Topics: Biodiversity, Conservation biology and Ecology

This article has been reviewed and approved by the following Topic Editor: Mark McGinley (other articles)

Last Updated: December 1, 2006

Introduction

Paget Marsh, Bermuda, UK (Photograph by Catherine Mastny)

The Bermuda islands were once covered in dense forest of endemic tree species, with mangrove forests lining the coasts and inland saltwater ponds. The islands are distinguished as having the northernmost mangrove forests in the Atlantic, which is made possible by the warm Gulf Stream current. Bermuda’s isolation led to the evolution of many endemic species, including the endangered Bermuda petrel (Pterodroma cahow), the Bermuda skink (Eumeces longirostris), and many endemic invertebrates. Restricted to this small archipelago, all endemic species are especially vulnerable to introduced predators and alien pests, and unfortunately the islands have seen the extinction of many species since the time of human settlement. Due to intense human activity, only very small areas of natural habitat remain on Bermuda today. Though the islands have a well-managed and well-funded system of protected areas, this is one of the world’s most densely populated regions. Additionally, Bermuda is subject to intense pressure from a heavy tourist industry.

Location and General Description

The Bermuda ecoregion is a crescent-shaped chain of some 150 coral limestone islands and islets, formed along the submerged rim of a long-extinct volcano. It is situated in the western Atlantic Ocean a little over 900 kilometers from the North American coast. Most of the land area is composed of 7 main islands that encompass 53 km². This land area is surrounded by about 750 km² of shallow reef platform, the most northerly in the Atlantic. The climate is subtropical, with mean air temperatures ranging from 19 to 30 °C. The average humidity is 77 percent, and the annual precipitation (146 cm) is distributed relatively evenly throughout the year.

The ecoregion is situated on a more than 75-meter-thick coralline limestone cap, covering a volcanic pedestal that rises to just below sea level. Roughly 110 million years ago (MYA), volcanic action along the mid-Atlantic ridge created a 2000-meter-high seamount, which was topped off by a second eruption some 33 MYA. Over time, changes in sea level led to the deposition on this seamount of alternating layers of soil (paleosols) and wind-blown calcareous sand. These dunes solidified during the Pleistocene into a cover of soil and highly porous limestone.

Paget Marsh, Bermuda, UK (Photograph by Catherine Mastny)

Bermuda's topography is moderately hilly and low, with the highest elevation reaching only 79 meters (m). The shoreline is composed of bays and inlets, with coral sand beaches lining the shores, primarily in the south. The ecoregion has no rivers or surface streams, and the limestone supports a shallow freshwater lens in only 20 percent of the land area, resulting in fewer than 20 brackish and freshwater ponds. This includes a total of 17 peat marshes.

The ecoregion originally contained two predominant vegetative features: a once densely forested plateau and mangrove forests. The woodlands were characterized by three endemic trees, each of which is listed as threatened by the IUCN: Bermuda cedar (Juniperus bermudiana), Bermuda palmetto (Sabal bermudana), and Bermuda olivewood (Elaeodendron laneanum). Also present are the threatened yellow-wood (Zanthoxylem flavum) and southern hackberry (Celtis laevigata). Wax myrtle (Myrica cerifera) dominates the understory of peat marshes, along with St. Andrew’s cross (Ascyrum hypericoides), Bermuda sedge (Carex bermudiana), saw grass (Cladium jamaicensis), and ferns. Bermuda maidenhair fern (Adiantum bellum) is found in cave damps.

Warmed by the Gulf Stream, the ecoregion’s mangrove forests are the most northerly in the Atlantic. These forests are isolated, small in size, and relatively low in tree diversity, with only three species present: red mangrove (Rhizophora mangle), black mangrove (Avicennia germinans), and buttonwood (Conocarpus erectus). An unusual feature of these mangroves is that roughly one-third are situated around inland saltwater ponds, which are mostly tidal and connected to the sea by submarine fissures. These inland forests are typically monospecific, with either red or black mangrove present. The remaining two-thirds of mangroves are located in coastal bays, where they display typical mangrove zonation. The most frequent coastal bay mangrove associations are with red algae, green algae, and three flowering plants: Asparagus sprengeri, Borrichia frutescens, and Sesuvium portulacastrum. The different pond mangroves tend to display unique assemblages of species.

Biodiversity Features

As many as 320 bird species have been observed in the ecoregion. But Bermuda’s position as an isolated oceanic island has contributed in large part to an overall low diversity of species in most taxa, low endemism, and absence of native mammals, amphibians, or large predators. Low floral diversity in particular is attributed to isolation and lack of anthropogenic influence prior to the 1600s. The ecoregion’s biological composition is also a product of prehistoric sea-level fluctuations of up to 150 meters, which alternately favored marine and terrestrial species and led to the demise of land snails, many endemic birds, and a tortoise. Other factors limiting biodiversity include the ecoregion’s low elevation, small size, geologic composition and age, as well as regional ocean currents and past and present climate and weather patterns.

Bermuda is home to 165 native vascular plants, and 15 of these are endemic. Endemic trees include: Bermuda cedar (Juniperus bermudiana), Bermuda palmetto (Sabal bermudana), and Bermuda olivewood (Elaeodendron laneanum). Other vascular plant endemics are: Bermuda spike rush (Eloecharis bermudiana), Bermuda sedge (Carex bermudiana), wild pepper (Peperomia septentrionalis), wild Bermuda bean (Phaseolus lignosus), St. Andrew’s cross (Ascyrum hypericoides), Bermuda snowberry (Chiococca bermudiana), Darrell’s fleabane (Erigeron darrellianus), and Bermudiana (Sisyrinchium bermudiana). There are also 4 endemic ferns: Governor Laffan’s fern (Diplazium laffanianum), Bermuda maidenhair fern (Adiantum bellum), Bermuda shield fern (Goniopteris bermudiana), and Bermuda cave fern (Ctenitis sloanei). The two endemic mosses are Campylopus bermudiana and Trichostomum bermudanum. Also present are 40 endemic fungi and ten endemic lichens.

Bermuda contains no native mammal or amphibian residents, although four species of visiting bats have been recorded. Two of the ecoregion’s bird taxa are endemic, representing a low endemism rate of less than one percent. These are the cahow, or Bermuda petrel (Pterodroma cahow), and the locally-termed "chick-of-the-village" (Vireo griseus bermudianus), a subspecies of the white-eyed vireo that has shorter wings, a larger head, and stout legs. The only native terrestrial reptile is the endemic Bermuda skink (Eumeces longirostris), a rock lizard that is also unique in being the sole non-avian, native land-vertebrate. There are at least 41 endemic insects, including 11 species of Lepidoptera, 17 Diptera, seven dragonflies, and three damselflies. There is also one potentially endemic spider, 11 endemic terrestrial mollusks, and one (now-extinct) endemic nemertean, Pantinonemertes agricola.

The ecoregion has witnessed the recent extinction of many endemic species, including the Bermuda spike rush (Eloecharis bermudiana) and the only endemic nemertean, Pantinonemertes agricola. An estimated 16 insect species have disappeared in the last century, including the flightless grasshopper, Paroxya bermudensis, and seven Diptera. The near-eradication of Bermuda cedar in the 1940s led to extinction of two associated endemic insects, the cicada Tibicen bermudiana, and the geometrical moth Semiothisa ochrifascia. Other losses include the apparent extinction of at least two endemic land snails, Poecilozonites spp., probably due to the introduction of carnivorous snails. Among birds, at least ten presumed endemics are known from Pleistocene fossils including the crane Baeopteryx latipes, the duck Anas paschyscelus, four species of rail, a woodpecker, a hawk, a heavy-billed passerine, and a small owl. Most of these birds are thought to have gone extinct due to sea-level changes before human settlement, although the passerine and owl are were present at the time of the first settlers. Finally, scientists are also preparing a description of a recently excavated fossil land tortoise.

Highly endangered endemics include the Bermuda petrel (Pterodroma cahow), whose nesting sites are currently restricted to a few outlying islets, and the Bermuda skink (Eumeces longirostris). Rare endemic plants include Bermuda olivewood (Elaeodendron laneanum), wild Bermuda bean (Phaseolus lignosus), and Bermuda sedge (Carex bermudiana), which is confined to Paget Marsh and 5 upland sites. The endemic fern Diplazium laffanianum is extinct in the wild, but a few individuals still survive in the Bermuda Botanical Gardens.

Current Status

Currently, some ten percent of the ecoregion’s land area is covered by forest or woodland. Within this, only very small and fragmented areas of natural habitat survive. An estimated 95 percent of the surviving population of native Bermuda cedar (Juniperus bermudiana) was destroyed between 1946 and 1951, following the accidental introduction of two coccoid scale insects. Only an estimated one percent of the original cedar forest survived the blight. Subsequent reforestation using a scale-resistant strain has returned the cedar to roughly ten percent of its former abundance, though these efforts have been hampered by the introduction of fast-growing casuarinas and other exotics into much of the cedar habitat. Of the 116 hectares of inland peat marshes present in the ecoregion in 1900, only some 48 hectares remain, including the 19.6 hectare Devonshire Marsh, Pembroke Marsh, and Paget Marsh. Only small, scattered areas of mangroves remain, totaling 16.7 hectares in 1980. The largest mangrove forests are found at Hungry Bay Mangrove Swamp and Mangrove Lake.

Bermuda holds the distinction of having passed the first conservation laws in the New World, protecting the cahow (Pterodroma cahow) and other birds as early as 1616 and limiting the uses of native cedar as early as 1622. A comprehensive and well-managed protected areas system currently exists, comprising 12 nature reserves that cover some 48 hectares, as well as 63 parks. The 25-acre Paget Marsh Nature Reserve is the best surviving example of native cedar, palmetto, and mangrove forests. The largest wildlife sanctuary is Spittal Pond, covering some 60 acres and home to at least 25 species of waterfowl. Other important protected areas include Devonshire and Pembroke Marshes, Warwick Pond, and the upland hills of Castle Harbour and Walsingham.

One important conservation success story has been the recovery of the endemic Bermuda petrel. Early visitors to Bermuda had been terrified by the cahow’s screeching cries, but they soon found the bird easy to catch and good to eat. Birds that were overlooked by humans were quickly consumed by introduced pigs, and as a result the cahow was thought to be extinct as early as the mid-1600s. But in 1951, 18 breeding pairs were rediscovered off the island’s East End, and subsequent recovery efforts have raised that number to 55 by 1998. The birds are currently protected in off-limits offshore sanctuaries.

Bermuda (the UK) is party to a number of relevant international environmental treaties, including: the World Heritage Convention, the Ramsar Convention on Wetlands, CITES, and the Bonn Convention on Migratory Species.

Types and Severity of Threats

In 1514, Spanish chronicler Oviedo y Valdes commented on the abundance of fish and bird life in Bermuda, and in 1593 shipwrecked English sailors joyfully discovered "an unbroken forest of cedar" from which to build their new vessel. But four centuries of settlement have all but eliminated Bermuda’s native flora and fauna. Predominant threats to the ecoregion include conversion of habitat for agriculture and development, introductions of exotic plant species, and sea-level rise.

By the end of the 17th century, settlers on Bermuda were already clearing the native land cover to make room for fields, gardens, hedgerows, and houses. They brought new pets and pests and planted ornamental plants, herbs and spices, and crops like tobacco and cotton. The conversion of land to agriculture continued through the 19th century, when Bermuda became a market garden for rapidly growing New York City. Over the centuries, residents cleared mangrove forests for development and used the bark in tanning and as fuel. The native cedar was felled for housing, shipbuilding, furniture, and export, while the thick-trunked palmetto was used for roof thatch, to weave fashionable hats, ropes, and baskets, and even to concoct a potent alcoholic beverage.

Over the past century, Bermuda’s agricultural importance has declined, but the pressures of development continue to grow. Twenty of Bermuda’s 150 islands are currently inhabited, and the country remains one of the most densely populated in the world. As the population has expanded over the last 20 years, and demand for housing has grown, undisturbed areas of natural vegetation have diminished rapidly. An estimated 10 percent of the land area is now covered by houses, roads, and other surfaces, and many peat marshes have been converted to landfills. The pressure on biodiversity is further intensified by the arrival of an estimated half million tourists each year.

Introductions of exotic species continue to crowd out native wildlife. An estimated 1500 plant species have been brought to the island over the centuries. Exotic trees like guava and mulberry threaten to replace native plant communities with monocultures, though conservationists employ culling and other techniques to keep these invasions at bay. Meanwhile, the activities of introduced birds like the great kiskadee (Pitangus sulphuratus) (brought in 1957 to control Anolis lizards) continue to aid in invasive plant dispersal.

In the future, sea-level rise will pose another serious threat to native vegetation as global temperatures increase, likely contributing to accelerated retreat of the region’s remaining mangrove forests.

Justification of Ecoregion Delineation

Bermuda’s position as an isolated oceanic island has contributed to a flora and fauna quite distinctive from any continental area or from Neotropical islands to the south. The ecoregion’s unique biological composition is also a product of prehistoric sea-level fluctuations as well as a lack of anthropogenic influence prior to the 1600s.

adapted by : http://www.eoearth.org/article/Bermuda_subtropical_conifer_forests

Some Facts About Climate

Adapted by: http://www.blueplanetbiomes.org/climate.htm
The sun's rays hit the equator at a direct angle between 23 ° N and 23 ° S latitude. Radiation that reaches the atmosphere here is at its most intense.
In all other cases, the rays arrive at an angle to the surface and are less intense. The closer a place is to the poles, the smaller the angle and therefore the less intense the radiation.
Our climate system is based on the location of these hot and cold air-mass regions and the atmospheric circulation created by trade winds and westerlies.
Trade winds north of the equator blow from the northeast. South of the equator, they blow from the southeast. The trade winds of the two hemispheres meet near the equator, causing the air to rise. As the rising air cools, clouds and rain develop. The resulting bands of cloudy and rainy weather near the equator create tropical conditions.
Westerlies blow from the southwest on the Northern Hemisphere and from the northwest in the Southern Hemisphere. Westerlies steer storms from west to east across middle latitudes.
Both westerlies and trade winds blow away from the 30 ° latitude belt. Over large areas centered at 30 ° latitude, surface winds are light. Air slowly descends to replace the air that blows away. Any moisture the air contains evaporates in the intense heat. The tropical deserts, such as the Sahara of Africa and the Sonoran of Mexico, exist under these regions.

World Climate Zones

Have you ever wondered why one area of the world is a desert, another a grassland, and another a rainforest? Why are there different forests and deserts, and why are there different types of life in each area? The answer is climate.
Climate is the characteristic condition of the atmosphere near the earth's surface at a certain place on earth. It is the long-term weather of that area (at least 30 years). This includes the region's general pattern of weather conditions, seasons and weather extremes like hurricanes, droughts, or rainy periods. Two of the most important factors determining an area's climate are air temperature and precipitation.
World biomes are controlled by climate. The climate of a region will determine what plants will grow there, and what animals will inhabit it. All three components, climate, plants and animals are interwoven to create the fabric of a biome
Adapted by :http://www.blueplanetbiomes.org/climate.htm

Animal Ecology

A habitat is any place where a particular animal or plant species lives. Examples of a habitat include a lake, a desert, or forest, or even a drop of water.
All habitats on Earth are part of the biosphere. Since the Earth is always changing, habitats are continually changing as well.
Descriptions of environments using temperature and rainfall are used to group habitats together. Habitats of similar climate and vegetation are called biomes. In different parts of the world, the same biome may contain different species, but will contain similar life forms. For example, trees are the dominant forms of the rain forest, no matter where the rainforest is located.
Animals, which live within a same-species group, and occupy an area at the same time, are part of a population. All members of the same population have certain traits in common. Populations of different plants and animals interact with each other, and together, these populations form communities. Plants and animals in a particular ecological community, or biome, must be adapted to the same living conditions so they can all survive in the same biome.
Many populations can live in the same area because each species fills a specific role in the community. This role is called a niche. What an animal eats, and where it eats are also part of its niche. Giraffes can live in the same area as gazelles because they eat different plants and don't compete with each other. Dung beetles bury the feces of these animals and lay their eggs in it. The hatching grubs feed on the feces. The buried feces also fertilize plants, which in turn feeds the gazelle and giraffe. Each plant and animal has its own niche in the ecological community, and is important in some way to the survival of the other.
Living organisms are usually classified as consumers (animals), producers (plants), or decomposers (fungi), depending on how they get their food. Consumers are, either herbivores, carnivores, or omnivores. Herbivores are called primary consumers because the feed directly on producers. Carnivores feed on other consumers. Omnivores eat both plants and animals. However, animals are seldom completely carnivorous or herbivorous. Some carnivores, such as bears, foxes, and the family cat or dog, will at times eat plants. Herbivores will sometimes eat small insects or grubs as well.
Adapted by :http://www.blueplanetbiomes.org/animals.htm

The First Organisms

Close to 2.5 billion years ago, the earth's surface and atmosphere were stable enough to support primitive life. Single-cell organisms began to develop in the seas that covered the planet. Most of them were very simple single-cell bacteria that fed on chemicals in the ocean's waters.
A simple organism known as blue-green algae appeared and spread across the seas. Blue-green algae are still alive today. It was very important to the future of the planet because blue-green algae used sunlight and water to make food, and in the process, created oxygen. As the blue-green algae grew in the earth's seas, they began to fill the atmosphere with oxygen.
The oxygen blue-green algae produced made it possible for other types of organisms to develop. These organisms needed oxygen to carry out their life processes of growth, feeding, responding and reproducing. Unlike the blue-green algae, these organisms could not produce their own food. They needed oxygen to perform their life processes of growth, feeding, responding, and reproducing. In return, they produced CO2, which the algae needed to perform its life processes. A precise balance between plants and animals was established.
Adapted By:http://www.blueplanetbiomes.org/animals.htm

Plant Life

Adapted by:http://www.blueplanetbiomes.org/rainforest.htm
Besides these four layers, a shrub/sapling layer receives about 3 % of the light that filters in through the canopies. These stunted trees are capable of a sudden growth surge when a gap in the canopy opens above them.
The air beneath the lower canopy is almost always humid. The trees themselves give off water through the pores (stomata) of their leaves. This process, called transpiration, can account for as much as half of the precipitation in the rain forest.
Rainforest plants have made many adaptations to their environment. With over 80 inches of rain per year, plants have made adaptations that helps them shed water off their leaves quickly so the branches don't get weighed down and break. Many plants have drip tips and grooved leaves, and some leaves have oily coatings to shed water. To absorb as much sunlight as possible on the dark understory, leaves are very large. Some trees have leaf stalks that turn with the movement of the sun so they always absorb the maximum amount of light. Leaves in the upper canopy are dark green, small and leathery to reduce water loss in the strong sunlight. Some trees will grow large leaves at the lower canopy level and small leaves in the upper canopy. Other plants grow in the upper canopy on larger trees to get sunlight. These are the epiphytes such as orchids and bromeliads. Many trees have buttress and stilt roots for extra support in the shallow, wet soil of the rainforests.
Over 2,500 species of vines grow in the rainforest. Lianas start off as small shrubs that grow on the forest floor. To reach the sunlight in the upper canopy it sends out tendrils to grab sapling trees. The liana and the tree grow towards the canopy together. The vines grow from one tree to another and make up 40% of the canopy leaves. The rattan vine has spikes on the underside of its leaves that point backwards to grab onto sapling trees. Other "strangler" vines will use trees as support and grow thicker and thicker as they reach the canopy, strangling its host tree. They look like trees whose centers have been hollowed out.
Dominant species do not exist in tropical rainforests. Lowland dipterocarp forest can consist of many different species of Dipterocarpaceae, but not all of the same species. Trees of the same species are very seldom found growing close together. This bio diversity and separation of the species prevents mass contamination and die-off from disease or insect infestation. Bio diversity also insures that there will be enough pollinators to take care of each species' needs. Animals depend on the staggered blooming and fruiting of rainforest plants to supply them with a year-round source of food.

Layers of the Rainforest

Adapted by : http://www.blueplanetbiomes.org/rainforest.htm
There are four very distinct layers of trees in a tropical rain forest. These layers have been identified as the emergent, upper canopy, understory, and forest floor.
Emergent trees are spaced wide apart, and are 100 to 240 feet tall with umbrella-shaped canopies that grow above the forest. Because emergent trees are exposed to drying winds, they tend to have small, pointed leaves. Some species lose their leaves during the brief dry season in monsoon rainforests. These giant trees have straight, smooth trunks with few branches. Their root system is very shallow, and to support their size they grow buttresses that can spread out to a distance of 30 feet.
The upper canopy of 60 to 130 foot trees allows light to be easily available at the top of this layer, but greatly reduced any light below it. Most of the rainforest's animals live in the upper canopy. There is so much food available at this level that some animals never go down to the forest floor. The leaves have "drip spouts" that allows rain to run off. This keeps them dry and prevents mold and mildew from forming in the humid environment.
The understory, or lower canopy, consists of 60 foot trees. This layer is made up of the trunks of canopy trees, shrubs, plants and small trees. There is little air movement. As a result the humidity is constantly high. This level is in constant shade.
The forest floor is usually completely shaded, except where a canopy tree has fallen and created an opening. Most areas of the forest floor receive so little light that few bushes or herbs can grow there. As a result, a person can easily walk through most parts of a tropical rain forest. Less than 1 % of the light that strikes the top of the forest penetrates to the forest floor. The top soil is very thin and of poor quality. A lot of litter falls to the ground where it is quickly broken down by decomposers like termites, earthworms and fungi. The heat and humidity further help to break down the litter. This organic matter is then just as quickly absorbed by the trees' shallow roots.