Mangrove forest

What are mangrove forests?

Mangrove forests are dense nutrient-rich forests that grow along the shoreline of tidal rivers, creeks, estuaries and lakes. They grow in the fine sands, muds and sediments laid down by rivers, tides and currents.

Mangrove forests grow in the zone where land meets water and are inundated by saltwater brought in by the tides. The salty water is diluted by freshwater run-off from the land from rainfall and freshwater creeks.

Mangrove trees are the only trees that can grow in saltwater environments.

Where are mangrove forests found?

Mangrove forests are found in temperate, tropical and subtropical intertidal estuaries, bays and rivers all around the world. They are found along the coast of mainland Australia, almost around the entire coast except for some areas along the southern coastline.

Mangrove forest lines the shores of the intertidal upper parts of the Lane Cove River.

Why are mangrove forests important?

Mangrove forests are complex ecosystems that are extremely important for biodiversity and humans. They provide shelter and breeding grounds for fish, prawns and crabs and habitat for a wide variety of animals. The specialised roots of mangrove trees, intertwined within a mangrove forest, hold together the shoreline mud and silt and protect shorelines from erosion.

Mangrove forests create a natural barrier for coastal environments against storm surges, floods, erosion, wind and waves. This protection is becoming increasingly important as the climate changes and sea levels rise. By stabilizing the soil, filtering out pollutants and recycling contaminants and nutrients, mangrove forests also maintain and improve water quality.

Mangrove forests have a great capacity to take carbon out of the atmosphere, acting as carbon sinks. Scientists have found that a patch of mangrove forest can absorb 10 times the carbon compared to the same size patch of traditional forest.

Still and peaceful with a variety of wildlife, mangrove forests are beautiful places to visit. Within Buffalo Creek Reserve and Lane Cove National Park there are constructed boardwalks that allow visitors easy access to these very important and beneficial environments.

Mangrove forest provide habitat for a variety of animals such as this cormorant perched on a fallen branch in a mangrove forest at high tide in Lane Cove National Park in Sydney.

Mangrove forests are peaceful places to visit. As the tide recedes the mud and roots of mangrove forests are exposed. This is Buffalo Creek at low tide in the late afternoon.

What plants grow in mangrove forests?

There are 80 different species of mangrove trees around the world. Australian mangrove forests contain 41 different mangrove species. Mangrove forests usually contain only one or 2 species of mangrove trees and have an open understorey. Other plant species do not usually grow within the forest.

Within the saltwater environments along the Lane Cove River and Parramatta River near the Field of Mars Reserve there are two species of mangrove trees. The most common species in this area is the grey mangrove whilst the river mangrove also grows here, usually closer to the shoreline.

Mangrove forests along Sydney's coast comprise grey mangroves as the dominant species. This mangrove forest in Buffalo Creek Reserve comprises grey mangrove seedlings, juveniles and mature trees with a few river mangroves dotting the shore.

River mangroves only grow close to the water's edge. They have bright green leaves with rounded tips.

Hundreds of grey mangrove seeds are washed onto the forest floor by the incoming tides. They are trapped by the pneumatophores and seedlings. Only a few will take root and grow into a single-stem seedling. A pneumataphore is a mangrove root protruding from the mud.

What animals live in mangrove forests?

Mangrove forests provide important food, shelter and habitat for a wide variety of animals. Invertebrates include red-fingered marsh crabs, semaphore crabs, mangrove whelks and golden orb-weaving spiders. Birds include ibis, spoonbills, cormorants and kingfishers. Reptiles include skinks and water dragons and mammals include flying foxes and bats.

There are many interactions between animals and plants within this environment such as the food chain of crabs feeding on fallen mangrove leaves whilst crabs are eaten by ibis.

Red-fingered marsh crabs live in the mud of a mangrove forest and feed on plant and animal material such as mangrove leaves, insects, small fish and other crabs.

The floor of a mangrove forest is typically wet mud covered in leaves, sticks and fallen logs. Close to the shore there are crab holes with crabs feeding on the surface of the mud.

How are mangrove forests used by Aboriginal Peoples?

Mangrove forests are traditionally used by Aboriginal Peoples as sources of food, including fish, mud crabs and shellfish. The timber from some mangrove trees can be used to make tools and weapons such as canoes and paddles, digging sticks, shields, boomerangs and spears.

The timber from mangrove trees can be used to make tools and weapons such as canoes and paddles, shields and boomerangs.

What threats do mangrove forests face?

Scientists have found that mangrove forests have declined globally over the last 40 years. The total area of mangrove forests has reduced by 35% in that time. Threats include land clearing and reclamation for building works such as marinas and housing estates, changes in water quality such as increased sediment and chemical pollution and impacts of climate change.

Extreme high temperatures and coastal erosion sped up by rising sea levels due to climate change are blamed for the dramatic shrinking of mangrove forests across the world.

Sedimentation and changes in water quality can cause dieback of a mangrove forest. These grey mangrove trees died when sandy sediment ran off from the land and covered their pneumatophores.