What is a Tree Island, and how does it help with Carbon Storage?

The Everglades in southern Florida are also known as a reserve of carbon storage. Some areas of the Everglades have “tree islands” and a recent study showed they are capable of storing more carbon and other nutrients than their marsh neighbors. The Soil Science Society of America’s (SSSA) October 15^th Soils Matter blog explores the findings of a recent study about tree islands that was performed by Florida scientists.

The Everglades contain a diverse set of habitats, including prairies and mangrove swamps. Other areas of woody vegetation embedded within the marsh landscape are known as tree islands. The variety of trees can vary from willows to cypress to various hardwood varieties.

The Everglades is a managed area. Water flow is controlled through a series of canals. Stormwater treatment areas were constructed in the 1980s to control damage from stormwater surges. There are three areas that scientists are currently focusing on to determine best practices within the Everglades:

1. sediment control best management practices.
2. nutrient management control best management practices.
3. water management control best management practices.

The current study by a group of scientists at Florida International University researched whether tree islands were less affected by changing water levels than neighboring marshes.

To study the soil, the researchers took “soil cores.” They place long tubes into the soil and pull them out, to capture the soil composition at various depths. Tree islands’ soils were composed of low-organic peat, heavy peat, and peat soils. These types of soil store large amounts of carbon in our ecosystems throughout the world (including cold areas like the arctic and subarctic).

The study found that tree islands could store nearly five times more organic matter (carbon) than marshy areas. They could store over twice the amount of nitrogen. Finally, they stored almost six times the amount of phosphorus.

The authors attribute these observed differences in nutrient storage capacity between the marshes and tree islands to two factors. First, the quality and quantity of litterfall and root biomass between marshes and tree islands are different. The leaf litter from marshes decomposes faster than leaf litter from trees. And the relationship between the roots and soil microbes differs, too. This allows for more nutrient buildup in the tree islands.