Hammock (ecology) facts for kids
A hammock is a special type of forest found in the southeastern United States. Imagine a small "island" of trees, usually with hard wood, surrounded by a different kind of natural area, like a wetland. These tree islands are called hammocks.
Hammocks usually grow on slightly higher ground, sometimes just a few inches above the surrounding wet areas. These wet areas are too soggy for many trees to grow, but hammocks thrive on their slightly drier spots. You can also find hammocks on slopes between wetlands and drier uplands, where different types of forests grow.
There are different kinds of hammocks in the United States, including tropical, temperate, and maritime (coastal) hammocks. Scientists also classify them based on how wet their soil is:
- Hydric hammocks have wet soil.
- Mesic hammocks have moist soil.
- Xeric hammocks have dry soil.
These types often blend into each other.
Unlike many other natural areas in the southeastern United States, hammocks do not handle fire well. They usually grow in places where fires are rare, or where they are protected from fires spreading from nearby areas. In recent times, some hammocks have started to grow in new places because people have stopped fires, or created higher ground by digging or building roads. However, many hammocks have also been lost due to construction, especially in popular areas like islands or waterfronts.
The word "hammock" itself has an interesting history. It might be an old form of "hummock" (meaning a small hill). It first appeared in English in the 1550s as a sailing term for a tree-covered island seen from a ship. Today, "hammock" is used to describe these tree stands from North Carolina all the way to Mississippi.
Contents
Types of Hammocks
Tropical Hardwood Hammocks
In the United States, tropical hardwood hammocks are found in southern Florida. These hammocks can be found in several unique spots:
- Rockland hammocks grow on rocky areas like the Miami Rock Ridge and in the Big Cypress National Preserve.
- Keys rockland hammocks are found in the Florida Keys.
- Coastal berm hammocks are along the coast in the Florida Keys and near Florida Bay.
- Tree island hammocks are special teardrop-shaped islands in the Everglades.
- Shell mound hammocks grow on old shell piles.
- Sinkhole hammocks are found in natural dips in the ground on the Miami Rock Ridge.
The trees that form the top layer (or canopy) of the southernmost tropical hardwood hammocks in Florida are mostly species from the Caribbean. The southern live oak is one of the few trees from cooler climates that regularly grows here. As you go further north along Florida's coasts, tropical hammocks start to mix with more temperate trees.
Tree island hammocks in the Everglades look like teardrops because of the way water flows around them. You can find tropical trees like mahogany, gumbo limbo, and cocoplum growing next to more familiar trees like southern live oak, red maple, and hackberry.
Maritime Hammocks
Maritime hammocks, also known as maritime forests or coastal hammocks, are found on stable sand dunes that are a bit away from the beach. You can also find them on small islands within salt marshes. These hammocks are common along the Atlantic Coast and the Gulf Coast of the United States. Some experts consider coastal hammocks to be a type of hydric (wet soil) hammock.
Temperate Hardwood Hammocks
Temperate hardwood hammocks are narrow areas of broadleaf forest found in the coastal plain of the southeastern United States. In most of the southeast, including the Florida Panhandle, the trees in these hammocks are mostly evergreen (they keep their leaves all year). In northern Florida, you'll see a mix of evergreen and deciduous trees (which lose their leaves in winter). In southern Florida, north of the Everglades, these hammocks have a mix of evergreen and tropical trees.
Hydric Hammocks
Hydric hammocks, also called low hammocks or wetland hardwood hammocks, grow in areas where the soil is poorly drained or has a high water level. They can sometimes be flooded. You'll often find them on gentle slopes just above swamps, marshes, or wet prairies. Hydric hammocks are scattered across Florida north of Lake Okeechobee, especially along the upper St. Johns River, the Atlantic coast of northeastern Florida, and the Big Bend section of Florida's Gulf Coast.
Mesic Hammocks
Mesic hammocks are found along the coasts of the southeastern United States (from North Carolina to Texas) and throughout peninsular Florida. These hammocks grow in soils that are rarely flooded but stay moist because of the shade from the trees and the thick layer of fallen leaves. The trees in mesic hammocks are mostly evergreen hardwoods and cabbage palms. The southern live oak is the most common tree here. Other trees you might see include southern magnolia, pignut hickory, water oak, and laurel oak. In southern Florida (south of Lake Okeechobee), you might also find tropical trees like gumbo limbo and satinleaf. Slash pines and loblolly pines are also common in many mesic hammocks.
Xeric Hammocks
Xeric hammocks, also known as xeric forests or sand hammocks, grow in sandy soil that drains very well, like old sand dunes. They need some protection from fire to grow. These hammocks are known for their sand live oak and saw palmetto plants. Xeric hammocks can develop from scrub or sandhill areas. Hammocks that come from scrub areas often have myrtle oak and Chapman's oak. Those that come from sandhill areas might have turkey oak and bluejack oak. Xeric hammocks need a long time without fire to fully develop, but once they are established, they can resist fire somewhat. Sand live oak and myrtle oak can regrow from their roots if the hammock does burn.
Prairie Hammocks
Prairie hammocks are a type of hydric and mesic hammock. They are mainly made up of live oak and cabbage palm trees. You can find them in central and southern Florida in prairies and floodplains, on river levees, and on slopes between dry uplands and wetlands.
Oak Domes
Oak domes, also called oak hammocks, are small patches of thick evergreen oaks. They grow in shallow dips or on slight hills. These areas look very different from the surrounding habitats, which are usually woodlands dominated by longleaf pine trees.
