Bog vs Swamp – What’s the Difference? [The Facts]

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Guide to Bogs vs Swamps – What is the Difference?

swamp wetland with trees
Swamps (pictured here) are just one of the dozens of types of wetlands. Public domain.

Other than both being a type of wetland, they’re not even close to being the same thing! Oftentimes, wetland classifications get rather muddled by the plethora of internet “resources” out there, with “swamp,” “marsh,” “fen,” and “bog” all being used interchangeably.

Over the next few articles, we’ll be focusing on breaking down these classifications and helping our readers to better understand the differences between their key structures, functions, and benefits. If you’d like a breakdown of the primary types of wetlands and how they are categorized, you can check out our informative, concise guide to wetland classification here.

Similarities Between Bogs and Swamps

Interestingly, bogs and swamps are often confused for one another, though they don’t have all that much in common other than both being a type of palustrine wetland. Palustrine wetlands are those that are dominated by trees, shrubs, and other emergent vegetation; this can include various species of mosses and lichens. Additionally, palustrine wetlands can be tidal (influenced by the ocean) or non-tidal, just so long as their salinity is less than .5 parts per thousand (ppt).

Additionally, they both serve a host of incredibly beneficial services to both the environment and humans (we’ll cover those later in the article).

Differences Between Bogs and Swamps

As there are many differences between these two wetlands, we’ll break them down into categories here.

1) How They’re Formed

sphagnum bog with heather and tamarack
Bogs are formed in depressions that over time fill with peat and become colonized by low-pH-tolerant species like sphagnum mosses and heather. Photo by W & J / CC BY-SA 2.0

Bogs are formed in existing depressions in the earth that were created by things like glacial retreat, outwashes, kettle and pothole depressions, and glacial lakebeds. Partially due to the nature in which they are formed, the soils that serve as the eventual foundation of bogs are acidic and low in nutrients, as things like glacial retreat and outwashes scrape and strip the ground.

Over a great deal of time, a bog can be formed in a couple of ways. Most commonly, plant matter and detritus, rain, and snowmelt all build up in the depression. Over hundreds (or thousands!) of years, these break down into a thick layer of peat that makes it difficult for water to drain away. As more precipitation occurs, gradually the depression fills in. Bogs are completely reliant on precipitation for their moisture rather than groundwater, which further adds to the acidity and lack of nutrients.

Another way bogs can be formed is if sphagnum mosses (sometimes referred to as peat moss for their propensity to thrive in peat) are able to take advantage of existing moisture and colonize the depression. Sphagnums are incredibly spongelike, consisting of up to 70% water, and many species prefer acidic conditions. These sphagnums hold onto moisture and allow the area to fill in with water, forming a bog over many centuries. Sometimes, sphagnums come after the area has filled in with peat deposits and water.

cypress swamp big cypress national preserve
Swamps are formed by lakes, oceans, or rivers (as is the case with this cypress swamp) flooding either often or permanently. Photo courtesy of Big Cypress National Preserve.

Swamps, on the other hand, are typically formed when a river, large lake, or ocean floods permanently or seasonally, thus significantly altering the composition of the area. In fact, swamps are described as being transitional zones between land and water, as they are, of course, flooded but also are dominated by shrubs and trees, most often occurring in forests. A true swamp is able to hold at least some water permanently, even when nearby water bodies are not overflowing.

Some swamps form as a result of succession; that is, lakes and ponds naturally fill in over time, and can be considered a swamp if trees and shrubs move in. Swamps can contain saltwater, freshwater, or brackish water, and exist coastally or inland.

Swamps are fed by flooded water bodies as well as precipitation, often resulting in water levels that fluctuate throughout the seasons.

2) Species That Call Them Home

Due to their acidic (pH is between 3.5 and 5) and nutrient-deprived nature, bogs are home to very particular, specially adapted plants and animals. Many of the plants can either survive without nitrogen, or are capable of fixing their own! You can expect to find thick, pillowy sphagnum mosses overlaying the top of many bogs (though don’t let their thick carpet fool you into walking on them – beneath the sphagnum, there is often a good deal of standing water!). If the ground moves like gelatin when you step on it, it’s not safe.

Large bog Lahemaa bog
Bogs contain many shrub and tree species, but will always have more open space than trees. Pictured is the Lahemaa bog in Estonia. Photo by François Philipp / CC BY-SA 2.0

Additionally, depending on the exact location and condition of the bog, you might find acidic-loving plants like pitcher plants, Venus flytraps, lowbush blueberries (sometimes known as bog blueberry), cranberries, Labrador tea, heather, leatherleaf, bog laurel, pickerelweed, and orchids, and often it will be bordered by shrubs and trees, or may exist in an opening in the middle of a forest.

The trees nearest the bog are likely to be somewhat stunted (typically under 10 feet tall) due to the nutrient-poor conditions in and near the bog. Common tree species found on the outskirts of bogs include tamarack, jack pine, white pine, buttonbush, and black spruce. All of these will differ depending on the exact type of bog.

As bogs don’t have water flow and sediment and vegetation tend to be quite thick, there isn’t much oxygen to be found. This means that vegetation and detritus break down incredibly slowly. As a result of these low-oxygen conditions, there are not many animals that live directly in bogs (and no fish), but a multitude of them do rely on the insects (like ants that are able to make substantial homes in the large sphagnum hummocks), small mammals, and various berries packed with nutrients that are often found in bogs.

These can include beavers, moose, rabbits and hares, muskrats, foxes, and the occasional bear. Additionally, in the midwestern and eastern United States, the endangered Eastern massasauga rattlesnake often makes its winter home in the pillowy, roomy sphagnum hummocks found in bogs, but move to fens where food is more plentiful in the spring and summer. In certain parts of the world, endangered mud salamanders and spotted turtles are also known to make their homes in bogs, due in part to the plentiful insects.

swamp species swamp lily
Thanks to their incredibly rich soils, swamps are home to a plethora of animals and plants like this swamp lily (Crinum americanum). Photo by Melissa McMasters / CC BY-SA 2.0

Swamps are a bit less picky about the types of life that they house as they can have more variable conditions than those of bogs, such as containing freshwater, saltwater, or brackish water. As might be guessed, the types of vegetation found in swamps can really differ depending on the location. For example, mangrove swamps are well-known in more tropical regions, cypress swamps are common in the American south, and northern hardwood swamps can be found in the northern U.S., Canada, and the U.K., to name a few. Generally speaking, swamps are wetlands that are dominated by trees and shrubs. This can include flood-tolerant species like red maple, willows, cypress, mangroves, cottonwoods, dogwoods, and many others.

Due to their variability in plant species composition and being found predominantly in forest ecosystems, swamps are able to host quite a variety of animal life with plenty of food to go around. Again, this depends on the location, but can include many types of waterfowl (such as wood ducks and herons), alligators, many songbirds such as warblers, a variety of fish, a plethora of aquatic and semi-aquatic insects and other invertebrates like shrimp, river otters, and many species of frogs and snakes. Beautiful plants like swamp lily and Spanish moss call these places home. All of these organisms serve critical roles, lending to the importance of swamps (discussed below).

3) Their Functions and Benefits

swamp with cypress trees and lilies
Far from being “wastelands,” swamps are full of a huge diversity of life. Pictured is Okefenokee Swamp in Georgia, US. Photo by TimothyJ / CC BY-SA 2.0

Though swamps and bogs are similar in that they both offer critical services to countless organisms, including humans, those exact services do differ somewhat.

Bogs serve the incredibly important function of acting as sponges. They are incredibly adept at soaking up excess moisture from runoff, flooding, and precipitation, thus allowing them to protect other areas from flooding while also aiding in the proper cycling of nutrients and pollutants like fertilizers and heavy metals. They are also incredible carbon sinks, able to capture and store more carbon than all of the other ecosystem types in the world combined due to their remarkably slow rate of decay. They are considered one of the most valuable ecosystems in the world. Additionally, their very particular conditions make them critically important to many plant and animal species that wouldn’t be able to survive anywhere else.

Swamps serve a similar role in that they act as nutrient sponges and greatly lessen the impacts of flooding. However, they differ in that their soils are incredibly rich due to overflow from rivers, lakes, and the like. These rich soils are part of what enables such an abundant diversity of plant and animal species.

Additionally, many of the tree species found in swamps are quite resilient to rot by nature, making them useful to people. When sustainably harvested, the rich soils found in swamps are able to facilitate the continuation of these species. The diversity of life also means that swamps are rich in food sources like insects, edible plants, and small animals like frogs and some rodents. This doesn’t just benefit those in the swamps themselves; they also benefit the surrounding ecosystems, as many surrounding animals (including people!) will visit swamps to grab a meal.

Coastal swamps are able to protect the delicate coastline and inland regions from storms, including hurricanes. In fact, in the deep southern U.S., the removal of over 50% of the swampland surrounding New Orleans has resulted in the city experiencing increasingly frequent flooding and damage from seasonal storms, as well as contributing to the city gradually sinking over time. They have also had to expend a great deal of money on trying to construct storm walls to do the job previously held by the swamps and bayous.

4) Human History and Perception of Swamps and Bogs

Human perception, too, is notably different between swamps and bogs.

peat bricks from a bog used for fuel
Historically, peat from bogs has been harvested as a fuel source. Photo by Larry Koester / CC BY-SA 2.0

Bogs have, overall, been viewed favorably by people throughout history. Their green, pillowy mosses and rich berries have provided us with a pretty aesthetic and tasty food for many, many generations. They are also a rich source of peat; particularly in northern Europe, peat was used, and sometimes still is, as a very reliable and dense fuel source, further adding to a favorable view of bogs. This, of course, can result in the degradation and demise of many bogs if not conducted in a respectful and sustainable manner.

Swamps, on the other hand, have historically been incredibly misunderstood and vilified in both the Americas and Europe. They were viewed as dark, sinister, smelly, and ridden with insects. This contributed to folklore describing them as “evil” and “wastelands,” home to dangerous creatures like snakes, alligators, and mosquitoes, as well as dark spirits. Pop culture capitalized on this negative idea of swamps, giving rise to many well-known villains like Swamp Thing. These misconceptions and strong folklore are large contributors to why we have destroyed, drained, and filled in many swamps around the world (particularly in the U.S.).

However, the tides are metaphorically turning. We now understand that swamps, like other wetlands, are among the most valuable ecosystems in the world. Their rich soils give rise to a vast array of life, protect us from flooding, and provide indigenous and modern peoples alike with ample food like fish, shrimp, clams, and nutrient-dense plants like okra and water chestnut.

Unfortunately, many bogs and swamps alike are still often viewed as “unproductive” and are destroyed, like other wetlands, to create land that can be either built on or used for agriculture as humanity continues to expand. Our hope is that these wetland articles can serve as gentle eye-openers and educate others on their incredible value and importance, uniqueness, and beauty.

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