String bog
A string bog is a kind of peatland whose surface is marked by a pattern of low ridges of peat, called strings, separated by wet hollows, called flarks. The strings lie along the contours of the gently sloping land, at right angles to the way groundwater flows through the peat.[1] They are usually less than a metre high, so the pattern can be faint and is sometimes easiest to see from the air. String bogs are also called patterned fens, patterned bogs, patterned peatlands, strangmoor or aapa mires.[2]
Where they are found
String bogs are a notable feature of the boreal and sub-boreal regions of North America, Europe and Siberia.[3] Within the European Union, the European Environment Agency reports that aapa mires are found only in the far north, in Finland and Sweden, where short summers and long, snowy winters shape them.[4]
Plants
The hollows are wet, open lawns of bog mosses (Sphagnum), sedges and rushes. The strings are drier and carry sedges, shrubs and a few small, stunted trees.[5]
How the pattern forms
Scientists do not yet fully agree on how the pattern forms. Most agree that the direction in which water moves is important, because the strings and flarks are consistently at right angles to the flow. Early researchers thought frost and frozen ground caused the pattern, but string bogs have since been found in places without permanently frozen ground. Other ideas are that peat slowly slips downhill and piles up against obstacles, or that small hollows grow and join together. A study of patterned fens in Labrador and Quebec supported the idea that the pattern develops slowly, as hollows widen and deepen and ridges build up because peat accumulates at different rates.[6] Michigan's natural heritage programme says that more research is needed.[7]
Conservation
The state of these habitats differs from place to place. In the European Union's 2007–2012 reporting under the Habitats Directive, aapa mires had a favourable conservation status in the Alpine region of Fennoscandia, but were still rated "unfavourable – inadequate" in the lower-lying Boreal region next to it.[8] In the US state of Michigan, the Michigan Natural Features Inventory ranks patterned fen as "imperiled" within the state; it gives no ranking for the habitat worldwide ("unrankable").[9] The main threat there is change to the flow of water through ditching, damming, logging and building trails and roads; peat digging is also a threat.[10]
See also
References
- ↑ Foster, David R.; King, George A.; Santelmann, Mary V. (1988). "Patterned fens of western Labrador and adjacent Quebec: phytosociology, water chemistry, landform features, and dynamics of surface patterns" (PDF). Canadian Journal of Botany. 66: 2402–2418. Retrieved 20 October 2026.
Ridges, which are elevated -sublinear landforms, are elongated along the slope contours and dam the lower margin of pools and flarks.
- ↑ "Patterned Fen". Michigan Natural Community Classification. Michigan Natural Features Inventory, Michigan State University Extension. Retrieved 20 October 2026.
a series of peat ridges (strings) and hollows (flarks) oriented parallel to the slope of the landform and perpendicular to the flow of groundwater. The strings vary in height, width, and spacing, but are generally less than one meter tall, resulting in a faint wave-like pattern that may be discernable only from aerial photographs. ... Patterned fens are also referred to as patterned bogs, patterned peatlands, strangmoor, aapamires, and string bogs.
- ↑ "Patterned Fen". Michigan Natural Features Inventory. Retrieved 20 October 2026.
Patterned fens are prominent features in the boreal and sub-boreal regions of North America, Europe, and Siberia.
- ↑ European Environment Agency (2015). State of nature in the EU: Results from reporting under the nature directives 2007–2012. European Environment Agency. Retrieved 20 October 2026.
the combined effects of short summers and long winters with abundant snow. Because of this, they are only found in the very north of the EU, in Finland and Sweden.
- ↑ "Patterned Fen". Michigan Natural Features Inventory. Retrieved 20 October 2026.
The flarks are saturated to inundated open lawns of sphagnum mosses, sedges, and rushes, while the strings are dominated by sedges, shrubs, and scattered, stunted trees.
- ↑ Foster, David R.; King, George A.; Santelmann, Mary V. (1988). "Patterned fens of western Labrador and adjacent Quebec: phytosociology, water chemistry, landform features, and dynamics of surface patterns" (PDF). Canadian Journal of Botany. 66: 2402–2418. Retrieved 20 October 2026.
expansion and deepening of flarks and development of ridges due to differential peat accumulation
- ↑ "Patterned Fen". Michigan Natural Features Inventory. Retrieved 20 October 2026.
Most researchers agree that the direction of water movement is an essential factor as the strings and flarks are consistently oriented perpendicular to the direction of water flow. Early research suggested that strings and flarks are a result of permafrost and frost action, but patterned peatlands have since been documented in northern Michigan, Minnesota, and southern Wisconsin, where permafrost is absent. ... Further research is needed
- ↑ European Environment Agency (2015). State of nature in the EU: Results from reporting under the nature directives 2007–2012. European Environment Agency. Retrieved 20 October 2026.
Aapa mires enjoy a favourable conservation status in the Alpine region of Fennoscandia but are still unfavourable – inadequate at lower altitudes in the adjacent Boreal region.
- ↑ "Patterned Fen". Michigan Natural Features Inventory. Retrieved 20 October 2026.
Global Rank: GU - Unrankable State Rank: S2 - Imperiled
- ↑ "Patterned Fen". Michigan Natural Features Inventory. Retrieved 20 October 2026.
A major threat to patterned fen is hydrologic alteration through ditching, damming, logging, and trail- and road-building activities, which can result in significant changes to peatland composition and structure. Peat mining also threatens pristine peatland systems.