Shades of Green: Earth's Forests -- Boreal Bog Forest

Boreal bog forests are found in northern areas that were covered by glaciers during the last ice age. They began to form about 18,000 years ago, when the ice sheets started to retreat. The glaciers left behind many hollows and depressions, some of which filled with water and formed lakes, some of which filled with sediment and formed bogs.

The trees around the edges of bogs are similar to those found in regular boreal forests. Moving farther into the bog, there are species such as black spruce and tamarack, followed by an area of shrubs and a dense zone of herbaceous plants including Sphagnum Moss. In the center of the bog there may also be an area of open water.

Evergreen trees belong to a group of cone-producing plants that first appeared over 300 million years ago, long before other flowering plants.

Larch trees, which lose their needles every winter, grow in both boreal and boreal bog forests. Photo courtesy Al Walters.

Doesn't the bog completely fill in with sediment? In theory, yes: over thousands of years the bogs would gradually become more solid, and each band of vegetation would move inwards until the bog was entirely transformed into forest. However, in reality, this rarely happens so evenly, and in some areas bogs are even expanding.

The soil in a bog is very acidic. This is because of the underlying soil type, lack of drainage, and chemical reactions caused by some bog plants. Some bacteria can not survive in these acidic conditions, and without as many bacteria or fungi to decompose organic material, almost nothing rots in a bog. Because decomposition rates are so slow, the soil remains poor. Some bog plants are insectivorous and obtain many nutrients by trapping insects to make up for nutrients they can't get from the soil.

Bog rosemary is small shrub with tough, needle-like leaves and pink bell-shaped flowers, common in boreal bog forests. Photo by Maya Walters.

Insect-eating plants including pitcher plants and sundews are common in boreal bog forests. These two plants have two very different methods for trapping insects. Sundews have sticky threads growing on their leaves, in which insects become entangled. Pitcher plants capture prey in hollow stalks, where, once trapped, insects can not escape. Other plants have evolved a variety of different strategies for capturing and digesting prey. All insectivorous plants have an advantage in boreal bogs because they are able to obtain nutrients directly from the insects they capture.

Yellow pitcher plant (Sarracenia flava) is one of the insectivorous plants that inhabits boreal bog forests. Photo copyright USDA, PLANTS database.

Bog sediments become important vegetation records over thousands of years. Grains of pollen from plants in the surrounding area collect in the sediments, and remain identifiable for thousands of years. Sediment samples can be extracted from bogs to determine the history of the vegetation in that area.

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