Boreal Bog (bog edge)

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Boreal Bog (bog edge)

Lab report by Jenifer Drummond

Introduction:
Boreal bogs are a result of glacially carved depressions which then fill with freshwater. In order for a boreal bog to form, the absence of a natural drainage system in the depression is required. A boreal bog is characterized by high soil moisture level and low soil pH. The edge of a bog can be recognized by the presence of black spruce and tamarack. The interior of a bog is composed of shrubs, sphagnum moss, and areas of open water. Cranberry can also be present in the interior of boreal bogs. Bogs are more or less a sheet of moss on top of water. As a result, they are unstable and the ground quakes when walked upon (Kricher and Morrison, 1998).

A boreal bog soil is moist for two reasons. First, the moss is absorbent and holds moisture well. Second, the moss is covering standing water. The soil is nutrient poor, particularly lacking in nitrogen, which plants depend on. To overcome this, plants have evolved to be carnivorous by eating insects because the protein from the insects is made of nitrogen-based amino acids. Two of the most common insectivorous plants encountered in a boreal bog are the pitcher plant and sundew (Kricher and Morrison, 1998).

The acidity of bogs can be accounted for by the combination of the spodosol type soil, lack of drainage, and presence of sphagnum moss. Because the bogs are so acidic, it is not a prime environment for decomposer bacteria to live; therefore, bogs experience low decomposition rates. The acidity also allows certain plants and trees that are tolerant to a low pH to grow in the bog. The species that normally compete with plants found in the bog are not necessarily tolerant to the low soil pH and are therefore not present, giving bog plants a chance to grow. This is demonstrated by the presence of tamarack in bogs. Tamarack is not shade tolerant and is usually easily overshadowed by other plants. The plants that normally overshadow it, however, cannot grow in the moist acidic conditions of the boreal bog thus allowing the tamarack to grow (Kricher and Morrison, 1998).

The purpose of this field exercise was to sample two quadrats in a boreal bog. One quadrat was elevated near the edge and the other was at a lower elevation in the interior. Both abiotic and biotic factors, including species diversity, were measured.

Materials and Methods:
The materials used in this experiment included: plastic stakes and tape to mark off two quadrats, field guides to identify species within the quadrat, a portable weather station, a compass, devices to measure soil moisture, soil pH, and light level, a global positioning system, altimeter, thermometer, and tape measure. A quadrat of 0.42 meters by 0.44 meters was marked off in the elevated bog area. Similarly, a quadrat of 0.61 meters by 0.48 meters was marked off in the low lying interior of the bog. Then, field guides were used to identify species inside the quadrats. The following abiotic factors were measured using appropriate instrumentation from inside the quadrat: latitude, longitude, altitude, soil moisture, soil pH, soil temperature, air temperature, average wind speed and direction, humidity, and light level. Additionally, species and other traces of animals occurring outside of each quadrat were also noted.

Results:
In the elevated boreal bog, seven species were identified (Table 1). Additionally, in the interior bog, eleven species were identified (Table 2). Sphagnum moss dominated both quadrats as it covered the ground completely. A combined list of species from inside and outside of both of the quadrats, as well as evidence of other species, is given in Table 3. A species diversity index was calculated for each quadrat: 1.28 for the elevated quadrat and 1.9 for the interior quadrat (Tables 1 and 2).

The only species that each quadrat had in common were leatherleaf, the pitcher plant, and sphagnum moss. The elevated quadrat also had lichen, a flower, a shrub, and spruce tree. The interior quadrat had several unidentified plants, grass, a sundew, and cranberry. Outside of both quadrats, scat and animal tracks were found (Table 3).

Soil moisture varied among the two quadrats, being 10% in the elevated area and 97% in the interior (Tables 4 and 5). Likewise, soil pH varied among the two quadrats, being 6.6 in the elevated area and 3.7 in the interior (Tables 4 and 5).

Discussion:
The difference in the number of species found on the elevated patch compared to the low-lying interior can be explained by the elevation. Plants present in the boreal bog are tolerant to both extreme moisture and acidic soil. The small rise in elevation – only approximately 10-20 cm – drastically decreased soil moisture and increased pH. Therefore, plants which are adapted to live in the bog cannot live there. Additionally, plants such as those found in a hardwood forest – maples and oaks, for example – are not found in the bog because they cannot withstand the low soil pH and high moisture level.

Elevation also explains the difference in species diversity. Because the range of abundance of species was practically the same for each quadrat – 1 to 21 for the interior and 1 to 22 for the elevated area – the difference must come from species richness, not species evenness. Plants in the bog are adapted to live in the moist acidic conditions of the bog and cannot live in the elevated areas; therefore there are not as many present.

The horizontal structure of the bog can also be explained in terms of the difference in elevation. Because the soil conditions change with elevation, there are places where some plants can live and other plants cannot. For example, the soil was too acidic and moist to find a pine tree in the interior of the bog; however, the elevated area had a pH and soil moisture of that comparable to a hardwood forest or pine tree stand and therefore there were pine trees in the elevated areas. With little patches of elevated areas among the bog, the horizontal structure is not uniform.

As previously mentioned, carnivorous plants are found in the boreal bog. Plants evolved to be carnivorous because the soil is so nutrient poor that they needed to find another source of nutrients. The soil is nutrient poor because decomposing bacteria, which recycle nutrients, cannot perform as well in the acidic conditions of the bog. As expected, sun dews and pitcher plants were both identified. Pitcher plants are designed to hold water and digestive juices in a “cup” formed by their leaves. They trap insects and digest them in order to extract nitrogen. Sundews have sticky hairs on their leaves which trap insects.

It is not surprising that ants were one of the species noted in the interior quadrat, particularly given the presence of the pitcher plants and sundews also found in the quadrat. Some traces of other animals were present, including scat and animal tracks. This suggests that animals frequent the area. One of the pieces of scat contained berries, the animal may have fed on some of the cranberry present in the bog. Also, it is quite probable that many animals come to drink from the areas of exposed fresh water. The presence of deer tracks is not surprising given the amount of edge present in the bog.

References Cited:
Kircher, J., and Morrison, G. 1998. Eastern Forests. Houghton Mifflin Company: New York.