Pemetic Mountain Species Diversity

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Pemetic Mountain Species Diversity

Lab report by Kerri Davis

Introduction:
Vast ecological changes are characteristic as altitude increases on a mountain (Kricher & Morrison). Wind increases as temperature decreases, replacing broadleaf trees with stunted and prostrate spruces and low-lying shrubs. The broadleaf trees are characteristic of northern hardwood forest communities, whereas the stunted trees and shrubs are characteristic of New England alpine forest communities. Both of these communities are found on Pemetic Mountain of Mount Desert Island, Maine.

Deciduous trees, such as sugar maple and American beech, dominate northern hardwood forests. Due to the greater grade of hardwood forests and much more developed canopy, light levels are less than in an alpine community. However, a well-developed understory of Eastern hemlock, ferns, and wildflowers is characteristic of the environment as good soil moisture and temperature are present, and the canopy is not too dense. In an alpine community, the canopy drops out completely leaving low-lying conifers and stunted spruce trees as the tallest plant layer. This growth is often the result of succession that begins when lichens take over the rock surfaces of the mountaintop. As a result, communities are often based on depressions of rock filled with a thin layer of soil. A covering of lichens, moss, bilberry, and bearberry are often present and a more acidic pH due to coniferous plants is expected.

Species diversity is a measure of both the species richness and eveness of a community. Species richness refers to the number of species in a community whereas species eveness refers to the relative abundance of individuals within a species. When comparing two communities, as in the northern hardwood and New England alpine, greater richness often equals greater diversity. However, in communities with equal numbers of richness, eveness must be turned to. Therefore, though two communities may both each have five species, a community with an equal number of individuals within each species would be more diverse than a community with 5 members of one species and 1 of each of the other 4 species. Using species number (richness) and abundance of each (eveness), a number called a species diversity index can be obtained. A higher number equals a more diverse community. The purpose of comparing northern hardwood and New England alpine communities was to determine which community was greater in terms of diversity using the richness and eveness of the site selected. Abiotic data was also gathered in order to understand what factors may have an affect on the plant species found there.

Materials and Methods:
To determine species diversity, a quadrat was set up in each of the two following locations: a representative northern hardwood community on the west face of Pemetic Mountain, and a representative New England alpine community at the top of the Mountain. The following methods were used at both quadrats. Quadrat area was determined and a Global Positioning System was used to determine the latitude, longitude, and altitude of the site. Wind speed, air temperature, and humidity were determined using a portable weather station. Additional abiotic readings of light level, soil temperature, soil pH, soil moisture, and grade were also obtained. All the plant species within the quadrat were identified and recorded. All members within the quadrat of each species identified were then counted and recorded to determine abundance.

Results:
11 plant species were identified at the northern hardwood community, with the Canada Mayflower being the most abundant in terms of numbers at 29.9%, followed by American beech at 19.2% (Table 1). 15 plant species were identified at the New England alpine community with an unidentified low-lying conifer having the most relative abundance at 54.0%, followed by the Canada Mayflower at 18.8% (Table 2). Despite a lower number of species, the northern hardwood forest had a greater species diversity index at 1.91, with the alpine forest at an index of 1.53.

Abiotic results reveal that air temperature dropped and wind speed increased as the altitude increased from the northern hardwood community to the alpine community. Land slope and soil moisture were less while soil temperature and pH, light level and humidity were greater at the alpine site (Table 3).

Discussion:
Moving a few hundred feet up a mountain is like moving a hundred or so miles north (Kricher & Morrison, 1998). Because of this, vast changes in abiotic and biotic findings were expected. In fact, there were only two species found in both the hardwood and alpine communities: sugar maple, which was sparse at both sites, and Canada mayflower, a hardy and dominant understory species often found in mixed hardwood environments (Rook, 1999). In the hardwood community, American beech was second to the Canada mayflower in terms of abundance and was clearly dominant in terms of biomass. This tree is often found in areas of moist, rich soils, which abiotic findings show was present at the site (Knopf, 1996). Light levels were moderate at 316 lux but high enough to support a well-developed understory of several unidentified ferns and wildflowers, including the Canada mayflower, characteristic of this community (Kricher & Morrison, 1998). Eastern hemlocks characteristic of northern hardwood communities were sparse, perhaps because they are often found on the cooler and moister north facing side of a mountain.

Northern hardwoods steadily drop out as altitude increases (Kricher & Morrison, 1998). Therefore, as expected, the alpine community was dominated by stunted black spruce trees, low-lying conifers, mosses, and bearberry, which were also limited by low soil levels of the quadrat. The community had only a thin layer of soil in a depression of rock more than likely pioneered by lichens, which were abundant on the rocks. Due to the highly coniferous nature of the site, a more acidic pH than the hardwood site was expected, though not obtained, perhaps due to the basic nature of the rock being broken down by the pioneering lichens and grasses. The high winds limit most plants to a relatively short stature, including the incredibly hardy black spruce, which dominated based on biomass. This tree gains a steady hold by rooting itself with lower branches when snowfall bends them to the ground (Knopf, 1996). The higher levels of sunlight afforded by the lack of canopy supports an interrupted ground covering of mosses and patches of thick bearberry, all with numbers too numerous and widespread to gain an accurate count. These plants, along with the low-lying conifers, made up a large relative abundance of plant life in the alpine community.

Though the New England alpine community had a greater number of species, the northern hardwood forest ended up with the higher species diversity index. This is due to two factors. First, three species in the alpine community were too numerous and clumped to gain an accurate count (reindeer lichen, moss, and bearberry), thus bringing the species richness close to even. Second, the northern hardwood forest ended up having greater species eveness. Even with the three uncounted species of the alpine community, the northern hardwood forest would still be more diverse because, whereas the alpine community has a few species that completely dominate in terms of numbers, the hardwood community has a more spread abundance of species, thus equaling greater eveness.

References Cited:
Knopf, Alfred A. (1996). National Audubon Society Field Guide to North American Trees. New York: Chanticleer Press, Inc.

Kricher, J. & Morrison G. (1998). Eastern Forests. Boston: Houghton Mifflin Company.

Rook, Earl. (1999). Pacific Northwest Network web page. “Canada Mayflower.” 27 June 1999. <<www.rook.org/earl/bwca/nature/herbs/maianthemum.html>>.