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Flora Exercise Comments
L. Meredith, 8/31/10
The goal of the flora exercise was to utilize vegetation as markers of the integrated weather that may be experienced at any one point on Mt. Washington. For biology to survive, it must adapt (especially to some of the harsh mountain climes) to its environment while competing for resources with other life. This means that we can note both the general environmental control on plant communities and also interesting, specific adaptations of plants that reflect the weather at Pinkham Notch (the base of Mt. Washington), the auto­road mile 4 stop, and at the top. 1. Environmental Control
We studied environmental control on plants by comparing vegetation as we ascended the climate gradient up Mt. Washington. Specifically, we noted the number of levels and the types of species found at each stop.
The Pinkham Notch flora is characteristic of the northern hardwood forest. The
community has 4 or 5 levels or layers (5 if you separate sub­canopy from shrubs), and includes upwards of 40 species:
Canopy: trees, about half and half deciduous and evergreen; 5 – 8 species.
Sub­canopy: smaller softwood trees (e.g., mountain ash, striped maple), young hardwoods, and conifers; the subcanopy is dominated by conifers, by nearly 3:1.
Shrubs: 3 or 4 species
Herbs and Grasses: a varied community, largely dependent of available light; upwards of 20 species.
Mosses and Lichens: dominated by mosses, several species.
An important observation is that the sub­canopy layer is dominated by conifers. This suggests that within 50 – 100 years, the canopy layer will change to a dominantly
conifer forest. This is evidence for the process called succession, in which more stable (i.e., climax) communities displace earlier, less developed communities.
The flora on the auto­road at mile 4 is on a ridge that is exposed to severe winter
weather. The community is a krummholz community in which there are potentially 3
layers. The tallest layer includes black spruce as the dominant species, with subordinate balsam fir and rare yellow birch. The groundcover layer includes mostly dwarf shrubs (mountain cranberry, crowberry), with subordinate herbs, sedges, rushes and grasses. There may be as many as 12 – 15 species in this groundcover layer. The third layer is the lichen layer that is on the rock surfaces. There may be 3 to 5 lichen species. The total species count here is less than half that at Pinkham Notch, and there is no development of a canopy layer. The flora at the top is typical of an alpine sedge community. The top of Mt. Washington is above treeline (determined by a short growing season – there is not enough time for trees to harden new annual growth before continuous freezing temperatures kill new growth), so the plant community is restricted to the groundcover and lichen layers. The groundcover is dominated by Bigelow sedge (triangular stems, with fruit at the tips of stems), with subordinate highland rush (round stems, fruit growing in clumps about midway up the stems), and two or three species of grasses. There are about 10 species of dwarf shrubs and herbs, most conspicuous of which is mountain sandwort, forming tight bunches with small, white flowers. There are 5 – 8 lichen species in the groundcover, also. The community has two layers, if you separate the lichens from the groundcover layer, and consists of fewer than 20 species.
1. Specific Adaptations
The class identified adaptation strategies of many plants on Mt. Washington. At Pinkham Notch we noted that competition is more fierce and nutrients more plentiful, so plants maximize their growth to compete for key resources, especially sunlight. At this elevation, hardwoods, such as maples, beech and birch, thrive. These deciduous trees invest large amounts of energy to leaf­out each year. This allows them to maximize their sunlight interception and grow only during the short growing season. Coexistent are evergreens, such as balsam fir and red spruce, which do not intercept as much light, but are able to begin photosynthesis as soon as temperatures rise above freezing and can grow longer than deciduous trees that require time to leaf­out.
Krummholz
The plants at the auto­road mile 4 stop had markedly different adaptation strategies than below. The evergreen krummholz clearly adapt to the high, icy winds by growing close to the ground, away from the wind. We noted larger patches of krummholz behind the shelter of rocks and ridges. Much of the plant community adapted to the high winds by 'growing low'; also an adaptive strategy to remain warmer in the winter by being insulated next to the ground under the snow pack. We observed diapensia plants that grow in cushions to retain heat. The steep soils do not retain the precipitation at these elevations, and plants such as Labrador Tea were found to coat the underside of their leaves with small hairs to collect and retain water vapor from clouds and fog that pass by. Many of the plants, even the cranberries, are actually evergreens at these elevations, which allows them to photosynthesize for longer of the short growing season. Purple­tinted Diapensia
Alpine communities at the top had many of the same adaptation strategies as at the mile 4 stop. We did note the presence of many more grasses, sedges and rushes, which adapt to high winds by being extremely flexible. We noted that many of the alpine plants, including diapensia, were more purple than below; this indicates that they employ purple anthocyanin pigments to shelter their cells from damaging uv radiation, which is more intense at higher elevations.
Observing the flora on Mt. Washington gave us a unique perspective on the year­
long weather patterns experienced at different heights on the mountain. The plant communities were found to change dramatically with elevation and specific plant adaptations gave us insight into how life has managed to survive under the challenge of Mt. Washington extreme weather.