Ecology

.. se we assume diameter at breast height (DBH) is a good indicator of tree age. This assumption may be false, because DBH doesn’t have to directly relate to age. Some species grow in diameter faster then they grow in height. Also some species grow rapidly in diameter while they’re juveniles and then stop growing in diameter and start growing in height, or vise versa.

There isn’t one set speed that a tree grows in diameter that could possibly make it a reliable method of determining age. In most cases a larger diameter does mean an older tree. But not in all cases and not when trying to determine juveniles from adults or middle-aged trees. 4.a. To determine if a species is increasing there must be a high number of juveniles.

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This indicates that there is high recruitment, which results in a growing population. More offspring equals more candidates that may be able to establish a supporting location and survive through adulthood and reproduce, figure five and seven are examples of increasing species. Their juveniles are high, therefore indicating a growth in its population. To determine if a species is declining there must be a high number of adults and low juveniles. This shows that there is minimal recruitment and the species is not reproducing fast enough to maintain its current population. Figures eight and nine are good examples of declining populations.

Both of these species have no juveniles present, which indicates that the adults are not reproducing. If no offspring are produced before these individuals present die, the species will fall into local extinction. To determine if a species is remaining approximately the same there must be low juveniles and adults, with high middle-aged trees. This is because if there are low juveniles then not many individuals are being added into the population and if there is a high number of middle aged trees then that suggests that most juveniles are able to establish themselves and survive. The low number of adults indicates that not a lot of middle aged trees survive to adulthood.

An example of a species population that is remaining approximately the same is presented in figure six, where juveniles and adults are low and middle aged trees are high. 4.b. Refer to “A Guide to the Common trees of the College Woods Natural Area” The present size structure of the species in College Woods suggests that there was a disturbance probably about 50 years ago and now the forest is reestablishing itself. The main observation supporting this is that the size of the DBH’s are quite small in comparison to what they would be if there had been no disturbance. The forest has now reestablished its self, and is acting as if there had never been a disturbance.

After the initial disturbance the forest grew, and is now is full of different species that are favoring the non disturbed land. The eastern hemlock is a poor colonizer of disturbed areas, its seedling establishes will in the forest understory and is very shade tolerant. These qualities are characteristic of an area that hasn’t received any disturbances and since the hemlock is the most abundant in College Woods this supports the conclusion that the forest is act as if there has not been a recent disturbance, otherwise the hemlock would not be thriving as it is. The second most abundant species in College Woods was found to be Black Birch. This species establishes itself in small canopy gaps left open by the hemlocks. Also the black birch is intermediate in shade tolerance, which is perfect with the dominance of hemlock creating intermediate shading of the understory.

The American beech is “the most shade tolerant northern deciduous tree”, seedling can establish in the understory, and it is also a poor colonizer of disturbed areas. The American Beech is the third most abundant in College Woods, which also supports the suggestion that there hasn’t been any recent disturbances. It is establishing itself under the shad of the hemlock and black birch, and wouldn’t be well established at all if the area were disturbed. Red Oak establishes itself in canopy gaps and is only an intermediate shade tolerater. Since most of the unshaded understory is now taken up by hemlock, birch and beech, this red oak is having a hard time establishing itself and that is why it is of low abundance (4th, 6 stems) in College Woods. Finally, White Pine need direct sunlight, and thrives best where disturbances have been present. In College Woods only one white pine was found and was an adult supporting the conclusion that there has not been any recent disturbances, other wise the white pine would be establishing itself and dominating, because disturbed/cleared out areas are where they establish best.

5. According to the Study Site section of the Forest Community Structure and Succession lab manual, about 100 years ago College Woods was dominated by large, old white pine. The white pine was dominating due to the observation that the area was most likely cleared during the 1600’s making is a perfect area for white pine to dominate, because they prefer abandoned fields, burned over areas or large canopy openings, areas where they can receive direct sunlight. It was also stated that the understory was exclusively of hemlock and a few beech; which are two of the most shade tolerate trees. Refer to figure ten, the white pine (Ps) was dominant 100 years ago rather then the hemlock (Ts) and black birch (Bl) which are dominant now. And the only two species in the understory were exclusively hemlock and beech (Fg), rather then having a more diverse population of species as we have now of beech, red oak (Qr), red maple (Ar), White pine, sugar maple (As), Yellow birch (Ba) and hophornbeam (Ov).

The rest of the species were either not present or at very low quantities, such as the white ash (Fa) is now. 6. As discussed in question 4.a. it was found that species of Hemlock and American Beech were increasing, species of Red Oak and White Pine are decreasing rapidly, to the possible point of local extinction, and that Black Birch is staying at approximately the same population. Without any disturbances, the trend should stay the same as it is now.

Therefore, in comparison to College Woods now, there will be an increase in hemlock and beech, a great decrease in oak and pine, and constant population of black birch. Also since the abundance’s of all other species ranked below white pine were even smaller then that of white pine, the decreasing trend of the pine it most likely a trait of those ranked lower, therefore the other species are at a very low abundance. 7. Throughout this exercise I have learned much about College Woods Natural Area, as well as, forests in general. I now know the names of certain trees and can identify them at site.

I have learned the difference between density and dominance of species. I have also learned what trees are present in College Woods and their different abundances. I have learned much about the tree community of the woods that are right here on campus, which is very interesting to me and I have done my best to predict successional change in this environment. Science Essays.

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