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Ecology Essay

The main purpose of this exercise is to see if College Woods Natural Area is experiencing succession and to observe and document the tree community structure. Other purposes of this exercise are to examine College Woods and measure the densities of different species of trees as well as diameters of stems and use these measurements to determine if the varying measurements lead to varying information about this tree community. Another purpose is to determine all species present, as well as the abundance of each species. We will also analyze the size structures of the trees to predict future change in College Woods Natural Area.

The extent of the estimation of absolute density from absolute dominance is variable when looking at figures two and three. Figure two would not be a good example of a good estimator of absolute density estimated from absolute dominance. The R-squared value, which tells how close the measurements are to the resulting fit line, is equal to 0.027 (whereas an R-squared value of 1.0 equals a perfect fit). This shows that there is a very small relationship between the absolute density of the Hemlock and the absolute dominance of the Hemlock. Figure three would be a good example of an estimator of absolute density from absolute dominance. The R-squared value is equal to 0.609, which is significantly higher than that in figure 2 (0.027). The higher the R-squared value, the stronger the relationship, in this case, of absolute density of Black Birch and the absolute dominance of Black Birch.

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The fact that in one case the ability to estimate absolute density from absolute dominance is great (Birch), and in the other is low (Hemlock), suggests that this is not a reliable method of estimating. There must be alternate factors to take into consideration to estimate absolute density. As seen in figures one and four, the estimation of absolute density from relative density has more merit than that of absolute density from absolute dominance. Figure one has an R-squared value of 0.229, which suggests a relationship between the absolute density of Hemlock to the relative density of Hemlock, but hardly a significant one. Figure four is a better example of a relationship between absolute density and relative density. Here the R-squared value is 0.697. This suggests that the estimation of absolute density from relative density has more of a relationship to each other and therefore is a better estimator of absolute density from relative density, than that of absolute density from absolute dominance, but still not a solid, reliable method of estimating.

Both cases seem to differ from each other enough to make it an unusable method of estimating. The relationships between absolute density and relative density and between absolute dominance and absolute density are weak due to the different arrays of measurements with the different species. The wider the range of measurements the more room there is for variation, which in turn, makes it harder to find relationships Figures one and two deal with the species, Hemlock. Hemlock had the largest ranges in all cases, absolute density (5-23), relative density (60-83.3), and absolute dominance (0.044-1.059). These figures had the lowest R-squares (1: 0.229, 2: 0.027) due to this high amount of varying measurements.

The Hemlock was the most prevalent species, therefore having the widest range of measurements due to the simple abundance of trees, as well as the different DBH’s (diameter breast height). This information suggests that the higher abundance and dominance result in a lower relationship between different factors. The relationships between absolute density and absolute dominance, and relative density and absolute density of the black birch also support this conclusion. The range of measurement dealing with the black birch is much smaller than that dealing with Hemlock, resulting in a closer relationship between factors. As seen in figure three and four, dealing with the black birch, the ranges are significantly smaller, absolute density (0-7), absolute dominance (0-0.212), and relative density (0-31.25) resulting in larger r-squared values of 0.609(figure three) and 0.697(figure four). When the ranges are small there is less space for the measurements to be spread out.

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The smaller range results in similar measurements and less room for variation, resulting in a tighter fit line and greater R-squared value. The abundance measurement to use when estimating the success of Hemlock seedling establishment and survival in a forest would be the abundance measure of the dominance of hemlocks present. This measurement would support that the original hemlock seedling had survived through its juvenile stage and established a supporting location where nutrients and other life-supporting resources are available for the hemlocks to continue to survive and thrive throughout adulthood. Dominance would be used in contrast with density because we want to measure how well the seedlings have established themselves, so you would want to look at the adult/developed hemlocks because these are the ones that have been able to establish themselves and survive.

The abundance measure to use when estimating the amount of useable wood fiber in a managed forest would be the abundance measure of dominance also because we are looking for trees with high DBH’s (diameter at breast height). This would be the appropriate measure because useable wood fiber depends on the diameter of the tree rather than the number of stems per unit area, as with density. Trees with a large DBH would be suitable for wood fiber, be able to be made into lumber. Trees with small DBH would be useless, like wood fiber because the lumber it is to be made into would be too small to be used as lumber.

The abundance measurement to use when assessing possible competitive relationships among tree species in forests on different soils would be the abundance measure of the densities of each species on different soils. This would be the best choice because one would be able to tell which species are outcompeting other species on that particular soil. For example, Hemlock is the densest in College Woods on the certain soil that is out there, this was determined through the abundance of measure of the densities of each type of species present in College Woods. In a different location where there is a different type of soil, Hemlock may not be the densest species, in order to find this out an abundance measure of densities of each species at the new location must be made to see which is denser.

The abundance measure to use when estimating the amount of habitat available for a warbler that nest and forages in the crowns of white pine trees would be the abundance measure of the dominance of white pines. The dominance should be found rather than the density because if the warbler uses the tree to nest and forage in, then the tree needs to be beyond its juvenile stage and have established itself. If we were to measure the density of white pine, that would also count smaller trees that are of no use to the warbler.

In this exercise, 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 than 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.

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To determine if a species is increasing there must be a high number of juveniles. 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.

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 is quite small in comparison to what they would be if there had been no disturbance. The forest has now re-established 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 nondisturbed 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 acts 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”, the 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 haven’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 tolerate.

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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 needs 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 have not been any recent disturbances, otherwise, the white pine would be establishing itself and dominating because disturbed/cleared out areas are where they establish best.

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 1600s making it 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 exclusive of hemlock and a few beeches; which are two of the most shade-tolerant trees.

Refer to figure ten, the white pine (Ps) was dominant 100 years ago rather than 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 than 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.

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 a constant population of black birch. Also since the abundance of all other species ranked below white pine was even smaller than that of white pine, the decreasing trend of the pine is most likely a trait of those ranked lower, therefore the other species are at a very low abundance.

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 the 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.

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Ecology Essay. (2021, Apr 03). Retrieved March 24, 2023, from