Tree species composition and frequency on Hubbard Hill oak forest

Ecology Field Trip

The purpose of this field experiment was to determine the composition of the oak forest on and around Hubbard Hill, determining tree type frequency and size through a random sampling process. This is important for ecological purposes in determining the overall needs and structure of the oak forest ecosystem, at least insofar as different tree species are concerned, and for tracking levels of forest growth, loss, or change through repeated measurements/sampled conducted over time. A secondary purpose of this field exercise more directly aimed at the educational objectives was an exposure to the methods and skills necessary for conducting an accurate and effective sample, giving students needed experience.

Methods

Two different sampling methods were utilized in the actual conducting of the field experiment, and the results later compared and combined in analysis. Both sampling methods began with the use of a random number chart to determine transect lines and compass directions, and to determine points along these transect lines for observations/sampling. A drag line was extended along the transect line, once determined, to aid in consistency and the ease of conducting the sample n an accurate manner. Trees included in the measurement were those greater than ten centimeters (in practice, nine-and-a-half centimeters, to account for measurement discrepancies) in diameter at breast height, with breast height defined as 137 centimeters. Measurements/estimates for split-stemmed trees were taken nearer the ground, below the split.

For the plot sample method, a square plot ten meters by ten meters was created around each plot, extending ten meters from the pre-determined observation point along the length of the transect line, and five meters in both directions perpendicular to the transect line. All trees within this square of appropriate size were recorded by species and size. The second sampling method originated with the same randomly predetermined point on the transect line that was used to mark the location of the plot, however this point was used as the center of four quadrants defined by the drag line and an imagined perpendicular line, and the tree nearest to the center point in each quadrant that met the size criteria was recorded. This led to some degree of overlap in the sampling, as there was always the potential for the trees in the forward quadrants to have also been included in the plot, and indeed this was frequently the case.

Discussion

The results of these two sampling methods have a variety of implications both for the ecological understanding of this forested area and for the practices of sampling and data collection that were utilized and explored in this field exercise. First, it is possible that the term "oak forest" is something of a misnomer here, as not only do pine trees represent a much more substantial portion of the tree population but also because compared to the whole, oak trees do not make up a majority or even an especially sizable minority of the forest's trees. This is not just an issue of nomenclature, but also could lead to different perspectives on fundamental ecological issues regarding the mix and balance of species -- both flora as well as fauna -- likely to be found and potentially threatened in this particular ecosystem.

The differences in the two sampling methods are perhaps of even greater importance, given the more direct nature of the results that can be observed in this area. With a population less than half that of the plot sampling method, it is of little surprise that the point-quarter method is less accurate, but the degree of difference is perhaps a bit surprising. Entirely different proportions of trees were found using the two methods, and in the second method there were several specific species that went entirely unobserved despite being fairly well represented in the plot sampling method. These differences could be significant ecologically -- almost certainly are significant, in fact -- as they represent more unique niches in terms of resources attainment and provision for other species of plant and animal life in the forest. There is also a fairly substantial risk of rather complex bias in the point-quart method of sampling, as the method of sampling necessarily chooses trees that are in a fairly close proximal relationship, even more so than with the plot-sampling method (which does contain some of the same bias). With only four trees selected for observation each point and each tree being the closest tree of substantial size to that point, if there was any reason that two species of tree or two specimens of the same species of tree would or would not bas as prone to grow in proximity to each other, then this sampling method is going to demonstrate this relationship rather than an accurate rendering of the forest as a whole.

It is not clear that this bias was actually influential in the measurements and observations made, but its potential is one more reason to recommend the plot sampling method. Still, with the inclusion of both methods the objectives of the field experiment were most definitely and most clearly met. A basic understanding of the forest's composition according to tree type was obtained, and a clear comparison of the two types of sampling method was also achieved. This comparison made the importance of designing and selecting research methods abundantly obvious, given the major difference that can occur with the use of different methods, and also led the researchers to bring a more critical attention to research processes and stated figures in general -- a study that only included point-quarter sampling could produce a very solid looking set of figures regarding the composition of the forest, and anyone not wise enough to examine the processes utilized in the creation of these figures and the preliminary collection of data would essentially be duped -- the results would be believed despite the inaccuracy of the method.

Conclusion

The so-called oak forest at Hubbard Hill is really more of a pine forest with oaks and birches also interspersed. This ecological understanding of the area could have significant implications in later observed issues or research. It is likely that no new understandings would have been reached had not a more comprehensive and accurate sampling procedure been utilized.