Forest Lab Essay example

Submitted By thedewman
Words: 1094
Pages: 5

Prof. A
EVST Section 002
Group 4
Forest Lab
November 28th 2013

Benedict Nature Preserve Ecosystem Analysis
1. Abstract
This labs purpose was to examine how an ecosystem and tropic compositions is structured in a nature preserve setting. Through various measurements of different aspects of the forest ecosystem we gathered results to analyze the certain plotted area’s ecological efficiency and biomass. We investigated the energy transfer as you go up the trophic hierarchy. In addition we took a T-test comparing the mean of the leaf litter we collected for the before and after weights.
2. Introduction
For the Forest Lab our goal was to observe and investigate how an ecosystem is structured. The purpose of the lab is for us to gauge the trophic composition as well as the productivity of an ecosystem. In this case we went to the Benedict nature preserve to conduct our experiment. We first went over all the details of the lab with our TA’s before we jumped into it. We were given the proper materials to perform our measurements and then we were told a location to occupy and measure. We split up into our groups and sectioned out our quadrants initially and we were assigned as 45m out from the original spot we met. From there we proceeded to mark our biggest quadrant (25m x 25m) to ultimately record the amount of trees in that area. We recorded that data and then moved on to sectioning off a 10m x 10m square to measure all the trees with a DBH greater than 3cm. Once we finished that we sectioned off a 1m x 1m plot of land inside the 10m x 10m area to measure the insects in the small square. Lastly we sectioned off an additional 1m x 1m square to collect all the leaf litter. All of these plots and measurements went into the overall analysis of the trophic pyramids we later developed. The bottom layer represents the autotrophs, the second level represents the herbivores/detritivores and the top level represents the carnivores. We then used the biomass for each tree species to create the biomass pyramid. From there an energy pyramid could be constructed. We used the previous biomass values to be able to estimate the energy equivalent for each level of the pyramid. This led us to calculating the ecological efficiency which is the transfer of energy from one trophic level to the next.
3. Methods
The methods utilized for this lab were relatively simple. We mainly used a tape measure and a coat hanger to gather our data with. So to measure off each section we would go the distance required and mark the spot in four corners to mark our area plot. As for the smaller plots we used a 1m x 1m coat hanger and recorded everything within that area. We used the tape measurer to find out the DBH of the trees. All of the methods to calculate the numbers/values for the various biomasses of the different trophic levels are contained in the lab manual pdf.
4. Results
We performed a two tailed T-Test of the decomposition of the leaf litter weights before and after. Here are the results we got for that.

Comparing Means [ t-test assuming equal variances (homoscedastic) ]

Descriptive Statistics

Sample size




Degrees Of Freedom
Hypothesized Mean Difference

Test Statistics
Pooled Variance

Two-tailed distribution

t Critical Value (5%)

One-tailed distribution

t Critical Value (5%)


Test Statistics

Critical Value (5%)

Pagurova criterion

Test Statistics

Ratio of variances parameter
Critical Value (5%)

DECOMP (fine mesh litter bag)

DECOMP + Detritivore (coarse litter bag)…