General Environmental Science I ENV 121 Forest Composition Lab Name: __________________________ Background Knowing the physical structure of a plant community can tell us something about the biological structure of the community, something about interactions between species, and how the community functions in gathering energy and cycling nutrients. The structure of the plant community determines the animals that can be present, so is of use in wildlife management. For instance, an oak-hickory forest produces lots of nuts. Animals that feed on nuts, like wild turkeys, blue jays, and squirrels will likely be present. Studies of plant communities over the course of many years have allowed biologists to understand ecological succession, the replacement of species by other species over time (and therefore the replacement of communities over time). Biological diversity means the variety of organisms considered at all levels; genes, species, higher taxonomic levels, and the variety of ecosystems on earth. Species diversity refers to the number or variety of species in a specific area. A community is a group of populations of different species occupying a specific area. We can speak of the animal community of a lake, the insect community in a vegetable garden, or the plant community of a city park. Measuring biological diversity sometimes means measuring species diversity in a particular area. The species composition (which particular species are present) is important as well, because two different communities may have the same diversity but contain completely different species. The diversity within a community is called alpha diversity. Diversity is an ecological concept that combines the number of species in a community (richness) with a measure of how evenly represented each species is in the community (evenness). Diversity is usually discussed with respect to a single kingdom or phylum of organisms (e.g., plants or vertebrates). A diversity index is a measure of species diversity that takes the relative abundances of different species into account. Diversity indices provide more information about community composition than simply the number of species; they combine richness with evenness using a mathematical formula. Simpson’s index is the most commonly used diversity index that describes alpha diversity for plant communities. Simpson’s index ranges from 0 to 1, where numbers closer to 0 indicate more diversity. If you have only one species in a community, Simpson’s index will be 1. Relative density values take in to account the abundance of each species relative to the total number in the community. Relative dominance takes in to account the size of each tree. For example, a community may only have a few oak trees, but each oak tree is much larger than the other tree species. Thus, measuring only the number of oak trees obscures the dominance of oak according to tree size. Importance values can be calculated after the size and number of individual trees of the various species is measured. The trees with the highest importance values will be those that exist in the greatest number and/or are of the greatest size -- these are the trees that may have the greatest effect on the community. Beta diversity is a comparison between the compositions of different communities or ecosystems. The simplest measure of the "overlap" between any two communities is simply the number of species shared in common between the two communities divided by the total number of species in the two communities. This number is simply a percentage, and varies from a low value of 0 (no species in common) to a high of 0.5 (all species in common). Since it is more convenient to have the value of the index increase to a whole number (at all species shared), the numerator is multiplied by 2. The resulting value for this calculation is called the Sørenson index where 0 equals no overlap and 1 equals complete overlap of species. We will determine species composition, alpha diversity using Simpson’s index, relative abundance, relative density, importance values, and beta diversity using Sørenson’s index. 1 Please read the instructions for day 1. This is what you would have done to collect the data. Since we are not meeting in person you will need to use the data sheet labeled “forest composition” you can find in the labs module on Canvas to do your calculations and answer the questions. This data was collected by a previous ENV 121 class. I have not done any quality control of the data. Ensure you create a data sheet that includes all of your calculations. You need to turn this in with the lab Day 1 – In the Field • • • Your instructor will take you to two forested locations (an upland plot, away from the stream, and a lowland plot, near the stream). Use measuring tape and flagging tape to create a 20m x 20m square plot in the forest. Record species and circumference (at chest height) for each tree in your plot with a circumference greater than 9cm. Mark measured trees with chalk to avoid counting them more than once. You must identify and measure all trees > 9cm circumference in your plot. Feel free to look under logs and rocks for wildlife, but leave your site just as you found it. Be respectful of the ecological community. Day 2 – Back in the Lab • • • Calculate basal area for each tree in your plot, then sum the values for individuals trees to get the sum basal area for each species. Use the formula A = π * (C/2π)2 Group your individual trees by species. You can work on a laptop or create a data sheet by hand with the following headings: species • • • • • • • • # in plot relative density sum basal area relative dominance importance value List your tree species in your data sheet. You should have one line of data for each species. Enter the total number of each species you found in your plot in the next column. To find the relative density of each tree species, divide the number of the tree species (i.e. white oak) by the total number of trees in your plot. Relative density should be between 0 and 1. Find the sum of the basal areas for each tree species from the field data sheet. To find the relative dominance of each tree species, divide the sum of basal areas of the tree species (i.e. white oak) by the total basal area of all trees in your plot. Relative dominance should be between 0 and 1. To find the importance value of each tree species, simply add its relative density and relative dominance. Record the importance values for each tree species on the board. Calculate Simpson's diversity index Simpson's index (D) measures the probability that two individuals randomly selected from a sample will belong to the same species. D = Σ (n / N)2 where n = # of individuals of a species (i.e. # 10 white oaks) in plot and N = total # of all trees in plot Basically, Simpson’s index is the sum of all relative densities squared. D= D= 2 • Calculate the Sørenson index (S) by dividing the number of species in common between the two communities by the total number of species in the two communities and then multiplying by two. o Use data from both plots in each of the two communities. S = (# species in common) * 2 / (total # species in lowland plot + total # species in upland plot) S= Discussion Questions 1. What is the difference between species richness and species evenness? 2. Describe a hypothetical tree community with high species richness, but low species evenness. 3. Which tree species was most abundant in your upland community plot? Which was most abundant in your lowland community plot? 4. What is the difference between relative dominance and relative density? 5. Describe a hypothetical tree community where one tree species has high relative dominance and also a low relative density. 3 6. Are your importance values similar to importance values for the same species in the other community? 7. What may be some reasons why the importance values for each species are different? 8. What is the purpose of the Simpson’s diversity index? 9. What is the purpose of the Sørenson index? 10. The Sørenson index and importance values both help to quantify the similarities and differences among different communities. What is a weakness of the Sørenson index in comparison to importance values? Don’t forget to turn in your data sheet with calculations in order to get credit for the lab END OF LAB 4
Purchase answer to see full attachment