Forest Management and Carbon Sequestration
Remote sensing data are not always accurate in their reflectance values on different land uses. This aerial view measures the dominant land cover of the highest canopy in woodlands. Canopy covers refer to the layers of the woodland vegetation. Multiple layers are normally present in woodlands. As a satellite passes over a site, it records the amount and wavelength of light reflected by all the vegetation it can see. In woodland sites like we will be working in, where there is space between the trees, there will be a contribution of reflectance values from the shrubs and the ground below the tree canopy, as well as the trees. Through the G.L.O.B.E. project, we are to ground truth: a 15 km by 15 km Landsat image of the Earth's surface surrounding our school. Using the modified UNESCO classification system, students determine the land use class for all of the types present in our image.
Students in the environmental landscape technology program must learn to do biometry measurements of woodlands. Biometry is the measuring of living things. The biometry measurements are of tree type, tree height, circumference, canopy cover, and ground cover. These types of measurements are important to understand the nature of a piece of land. Through these measurements, we can show the amount of nutrients and gases living things store. This includes the amount of carbon stored in trees.
Students will equate their biometry measurements to the amount of carbon that is being sequestering in the woodland at our school. These measurements will be ongoing throughout the unit in order to quantify, with relative accuracy, how much carbon typical woodlands can sequester.
Through this activity, students will be trained in a number of skills that are part of their task list. These skills apply the content students learn through lecture and readings and put them into action. Students will learn about orienteering and all the skills that go with that. This includes learning to become a human tape measure, through pacing, in order to estimate distances. They will also learn to properly use a compass. I guess there are very few Scouts anymore since I rarely meet a high school student that can use a compass. They will also learn how to use a builder's level in order to determine the slope of the site. These skills can be taught in a number of ways and I find that infusing them into a project like this one makes the students learn the skills while they determine the distances and elevations of the site.
Tree and plant identification is also a very important skill for my students to master. Looking at preserved leaves or reading keys will not get students to understand the principles of identification. This type of project challenges them to properly identify all of the trees to ensure that they return accurate results. We will focus just on leaves since that is the easiest way to identify trees. If you have not taught this topic before, here is just a brief intro and some basic information you should share with your students about using a dichotomous key to identify trees. I would recommend that you purchase some tree finder books for your classroom; they are very affordable and are easily used by students of all ages since they identify trees by using by using pictures to guide you.
To identify trees easily, look at their leaves. Trees have leaf characteristics that set them apart from other trees. Discuss the difference between evergreen and deciduous trees with the students; that should be easy, but do not forget broadleaf evergreens. Drawing pictures on the board or creating some overheads or a PowerPoint with photos will help them understand the concepts. Be sure you discuss the parts of the leaves so students have a working vocabulary before being introduced to dichotomous keys. Some of the more important leaf characteristics that need to be discussed are leaf arrangement, simple versus compound leaves, and leaf margin. Trees can have oppositely or alternately arranged leaves. Oppositely arranged leaves are positioned directly across from each other. Alternately arranged leaves alternate the sides of the branches as they grow down the branches. Simple leaves are composed of one leaflet, whereas, compound leaves are composed of many leaflets per petiole. Lastly, discuss the leaf margin (leaf edges) and the myriad of different margins that exist on plants. You should discuss smooth (entire), serrations/teeth (dentate), curves or projections (lobes), and any bristles that are included on the tips of the margin. If you have never used a dichotomous key, the Michigan state tree identification website will be very helpful to you and your students [21].
Effective analysis and proper experimental design are important skills of a scientist and are skills that should be taught in an environmental classroom. Through this biometry protocol, students divide up the woodland and define plots in which they will identify all the tree species present and determine their height and diameter a breast height (DBH). The measurements for height are determined by having students construct clinometers out of a grid, a piece of cardboard, a piece of string and a washer. The clinometer uses elementary trigonometry to determine the height and may be a great way to integrate with a teacher in your math department (more students to measure the trees, the quicker it will be done!). The diameter can be determined by using a Biltmore stick, which can be constructed by the students (good measurement activity), or a diameter tape. Fear not, data sheets used in the field for these protocols are downloadable from the G.L.O.B.E. website. Once the data in the field are collected, students will then input their data into an Excel spreadsheet. Having students input these data makes them appreciate the power of calculations and graphing of Excel. I like to infuse technology whenever possible; students need to see the application of software other than in their computer classes in high school.
I thought that determining the amount of carbon sequestered by trees may be a relatively easy task, but I will tell you that I read many articles from scientific journals on this and in fact it is one of the things current research is focusing on. Most look just at remote sensing data or overall area of a forest or woodland and equate the carbon sequestered to an acceptable value. Species specific sequestration is hard to find being studied but, I was fortunate enough to finally determine a way to equate the tree species and age to the amount of carbon sequestered. This will bring a great mathematics component to the unit and require students to really work, not only within their groups but, to share their information with the class as a whole. Tallying up field data and running statistics on the plots is a good exercise and will make them apply and reinforce a number of skills from the mathematics classroom.
Once students get a sequestration value to their studied piece of wooded property, they will then extrapolate their findings to other areas in their local environment. Students will use aerial photos of the county taken in 1998. Through aerial photo interpretation, students will determine local land areas that can sequester carbon. These areas are traced on vellum laid over the aerial photo and then calculated into the amount of area they cover. Students will convert their sequestration value to the same units and then determine the approximate amount of carbon the land on this aerial can sequester.
Using the data calculated on the number of cars used to commute in New Castle County and the carbon they emit, students can then determine the amount of wooded area needed in the county to offset these carbon emissions. Have students compare that to the actual value of wooded land in your county. I was able to get this number from a recent land-use study of our county. Have students analyze the differences between these two numbers and use the data collected through aerial interpretation to write a one-page letter to their local representative describing the problems associated with the difference in these values and what the county may be able to do to sequester this amount of emissions.
Students must also look at the trends of the land use to see if we are going in the right direction in the county. Students can use Google Earth to determine which areas that were there in 1998 are now converted to another type of use. My students are fascinated with using Google Earth and even if you do not feel that comfortable using it, they will catch on quick! I would encourage you to have them look at their own house first to become familiar with how to locate something using the software.
I have come to the realization through writing this unit that the only way we can sequester more carbon on the planet is through managing the terrestrial carbon sink much better. I am not sure how things in your neck of the woods are, but in Delaware all of our "wild" spaces seem to be turned into suburbia and the farms are now growing houses instead of crops for food or biofuels. This trend in land use equates to a diminishing amount of terrestrial carbon sinks in a time when we need to, not only preserve what we have but also, convert lands into ones conducive to carbon sequestration.
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