Biology 317 Principles of Ecology October 19, 2017 Field Study of Plant Competition. Introduction. Observational Field Study

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1 1 Biology 317 Principles of Ecology October 19, 2017 Field Study of Plant Competition Introduction The survivorship, growth and reproduction of plants are often influenced by competition for light, water or nutrients. Mortality of individuals that begin to grow too close to an established, mature individual tends to lead toward a more uniform spacing of individuals in the population. Individuals growing close together are also likely to show stunted growth and reduced reproduction due to a shortage of resources. This field study will allow us to use some observational techniques to measure the intensity of intra- and interspecific competition among the predominant species potentially involved in plant competition. Observational Field Study Competition often leads to a positive correlation between plant size and interplant distance. For plants of the same species, a correlation between the combined size of a pair of individuals and the distance between them is both an indication of intraspecific competition and a measure of its intensity. The greater the intensity of competition, the stronger the correlation. The same will be true for plants of different species. To evaluate plant competition we will work in the Old Growth Forest region of Green Oaks. We are working in this area because it has fairly uniform resources for plant growth. Differences in topography, moisture supply or soil nutrients can cause variations in plant growth for members of the same species. Thus we will just work on the flat areas of the Old Growth Forest. It is also an area that has been relatively undisturbed for a long time thus there is the potential for competitive interactions to become increasingly important. The basic technique we are using was developed by Yeaton and Cody (1976). Several common species are selected for sampling. I know from previous sampling for my own research that white oak, sugar maple, white ash, and hornbeam are especially common in the Old Growth Forest. We will collect data on the sizes and interplant distances of individuals of all possible intraspecific and interspecific pair combinations. We will measure the following combinations of individuals: Intraspecific: White Oak White Oak; Sugar Maple Sugar Maple; White Ash White Ash; Hornbeam Hornbeam Interspecific: White Oak Sugar Maple; White Oak White Ash; White Oak Hornbeam; Sugar Maple White Ash; Sugar Maple Hornbeam; White Ash Hornbeam Methods 1. Select the first member of a plant pair randomly. We will do this by extending a tapemeasure transect through the stand of vegetation. Random points will be selected along

2 2 the transect (we will use the attached random numbers table). The plant of the desired species nearest each random point is designated as the first member of the plant pair. 2. The second member of the plant pair is the individual of the desired species that is the nearest neighbor of the first member of the pair. This neighbor is only acceptable if no member of an undesired species intercepts the line between it and the first member of the pair. For trees this includes the overhead canopy. We may have a hard time finding white oak white oak intraspecific pairs due to their being spread out in the forest. 3. The distance between the center of the rooted base of the first plant and that of its nearest neighbor is measured. 4. The sizes of the plant members are measured in the appropriate units. We will measure size using DBH diameter at breast height, a standard forester s measure. DBH is the diameter of the tree at 1.5 m high off the ground. If your tape is not a special DBH tape, we will need to divide circumference by π. 5. We will try to obtain equal numbers of measurements for all of the intra- and interspecific plant pairs. Data Analysis We will analyze our data in two ways. First we will use the Chi-square test to determine whether our plant distances are greater or lesser than expected. Calculate the average distance for all of the plant pairs measured. That will be our expected distance. Then take our measured data to determine whether the actual distances are greater or lesser than expected for each plant pair you will need to do 10 Chi-square tests. If the distance is greater than expected that indicates competition is occurring because the plants are becoming more widely spaced. Then we will plot the combined sizes of each plant pair versus distance between the plants in each pair. You should do a linear regression to determine whether there is a significant relationship between distance and combined size. I think one overall regression should be good enough. So did we find evidence of competition among the tree species in the Old Growth Forest at Green Oaks? If so, why might that be happening? If not, why not? Did all species pairs indicate competition or just some of them? References: This lab is based on an exercise in: Cox, G.W Laboratory Manual of General Ecology, 7 th Edition. Wm. C. Brown Publishers, Dubuque, IA. Yeaton, R.I. and M.L. Cody Competition and spacing in plant communities: The Northern Mojave Desert. Journal of Ecology. 64:

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4 4 Plant 1 White Oak DBH Distance - cm Plant 2 White Oak DBH Plant 1 Sugar Maple DBH Distance - cm Plant 2 Sugar Maple DBH Plant 1 White Ash DBH Distance - cm Plant 2 White Ash DBH Plant 1 Hornbeam DBH Distance - cm Plant 2 Hornbeam DBH Plant 1 White Oak DBH Distance - cm Plant 2 Sugar Maple DBH

5 5 Plant 1 White Oak DBH Distance - cm Plant 2 White Ash DBH Plant 1 White Oak DBH Distance - cm Plant 2 Hornbeam DBH Plant 1 Sugar Maple DBH Distance - cm Plant 2 White Ash DBH Plant 1 Sugar Maple DBH Distance - cm Plant 2 Hornbeam DBH Plant 1 White Ash DBH Distance - cm Plant 2 Hornbeam DBH