Spatial pattern model of herbaceous plant mass at species level |
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| Affiliation: | 1. College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi 712100, China;2. The Open University of Japan, Ibaraki Study Center, Bunkyo 2, Mito 310-0056, Japan;1. AgResearch Limited, Ruakura Research Centre, Private Bag 3123, Hamilton 3240, New Zealand;2. University of Waikato, Faculty of Science and Engineering, Private Bag 3105, Hamilton 3240, New Zealand;1. Space Informatics Lab, Department of Geography, University of Cincinnati, Cincinnati, OH 45221-0131, USA;2. Department of Computer Science, University of Massachusetts Boston, Boston, MA 02125-3393, USA;1. U.S. Geological Survey, Southwest Biological Science Center, Rm. 123, University of Arizona, 1110 E. So. Campus Drive, Tucson, AZ 85719, United States;2. U.S. Geological Survey, Core Science Analytics and Synthesis, Denver Federal Center Bldg. 810, Lakewood, CO 80225, United States;3. U.S. Geological Survey, USA National Phenology Network, 1955 E 6th St., Tucson, AZ 85721, United States;4. NOAA Fisheries Service, Office of Science and Technology, 1315 East West Highway, Silver Spring, MD 20910, United States |
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| Abstract: | Individual plant species distribute according to their own spatial pattern in a community. In this study, we proposed an index for measuring the spatial heterogeneity in mass (dry weight) of individual plant species. First, we showed that the frequency distributions for mass of individual plant species per quadrat in a plant community are expressed using the gamma distribution with two parameters of λ (mean) and p. The parameter p is a measure indicating the level of spatial heterogeneity of plant mass as follows: (1) when p = 1, the plant mass per quadrat has a random pattern; (2) when p > 1, the plant mass has a spatial pattern with a lower heterogeneity than would be expected in the random pattern; and (3) when p < 1, the plant mass has a spatial pattern with a higher heterogeneity than would be expected in the random pattern. The p value for a given species can easily be calculated by the following equation if we use the moment method: (mean plant mass among quadrats)2 / (variance of plant mass among quadrats). The scatter diagram of (λ, p) for individual plant species, exhibits the spatial characteristics of each species in the community. We illustrated two examples of the (λ, p) diagram from data for individual species composing actual communities in a semi-natural grassland and a weedy grassland. Frequency distributions for the plant mass of individual species per quadrat followed the gamma distribution, and indi vidual species exhibited an inherent level of spatial heterogeneity. |
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