Deviation of Mass-Density Allometry in Ramet Populations of Switchgrass

Abstract:

We studied a ramet population of switchgrass, caespitose in appearance, and proved the absence of density-dependent mortality. We present a deviation of mass-density allometry based on spatially explicit densities along the vertical space of the population. The number of ramets in the mean-ramet-height space explains the variation in the average weight of whole ramets (M) more accurately, with an asymptote towards critical self-thinning trajectory for such a mass-density relationship. With the development of size heterogeneity, a ‘vertical packing’ process appears in the population. We define the process as a similar ‘self-thinning’ trajectory, through the initial crowding of ramets in the mean-ramet-height space and continued transferring into the upper space and the lower space. The process presents a possibly competitive mechanism of self-thinning, local-competition-driving size deviation and vertical space packing. Here, log10 (M) = 2.91 - 1.25 log10 (N_L). Local crowding degree (N_L) is the number of ramets per unit area (m₂) in the mean-ramet-height space class. Similar ‘self-thinning’ occurs in the ramet population, but it just indicates how those ramets escape out of the mean-ramet-height space class, and therefore how the mean weight of whole ramets increases. Self-thinning should be the result of local competition among effective number of individuals in a population, rather than apparent crowding degree presented by whole individuals. The critical mass-density allometry based on whole individuals should be only a special case.

• Periodical: Advanced Materials Research (Volumes 518-523)
• Pages: 5316-5319
• DOI: https://doi.org/10.4028/www.scientific.net/AMR.518-523.5316
• Online since: May 2012
• Authors: Xin Guo Yang
• Keywords: Mass-Density Allometry, Ramet Population, Size Heterogeneity, Switchgrass, Vertical Packing

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