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Franklin et al - Spatial analysis of density dependent...

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Spatial analysis of density dependent pattern in coniferous forest stands* Janet Franklin 1, Joel Michaelsen 1 & Alan H. Strahler2**, *** 1Department of Geography, University of California, Santa Barbara, California, 93106; 2Department of Geology and Geography, Hunter College, New York, New York, 10021, USA Keywords: Coniferous forest, Multi-scaled pattern, Nearest neighbor distance, Pattern, Quadrat variance analysis, Spectral analysis Abstract An investigation of spatial pattern in relatively sparse Pinusponderosa-P. Jeffreyi stands showed that a simple Poisson model of random distribution described the pattern at 5 to 50 m scales in the denser stands examined when allowance is made for inhibition between nearest neighbors. There is evidence for a clumped distribution in large quadrats for the sparsest stands, which concurs with prior work where a mixed Poisson model was fit to the data. The technique used was innovative in that it involved digitally recording tree locations from high resolution aerial photos, which allowed for the automatic application of several statistical techniques in order to determine how pattern varies with plot density and scale. Point locations were recorded for six 11.3 ha plots in three density regions of a 340 ha study area in northeastern California, USA. The inter-event distance distribution, and one- and two-dimensional power spectra were calculated, and variable quadrat analysis was performed for the data sets. The second order and spectral analyses showed no evidence of a distinctive clumped pattern at any scale, and all analyses showed that the pattern was regular at the scale of the average inter-plant distance in the denser stands. For the sparser stands, the counts in large quadrats did not fit a Poisson distribution, but were better fit by a mixed Poisson model describing aggregated pattern. Introduction The purpose of this paper is to present the results of some studies of the spatial pattern of conifers in low to moderate-density stands in northeastern Cali- fornia, USA. We used air photos and a coordinate digitizer to plot the position of 5,147 trees in six large * Nomenclature follows Munz & Keck (1968). ** We would like to thank Frank Davis, Arthur Getis, and the anonymous reviewers for their very helpful comments on the manuscript, Joseph Scepan and Gloria Fletcher for the artwork, and Li Xiaowen and Arthur Getis for their help and advice with the analysis. *** This research was supported in part by a grant from the National Aeronautics and Space Administration (NAG 5-273). (I 1.3 ha) plots, characterizing three stands of differ- ent densities. Since the position of each tree was known, it was possible to examine quadrats of arbi- trary size within'a large range, and therefore assess spatial pattern by a number of different procedures.
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