Relationships between Height, Diameter and Weight Distributions of Chenopodium album Plants in Stands: Effects of Dimension and Allometry

Frequency distributions of height (H), stem diameter (D) anddry weight (W) of Chenopodium album plants in even-aged monoculturesat the initial plant densities of 400, 800 and 1200 plants m^-2(400-, 800- and 1200-plots) were compared. The height distributionsat the end of the growing season were bimodal for the 400-plotbut L-shaped for the 800- and 1200-plots. The distributionsof diameter and dry weight were L-shaped for all the plots.When the size measures were expressed on the log scale so asto eliminate effects of the differences in dimension, frequencydistributions of log W and log H for the 400-plot were bimodal.In contrast, the log D distributions were bell-shaped for allthe plots. To elucidate factors responsible for the differences in frequencydistributions among log size measures, we examined allometricrelationships between log size measures. They were all non-linearall non-linear mainly because the allometric relationships weremarkedly different between the plants forming the upper-mostleaf layer ('upper' plants) and the suppressed plants ('lower'plants). A striking feature was that the heights of the 'upper'plants were almost uniform in spite of their varied diameters.Continuous monitoring of growth of the individual plants inthe stand revealed that the height of the 'upper' plants becameuniform just after the canopy closure, at about 30 d after emergence,and that uniform growth in height of these plants continuedfor about 70 d until the end of the growing season. On the otherhand, growth of the suppressed 'lower' plants terminated atvarious stages before flowering. The 'height convergence' ofthe 'upper' plants was thus identified as a key factor for thesegregation of the plants into the two groups of distinctlydifferent allometries. Since the segregation of the plants into 'upper' and 'lower'plants was reflected in their dry weights, frequency distributionsof log W were similar to those of log H. The bell-shaped distributionsof log D were attributed to the overlapping of the diametersof slender 'upper' plants with those of larger 'lower' plants.Significance of 'height convergence' is discussed.Copyright1995, 1999 Academic Press Chenopodium album L., fat hen, height, size structure, bimodal distribution, L-shaped distribution, allometry, growth