. The distribution of vegetation in the United States, as related to climatic conditions. Phytogeography. 534 CORRELATION OF DISTRIBUTIONAL FEATURES. The narrowest amplitudes for the center are in the three moisture ratios and in the number of days in the longest dry period; and in all four of these cases a slightly wider amplitude of conditions brings us to the extremes for the fringe. A comparison of plate 5 with plate 59 shows that the whole region occupied by the center, subcenter, and fringe is very nearly confined between the isoclimatic lines for mois- ture-ratio values of and
. The distribution of vegetation in the United States, as related to climatic conditions. Phytogeography. 534 CORRELATION OF DISTRIBUTIONAL FEATURES. The narrowest amplitudes for the center are in the three moisture ratios and in the number of days in the longest dry period; and in all four of these cases a slightly wider amplitude of conditions brings us to the extremes for the fringe. A comparison of plate 5 with plate 59 shows that the whole region occupied by the center, subcenter, and fringe is very nearly confined between the isoclimatic lines for mois- ture-ratio values of and , although the fringe enters regions with higher values. The range from to is scarcely exceeded by the center. The isoclimatic line for dry periods of 50 days is close to marking the western limit of the fringe of deciduous trees. In the center the extreme range is from 4 to 56 days, values above 50 being extremely local in this region, however. Figure 43 should be compared with figure 31, which shows the climatic extremes for the Deciduous Forest region. The extremes for the Deciduous Forest lie, in general, outside those of the center of the 13 common species and inside those of the fringe. Liriodendron tulipifera (fig. 44).âThe area in which this tree is of commercial importance may well be regarded as its ecological center, while the region in which it occurs too infrequently to have such importance may be designated as its fringe (plate 9). The center for Liriodendron lies almost wholly within the center for the 13 decid- uous trees just treated, and its distributional limit is similar to that of the subcenter of the deciduous trees, although not extending quite so far west. The conditions for the center and fringe of Liriodendron have been shown by pairs of graphs in figure 44. The region of greatest abundance for Liriodendron is one of the very few botanical areas investigated in which the edge lies entirely within the United States and is nowhere formed by a
Size: 2424px × 1031px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjectphytoge, bookyear1921
