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doi: 10.1007/BF02390890pmid: N/A
Summary Habitat specialization in populations of three broadly distributed trees includes adaptive differentiation to day length and temperature. Low sensitivity to environmental cues is the adaptive strategy of the southernmost populations (from northeastern Mexico). Early cessation of growth and sensitivity to the environment is adaptive for the northernmost populations (southern Illinois). Intermediate responses characterize trees of Texas. In a comparison under four photoperiod-temperature conditions, the Mexico plants were adapted to the longest growing season. Under out-of-doors conditions in central Texas, these trees from Mexico continue to demonstrate adaptive strategies different from those of Texas or Illinois trees. Stipule production and leaf area inPlatanus showed modifications correlated with latitude. Northernmost trees had the smallest leaves and did not produce stipules under 12-h day lengths and 24–15 °C temperatures. The Mexico trees had stipules under each of the four experimental conditions. The results suggest that populations of deciduous trees in a given climate are selected toward convergence in some responses to that climate. As a result, populations of the three trees resemble each other in behavior in a given ecosystem.
doi: 10.1007/BF02390891pmid: N/A
Summary The path of information flow is described and major sources of information loss are identified in ordinations. These sources are shown to be related to the resemblance function and to the transformations which produce the ordiantion co-ordinates. Preventive steps to minimize information loss are suggested.
doi: 10.1007/BF02390892pmid: N/A
Summary A new method in classification of anthropogenic plant communities is discussed. Three kinds of basic categories of communities have been distinguished and defined: (1) basal communities, (2) derivate communities, and (3) cenologically saturated communities. These new basic syntaxonomical units are arranged within the auxiliary net of higher units: alliances, orders and classes. This method also enables the classification of those communities with a synsystematical position between certain higher units. One advantage of this procedure is that the majority of really existing anthropogenic communities, the number of which is steadily increasing in cultivated landscapes, can be adequately classified. Furthermore it is possible to classify communities into which synanthropic species enter repeatedly, leading to new species combinations; the typification of such communities by current methods (in the rank of associations) becomes increasingly difficult.
doi: 10.1007/BF02390895pmid: N/A
Summary The succession of the dune slack vegetation around an artificial lake was studied by means of successive mapping. A succession scheme was prepared on the basis of comparison of the maps made in various years. This scheme was discussed in terms of systems theory, with reference to a kinematic graph prepared on the basis of the transformations. The succession derived from the vegetation maps was compared with that derived from the permanent plots; the results of this comparison indicated that only a small proportion of the total number of succession lines could be detected with the aid of the permanent plots. In addition, the information that could be derived from the permanent plot analysis depended on the degree of change of the vegetation in the area; more information could be derived from drier areas which showed the least degree of change. The best method for the investigation of the succession proved to be a combination of a restricted number of permanent plots and successive mapping.
doi: 10.1007/BF02390896pmid: N/A
Summary A report is given on the activities of the Group in 1972–1973, with emphasis on the Symposium on Data-Processing in Phytosociology at Prague, September 1973. The scientific program and the main results of this symposium are summarized. An extensive bibliography of publications on the subject by members of the Group is presented.
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