| Zusammenfassung: | Five major climatic types have been distinguished in a cross section of the Sierra Madre Oriental in the state of Nuevo Leon (P1. 1). These climates are characterized by distinct vegetational types and growth forms. There follows a brief description of each. 1. Warm and arid. This climate has been assigned to the eastern coastal plain, the low broad interior valleys, and the central plateau west of the mounrains. On the coastal plain it is characterized by growths of thorny shrubs, principally mesquite, yucca, acacia, cacti, and the like (Figs. 1 & 2). In the western valleys-and on the adjacent plateau and low slopes the shrubs are more stunted in form and consist mostly of creosote bush or governadora (Larrea tridentata), lecheguilla (Agave lecheguilla), cacti, and similar forms. On the east this zone reaches an altitude of about 750 m. (2500 ft.), but on the western edge of the mountains it reaches over 2000 m. (6500 ft.). 2. Cool and semi-arid. Areas of this nature lie about the skirts of the mountains generally above the warm and arid zone but definitely below the truly forested zones. They are characterized in this region by shrubs which include manzanita, sumac, pinon, maguey, and scrub oaks (Figs. 3, 4, 5, & 6). The most outstanding difference between this zone and the preceding one is the reduction in thorny species and the increase in broad-leafed evergreen forms. The height of growth in some cases may be less than that on the coastal plain, but the impression is one of greater density. This area is usually encountered between 1000 m. (325O ft.) and 1550 m. (5000 ft.), but on south and west exposed slopes it may reach 2150 m. (7000 ft.) to 2500 m. (8125 ft.). 3. Cool and sub-humid. The lower forest areas coincide with the areas having this climatic type. They include forests of pine, pine and oak, pure oak, and oak and hickory (Figs. 8, 9, & 15). The areas are heavily wooded and, by the means of the slender crowded trunks of the trees, usually give a definite impression of good moisture conditions. This area is encountered between 1500 and 2800 m. (4875 to 9000 ft.). 4. Cold and humid. On the higher peaks there occur areas which have a climate of this nature. Readily sensible low temperatures in summer and frequent precipitation have resulted in the development of a heavy subalpine forest between 2800 and 3600 m. (9000 to 11700 ft.) (Figs. 10, 11, & 12). Pinus montezumae is the principal tree. It is not, however, an infallible indicator. It should be regarded as subalpine only when accompanied by, or closely adjacent to, Douglas fir, aspen, and/or Pinus ayacahuite. Of course, any pure stand of Pinus montezumae at a higher altitude than an adjacent forest of Pinus ayacahuite and Douglas fir may safely be considered subalpine in character. Shrubs in this area are reduced to one species of gooseberry and an ocasional occurrence of other species. 5. Cold and semi-arid. Alpine meadows and stunted forests of pine with shrubs of gooseberry, juniper, and stone pine on the highest peaks (3600 to 3800 m. or 11700 to 12350 ft.) indicate a climate of this type. (Figs. 13 & 14). At all times it must be kept in mind that protected ravines and poleward facing slopes, by reason of localization of soil moisture and reduced insolation, wind movement, and evaporation, will bear a more highly developed growth than general climatic distribution would suggest. Thus, the occurrence of Douglas fir in a cation well within the cool and sub-humid zone of pine-oak forests is merely an indication of locally increased moisture and not of subalpine forest conditions. Similarly, the occurrence of trees in a ravine in the warm and arid shrub zone is of no climatic significance. Extensive poleward facing slopes and broad cation floors, on the other hand, which bear more highly developed forests as a result of reduced insolation and evaporation may be regarded as having a different climate of sufficient extent to be mapped.
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