We suppose that all sorts of plants got started on this new land, but only those species which happened to be adapted for the particular conditions of their time would last long enough to become well established and to produce ample seeds for future generations. This selective elimination of plants which were not adjusted to the changing conditions results in the dominance of certain well-adjusted species. In this way, according to scientists, a climax vegetation develops for a particular situation. As long as the climate remains about the same, the climax vegetation remains relatively stable. [Illustration: Rugged cliffs and mighty peaks are spectacular products of geologic forces.] Although it has been thousands of years since these plant communities first started on the glaciated bedrock, the struggle for dominance among the plants still goes on. Conditions are not yet completely static and probably never will be. The meadows, the forests, and the barrens of today may be quite different in a distant tomorrow. PLANT COMMUNITIES Below 9,000 Feet In the lower slopes of the park, below approximately 9,000 feet altitude, usually described as the Montane zone, the climate is relatively warm and dry. This type of climate has encouraged a fairly consistent pattern of vegetation that may be considered climax. The forests in this zone are open. The trees are likely to be scattered in characteristically parklike stands and are made up mostly of ponderosa pine. On cool north slopes the stands are thicker, with Douglas-fir sprinkled in or even dominant. With the ponderosa pine on drier sites is juniper (commonly called “cedar”), and above 8,000 feet thick stands of lodgepole pine are sometimes admixed. Along the streams are the distinctive and graceful Colorado blue spruce, associated with willows, birch, and alder. Aspen groves and, in lower altitudes, cottonwoods appear here and there. Many types of shrubs, some characteristic of the foothills, grow in the Montane zone.