After fire or other catastrophe wipes out the spruce-fir forests, a cycle of natural revegetation must take place before the climax forest again becomes established. The first step in this recovery process is the appearance of fireweed and many annual herbs, among which shrubs such as CLIFF JAMESIA, or “waxflower,” become established, and aspens begin to appear as succession plant types. They are replaced eventually by longer-lived lodgepole pines, also sunloving and tolerant of burned or denuded sites. The trees increase the wetness of the forest floor, provide the shady sites necessary for seeds to grow in, and shelter the young spruce and firs as they slowly increase and approach maturity. Eventually, the spruces and firs crowd out the pioneers which have helped them get established. This dense spruce-fir forest seems to resist competition of other species and will maintain itself indefinitely by gradual replenishment of its own kind, unless it is again fire-swept or there is a change of climate. The spruce-fir forests of the park seem to be as nearly fixed and static as forests can be; or, in the scientists’ words, they are the _climax forest_ for the sites they occupy. [Illustration: Lodgepole pine forests along Trail Ridge Road.] The higher part of the Subalpine zone (10,500 to 11,500 feet) is often called Hudsonian for its biological similarity to the region around Hudson Bay. It is a sort of frontier zone where the climate is more severe. Not only is it colder, but it is much windier, and loss of water by evaporation is much greater than it is a thousand feet lower. Although spruce and fir remain the dominant species, they are usually shorter and less symmetrical in appearance. Near the upper limits of this zone the trees are twisted and grotesque, often flat and ground-hugging, sprawled behind boulders or fingering into the dwarf willow clumps so characteristic of the alpine mountaintops. Here, also, the only 5-needle pine in the park, LIMBER PINE, a rocky-soil tree of the Subalpine zone, assumes its most picturesque aspect. Limber pine at treeline is readily identified by its grotesque, twisted, ragged appearance. Several splendid specimens can be seen beside Trail Ridge Road about a half mile above Rainbow Curve. The name, limber pine, comes from the ease with which the branches can be bent without breaking. The cones are often 6 inches long, the largest of any conifer in Colorado.