Ecology of the Black Forest of Colorado

Abstract

The Black Forest of Colorado is an eastward extension over the plains and tablelands of the foothill forest of ponderosa pine [Pinus ponderosa scopiloru ni (Engelm.) Lemmon]. It covers an area approximately fifty miles long and twentyfive miles wide. The present studies were made near the northern edge of the Black Forest where zonation of pines, scrub oaks, and grasses is especially well marked. The altitude at this point is approximately 6400 feet, and the approximate location is at the intersection of meridian 1040 41' and parallel 390 20'. This region is chiefly underlain by stratified sandstone, and areas of subaqueous deposits are shown on United States Geological Survey maps. The vegetation varies with the topography. Ponderosa pine dominates the hilltops, scrub oak [Qitercus ganb efliii Nutt. and Q. gunnisonii (Torr.) Rydb.] the upper slopes, and the lower hillsides are occupied by both tall and short grasses, together with an abundance of yucca, cacti, various mustards, etc. Apparently the present communities are well stabilized in their respective locations. The zonation in the Black Forest is similar to that of a large area in southeastern Colorado and northern New Mexico and Arizona. Through much of the latter region the hilltops are occupied by trees of western red cedar (Juniperus scopulorumi Sarg.), ponderosa pine, or pinyon pine (Pinus edulis Engelm.). Farther down the hillsides the trees are smaller in size and at the bottom they constitute only a shrubby growth or are lacking entirely. Ramaley ('31), in a study of the chaparral-covered foothills southwest of Denver, Colorado, found heavy growths of scrub oak in the vicinity of the mouth of the Platte Canyon, but as he proceeded higher up the canyon, the oak growth became sparse and the number of pines greater. Weaver and Clements ('38) state: On the western borders along the front range of the Rockies, postclimax savannah of pines extends outward along streams, escarpments, or plateaus with higher rainfall, far into the mixed prairie. Our problem is, then, todiscover (1) the reason for the extension of the ponderosa pine forest out over the plains, and (2) the causes of the prevailing zonation, especially the peculiar location of the Pines at the tops of the ridges.