Natural Revegetation of Abandoned Crop Land in the Ponderosa Pine Zone of the Pike's Peak Region in Colorado

Abstract

Cultivation in the ponderosa pine zone of Colorado has, in many instances, been unprofitable because of the uncertainty of crops and eventual loss of soil fertility. Consequently, many areas have been abandoned, and natural revegetation has resulted in the presence of all stages of the secondary succession, from the initial invasion to almost complete return to the original subclimax grassland community. Some of the more recently abandoned fields have been protected from grazing, while others have been grazed at different rates and different seasons of the year. Therefore, areas representing different periods of abandonment and different types of grazing use are available in the Pike's Peak region for the reconstruction of the abandoned field sere in the ponderosa pine-Douglas fir association. Previous investigations of the rate and manner in which abandoned farm lands in the ponderosa pine zone revert to natural cover are not abundant. Hanson ('24) discussed briefly the secondary succession on abandoned fields in the ponderosa pine zone of northeastern Arizona. He described a first weed stage (Verbesina-Amaranthus associes), a second weed stage (Senecio-Eriogonum associes), a first grass stage (Bouteloua-Agropyron associes), and a subclimax grass stage (Festuca-M uhlenbergia-Blepharoneuron associes). In some instances the subclimax grass stage was omitted, and the succession passed directly from the first grass stage to the ponderosa pine climax. Shantz ('11), and Savage and Runyon ('37) discussed various aspects of the succession that occurs on abandoned farm lands in the central and southern Great Plains. Similar discussions for other areas have been presented by Booth ('41) for Kansas and Oklahoma; Whitman, Hanson, and Loder ('43) for western North Dakota, and Costello ('44) for northeastern Colorado. In general, on the areas where these investigators have worked, there are four distinct associes, beginning with an annual weed type and progressing upward through perennial forb, mixed grass and forb, and, usually, a subclimax grass type-all preceding the final or climax association. Other factors affecting the rate of revegetation of abandoned farm lands have been discussed by various workers. Runyon ('36) evaluated the distribution of the seed supply, Booth ('41) the effect of cultural methods and burning, and Weaver and Albertson ('40) the effects of drought. The present study was made to determine, insofar as possible, the rate of revegetation and the stages of secondary succession on abandoned farm lands in the vicinity of the Manitou Experimental Forest 2 near Woodland Park, Colorado. Detailed studies of ten fields in various stages of succession were initiated in 1936 and were concluded in 1944. The development of the vegetation has been traced only from the initial invasion to the subclimax grass community. It is recognized that the ponderosa pine-Douglas fir association is the potential climax of this area and that the subclimax grass community may eventually be replaced by the conifers.