A comparison of vegetation structure on three different soils at Bandelier National Monument, New Mexico, U.S.A. : Rough draft

Julius, Christian

Introduction Accelerated soil erosion causes major natural and cultural problems across the landscape of Bandelier National Monument. Development of soil instability made it imperative to formulate further requirements of research. The main goal of experimental revegetation work at Bandelier is to be able to implement a parkwide piñon-juniper woodland restoration program in order to stop erosional processes. Present studies focus on the reduction of tree density combined with the leaving of slash in the treated area in order to reestablish herbaceous ground cover. A possible influence of soil profile towards vegetation structure has been neglected so far. The object of the current study is to find out whether there is a significant difference in vegetation structure corresponding to some specific soil characteristics on South Mesa at Bandelier National Monument. Both the presence of a pumiceous surface layer and a clay horizon (argillic horizon) in a soil depth of up to 120 cm (48 inches) is supposed to favor the development of a grassland structure due to a higher amount of soil water available for forbes and grasses. On both deep, pumiceous soils without an argillic horizon and shallow, rocky soils a predominance of Pinus edulis (Colorado piñon pine) and Juniperus monosperma (one-seed juniper) is assumed. Ground cover and density of trees as well as biomass and ground cover of shrubs and herbaceous plants were measured to get an idea about possible differences of vegetation structure in the present environment. In the past century, most vegetation types in the landscape of Bandelier National Monument have undergone major changes caused by the often intertwined effects of grazing history and fire suppression (ALLEN 1989). Hence, the age class structure of the existing tree population of one-seed juniper and Colorado piñon pine was estimated to compare potential changes of vegetation structure in times past. To know whether some specific soil characteristics favor the development of a herbaceous cover significantly can be useful for further procedure of experimental revegetation work at Bandelier National Monument.