Amount and Distribution of Dry Matter, Nitrogen, and Organic Carbon in Soil-Plant Systems of Mesquite and Palo Verde

Abstract

Over a 3-year period, soil-plant systems of velvet mesquite and palo verde from the Sonoran Desert were sampled by standing crop, litter, and soil components and analyzed to describe the amount and distribution of dry matter, nitrogen, and carbon in the systems. Honey mesquite was sampled on a limited basis in southern New Mexico. Velvet mesquite averaged about one-third larger in crown area and weight than palo verde, but the two shrubs were similar in the distribution of dry matter, N, and C. Honey mesquite was much smaller and differed in distribution of dry matter, N, and C. Regression analysis showed that dry matter, N, and C in components of shrub systems of velvet mesquite and palo verde varied in a predictable manner and can be estimated with good precision using height, average crown diameter, or crown area of shrubs as the independent variable. Functional analysis showed that soil under palo verde did not accumulate N or C with increase in shrub size, whereas that under velvet mesquite accumulated N at the rate of 11.2 g/m2 per meter of height and C at the rate of 0.11 kg/M2 per meter of height. Shrubs dominate the vegetation on over 200 million hectares of land in the conterminous United States, mostly in the Southwest and the Intermountain Basin. Many authorities consider shrubs the climax vegetation on about one-half this area, while on the remaining 100 million hectares shrubs now dominate where grasses were once the climax dominants. Man has been using shrublands since prehistoric times, but until recently little management has been applied. When used, management usually has been directed at eliminating shrubs. Because shrubs play an important role in terrestrial ecosystems, we should understand their ecological role. This is especially important in arid areas where shrubs are an important component of the vegetation. This paper reports on a study to determine how dry matter, nitrogen, and carbon were accumulated and distributed in soil-plant systems of two desert shrubs: velvet mesquite (Prosopisjuliflora) and palo verde (Cerdicium floridum). Limited data on honey mesquite (Prosopis juliflora var. glandulosa) are included as an adjunct to the main study.