Factor analysis of nutrient distribution patterns under shrub live-oak in two contrasting soils

In shrub-dominated ecosystems, many soil properties are correlated, confounding changes in nutrient distribution associated with soils and shrub canopies. The objectives of this research were to: (i) identify underlying patterns in soil properties using factor analysis, and (ii) analyze factor scores to determine how the factor patterns varied between soils, canopy covers, and depth. White House (fine, mixed, thermic Ustic Haplargid) and Romero (loamy-skeletal, mixed, nonacid, thermic, shallow Ustic Torriorthent) soils were sampled at 0- to 4- and 4- to 8-cm depths under shrub live-oak (Quercus turbinella Greene) canopies and adjacent open areas and analyzed for sand, silt, and clay contents, ration exchange capacity (CEC), pH, organic C, total N, extractable P, and exchangeable K, Ca, and Mg. A threefactor model accounted for 81.2% of the total variation in the data. The first factor had high positive loadings on organic C, total N, and extractable P, and represented aggrading soil processes produced by accumulated litter and organic matter under shrubs. The second factor had high positive loadings on silt and clay contents and exchangeable K, had high negative loading on sand content, and was influenced by textural changes resulting horn the interaction between shrub canopies and the two soils. The third factor had high positive loadings on exchangeable Ca, Mg, and CEC, and varied significantly between the two soils but was not affected by the presence of shrub live-oak canopies. Factor analysis provided a statistical tool for grouping the 11 correlated soil variables into three uncorrelated factors. Analysis of factor scores allowed independent assessment of soils, shrub cover, depth, and their interactions on soil properties.