Properties of alluvial and non-alluvial soils in fragmented mixed deciduous forest patches in southern Québec, Canada

Abstract

Soils and tree species are studied in mixed temperate forests along the Coaticook River (Southern Québec, Canada) to examine the effect of frequent floods on soil properties and vegetation. The soils and tree stands are located in the flood zones (FZ) and no-flood zones (NFZ) in 49 quadrats. Different statistical analyses were carried out on soils and tree data, including ANOVA, Kruskal-Wallis, Principal Component Analysis (PCA) and Canonical Correlation Analysis (CCA) ordinations. The variables used for soil property analysis were pH, total organic carbon, total nitrogen, C/N ratio, total sulfur, Fe + Al, texture, bulk density, soil moisture, and soil biomass (litter), while the vegetation variables consisted of the number of tree species, their density, and the diameter and measurement of the basal area. The soil property analyses show significant differences between alluvial and non-alluvial soils, including organic carbon, nitrogen, pH, Fe + Al, soil moisture, texture, and plant litter thickness (cm). The PCA ordination realized on soil variables shows two distinct axes, including a first axis (PC1) grouping TOC, TN, TS, soil moisture and pH variables, and accounting for 35% of the total variation, and a second axis (PC2) that includes textural variables (clay and silt) and representing 21% of the total variability. The species richness and diversity analyses did not show statistical differences for the tree species between the two zones that were analyzed (FZ and NFZ), although some tree species are associated with the specific edaphic conditions. The results of the CCA ordination conducted on soil and vegetation data revealed that the tree communities have a significant response to soil variables and flood frequency. All the variables that were studied account for 40% of the variation in species composition based on soil properties. This study shows that successive floods affect soil properties, including depletion of soil organic carbon and nitrogen, and that floods and soil conditions can have a direct effect on the distribution of certain tree species.