Soil condition, size and tree health in urban green areas

Urban trees generally grow in soils highly influenced by humans where conditions are unfavorable. A site assessment tool would be useful for arborists to improve species site adaptation. To investigate the problematic above, the goal of this work was to determine the relationship between soil condition and tree health in 21 green areas of the city of Texcoco de Mora, Mexico. Three soil samples were collected at three depths (0-5, 5-10 and 10-15 cm) in each green area and analyzed for pH, bulk density (BD), total soil porosity (SP), electrical conductivity (EC), total dissolved salts (TDS), organic matter (OM), organic carbon (OC), and soil texture. Growth (diameter at breast height and total tree height), tree health condition (chlorophyll fluorescence), tree visual metrics (TC), typology and management intensity in green areas were evaluated, and the Rapid Urban Site Index (RUSI) was determined. Descriptive and non-parametric statistics were used for the analysis. A total of 549 trees were evaluated. Soil analysis revealed that conditions are generally suitable for tree growth, except for BD that showed high values. The mean values for the soil variables were: pH, 7.04; BD, 1.35 g cm-3; SP, 49.07 %; EC, 0.75 dS m-1; TDS, 482.06 mg L-1; OM, 2.79 %; OC, 1.62 %; sand, 66.19 %; silt, 22.27 %; clay, 11.54 %. The Kruskal-Wallis test found significant differences (p < 0.05) at the green area level, indicating that the main variables that can restrict tree growth and health condition are BD and EC due to their high values. The soil properties that significantly changed (p < 0.05) along soil depth were OM, OC and pH, which is normal in soils. RUSI indices were significantly correlated to tree growth and health condition (p < 0.0001), as well as with the typologies and management intensity (p < 0.05) of the green areas analyzed, because the variables have implications on the physicochemical and biological characteristics of the soil.