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Soil degradation and subsequent amelioration were studied on soil chronosequences of old-growth forest, abandoned fields, and young and mature conifer plantations on the Oak Ridges Moraine, an environmentally vulnerable landform near Toronto threatened by encroaching urban development. The chronosequences reflect a history of pre-settlement deforestation, exploitive pioneer agriculture and ensuing land abandonment that led to soil fallowing and/or wind erosion in the 1920s followed by soil stabilization after extensive planting with red pine (Pinus resinosa Ait.). Key pedogenic processes were identified and rates and magnitude of soil recovery were quantified in terms of morphological, physical and chemical characteristics of soil profiles. Soil degradation generally involved reduced fertility with profile simplification (haploidization) on non-eroded fallowed fields, and topsoil loss by wind erosion (deflation) on more exposed eroded fields. After reforestation, soil restoration was characterized by cessation of erosion, accelerated horizon development and differentiation, reduced soil bulk density, and increased fertility and acidification of the soil. Chronofunctions revealed substantial recovery in soil organic C, total N, available P, and exchangeable K, Ca and Mg status within 75 yr of initial reforestation on non-deflated, fallowed sites. In contrast, estimated recovery of these parameters on severely deflated sites was delayed far beyond plantation maturity.
