Soil changes during secondary succession in a tropical montane cloud forest area

The development of second-growth forest after abandonment of agricultural fields in tropical montane cloud forest (TMCF) areas is common in southern Mexico, hut little is known about how such changes affect soil properties. We evaluated the changes in soil properties at the 0- to 20- and 20- to 40-cm depths during this conversion in three chronosequences, each composed of a cornfield, and adjacent forests of ≈15, ≈45, ≈75, and ≥ 100 yr after abandonment at El Rincón, Oaxaca, Mexico. All studied soils were acidic, rich in organic C and total nitrogen (TN), and had low levels of plant-available P, exchangeable Ca, Mg, Na, and K, and high levels of exchangeable Al. Most of the soil properties analyzed changed significantly with the age after abandonment, but in most cases the patterns of response varied with the chronosequence, usually ≈15 to 45 yr after abandonment. In all chronosequences, soil pH and N/P ratio decreased, and the thickness of the O horizon increased, during the first 100 yr of forest development. The highest rates of soil C sequestration and the highest drop in exchangeable K, Mg, and Ca concentrations took place the first 15 yr of forest development. Most of soil changes can be associated with nutrient retention by vegetation and litter, the concentration of exchangeable Al in soil, and the role of soil pH in mineralization rates, ion solubility, and rock weathering. The different patterns of response found among chronosequences illustrate the importance of having replicates before making general statements about changes in soil properties after disturbance.