Tropical Rain Forest Conversion to Pasture: Changes in Vegetation and Soil Properties

Abstract

The effects of converting lowland tropical rainforest to pasture, and of subsequent succession of pasture lands to secondary forest, were examined in the Atlantic Zone of Costa Rica. Three replicate sites of each of four land—use types representing this disturbance—recovery sequence were sampled for changes in vegetation, pedological properties, and potential nitrogen mineralization and nitrification. The four land—use types included primary forest, actively grazed pasture (10—36 yr old), abandoned pasture (abandoned 4—10 yr) and secondary forest (abandoned 10—20 yr). Conversion and succession had obvious and significant effects on canopy cover, canopy height, species composition, and species richness; it appeared that succession of secondary forests was proceeding toward a floristic composition like that of the primary forests. Significant changes in soil properties associated with conversion of forest to pasture included: (1) a decrease in acidity and increase in some base exchange properties, (2) an increase in bulk density and a concomitant decrease in porosity, (3) higher concentrations of NH4+, (4) lower concentrations of NO3—, (5) lower rates of N—mineralization, and (6) in some cases, lower rates of nitrification. Chemical changes involving cations associated with conversion from forest to pasture indicated increases in soil fertility under the pasture regimes, while changes associated with nitrogen indicated decreases in fertility. Physical changes in density and porosity were deleterious with respect to infiltration, percolation, aeration, and, ultimately, erodability. Beyond the practical aspects of land management, many of these changes are very important to carbon and nitrogen cycling and to the emission and consumption of biogenic trace gases.

A Molecular Survey of the Diversity of Microbial Communities in Different Amazonian Agricultural Model Systems

“…The deforestation of tropical forests alters many soil properties. Previous studies have shown that conversion to pasture causes an increase in pH and soil bulk density as well as a decrease in soil porosity [33][34][35]. As seen in Table 1, the Amazonian soils also have undergone a similar transformation.…”

Efectos de la perturbación antrópica en petenes de selva en Campeche, México

“…= capacidad de intercambio catiónico. lo observado en el estado de Quintana Roo, México, con respecto a aquellos que han sido impactados por incendios (Sánchez et al, 2007), extracción en selvas húmedas de Australia (Congdon y Herbohn, 1993), y en secuencias de sucesiones forestales de diferentes edades en Brasil (Reiners et al, 1994). En bosques afectados por extracción en el corto (2.5 años) y largo plazo (50 años) estudiados por Seng et al (2004), no se observaron cambios en la composición de las especies.…”

Nitrogen dynamics in Amazon forest and pasture soils measured by 15N pool dilution

“…Two patterns of changes of N turnover following forest clearing and pasture creation are apparent from previous studies. First, rates of net mineralization and net nitri®cation are consistently lower in soils of pastures 3 yr old or older than in soils of the forests from which they were created (Reiners et al, 1994;Neill et al, 1995Neill et al, , 1997Verchot, pers. comm.).…”