GEOPHYSICAL MONOGRAPH SERIES, VOL. 186, PP. 299-309, 2009
Nutrient limitations to secondary forest regrowth
The old, highly weathered soils of the lowland forest within the Amazon Basin generally exhibit conservative P cycles and
leaky N cycles. This generalization applies to mature forests, but accelerating land use change is altering Amazonian landscapes.
About 16% of the original forest area has been cleared, and about 160,000 km2 is in secondary forest cover. Secondary forests are common in agricultural regions, but few persist in one place for much
more than 5 years. The nutrients within ephemeral forests are important for smallholder traditional slash-and-burn agriculture
and in alternatives developed to conserve nutrients. Forest clearing causes an initial loss of nutrients through timber harvesting,
fire, erosion, soil gaseous emissions, and hydrologic leaching, with N losses exceeding P losses. In contrast, the Ca, Mg,
and K present in woody biomass are largely conserved as ash following fire, redistributing these nutrients to the soil. After
the initial postclearing pulse of nutrient availability, rates of N cycling and loss consistently decline as cattle pastures
age. Fertilization experiments have demonstrated that growth of young forests in abandoned agricultural land is nutrient limited.
Several N cycling indicators in a secondary forest chronosequence study also demonstrated a conservative N cycle in young
forests. Variable N limitation in young forests helps explain a negative relationship observed between the burn frequency
during previous agricultural phases and the rate of forest regrowth. Recuperation of the N cycle gradually occurs during decades
of secondary forest succession, such that mature lowland forests eventually recover abundant N relative to a conservative
Citation: Davidson, E. A., and