Effects of forest clearing and succession on the carbon and nitrogen content of soils in Puerto Rico and US Virgin Islands

Background

Conversion of tropical forest lands to agriculture or pasture affects soil organic matter, moisture, and nutrients. This study examines the effects on soil carbon, nitrogen, and moisture at depths up to 100 cm of conversion from forest to agriculture and pasture.

Research & Methods

Sites were selected within subtropical wet, moist, and dry zones in Puerto Rico and the US Virgin Islands that had land uses including agriculture, pasture, young and mature forests. Soil carbon in forests (1.5-4.3%) exhibited a higher range than in pasture (2.5-3.1%) while agricultural soils had the lowest carbon content (1.0-1.8%). Within each category, carbon content in drier zones was higher than that in moist and wet zones. Carbon concentrations decreased with soil depth. Patterns of nitrogen concentration were similar to carbon.

Conclusions & Takeaways

The study finds that the loss of soil carbon upon conversion to agriculture is proportional to the initial amount of carbon and the local moisture regime. More soil carbon and nitrogen are lost upon conversion, proportionally, in wet and moist zones than in dry zones – a loss of 30-40% from initial levels compared to about 15%. However, cropland converted to pasture accumulates carbon.