Soil carbon differences among forest, agriculture, and secondary vegetation in lower montane Ecuador

Background

Changes in land use and land cover may affect soil properties and processes. Conversion of forest to cultivation is assumed to result in a decrease in soil nutrients. In the lower montane region of Ecuador, shifting cultivation patterns mean that forest clearing is occurring simultaneously with recolonization of secondary vegetation on abandoned agricultural lands.

Research goals & methods

This study examines differences in soil carbon among forest, agriculture, and secondary vegetation in the lower montane region of northwestern Ecuador. Changes in forest-derived carbon and accumulation of carbon from replicate sugar cane and pasture vegetation were estimated using a stable C isotope technique. Differences in the proportion of soil C derived from C3 and C4 plants were also measured across a land-use progression from agricultural fields through successional communities and undisturbed forest.

In the cultivated field, the net net change in soil carbon consisted of 1.3 Mg ha^-1 yr^-1 losses of forest carbon and 0.9 Mg ha^-1 yr^-1 gains from sugar cane for a total loss of 23 Mg/ha over 50 years. In pastures, rates of forest carbon loss and C4 carbon accumulation differed little between two distinct pasture types; both had substantially more soil carbon compared to cultivated fields. Under second-growth forest, the total soil carbon pool returned to preclearing levels within 20 years.

Conclusions & takeaways

This study suggests that pasture is superior for soil carbon as compared to field cultivation. While widespread reforestation may be thwarted by high demands for cultivated and pastureland in northwestern Ecuador, the option of pasture carries advantages for contributing to carbon stocks.