Means¹ (± SE) of soil characteristics of land-use types.

1<p>Means of the 0.3–1.2 m depth interval are means of the 0.3–0.6-m, 0.6–0.9-m and 0.9–1.2-m depth intervals.</p>2<p>Within a row, means followed by different letters differ significantly between rubber plantation and secondary forest (linear mixed effects model at P≤0.05).</p

Soil carbon remaining after land-use change at (A) 0–0.15-m, (B) 0.15–0.3-m, and (C) 0.3–0.6-m depth.

<p>Soil carbon remaining is expressed as the proportion of soil carbon in rubber plantations relative to the secondary forest. The dashed lines represent fitted mono-exponential models (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069357#pone.0069357.e002" target="_blank">Equation 2</a>). r = Pearson’s correlation coefficient between observed and fitted values; k = decay rate (year⁻¹) and X_e =  equilibrium ratio (%), and values in brackets are SE. Pearson’s r and parameter estimates are significant at *P≤0.05, **P≤0.01, and ***P≤0.001.</p

Location of the study area in Xishuangbanna prefecture, Yunnan province, China.

<p>Location of the study area in Xishuangbanna prefecture, Yunnan province, China.</p

Soil Carbon Stocks Decrease following Conversion of Secondary Forests to Rubber (<i>Hevea brasiliensis</i>) Plantations

<div><p>Forest-to-rubber plantation conversion is an important land-use change in the tropical region, for which the impacts on soil carbon stocks have hardly been studied. In montane mainland southeast Asia, monoculture rubber plantations cover 1.5 million ha and the conversion from secondary forests to rubber plantations is predicted to cause a fourfold expansion by 2050. Our study, conducted in southern Yunnan province, China, aimed to quantify the changes in soil carbon stocks following the conversion from secondary forests to rubber plantations. We sampled 11 rubber plantations ranging in age from 5 to 46 years and seven secondary forest plots using a space-for-time substitution approach. We found that forest-to-rubber plantation conversion resulted in losses of soil carbon stocks by an average of 37.4±4.7 (SE) Mg C ha⁻¹ in the entire 1.2-m depth over a time period of 46 years, which was equal to 19.3±2.7% of the initial soil carbon stocks in the secondary forests. This decline in soil carbon stocks was much larger than differences between published aboveground carbon stocks of rubber plantations and secondary forests, which range from a loss of 18 Mg C ha⁻¹ to an increase of 8 Mg C ha⁻¹. In the topsoil, carbon stocks declined exponentially with years since deforestation and reached a steady state at around 20 years. Although the IPCC tier 1 method assumes that soil carbon changes from forest-to-rubber plantation conversions are zero, our findings show that they need to be included to avoid errors in estimating overall ecosystem carbon fluxes.</p></div

Means (± SE) of litter and tree characteristics of land-use types.

1<p>Within a row, means followed by different letters differ significantly between rubber plantation and secondary forest (linear mixed effects model at P≤0.05).</p>2<p>Total basal area is calculated as the sum of the basal area of trees and bamboos.</p

SOC stocks, soil properties, topographical attributes and vegetation characteristics of a tropical montane landscape

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