Expected carbon emissions from a rubber plantation in Central Africa

Abstract

The development of agriculture on degraded lands is increasingly seen as a strategy to boost food availability and economic productivity while minimizing environmental degradation and loss of forests. To understand the effects of agricultural production on forest carbon, we quantify the aboveground carbon (AGC) of a degraded forest in northeast Gabon (the Olam Rubber Gabon concession) designated for development to a rubber plantation. Combining field measurements from 19 1-ha tree plots and aerial LiDAR, we estimate forest AGC stocks and emissions under four development scenarios: no development, 30-year rubber rotation, extended rubber rotation (replanting of plantation in stages at 30 and 40 years), and 30-year oil palm rotation. On average, the degraded forest in the study area stored 123.8 Mg C ha−1, a mean AGC lower than the Gabon average (141.6 Mg C ha−1) but substantially higher than the 75 Mg C ha−1 threshold recommended by the High Carbon Stock protocol. Converting secondary forest to plantation might incur high environmental opportunity costs from lost carbon sequestration through forest succession and growth. In this study, we estimate that a rubber plantation can sequester similar amounts of AGC as secondary forest by the end of a 30-year rotation; however, the time-averaged AGC of regenerating secondary forests under no development would be 184% higher than a mature rubber plantation with a 30-year rotation, 169% higher than an extended rubber rotation, and 512% higher than a 30-year oil palm rotation. When degraded forest is developed for agriculture, measures should be taken to avoid emissions and prolong carbon retention. We specifically estimate carbon retention from extended harvest rotations and conserving high carbon value areas as set-asides and highlight recommendations from the literature such as minimizing soil disturbance and creating rubber timber products (e.g. furniture). To minimize carbon emissions from agriculture, crop plantation area should be minimized at national and regional scales in highly forested countries, and new plantations should be coupled explicitly with effective forest restoration actions, through suitable regulation and planning, to mitigate or compensate for their climate and biodiversity impacts.