Uncertainty in below-ground carbon biomass for major land covers in Southeast Asia

Owing to difficulties associated with measuring root biomass accurately in space and time, below-ground root biomass is often calculated indirectly from above-ground biomass measurements via general allometric equations. Of concern is that general equations may not provide accurate site-specific calculations for accurate carbon stock assessments. This review comparing more than 100 root-related studies conducted in SE Asia shows highly variable and uncertain below-ground woody carbon (BGC) biomass estimates for many vegetation types associated with on-going land-use changes throughout the region. Most BGC data exist for Indonesia, Malaysia, and Thailand; only a few studies have been conducted for Brunei, Cambodia, Lao PDR, Myanmar, Papua New Guinea, Philippines, Singapore, Timor Leste and Vietnam. While substantial data exist for a variety of forests and timber-plantations, little work has focused on key transition land-covers including rubber, oil palm, swidden fallows, agroforests, grasslands, and croplands. Mangroves (12–219 Mg C ha−1), peat forests (11–71 Mg C ha–1) and other forest types (11–74 Mg C ha–1) have the highest BGC values. The limited data for rubber plantations (5–32 Mg C ha–1), oil palm plantations (4–22 Mg C ha–1), swidden fallows (3–16 Mg C ha−1), and non-swidden agroforestry (3–16 Mg C ha−1) indicate modest differences in the amount of BGC for several land covers that are at the heart of ongoing debates regarding the human and environmental impacts of agricultural intensification. The paucity of data currently in existence for the region highlights the need for additional field investigations—following accepted protocols—of root biomass to facilitate efforts to improve carbon stock estimates. Government agencies, private enterprises, and development agencies could help lead the way in developing a better forest carbon database by teaming with researchers to assess total ecosystem carbon stocks prior to vegetation being removed for construction, mining, or stand rotations.