  Borneo contains some of the world's most biodiverse and carbon dense tropical
forest, but this 750,000-km2 island has lost 62% of its old-growth forests
within the last 40 years. Efforts to protect and restore the remaining forests
of Borneo hinge on recognising the ecosystem services they provide, including
their ability to store and sequester carbon. Airborne Laser Scanning (ALS) is a
remote sensing technology that allows forest structural properties to be
captured in great detail across vast geographic areas. In recent years ALS has
been integrated into state-wide assessment of forest carbon in Neotropical and
African regions, but not yet in Asia. For this to happen new regional models
need to be developed for estimating carbon stocks from ALS in tropical Asia, as
the forests of this region are structurally and compositionally distinct from
those found elsewhere in the tropics. By combining ALS imagery with data from
173 permanent forest plots spanning the lowland rain forests of Sabah, on the
island of Borneo, we develop a simple-yet-general model for estimating forest
carbon stocks using ALS-derived canopy height and canopy cover as input
metrics. An advanced feature of this new model is the propagation of
uncertainty in both ALS- and ground-based data, allowing uncertainty in
hectare-scale estimates of carbon stocks to be quantified robustly. We show
that the model effectively captures variation in aboveground carbons stocks
across extreme disturbance gradients spanning tall dipterocarp forests and
heavily logged regions, and clearly outperforms existing ALS-based models
calibrated for the tropics, as well as currently available satellite-derived
products. Our model provides a simple, generalised and effective approach for
mapping forest carbon stocks in Borneo, providing a key tool to support the
protection and restoration of its tropical forests.
