Living biomass of fallow areas under a REDD+ project in mountainous terrain of Northern Laos

There has been an expansion of the fallow areas in the mountainous terrain of Northern Laos, resulting in a significant effect on greenhouse gas emissions in the region. This study estimated living biomass of variously aged fallow areas (4–35 years old) in mountainous terrain. The living biomass of study sites, which was estimated by applying original allometric equations in each plant component, ranged from 49.4 to 390.1 Mg ha⁻¹. Using individual biomass data, we then developed a growth model based on a correlation between stand age (years after slash-and-burn) and living biomass in fallow areas >20 years old. The developed growth model was well fitted by a theoretical formula of Mitscherlich (Living biomass = 372.9 × [1–1.117 × exp(−0.05556 × stand age)]) (R² = 0.670). In addition, the area of each aged fallow area was estimated by analysis of time series of satellite imagery and change-detection analysis to detect past fire events (slash-and-burn). All of the living biomass of the fallow areas in each age were estimated using the developed model and were analyzed. The age-classed weighted mean value of living biomass in fallow areas was estimated as 111.4 Mg ha⁻¹. These results clarified that living biomass in fallow areas was dependent on age, and estimation methods including age data are essential for improving the estimation accuracy of forest carbon stocks in fallow areas during long-term Reducing Emissions from Deforestation and Forest Degradation projects in Northern Laos and surrounding regions.