Development of allometric models for above and belowground biomass in swidden cultivation fallows of Northern Laos

• Published in: Forest ecology and management 2015-12, Vol.357, p.104-116
• Main Authors: McNicol, Iain M., Berry, Nicholas J., Bruun, Thilde Bech, Hergoualc’h, Kristell, Mertz, Ole, de Neergaard, Andreas, Ryan, Casey M.
• Format: Article
• Language: English
• Subjects: Biomass; Carbon; Chronosequence; Cultivation; Land use; Landscapes; Raw materials; Roots; Shifting cultivation; South-east Asia; Swidden; Tree allometry; Trees
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/j.foreco.2015.07.029

•We created new allometric models of AGB and BGB for swidden fallows in SE Asia.•Resprouting is a common plant trait in these regularly disturbed systems.•A single AGB model can be used for resprouting and non-resprouting trees.•DBH-only models are acceptable to use, but resprout status should be noted for estimating BGB.•Root biomass stocks were 58% higher after accounting for the allometry of resprouts. Shifting, or swidden, cultivation remains an important land use across Southeast Asia and other parts of the tropics, albeit under pressures from other land uses. The swidden cycle of cultivation and regrowth creates mosaic landscapes with regrowing fallows of various age interspersed with active fields and patches of mature forest. Quantifying tree biomass in these landscapes is limited by the availability of reliable allometric models, hindering accurate carbon stock estimation and thus quantification of GHG emission associated with land use transitions. We therefore developed new allometric models for the prediction of both above- and below-ground woody biomass in swidden systems based on a destructive harvest of 150 trees in Luang Prabang Province, Laos People’s Democratic Republic (PDR). This study is the first to develop allometric models of root biomass for swidden landscapes in this region, which we hypothesised would be a major carbon pool given that resprouting, and associated high root biomass, is a common physiological/morphological trait in regularly disturbed ecosystems. We found that a general model including tree diameter (DBH, cm) and height (H, m) was best for estimating aboveground biomass (AGB, kg) for both resprouts and trees growing from seed (AGB=1.09+0.027D2H) though the inclusion of H only resulted in a marginal increase in model performance meaning a DBH-only model is acceptable to use in the absence of height data (AGB=0.1286DBH2.134). Tree height was less important for estimating root biomass, with models including only DBH performing best. Re-sprouting trees exhibited greater root biomass (BGB=0.355DBH1.732) compared to those growing from seed (0.016DBH2.597) meaning different root allometric models were developed for each tree type. Thus, we suggest that field efforts should be directed towards checking resprouting status over the estimation of tree height. We also found that models fit using non-linear regression provided equally good fits to the data compared to the traditional approach of log-transforming the data. Our mod