Grass allometry and estimation of above-ground biomass in tropical alpine tussock grasslands

The puna/páramo grasslands span across the highest altitudes of the tropical Andes, and their ecosystem dynamics are still poorly understood. In this study we examined the above-ground biomass and developed species specific and multispecies power-law allometric equations for four tussock grass species in Peruvian high altitude grasslands, considering maximum height (hmax), elliptical crown area and elliptical basal area. Although these predictors are commonly used among allometric literature, they have not previously been used for estimating puna grassland biomass. Total above-ground biomass was estimated to be of 6.7¿±¿0.2 Mg ha-1 (3.35¿±¿0.1 Mg C ha-1). All allometric relationships fitted to similar power-law models, with basal area and crown area as the most influential predictors, although the fit improved when tussock maximum height was included in the model. Multispecies allometries gave better fits than the other species-specific equations, but the best equation should be used depending on the species composition of the target grassland. These allometric equations provide an useful approach for measuring above-ground biomass and productivity in high-altitude Andean grasslands, where destructive sampling can be challenging and difficult because of the remoteness of the area. These equations can be also applicable for establishing above-ground reference levels before the adoption of carbon compensation mechanisms or grassland management policies, as well as for measuring the impact of land use changes in Andean ecosystems