Estimating mistletoe biomass in a semi-arid savanna woodland, southwest Zimbabwe

Abstract

Despite the biological importance of mistletoes in forests and woodlands globally, mistletoe biomass is rarely quantified, particularly in tropical regions. Thus, we constructed allometric models to predict the biomass of three mistletoe species (Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum) in semi-arid savanna, southwest Zimbabwe. We destructively sampled 30 individuals of each mistletoe species and recorded their broad haustorium diameter, narrow haustorium diameter, and the width, breadth, vertical depth, and percentage of leaves of the whole plant. After measuring the dry biomass of each mistletoe, we fitted linear regression models – selected and compared based on corrected Akaike Information Criterion (AICc) minimization. Mistletoe volume (r2 = 0.95) best predicted biomass in E. ngamicum, while mistletoe size was the best predictor for P. kalachariensis (r2 = 0.90) and V. verrucosum (r2 = 0.95). Models using haustorium diameter had the lowest predictive power in all species. V. verrucosum and P. kalachariensis had greater total mean dry biomass than E. ngamicum. Stems constituted the larger proportion of total biomass than leaves in E. ngamicum (75 vs. 23%) but the reverse is true for P. kalachariensis (40 vs. 58%). Of the total biomass, fruits and flowers constituted 6% in V. verrucosum and E. ngamicum and 2% in P. kalachariensis. The leaf to stem biomass contribution decreases in E. ngamicum but increases in P. kalachariensis as the plant grows. Models using mistletoe biometry (width, breadth, and vertical depth of the whole plant), rather than host size (height, diameter at breast height, and canopy area), best predicted total mistletoe biomass. Not only does this enable estimation of mistletoe biomass beyond the scale of infected individuals, but the contribution of mistletoes to local biomass, carbon stock, and ecosystem processes (e.g., nutrient cycling) can also be quantified at different spatial scales helping elucidate their keystone role in semi-arid savanna.