Biomass allometries and coarse root biomass distribution of mountain birch in southern Iceland

• Main Authors: Matthias Hunziker, Bjarni Diðrik Sigurðsson 1966-, Guðmundur Halldórsson 1952-, Wolfgang Schwanghart, Nikolaus Kuhn
• Other Authors: Landbúnaðarháskóli Íslands
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2014
• Subjects: Birki; Rætur (plöntur); Iceland
• Online Access: http://hdl.handle.net/1946/19813

Root systems are an important pool of biomass and carbon in forest ecosystems. However, most allometric studies on forest trees focus only on the aboveground components. When estimated, root biomass has most often been calculated by using a fixed conversion factor from aboveground biomass. In order to study the size-related development of the root system of native mountain birch (Betula pubescens Ehrh. ssp. czerepanovii), we collected the coarse root system of 25 different aged birch trees (stem diameter at 50 cm length between 0.2 and 14.1 cm) and characterized them by penetration depth (< 1 m) and root thickness. Based on this dataset, allometric functions for coarse roots (> 5 mm and > 2 mm), root stock, total belowground biomass and aboveground biomass components were calculated by a nonlinear and a linear fitting approach. The study showed that coarse root biomass of mountain birch was almost exclusively (> 95 weight-%) located in the top 30 cm, even in a natural old-growth woodland. By using a cross-validation approach, we found that the nonlinear fitting procedure performed better than the linear approach with respect to predictive power. In addition, our results underscore that general assumptions of fixed conversion factors lead to an underestimation of the belowground biomass. Thus, our results provide allometric functions for a more accurate root biomass estimation to be utilized in inventory reports and ecological studies. Rótarkerfi trjáa innihalda umtalsverðan lífmassa og traust mat á honum skiptir máli til dæmis þegar kolefnisforði skóga er metinn. Langflestar rannsóknir á trjáa lífmassaföllum (spálíkön út frá bolþvermáli) hér og erlendis hafa hinsvegar einskorðast við ofanjarðarlífmassa þeirra. Þegar reynt hefur verið að áætla rótarlífmassa hefur hann yfirleitt verið metinn sem fast hlutfall af ofanjarðarlífmassa. Í þessari rannsókn voru 25 birkitré á mismunandi aldri (bolþvermál þeirra í 50 cm frá jörðu var 0,2 – 14,1 cm) uppskorin á Rangárvöllum. Allt rótarkerfi þeirra var grafið ...