Carbon storage in roots of urban tree cultivars

Urban trees can favorably affect factors underlying global warming by storing carbon and by reducing energy needs for cooling and heating buildings. However, in most ecosystems, especially the urban forest ecosystem, an overlooked and understudied aspect of the total amount of carbon stored is that of the below-ground components. To estimate below-ground carbon storage data was collected consisting of whole tree sampling of selected samples of Amelanchier, Malus, Pyrus calleryana, and Syringa reticulata cultivars. In estimating the carbon storage in the below-ground portions of urban trees, roots were excavated using an Air-Spade™. Regression analysis resulted in two equations for predicting total carbon storage based on height and diameter for trees up 20 cm dbh: Y = 0.06409 (dbh2) − 0.09550 (height) for root carbon storage, and Y = 0.0305 (dbh2*height) 0.9499 for above-ground carbon storage, explaining 98% and 96% of the variation, respectively. Average carbon stored in roots for individual trees was 0.6 kg for smaller trees, those less than 5 cm dbh, to more than 10.8 kg for trees greater than 14.0 cm dbh. Average carbon stored in trunks and branches and leaves for individual trees was 1.6 kg for trees less than 5 cm dbh to 44.1 kg for trees greater than 14.0 cm dbh. Average total carbon stored by individual trees ranged from 2.2 kg for trees less than 5 cm dbh to 54.5 kg for trees larger than 14.0 cm. The sampling method for foliar carbon storage predicted an average range of 3 to 8% of total carbon storage. Root-to-shoot ratios decreased as diameters increased, ranging from 0.15 to 1.00 for smaller trees (those with diameters less than 5 cm) and 0.18 to 0.50 for larger trees (those with diameters greater than 10cm). Smaller diameters stored more carbon inside a standard rootball than larger diameters, with trees less than 6 cm dbh storing between 53% to 100% of biomass/carbon inside a standard rootball; trees between 6 cm and 12 cm dbh stored 29 to 83% of total biomass/carbon inside a standard rootball, and trees sampled with diameters greater than 12 cm dbh stored 39% to 67% of total biomass/carbon inside a standard rootball. The average root lengths for each cultivar in all locations were longer along nursery rows than across the row.