Assessing growth rates and standing biomass yield of urban trees

© 2018 Dr. Luis Alberto Orozco AguilarCurrently models used to quantify tree carbon stocks and growth rates do not consider the unique issues inherent in urban tree growth and management. This research addresses these knowledge gaps in urban forestry by examining: 1) the reliability of a faster method for assessing growth rate, 2) the extent of decayed wood in urban trees and its effect on stored carbon and; 3) canopy structure and standing volume distribution of several urban tree species in the city of Melbourne, Australia. Assessing the accuracy of resistance drilling (RD) to perform ring analysis on Quercus robur, Ulmus procera, and Platanus x acerifolia trees was done by comparing core-derived growth series with the corresponding resistance-drilled growth series. This research confirmed the ability and reliability of RD to measure average growth rate at population level but was unable to detect the interannual growth pattern at tree level. Hence, RD cannot be used to replace dendrochronology for growth-climate studies of urban trees. Decay is a common issue in urban forests which deteriorates wood structure and tree vitality over time yet, its effect on standing biomass yield has been overlooked. An existing theoretical model of decay infection was combined with an expert system to quantify the extent of internal decayed wood in 43 trees of three species (U. procera, P. x acerifolia and Corymbia maculata). This study demonstrated a substantial reduction of tree stem volume of U. procera sampled trees due to decayed wood and reported the occurrence of decay in a wide range of stem diameter and tree vitality. This study suggested the application of a species-decay factor, rather than a standard factor, for a more accurate calculation of stored carbon in urban forests. Understanding standing biomass yield of several tree structural parts and the subsequent development of allometric equations may aid in reducing the error in whole tree volume estimations. Full tree measurements and non-destructive approach namely randomized branch sampling were used to estimate standing volume, capture canopy structure, assess biomass distribution and further develop allometric equations of 45 trees comprising three species (U. procera, P. x acerifolia and C. maculata). This research reported significant differences in biomass distribution among sampled trees which also differed from published data for other urban trees. This PhD study provided a set of allometric equations and quantitative inputs on tree structure and dimensional relationships which can be used for tree growth modelling