Estimation of fine root mortality and growth from simple measurements: a method based on system dynamics

This study is a further development of a dynamic compartment-flow analysis, intended as an analytical tool for the empirical estimation of fine root g rowth, mortality and decomposition in forest soil. General properties of th e dynamic system are utilised to interpret relatively simple measurements o f standing biomass, necromass, and decomposition, in order to derive estima tes of the process rates. The method is based on the finding that the ratio of fine root necromass to biomass is related to the specific rates of deco mposition, mortality, and net growth. If the decomposition rate is measured and the net growth trend is determined from live root measurements, mortal ity and gross growth can be estimated using these relationships, provided c ertain regularity requirements are met. These requirements are explicated, such that the estimates can be easily assessed for reliability. To illustra te the use of the method, it was applied to the estimation of specific mort ality rates in seven Scots pine stands of different ages and site types. A reanalysis of a previous sequential coring study yielded consistent results . The advantage of this method is that, unlike the standard analysis of seq uential cores, it accounts for the possibility of simultaneous growth, mort ality and decomposition. It is therefore applicable to situations with no a pparent fluctuations or trend in the biomass and necromass levels. No minim um sampling interval is required; hence the method also allows for more ext ensive or prolonged studies.