Fine-root parameters as indicators of sustainability of forest ecosystems

Abstract

The potential of fine roots as indicators of forest sustainability is discussed. In 10 oak ( Quercus petraea, Q. robur) trials, where moderate doses of lime had been applied up to 27 years ago, the effects on soil, root and foliar chemical parameters were compared with above- and below-ground growth. The effects of liming on growth appeared positive and sustained for ca. 25 years after application, whereas effects on soil, root, and foliar chemical parameters only lasted for 10–25 years. Fine-root biomass or length appeared to be significantly increased by liming and comparable to the effects on above-ground tree growth, but were considered to be too time-consuming for use as indicators of ecosystem function. A combination of soil and root chemical parameters predicted fine-root mass and length the best – and thus tree growth – with foliar chemical parameters being of minor importance. When this best-fitting linear regression model was applied, separately for both the lime treatment and the control, the contribution of root chemical parameters in the model decreased in the lime treatment as compared to the control, while that of foliar chemical parameters increased. Consequently, root as well as soil chemical parameters appeared to be more sensitive to changes in the chemical status of the site. In general it is recommended, that studies aiming to define useful indicators, should start with a feasibility study (e.g. comparing the utility of soil, root and foliar chemical parameters) before defining a smaller set of most sensitive parameters. For the sites examined, a combination of parameters such as fine-root Ca, Al, Mg, Ca/Al, Mg/Al, soil exchangeable Ca, Al, and Mg gave a good insight into the actual uptake capacity of roots or constraints on that capacity.