Root biomass studies in forest ecosystems

Abstract

Biomass studies are fundamental to understanding the dynamics of ecological syst ems Estimations of biomass are essential in determining the distribution and flow of materials in ecosystems, and necessary to understand the dynamics of these systems (ANDERSSON1971). However, biomass determinations are only static, descriptive studies, estimating how; much living material is contained in a given space or system at a particular time. Dynamic studies deal with the system, as it functions and generally consist of a series of static studies performed over an interval of time. Dynamic aspects such as growth, productivity, turnover, and so on, may be characterized by monitoring the changes in biomass during these intervals. In this manner, biomass studies may be employed to describe quantitatively the static distribution of materials in ecological systems, and they may also be repeated in sequences to study the dynamic relations of components within these systems. The last 20 years have brought an emergence of ecosystem studies. This growing interest in the dynamics and productivity of ecosystems has pointed out the need of, and has led to attempts for, a better understanding of roots as a part of the entire system. Progress in understanding the belowground portions of ecosystems has lagged, however. W. F. HARRIS (1971) states: "Although the importance of roots as structural, storage, and physiologically active organs has been known, they have been neglected for the most part in 'ecosystem studies' to date because of difficulties surrounding their study". Studies of roots inherently must cope with some difficult problems, the most obvious being the overburden of the soil. This overburden makes these systems invisible; observation is not possible without a great deal of effort and disturbance. Moreover, the soil is generally the environment of the roots; its removal constitutes such a drastic change that subsequent observation is likely to give an atypical picture. Because of these limitations, most investigations of roots are still exploratory in nature. The approach presented in this paper provides a flexible structure for performing studies of the distribution and dynamics of the belowground components of ecosystems. The present investigation was carried out as a part of an integrated study by the U. S. International Biological Program. The Coniferous Forest Biome seeks to analyze and model coniferous forest ecosystems. The forest ecosystem has been divided into five major compartments: the canopy layer, the subordinate vegetation layer, the forest floor layer, the rooting zone layer, and the subsoil. A major objective of the modeling effort has been to quantify descriptive and dynamic aspects of biomass, productivity, and the flux of materials for each compartment. The principal objective of this study was to describe quantitatively the total root biomass contained within the rooting zone layer of an old-growth stand of Douglas-fir (Pseudotsuga menziesii var. menziesii (MIRB.) FRANCO]. Another objective was to sample in a manner that would yield data amenable to analyzing the spatial distribution of root biomass around individual trees as well as between different plant communities within a small