Forest observational studies: an alternative to designed experiments

With Ernst Assmann’s appointment to the chair of Forest Yield Science in Munich in 1951, he assumed responsibility for the maintenance of the extensive network of growth-and-yield plots of the Bavarian Forest Research Institute. This network, with some plots having been remeasured since 1870, proved to be a rich source of observations, and constituted the empirical basis for Assmann’s fundamental theories in production ecology. Realizing the strategic value of long-term field observations, scientists are using (a) designed experiments and (b) observational studies to study forest structure and dynamics. This contribution is an attempt to clarify fundamental differences, and to present examples, of these two approaches. We present recent developments regarding the installation of Designed Experiments and show that rigorous experimental design, usually found in planted forests and based on very specific manipulations, that are normally not found in the natural environment is required to address a particular hypothesis that cannot be tested by merely using available observations. We also present examples of new Forest Observational Networks established in China, India, Africa and America. These alternative research infrastructures are especially suitable for the study of natural forests that exhibit a high diversity of tree species with varying size and age structures. Our conclusion is that Forest Observational Studies are emerging as an important alternative to Designed Experiments because they provide a vast amount of information about complex natural forest communities rather quickly. However, long-term commitment is essential to ensure a steady flow of observations about forest dynamics. Manipulated experiments and observational studies can be complementary, but the optimum use of both installations requires careful planning and coordination.