Sampling strategies in forest soils

Many studies have revealed the high variability of soil properties, especially on the forest floor. Sampling techniques have been developed to reduce this variability so as to obtain more precise mean values. Little attention has been paid to the frequency distributions of variables, even though they could provide information on factors that control variability. This paper addresses the selection of the sampling strategy considering the type of study. For the characterization of ecosystems, stratified sampling or systematic sampling is proposed, depending on previous knowledge of the study area. To study processes, two cases were considered: processes that occur within the ecosystem, such as organic matter decomposition, and processes that concern the whole ecosystem, such as fire. In the first case subjective sampling was useful, since it reduced the extrinsic variability of the processes. In the second case, both stratified and systematic sampling were very effective. Frequency distribution analysis was proposed as a tool to detect some factors that control litter accumulation.