Sampling The Soil In Long-Term Forest Plots: The Implications Of Spatial Variation

Abstract

Long-term monitoring of forest soils as part of a pan-European network to detect environmental change depends on an accurate determination of the mean of the soil properties at each monitoring event. Forest soil is known to be very variable spatially, however. A study was undertaken to explore and quantify this variability at three forest monitoring plots in Britain. Detailed soil sampling was carried out, and the data from the chemical analyses were analysed by classical statistics and geostatistics. An analysis of variance showed that there were no consistent effects from the sample sites in relation to the position of the trees. The variogram analysis showed that there was spatial dependence at each site for several variables and some varied in an apparently periodic way. An optimal sampling analysis based on the multivariate variogram for each site suggested that a bulked sample from 36 cores would reduce error to an acceptable level. Future sampling should be designed so that it neither targets nor avoids trees and disturbed ground. This can be achieved best by using a stratified random sampling design.

Soil microbial characteristics at the monitoring plots on windthrow areas of the Tatra National Park (Slovakia): their assessment as environmental indicators

“…In long-term research or monitoring, study plots are re-sampled on a regular basis and because it is impossible to take samples in exactly the same location, the disturbance of the soil increases at each sampling. That is why the sampling design must be carefully planned (Kirwan et al 2005). In our case, we took ten soil samples at each plot; it was the number, which we were capable to handle in due time to achieve sufficient precision of measurements in the laboratory.…”

Variation in Soil Nitrate Concentrations in Two N-Saturated Norway Spruce Forests (Picea abies (L.) Karst.) in Southern Bavaria

“…Manderscheid and Matzner (1995a, b) suggest ≥20 seepage water samples per investigated depth to represent the area of a stand (about 1ha). Kirwan et al (2005) computed a minimum requirement of 36 samples using a multiple variogram to reliably assess solid-phase soil parameters. From our findings, we also recommend avoiding small samples in order to obtain acceptable confidence intervals.…”

“…Some experience exists on determining stand-level spatial and temporal variation of soil properties (Manderscheid and Matzner 1995a, b) and accurately estimating their mean characteristics (Kirwan et al 2005). However, simpler and less expensive methods are needed to accurately estimate nitrate concentrations in the soil solution while taking into account the potential high variation over space and time in the soil solution.…”

Quality assurance (QA) in international forest monitoring programmes: activity, problems and perspectives from East Asia and Europe

“…(iii) Field sampling was not properly addressed by the two programmes. This is unfortunate, as field sampling has been shown to account for the largest part of error in monitoring (e.g., Bargagli, 1998;Bleeker et al, 2003;Kirvan et al, 2005). This goes together with the little attention given by both programmes in providing explicit and formal definition of monitoring objectives, in term of expected precision level of estimates and change/trend detection.…”

“…Considerable differences were reported for target population, plot type and sample trees selection for crown Draijers et al, 2001;Erisman et al, 2003). Sampling issues have also been investigated for the Level I network (crown condition assessment, Köhl et al, 1994) and for individual Level II plots (soil variables: Kirvan et al, 2005;deposition: Houston et al, 2002) and reviewed by Thimonier (1998) for deposition.…”