Tuesday, January 27, 2009

Small experimental plots predict entire ecosystem responses! (if you work in peatlands…)

The possibility of extrapolating results from experimental plots to larger (or “real”) scales is a major issue in ecology. For several reasons ecologists conduct manipulative experiments in relatively small experimental units. This that has been suggested to be a big problem since the effect of the studied factor could change with spatial scale. An example of this can be found in biological invasions where there is some evidence that the more species you have at a small scale (e.g. a plot), the less likely an exotic can invade; but, at the regional level, the more species there are, the more likely that exotics can invade, so invasion has a scale-dependent response to species richness. However, if you work on peatlands you are very lucky! A recent paper by Magdalena Wiedermann and collaborators found that in peatlands, experiments in 2 x 2 meter plots represented really well what was happening at the entire ecosystem level. They compared a manipulative experiment where they added nitrogen at different concentrations, with an observational study in a region with gradient of nitrogen concentrations similar to the ones used in the experiment. They found that cover of Sphagnum and vascular plants could be explained by the levels of nitrogen equally well at plot and regional scales

Magdalena M. Wiedermann, Urban Gunnarsson, Mats B. Nilsson, Annika Nordin, Lars Ericson (2009). Can small-scale experiments predict ecosystem responses? An example from peatlands Oikos DOI: 10.1111/j.1600-0706.2008.17129.x

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