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Questions
What are the most likely environmental drivers for compositional herb layer changes as indicated by trait differences between winner and loser species?
Location
Weser-Elbe region (NW Germany).
Methods
We resurveyed the herb layer communities of ancient forest patches on base-rich sites of 175 semi-permanent plots. Species traits were tested for their ability to discriminate between winner and loser species using logistic regression analyses and deviance partitioning.
Results
Of 115 species tested, 31 were identified as winner species and 30 as loser species. Winner species had higher seed longevity, flowered later in the season and more often had an oceanic distribution compared to loser species. Loser species tended to have a higher specific leaf area, were more susceptible to deer browsing and had a performance optimum at higher soil pH compared to winner species. The loser species also represented several ancient forest and threatened species. Deviance partitioning indicated that local drivers (i.e. disturbance due to forest management) were primarily responsible for the species shifts, while regional drivers (i.e. browsing pressure and acidification from atmospheric deposition) and global drivers (i.e. climate warming) had moderate effects. There was no evidence that canopy closure, drainage or eutrophication contributed to herb layer changes.
Conclusions
The relative importance of the different drivers as indicated by the winner and loser species differs from that found in previous long-term studies. Relating species traits to species performance is a valuable tool that provides insight into the environmental drivers that are most likely responsible for herb layer changes.
In this study, Nuclear Magnetic Resonance (NMR), a non-destructive measurement technique, has been applied for investigation of iron turn-over processes. In non-invasive laboratory experiments, iron dissolution and precipitation reactions in saturated natural sands were observed spatially and temporally. These processes play an important role in groundwater with varying redox and pH conditions. Redox reactions turning Fe2+ into Fe3+ and Fe3+ into Fe2+ were detected in aqueous solution by the difference in magnetic relaxation times. Furthermore, the spatial distribution of the iron reduction reaction, the consumption and diffusive transfer to and from the reaction sites, was observed in a 1D set-up with natural sands. The achieved spatial resolution was less than one millimetre while repeating measurements every half an hour. It showed the system changing from diffusion-limited to reaction-limited.