| Eco-engineering first and foremost, aims at stabilising soil and slopes in order to protect
humans and infrastructure from potential damages caused by soil failure, usually due to
heavy rainstorms. Whereas the technical constructions are well-defined and their protective
effects in general calculable, this is rarely the case for biological measures. Furthermore,
unlike engineering structures which are immediately useable and operative after
their completion, the effects of plants are developing as a function of time. Within
this scope, soil aggregation processes play a decisive role in in the re-colonisation
process and the re-establishing of a protective vegetation cover. The strength of
soil aggregates is not only critical to the stability of slopes but plays a key role in
ecosystem functioning in general as it affects water, gas and nutrient fluxes and storage
influencing the activity and growth of living organisms. Not by chance, therefore, soil
aggregate stability has been proposed as an indicator reflecting multiple aspects
allowing extensive information on ecosystem status to be gathered in a relatively short
time, in particular in respect of protecting slopes from erosion and shallow mass
movements. Various methods and approaches have been used to quantify soil aggregate
stability but the lack of standardisation complicates the comparison of different
investigations.
From this perspective we investigated soil samples from the field as well as samples
artificially prepared in the laboratory using the same soil material and testing procedure. The
field samples were collected at two sites in the landslide area of Dallenwil-Wirzweli in
Central Switzerland, once in a gully recently affected by erosion and landslide processes bare
of vegetation (control site) and once in a re-stabilised gully with 25 year old eco-engineering
measures dominated by Alnus incana (re-vegetated site). The laboratory samples
were prepared with the soil from the control site. Two different treatments were
used in this comparison including untreated soil (control) and soil planted with
A. incana inoculated with the mycorrhizal fungus Melanogaster variegatus s.l.
(vegetated).
In both cases, the vegetated specimens had a significantly higher soil aggregate stability
compared to their respective control samples without vegetation. Furthermore, it turned out
that the increase in soil aggregate stability in the samples with vegetation was quite similar in
both the artificially prepared laboratory and the natural field samples. However, the level was
remarkably higher in the latter. In order to better understand this different behaviour,
various parameters were analysed. Aspects of the development and succession
processes of plants are compared as well as rooting and the degree of mycorrhization.
Additionally, soil development and the methodical approach are presented and discussed. |