The Upper Orcia Valley (Southern Tuscany, Italy) is a key site for the
comprehension of denudation processes typically acting in Mediterranean
badlands (calanchi) areas, thanks to the availability of long-lasting
erosion monitoring datasets and the rapidity of erosion processes development.
These features make the area suitable as an open air laboratory
for the study of badlands dynamic and changes in geoheritage due to
erosion (i.e. active geomorphosites).
Decadal multitemporal investigations on the erosion rates and the
geomorphological dynamics of the study area allowed to highlight a decrease
in the average water erosion rates during the last 60 years. More in
detail, a reduction of bare land and, consequently, of erosion processes
effectiveness and a contemporary increasing frequency of mass wasting
events were recorded. These trends can be partly related to the land cover
changes occurred in the study area from the 1950s onwards, which
consist of the significant increase of reforestation practices and important
other forms of human impacts on slopes, mainly land levelling for
agricultural exploitation.
In order to better identify the most significant phases of geomorphological
instability occurred in this area during the last decades, an
integrated approach based on multitemporal geomorphological mapping
and dendrogeomorphology analysis on specimen of Pinus nigra Arn.
was used. In detail, trees colonizing a denudation slope located in the
surrounding of the Radicofani town (Tuscany, Italy) and characterized
by calanchi and shallow mass movements deposits, were analyzed for
the 1985-2012 time period. The analysis of the growth anomaly indexes
and of compression wood allowed to determine a spatio-temporal differentiation
along the slope and respect to an undisturbed reference site.
The negative anomaly index results to be more pronounced in the trees
located on the investigated slope with respect to the ones sampled in
a non-disturbed area. Compression wood characterizes trees on slope
sectors mainly affected by runoff and/or mass movements with a different
persistence. Erosion rates were finally calculated through dendrogeomorphological
analysis on tree roots exposure (0.31-3 cm/y runoff
prevailing; 5.86-27.5 cm/y, mass movements prevailing). Dendrogeomorphological
results are in accordance with those obtained in the investigated
areas with multitemporal photogrammetric and geomorphologic
analyses
