Geographical traceability of Picea abies in Trentino

Exploitation of local timber is of central importance to mountain communities and local economies. As markets have expanded from local to global, many timber species have now been superseded on the local market by cheaper, imported timber species. Recognising the added value of local timber, consumers are often prepared to meet the higher costs of these products for ecological, social and ethical reasons. This is particularly significant for an Alpine region like Trentino, which boasts 60% forest cover.

The development of a suitable method for identifying the geographical provenance of timber would be a very useful tool for protecting the local economy. Of the various available techniques, stable isotope ratio analysis has proved to be a powerful method for identifying the origin of many agricultural products.

In this study, we used kriging procedures to study the spatial distribution of δ2H and δ18O in Norway spruce (Picea abies) with samples from 151 sites in Trentino. We tested the accuracy of four spatial interpolation methods (ordinary kriging, two universal kriging methods with spatial trends, cokriging) using an annual resolution of δ2H and δ18O measured in the tree rings formed in 2013 and 2014.

Statistical analysis revealed that the cokriging model is the best method for this species due to its low error rates in the prediction of area of origin for timber. Altitude proved to be the most appropriate covariate for along with mean summer tempera- ture, longitude and latitude. Regional maps of interpolated δ2H and δ18O in P. abies wood together with the 95% confidence intervals were created. The isoscapes revealed the δ2H values to have a strong latitudinal dependency, with the northern area having lower δ2H values. For δ18O there was a slight separation between east (higher δ18O) and west (more depleted). The spatial structures of both the δ18O and δ2H values are quite stable and are mainly influenced by altitude, although there is a certain inter-annual variability. Analyses of the two superimposed stable isotope maps reveals that five main areas can be identified: the north, centre and south reflecting the δ2H north-south gradient (the latitude effect), and the east and west, reflecting the relationship between δ18O and longitude. The strong spatial structure of the data demonstrates the potential of multivariate spatial interpolation, even in a highly heterogeneous area such as Trentino. We believe that this geospatial approach can be successfully applied on a wider scale in order to combat illegal logging.

DANIELE ARNOLDI

VALENTINA TAGLIAPIETRA

FAUSTA ROSSO

GIOVANNI MARINI

MATTIA MANICA

ROBERTO ROSÀ

ANNAPAOLA RIZZOLI