A novel framework of smart monitoring to face the challenges of tree management in historic gardens.

Historic gardens are green spaces characterised by tree stands with several veteran specimens of high artistic and cultural value. Such valuable plant components have to cope with biotic and abiotic stress factors as well as ongoing senescence processes. Maintaining tree health is therefore crucial to preserve their ecosystem services, but also to protect the monument and visitor health. In this context, finding smart, fast and cost-effective management solutions to monitor health and detect critical conditions for both stands and individual veteran trees can promote garden conservation. For this reason, we developed a novel framework based on Sentinel2 imagery, LiDAR sources and automatic cameras to identify risk spots regarding trees in historic gardens. The pilot study area consists of two closed Italian gardens from the 16th century, which were analysed as a unique Historic Garden System (HGS). The tree health status at stand level was assessed using a criterion based on the Normalized Difference Vegetation Index weighed on tree volume (NDVIt) and validated by a visual crown defoliation assessment. At the tree level, the health status of four veteran trees defined by the NDVIt was also evaluated using green chromatic coordinates (GCC) obtained from digital images acquired by cameras at daily intervals during one growing season. The 33% of the tree population was classified as being in poor health, i.e. "at risk". Veteran trees classified as "at risk" showed an anticipation of phenological phases and a lower GCC compared to reference trees. Despite variability determined by Sentinel medium resolution, the proposed framework showed good accuracy (0.74) for monitoring historical gardens. The semi-automatic risk point mapping system tested here proved to be effective in facilitating the management of historic gardens, which in turn could be applied in the wider context of urban greening.

A multi-analytical approach for the study of red stains on heritage marble.

Red stains are a common discolouration on stone cultural heritage all over the world. These are very difficult to remove and little is known about the reddish pigmentation. Numerous red stains were mapped on the Baptistery of San Giovanni in Florence, one of the most important monuments in Italy. This paper is focused on red stains on marble stone and the results of a detailed multidisciplinary approach are presented. Several analytical and investigation techniques (such as optical microscopy, X-ray fluorescence mapping, X-ray micro-tomography, micro-Raman spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, microbial isolation, colorimetric measurements and isotopic analyses) were used to better understand the origin and processes involved in this kind of alteration. Analyses of the red stains led us to believe the presence of minium (lead tetroxide) and Pb are usually concentrated in the spaces between calcite grains. Red stains of Pb isotopic composition also overlap with data from Sardinian mines. These preliminary data seem to reinforce the suggestion of a source of lead from some metallic items (during restoration campaigns between 1938 and 1944, damaged parts were removed and replaced, and the new marble cladding was fixed with iron brackets treated with minium).