• prove di trazione delle radici
• ontano
• frassino
• controllo dell'erosione.
• carpino
• biodiversità
• salice

Slope instability and erosion of the soil by water and wind are major environmental hazards. Although they are the result of natural geomorphological processes, they are both affected by and have consequences for human activity, often incurring economic and social damage. In nature, vegetation is one factor maintaining equilibrium in the landscape between the destructive forces of landscape instability and the constructive or regenerative forces of stability. The risk of slope failures and erosion is enhanced when the vegetation cover is removed. The question is whether the situation can be repaired if the vegetation cover is restored. The use of vegetation for slope stabilization and erosion control can be referred to as bioengineering. Biotechnical engineering refers to techniques where vegetation is combined with inert structures such as crib walls, so combining the structural benefits both the vegetative, usually Salix species, and non vegetative components. In Europe (especially in Germany, Switzerland and Austria) and in USA, pioneers have been using bioengineering and biotechnical engineering techniques for many decades. In Italy, the bioengineering has spread from the Südtirol by Dr. Schiechtl and in the last twenty years in the rest of the country. In particular, areas of Tuscany coast, hills and mountains ones have undergone major events of hydrogeological instability. In fact, this study regards the area of Cardoso valley in Alta Versilia. In this area, more of 200 bioengineering works were realized since 1996. A survey of these works has revealed that Salix species were not survived and often substituted by other species. Therefore, the first goal of research was to identify the most frequent species found in this area and suitable for areas of Mediterranean environments. Another goal was to assess a protocol of propagation in cold greenhouse, available in the field, and the biotechnical characteristics or the plants in a bioengineering work. For the purpose, a small forest nursery was designed in Retignano and a simple palisade was realized in Pontemazzori, where three wood species plants (Ostrya carpinifolia, Fraxinus excelsior, Alnus glutinosa) were compared to Salix sp. plants. Increasing of biotechnical characteristics such as root volume, root:shoot volume or weight ratio, adventitious roots from stem nodes, tensile strength of roots, were investigated using Azospirillum brasilense Sp245. This bacterium is a well-known PGPR (plant growth-promoting rhizobacteria) and has been considered in order to evaluate the effects on the nursery propagation, and especially to test the ability of the inoculated bacterium to improve rooting parameters for some wood species, which do not easily root by means of conventional techniques.
Nursery trials, field trials, growth observations of the wood plants were performed along four years, from 2010 to 2014. The nursery trials were executed in a cold greenhouse (propagation) and in an unconventional nursery; cuttings were collected from trees in the wood and plant material furnished by the nurseries as well. All willow cuttings rooted with and without treatment; on the contrary the other species cuttings produced sometimes, only a callus at the base (ash and hornbeam) or few roots (alder). IBA and bacterium treatments did not increase enough the rooting potential of plants so to make valid their use in nurseries.
The starch analyses of plant material revealed that willow cuttings had a greater content of this compound, while the cuttings of the other species showed much lower content of starch, in particular ash and hornbeam.
Nursery trials in pot showed that the root systems of the treated plants had grown more, but no cells of Azospirillum brasilense were found inside the examined tissues, suggesting that the observed inoculation effects did not depend on the penetration of the bacterial cells inside the plants. Physiological and growth measures (chlorophyll index, fresh and dry weight of epigeous and hypogeal portions, shoot growth) confirmed a positive influence, whether in pots or in field, showing that the growth of roots was in general higher in inoculated plants and plant mortality decreased. The stomatal conductance of the leaves of the treated plants was lower than the control, suggesting an increased resistance of the treated plants to drought stress.
In the bioengineering work of Pontemazzori, the excavation by airspade confirmed that willow cuttings developed many roots from the underground nodes; plants of common alder, ash and hop hornbeam produced few and smaller roots from nodes, maybe due to the power of the main root system. Therefore, the shoots of these plants showed a lower number but a higher length when treated with the bacterium, significantly in alder.
Uprooting resistance was lowest in saplings of Alnus sp. and Salix sp., intermediate in Ostrya carpinifolia, and highest in Fraxinus sp.; there was the evidence that Azospirillum brasilense Sp245 treatment increased that resistance in willow and ash plants.
In conclusion, some of the species tested, like Fraxinus sp. and Alnus sp., could substitute the willow cuttings in bioengineering works in Mediterranean contests, but using only rooted plant. Therefore the possibility that Azospirillum brasilense Sp245 treatment could induce greater or more rapid development of the root system and systemic resistance to abiotic stresses in plants could be of great importance, whether in nursery propagation or better in bioengineering works.