Forests and forestry: intercropping effects on soil properties and leaves compounds in a circular economy perspective

Forests are known to play a key role in the ecosystem health. In fact, they provide a wide range of ecosystem services, such as carbon sequestration for climate change mitigation, nutrient cycle regulation, and biodiversity conservation. For these reasons, the reforestation of degraded sites is listed as a nature based solution. On the other hand, forests represent the main wood source available to meet global needs and could play a fundamental role in the transition of a traditional linear economy towards a circular economy. This implies an economy where raw materials and their value are employed as efficiently as possible, converting the under-valued forest residues into value-generating market forest waste use. In this context, the reforestation of exploited soils for soil requalification could offer the owners an economic yield beyond that by wood, also considering the valorisation of the abundant waste material (e.g. leaf material). To this purpose, and in order to avoid the impacting abandonment phenomenon, our reforestation approach innovatively aims at identifying a specific forest management type, capable of achieving these goals.

A mixed-species plantation in Central Italy was of our interest. It consists of three different associations: particular ancillary species, namely Alnus cordata, Elaeagnus umbellata (both N-fixing species), and Corylus avellana, are in association with valuable species, such as Populus alba and Juglans regia planted on a former agricultural land. The relationship between the chemical and biological topsoil (0-10 cm) properties was evaluated, as well as the leaf antiradical capability of both the valuable species, observing that they vary among different intercropping systems. The lignin and cellulose content, both in soil and leaves, was assessed, along with soil total organic carbon, soil total nitrogen, soil fluorescein diacetate hydrolase activity. Furthermore, Populus alba and Juglans regia leaves were investigated for their phenol content, and for their anti-radical activity by means of DPPH (2,2-diphenyl-1-picrylhydrazyl) and ABTS [2, 2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid)] assays. Data acquired highlight that the leaf material represents an important source of bioactive compounds and that the different associations have a notable influence both on the soil properties and on leaves phenol content and anti-radical capacity. The accessory N-fixing species seems to play a key role since, when Elaeagnus umbellata occurs, a marked decrease in leaf phenol content and the antiradical activities of both the investigated species is observed, while Alnus cordata positively affect phenols in Populus alba leaves, augmenting their radical scavenging capability.

Therefore, it is possible to consider a specific forest management as a tool for soils requalification and, at the same time, a source of income in a circular economy perspective.