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• Walnut growing on mine spoil banks, alone or associated with a N-fixer, was studied. • Italian alder positively influenced walnut growth, also by improving stem shape. • Black locust enhanced soil quality more than alder, increasing organic matter and porosity. • Due to its invasive nature, black locust eventually depressed walnut, nearly eliminating it. Mining activities have a major impact on the environment, depressing several ecosystem services. Afforestation is an efficient approach to recovering abandoned mining areas. This paper aims to assess the suitability of common walnut (Juglans regia L.) for planting on mine spoil banks for wood production, hydrogeological protection, and climate change mitigation. The paper also examines if associating walnut with a nitrogen-fixing species, such as Italian alder (Alnus cordata (Loisel.) Duby) or black locust (Robinia pseudoacacia L.), is advantageous compared to monoculture for the mentioned objectives. For this purpose, contiguous stands of pure walnut and walnut intercropped with one of the two nitrogen-fixing species were studied. The stands had been growing for 34 years on the spoil banks of a lignite mine in central Italy that was abandoned in the 1980s. Overall, walnut in monoculture showed good performances on the infertile substrate, in terms of both growth and stored carbon. On average, in fact, walnut showed a mean height of 16.2 m and a woody volume of 70.1 m3/ha, and had stored 16.5 Mg C/ha between above and below ground. However, walnut significantly benefited from the association with Italian alder, which stimulated the early growth of walnut (up to 15 years) and improved the commercial quality of woody assortments. At the current age, walnut showed significant differences in diameter at breast height (DBH, 44.6%) and total height (H, 17.9%) between the stand where it was originally interspersed with 75% Italian alder and the stand where it grew in monoculture. Alder did not improve soil carbon sequestration, while black locust showed a greater soil improving capacity than alder when associated with walnut, both in terms of organic matter enrichment and bulk density decrease. However, black locust impressive growth rate and strength in chasing suckers induced high walnut mortality. Our results demonstrated that Italian alder is to be preferred to black locust as a nitrogen-fixing species to be associated with walnut, at least in the pedoclimatic and environmental conditions we dealt with. [ABSTRACT FROM AUTHOR]

Mixed-species plantations containing non-nitrogen (N)-fixing species and N-fixing species have the potential to increase the productivity and the ecophysiological performance of the target tree species in comparison to monoculture. However, there are few and conflicting data on the effects of fixed N transfer on species water use efficiency in the short, medium and long term. In this paper, we evaluate the productivity and intrinsic water use efficiency (WUE i ), i.e., the ratio of photosynthesis (A) to stomatal conductance (g s ), in Quercus robur L. (pedunculate oak) stands growing in monoculture and in combination with Alnus cordata Loisel. (Italian alder) in a ratio of 25% (stand F25%) and 50% (stand F50%). We analyzed δ 13 C in tree rings as a proxy of the inter-annual changes in WUE i , while the influence of the stomatal conductance was explored through δ 18 O data. Our results indicate a considerable increase in cumulative basal area (BAI) and in WUE i in the two mixed stands during the period 1990–2002, largely resulting from an increase in N availability, due to the N-fixing species that induced an enhancement of A. After 2002, the differences between the three stands in terms of N% in tree rings, BAI and WUE i leveled off, when natural mortality or management practices decreased the competitive ability of Italian alder. Our study shows the importance of intercropping with a suitable N-fixing species to ensure high levels of productivity and water use efficiency of the target tree species in a Mediterranean-type agroforestry system, but also the need to understand how species interaction changes in time and space with a view to setting the management criteria to maximize tree performance. [ABSTRACT FROM AUTHOR]

• Simple coppicing is the best suited coppice system for a light demanding species such as the chestnut tree. • The growing performance of chestnut coppices is a function of stool and standard densities. • Any standard release is detrimental for the growing performance of the chestnut shoots. • We recommend simple coppicing to produce high quality chestnut wood. In the last decades, releasing standards have become a very common and in some cases even mandatory management options in coppice systems in Europe. As for the chestnut tree, a light demanding and fast-growing species, however, there is a lively debate and a lack of scientific evidences about the pros and cons of releasing standards, especially in stands devoted to quality wood production. In this paper we used nine chestnut coppice stands growing on similar site conditions - but differing in stool density and number of standard trees released - to analyze the effects of the stand structure (i.e., stool and standard density) on the growing performance in terms of diameter increment of the dominant shoots and overall basal area production. Simple coppicing (i.e., no standards release) confirmed to be the most suitable system to enable an initial full growing performance of a light-demanding species such as the chestnut. We thus recommend avoiding the release of standards in quality-wood chestnut coppices in order to allow the new shoots generation to develop undisturbed until the stage of the first thinning. The release of standards in chestnut coppices may however be appropriate in particular cases, such as in stands whose main aim is to protect against shallow landslides along steep slopes. [ABSTRACT FROM AUTHOR]

• Three thinning treatments of different intensity were applied to Quercus robur mixed plantation. • Tree growth and WUEi were affected by crown asymmetry and competition. • High presence of alder influenced tree growth due to resources competitions. • The very high selective thinning resulted to be the most appropriate management practice. • Thinning increased productivity and limited water loss. Thinning intensity is an important factor affecting forest structure and density and influencing tree growth. The main objective of the study is to evaluate how the different intensity of thinning can influence, in the short and long term, the productivity and intrinsic water use efficiency (WUE i) of Quercus robur L., a widespread European species. Three thinning types of different intensity were applied in 14-year mixed plantation of Quercus robur L. growing with Alnus glutinosa (L) Gaertn., a N-fixing species, with an initial density of 625 trees/ha. A multidisciplinary approach was applied, coupling the tree-ring analyses with the measurements of stable isotopes of carbon and oxygen. Findings highlighted how the different conditions of light and competition, determined by the type and intensity of thinning, triggered different responses of Q. robur species in terms of growth and WUE i. Data suggested that the moderate selective thinning (31% reduction of total biomass) was not able to reduce the high competition for resources among individuals: this condition negatively influenced the trees growth. The presence of the N-fixing species, left after the thinning, was not able to counteract the negative effect of competition. A negative effect on productivity was recorded with the geometric thinning (62% reduction of total biomass). Indeed, this treatment resulted in an increase of asymmetry of the canopy (0.90 vs 0.83, respectively in pre- and post-thinning period), due to the partial crown competition from one side and with a consequent limitation of the photosynthetic activity of the trees. Finally, the very high selective thinning (75% reduction of total biomass) resulted to be the most appropriate management practice, as it guarantees positive effects both in terms of growth and intrinsic water use efficiency. The post thinning conditions determined high photosynthesis rates, an increase of productivity and a limited water loss. [ABSTRACT FROM AUTHOR]

• Natural seed regeneration of chestnut is a key issue in recovering overaging chestnut coppices. • The establishment of seed regeneration was more than sufficient to guarantee a safe turnover of dead stools. • Chestnut trees released (standards) after coppicing do not play a relevant role as tree-seeders. • The presence of standards inhibited the growth of seedlings up to 10 m away. • An excessive presence of standards has promoted the settling of regeneration of shade-tolerant species. The management of Italian chestnut coppices has gradually been suspended after World War II, causing a widespread overaging of the concerned stands. In recent years, the renewed interest in coppice wood products increased the need of a solid knowledge on the most suitable restoration practices of overaged coppices. In this context, a key issue is assuring a qualitative and abundant seed regeneration of the chestnut tree (Castanea sativa Miller) in order to substitute overaged stools. Open questions still exist however on the role of the standards (trees released after coppicing) and, in particular, on their interaction with the post-coppicing establishment of seed regeneration. In order to clarify these aspects, we applied different coppicing systems in overaged chestnut coppices so as to create a gradient of residual coverage ranging from full coverage left (no intervention) to simple coppicing (all trees cut, no standards released). The impact of different treatments on chestnut regeneration has been then assessed through field surveys in the second and fifth year post-coppicing, respectively. Chestnut seed regeneration promptly and abundantly established to guarantee the replacement of dead stools also in the simple coppicing. The post-coppicing pulse of chestnut seed regeneration mostly originated from the existing annual seed bank and it was concentrated in the first two years after the intervention, whereas seed inputs by standards or by adult trees at the forest edge played a secondary or negligible role from the third post-coppicing year onwards. Thus, the presence of standards did not benefit regeneration. Rather, it displayed a marked depressive effect on the growth rate of young chestnut seedlings and, under significant shading conditions, enhanced the establishment of shade-tolerant tree species. From a silvicultural point of view, simple coppicing of overaged chestnut coppices represents a valuable management option combining a rapid establishment of natural seed regeneration of chestnut with the resprout and development of the most vigorous stools. [ABSTRACT FROM AUTHOR]