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Europe has a history rich in examples of successful and problematic introductions of trees with a native origin outside of Europe (non-native trees, NNT). Many international legal frameworks such as treaties and conventions and also the European Union have responded to the global concern about potential negative impacts of NNT that may become invasive in natural ecosystems. It is, however, national and regional legislation in particular that affects current and future management decisions in the forest sector and shapes the landscapes of Europe. We identified all relevant legal instruments regulating NNT, the different legal approaches and the regulatory intensity in 40 European countries (no microstates). Information on hard and effective soft law instruments were collected by means of a targeted questionnaire and consultation of international and national legislation information systems and databases. In total, 335 relevant legal instruments were in place in June/July 2019 to regulate the use of NNT in the investigated 116 geopolitical legal units (countries as well as sub-national regions with their own legislation). Countries and regions were empirically categorized according to ad hoc-defined legislation indicators. These indicators pay respect to the general bans on the introduction of non-native species, the generally allowed and prohibited NNT, approval mechanisms and specific areas or cases where NNT are restricted or prohibited. Our study revealed a very diverse landscape of legal frameworks across Europe, with a large variety of approaches to regulating NNT being pursued and the intensity of restriction ranging from very few restrictions on species choice and plantation surface area to the complete banning of NNT from forests. The main conclusion is that there is a clear need for more co-ordinated, science-based policies both at the local and international levels to enhance the advantages of NNT and mitigate potential negative effects.

[1] This paper establishes that absolute optical air mass and hydrostatic atmospheric delay of electromagnetic waves are proportional magnitudes, and, consequently, their respective obliquity ratios are identical dimensionless quantities. This means that a potential source for developing new models for relative optical air mass can be found in the formulae for the atmospheric delay in electromagnetic signals (and vice versa). In this respect, for estimating relative optical air mass, we demonstrate that Herring's (1992) family of mapping functions for modeling atmospheric delay is more accurate than functional forms devised expressly for the purpose, such as that of Kasten (1965).

The restoration of dry lands in the Mediterranean is a challenging task because harsh abiotic conditions hamper the counteraction of feed-back degradation processes. Active restoration through planting must be performed to deter this process. In this study, we tested the influence of mineral nutrition in the nursery (two formulations of controlled release fertilizer at two rates each) and tree protection after planting (by using tube shelters) on the nine-year performance of Acacia salicina irrigated with low-quality (saline) water. The overall survival at the end of the study period was 58.2%, with the electrical conductivity of the soil saturation extract reaching 5.4 dS·m -1 after nine years. The survival and growth (in height) were greater for seedlings fertilized with more than 1.5 g·L -1 of 9-13-18, although the survival differences became significant only after the seventh year. The basal stem diameter (BSD) of seedlings that were fertilized at higher rates was significantly greater than those that were fertilized at lower rates during the first two years of planting; the differences were no longer present thereafter. The seedlings in shelters had marginally superior survival, faster growth during the first four years, and smaller BSD values after the third year compared to those of the unprotected seedlings. In comparison with a parallel study that was conducted under drought conditions, irrigation reduced some differences among treatments, but it increased others. These results emphasize the importance of the size and mineral nutrient status of nursery stock in irrigated plantations under dry Mediterranean conditions, with highly fertilized seedlings showing superior performance. Long-term planting studies are crucial for gaining a greater understanding of seedling performance and for providing a better rationale for treatment recommendations.