City street trees are prominent features of urban green infrastructure and can be useful for climate change adaptation. However, street trees may face particularly challenging conditions in urban environments. Challenges include limited soil and space for growth surrounded by sealed surfaces, construction that damages roots, poor pruning and management, and direct vandalism. All of these challenges may reduce the capacity of street trees to provide social-environmental benefits, such as attractive landscapes, shading and cooling. Thus, street trees need specific care and resources in urban environments. In this perspective article, we call for a conversation on how to improve the conditions for city street trees. While research has broadly investigated street tree mortality and vulnerabilities, the social perspective may be missing, one that also involves the actions and care by human inhabitants. Here we share perspectives on current management options and discuss from a social-ecological perspective how these can be extended to involve urban residents.

This paper presents recent developments in the interdisciplinary topic of planetary sustainability and discusses its potential implications for space research. The current COSPAR Planetary Protection Policy address scientific space exploration only and is primarily concerned with the issue of contamination with micro-organisms. Other impacts of human space exploration that may be detrimental to space exploration itself are not covered. The best known example is the anthropogenic space debris orbiting Earth, but similar problems will occur in other places due to scientific and commercial space exploration in the near future. One possible approach to discuss and mitigate the impact of space exploration on the environment is to consider the space environment as integral part of sustainable development. The resulting concept of planetary sustainability and its ethical, scientific, economic, and legal ramifications were discussed during a workshop co-sponsored by the International Space Science Institute in March 2018. In this paper, we first summarize the results of this workshop. Then we propose potential implications of this concept for space research and report reactions and suggestions by members of the space research community during the COSPAR assembly 2018.

The Outer Space Treaty makes it clear that the Moon is the 'province of all mankind', with the latter ordinarily understood to exclude state or private appropriation of any portion of its surface. However, there are indeterminacies in the Treaty and in space law generally over the issue of appropriation. These indeterminacies might permit a close approximation to a property claim or some manner of 'quasi-property'. The recently revealed highly inhomogeneous distribution of lunar resources changes the context of these issues. We illustrate this altered situation by considering the Peaks of Eternal Light. They occupy about one square kilometer of the lunar surface. We consider a thought experiment in which a Solar telescope is placed on one of the Peaks of Eternal Light at the lunar South pole for scientific research. Its operation would require non-disturbance, and hence that the Peak remain unvisited by others, effectively establishing a claim of protective exclusion and de facto appropriation. Such a telescope would be relatively easy to emplace with today's technology and so poses a near-term property issue on the Moon. While effective appropriation of a Peak might proceed without raising some of the familiar problems associated with commercial development (especially lunar mining), the possibility of such appropriation nonetheless raises some significant issues concerning justice and the safeguarding of scientific practice oh the lunar surface. We consider this issue from scientific, technical, ethical and policy viewpoints. Published by Elsevier Ltd.

There is a small finite upper bound on the amount of easily accessible water in near-Earth space, including water from C-type NEAs and permanently shadowed lunar craters. Recent estimates put this total at about 3.7 x 10(12) kg. Given the non-renewable nature of this resource, we should begin thinking carefully about the regulation of near-Earth water sources (NEWS). This paper discusses this issue from an ethical vantage point, and argues that for the foreseeable future, the scientific use of NEWS should be prioritized over other potential uses of NEWS. (C) 2016 COSPAR. Published by Elsevier Ltd. All rights reserved.