Climate Change and Air Pollution Effect on Forest Ecosystems

Climate change, air pollution, urbanization, globalization, demographic changes and changing consumption patterns affect forests and their social, cultural, ecological and economic functions, resulting in consequences for the social value of forests and for people’s livelihoods, health and quality of life. These consequences are more acutely felt in regions where people are directly dependent on the environmental services provided by forests. Additionally, these consequences rapidly affect growing urban populations, as forests and trees make important contributions to urban resilience and human health and wellbeing.

Achieving a better understanding of the drivers of the changing relationship between forests and people is a major challenge of forest research and a prerequisite for the development of more sustainable relationships between forests and society. Additionally, scientific transdisciplinary and interdisciplinary research, at different regional levels, is needed in order to contribute to the successful adaptation of forests to climate change, and to the strengthening of tree health, resistance and resilience. At the same time, all scientific results are a precondition for maintaining and improving the potential to mitigate the effects of climate change and air pollution on the natural environment.

Climate change and air pollution have large negative impacts on physiological processes and functions at both an individual tree level and on the whole forest ecosystem. Our ability to take urgent measures to combat climate change and its impact on forest ecosystems, and conserve forest biodiversity, depends upon knowing the latest scientific results on the status of forest ecosystems.

At present, climate and air quality monitoring in forests around the globe is performed in different networks, by different organizations. Unfortunately, there are a lot of gaps in our knowledge concerning the detection and monitoring of the effects on forest ecosystems. There is a need to better understand the interactions and fluxes at an ecosystem level, and to understand how different pollutants and climate effects are reflected or transferred in quantifiable ecosystem variables, in both the short and long term. For the detection and monitoring of air pollution actions in the climate change context to be relevant, there is a need for better science–policy interactions. Using Earth Observation data for processing, validation and analysis, new technical developments may provide us with new results in air pollution investigations.

This Special Issue, “Effects of Climate Change and Air Pollution on Forest Ecosystems”, includes 10 peer-reviewed contributions, dedicated to increasing the visibility of forest science in the European and global change research policy, and developing the link between forest science and practices in a changing environment and society. The topics addressed in these scientific articles refer to a range of themes, including: the promotion of adaptive management concepts; methods and techniques of restoring forest ecosystems; monitoring the forest’s condition under climate change, atmospheric pollution and other biotic and abiotic stressors; the conservation of nature and forest-protected areas; forest genetic resource conservation; forest pests and diseases; and the value of the forest ecosystem services in the context of climate change, for the sustainable, adaptive, management of forests.

Nowadays, climate change and biodiversity losses are major challenges of global society. Forests, which cover one-third of the Earth’s land surface, are an immense and renewable source of ecosystem services (ES). Understanding forest species interactions and their responses to past climates, as well as the different concepts of management, is critical in foreseeing forests’ responses to future conditions, and in creating optimal strategies for climate change mitigation and adaptation. Thus, forest management, which is one of the main factors modifying forest structure and succession, can be used to promote resilient mixed forests, which are expected to accumulate a higher biomass quantity under intense climate change, and contribute to climate change mitigation and adaptation [1]. Additionally, research results suggest that climate change will alter the forests’ composition and species abundance, with some forests being particularly vulnerable to climate change, e.g., F. Sylvatica forests in the Southern Carpathians. As far as productivity and forest composition changes are concerned, management practices should accommodate these new conditions, in order to mitigate the impacts of climate change [2]. In many cases, human activities change the condition of natural vegetation, leading to disturbances such as the degradation of vegetation, the erosion of soil, a decline in land productivity and even a reduction in ecosystem services. Gaining a better understanding of natural colonization with a pioneer woody species, for example by studying primary natural succession, can offer valuable knowledge about the species that are most adapted to these particular environmental conditions [3]. For the sustainable management of forests, knowledge on the increments of the main dendrometric characteristics of trees (diameter, height and volume) and the relationships among them, can contribute to adaptations in silvicultural work, with the purpose of reducing the risks generated by environmental factors at the stand level. Thus, the existence of stable stand structures is the main condition for an adaptive forest management [4].

Climate change and anthropic activities have given rise to serious environmental problems, and in an increasing number of ecosystems human influences are harming biodiversity and their functions. Through compiling the results of diagnostic assessments of damaged forest ecosystems by air pollution and reference information collected from intact natural forests, restoration plans have shown that ecological restoration is required urgently, as the extent of vegetation damage and soil acidification is very severe. However, tree growth recovery has been observed when the environmental condition has improved due to a significant reduction in air pollution [5,6]. Future climate change projections also underline the importance of hydrological assessments to investigate watershed behavior under climate-related risks and the endangered economic objectives, where it is necessary to intervene in protected forest areas. In this way, a hydrological model, the Soil and Water Assessment Tool, was built and tested in order to support decision makers in conceiving sustainable watershed management; thus, it has also contributed to guides that prioritize the most suitable measures to increase small river basin resilience, and ensure the water demand under climate change [7]. In order to ensure the benefits of forests in the future through the conservation and sustainable use of the forest tree species, silvicultural practices and forest adaptive management should increase, and maintain high genetic diversity and resilience within forest stands. One of the adaptive measures could be the selection, transfer and planting of highly productive and drought-resilient forest reproductive material in reforestation programs (assisted migration) [8].

To emphasize and maximize the ecological, social and economic benefits of forests, suitable assessment methods are required. Active remote-sensing technology, with proven advantages and characteristic limitations, can represent the foundation of multiple approaches, aiming to quantify the capacity of the forest ecosystem to provide services [9]. Representing an immense opportunity to mitigate climate change through carbon sequestration, soil stabilization and natural disaster mitigation, an integrative approach for valuing and assessing forest ES is needed, taking into account the many interdependent factors involving ES and their associated values, as well as the current challenges that people face [10].

All the scientific contributions to forest science in this Special Issue, “Effects of Climate Change and Air Pollution on Forest Ecosystems”, will have an important role in promoting sustainable forest management based on mitigating the effects of climate change and air pollution on forests, and their adaptation to a changing environment and society in the global context.

This information will bring new knowledge concerning forests’ conditions and their ecosystem service values in the context of climate change, air pollution and other biotic and abiotic factors. Additionally, they will promote adaptive management concepts, methods and techniques of restoring forest ecosystems based on nature and forest genetic resources conservation, for the sustainable and responsible adaptive management of forests.