Introduction 

According to its 4^th report, IPCC estimates the global warming at a level of 0.2 °C per decade ([11]). The consequence of this warming projection corresponds to various climate change scenarios at regional level. Adaptation of ecosystems to climate change is likely to become a more significant part of the issue in the near future. From another perspective; this also means less resistant ecosystems to air pollution in some regions of the world. In fact, the effects of both climate change and air pollution are heterogeneously distributed. Forest ecosystems may be adversely affected in some regions but may benefit from milder climatic conditions or nitrogen fertilizing at some other regions. At this point one important tool that should be prioritized is global networks for monitoring and assessment.

Air pollution and climate change effects on forest ecosystems constitute significant scientific research fields today. Strong scientific research enables healthy forest ecosystems. It has been widely accepted that not only the sustainability of ecosystems but also of communities depends on healthy forests ([22]).

International policy on environmental problems has never required more scientific research than today. IUFRO is the major provider of scientific research on climate change and air pollution effects on forest ecosystems. Many aspects of this research field are covered by IUFRO research group RG 7.01.00, that is titled “Impacts of Air Pollution and Climate Change on Forest Ecosystems”. In this RG, monitoring, indicator development, mechanisms of action, atmospheric deposition, soils and nutrient cycles, ecophysiology, genetics, molecular approaches, multiple stressors, water cycle and water related ecosystem responses, mechanisms of action and response measures, and social and political aspects are existing as active research spots. The interrelations and flow of the mechanism towards solid management solutions are given in Fig. 1.

Fig. 1 - The research bridge between effects and measures. The bold terms reflect the study fields of the subdivisions of IUFRO 7.01.00 Research Group.

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The scientific research on air pollution and climate change requires long term reliable data of atmosphere, soil, water, and vegetation. These components of ecosystems are monitored and human interpherences on them are identified as the basis of research. The cumulative effects of multiple stressors like drought, pollution, diseases, fire and insects, changes in moisture and temperature conditions can also be assessed by monitoring. The changes in precipitation and temperature patterns in a region directly affect evapotranspiration which is the key parameter of water budgets of lotic and lentic systems embedded in forest ecosystems. This linkage is vital for the adaptation ([25]) and biodiversity of forested regions. Water shortage may cause extended dry flow conditions in some regions like the Mediterranean ([28]), while excessive rainfall in some parts of Europe and northern US and Canada may result in increase in flooding of streams in forests ([12]).

In the IUFRO RG 7.01.00, the researches on these aspects of climate change are evaluated towards mechanisms of action and then turn into management strategies and political decisions.

The aim of this paper is to discuss the research topics on impacts of air pollution and climate change to put forward gaps and priorities as emerging from the 24^th IUFRO RG 7.01 conference “Adaptation of Forest Ecosystems to Air Pollution and Climate Change”, held in Antalya (Turkey) in March 2010.

  Advances in air pollution and climate change impacts research fields 

Monitoring

Climate change with increasing air temperature by 3-6 °C over 100 years may affect forest production ([17]) and forest adaptation to unfavourable environmental conditions such as acid deposition and tropospheric ozone ([2]). To date, however, it is still unclear whether local meteorological conditions affected by climate change will reduce or enhance air pollution effects on forest functioning and health. The Pan-European Program for Intensive and Continuous Monitoring of Forest Ecosystems (UNECE/ICP-Forests) that was implemented to gain a better understanding of the effects of air pollution on forests, has recently started to evaluate not only the direct impact of changes in climatic parameters on forest ecosystem but also on sulphur (S) and nitrogen (N) deposition, soil-mediated parameters and surface ozone concentrations. Their integrated impact on forest ground vegetation ([29]), health and increment of the trees in relation to carbon sequestration as well as forest functioning and sustainability is becoming of increasing concern.

Results suggest that despite decreases in the emission of precursor substances (VOC, NO, NO₂), a rise in ozone concentrations is still evident (Paoletti 2007). Tropospheric ozone (O₃) air pollution has been recognized as a major phytotoxic agent since the middle of the last century. Also nitrogen (N) and ammonium (NH₄ ⁺) concentrations and deposition are showing decreasing trends (EEA 2010). Due to enhanced acidification processes in the soil and imbalances in nutrition, however, they still represent one of the key threats to forest ecosystems in the near future, especially in Central and Northern Europe. It has been well documented that N-deposition may affect species diversity of ground vegetation, and increase tree growth (based on N concentration data from foliage and soil solution) and the risk of drought stress and pests ([5], [27]) in certain ecological conditions. In combination, these effects could result in an extreme deterioration of forest conditions. On the other hand, a clear direct impact of N-deposition on crown condition could not be well established and requires further investigations. The lack of long-term monitoring data and the use of short time data series may lead to misinterpretations and, in the context of global change, may contribute to the current uncertainties.

There is a general agreement that atmospheric deposition and soil solution have a medium- to long-term influence and significant cumulative effects on forest conditions and vegetation in the context of global change. An extended and integrated assessment of environmental indicators for global change consistently turns out as one of the most important emerging monitoring and research needs. An improved assessment of environmental indicators for global change should provide an increased knowledge of the diagnostic and mechanistic processes occurring in forest ecosystems and allow a more precise prediction of forest health and the state of forest ecosystems for the current global change scenarios. The seasonal variability of environmental contaminants and the main meteorological parameters such as air temperature and soil water regime are suggested as key research areas for investigating climate change effects on forest ecosystems.

Uncertainties in this field could be reduced by means of assessing tree condition using remote sensing technologies, which emphasize aerial photography, satellite images, and laser scanning for collecting data on forest conditions. Based on the application of hyperspectral cameras, most recent research was conducted in the fields of forest condition assessment, forest inventory, and soil and water quality ([26], [32]). These advanced techniques offer new possibilities in sustainable forest management under changing climate, which might help to develop reliable scenarios of climate change and air pollution effects on forest adaptation and mitigation abilities.

Indicator development and mechanisms of action

Ground-level ozone is recognized as a global agent of climate change, which requires merging research on air pollution and changing environment into one common perspective ([21]). The separation between these two research communities needs to be overcome. The argumentation is based on the capacity of ozone to interact in tree and forest ecosystem response with other environmental factors like CO₂, N and drought, even driving below-ground processes and influencing carbon sink strength and pool formation in the entire plant-soil system ([31], [19]). Effects on competitiveness and stress defence, as mediated through genotype and site conditions, demand for enhanced research efforts on ozone effects on plant competition and biodiversity. In addition, awareness has proceeded recently about ground-level ozone as a local towards trans-continental agent, with new “hot spots” of distinctly enhanced regimes arising both in the northern and southern hemisphere. Conversely, ozone effects on global C fixation and storage remain uncertain, mostly because prognoses suffer from the lack of empirical databases and, hence, rigorous validation of modelling. Integrated research concepts are required that unify modelling with ecologically relevant experimentation on the actual O₃ uptake and the sensitivity per unit of O₃ uptake (“effective dose”) in trees and forests, in order to develop robust tools for reliable O₃ risk assessment.

Atmospheric deposition, soils and nutrient cycles

Various aspects of deposition of air pollutants to forests, their effects on watershed chemistry and forest health, and management recommendations for improving sustainability of the impacted ecosystems have been subject to studies on atmospheric deposition and nutrient cycles ([4], [23]). More studies on interactions between science and management present activities where long-term monitoring of N and S deposition and inputs of other toxic pollutants and their effects on multiple watersheds are needed. In modern forest management practices, there is a need for including information on nutritional status of forest stands for sustainable forest management. In that regard, it is imperative to maintain long-term monitoring programs and to account for the effects of extreme years as well as past and present management practices. Improved understanding of N deposition, N leaching, soil acidification and biogeochemical processes in forest stands between forest edges, forest gaps and forest stand interiors may help understanding the stand structure and nutrition interaction ([24]). Another point is the individual components of the hydrologic cycle. Better understanding of throughfall measurements and interpretation is needed, especially when estimates of the dry component of total deposition are concerned. Importance of N atmospheric dry deposition in arid and semi-arid ecosystems and a need for developing reliable methodologies for its estimates is emphasized.

Forests play a crucial role in the global C cycling acting both as sinks and sources. More reliable methods and data are needed to identify the C compartments of various stand and soil types. Understanding these relationships is mandatory for a better evaluation of C sequestration in forests under various climate change scenarios. Ground-level O₃ has a strong phytotoxic potential and affects abilities of forests to sequester C. Several research groups in Europe and north America have been developing new, physiology-based standards for ozone ([21]). Although environmental problems related to effects of heavy metals are quite limited in Europe and north America, biomonitoring methodologies could be valuable for evaluation of potential effects of heavy metals on forests and other ecosystems in developing areas of Asia, south America or Africa.

Ecological impacts and genetic aspects

The topics of ecological impacts and genetic aspects ranges between the identification of stress indicative genes and the integration of genetic markers in the long-term monitoring of the response of tree populations to various abiotic and biotic stresses.

Generally, the door is wide open for integration of genetic information in the study of ecosystem dynamics (“from gene to environment”). Particularly the fields of molecular genetics and corresponding studies of the function of genes supply a variety of applications. The understanding of complex processes of adaptation and survival of populations under various stress conditions requires synergistic approaches which combine information about gene expression with the large variety of physiological and morphological traits ([16]). Information on the function of genes of tree species as compared to other plant species is still fragmentary. Filling these gaps in the frame of environmental genetics (“ecosystem genetics”) was and still is a major challenge for current and future ecological research.

Impacts of air pollution and climate change on forest ecosystems: multiple stressors and ecosystem services

Research on evaluation of multiple stressors on forest species and ecosystem health and services are emphasized under this topic. Different approaches are possible for assessing multiple stressors, including the use of environmental gradients ([1]) and free air factorial exposures ([20]), and tools such as stem or sap flow gauges that allow evaluation of chamberless, whole tree responses. Another focus of the subject is to shift the endpoint of interest from individual plant or forest stands to ecosystem functions or services, the latter being society’s valuation of the physical and biological functions of ecosystems. Examples of ecosystem services include water quality and quantity, clean air, greenhouse gas mitigation, and habitat protection. Understanding and quantifying ecosystem services requires integrative, interdisciplinary research at several levels of biological organization. The overall goal is to help bring awareness to and to promote investigations at this higher level of physical and biological complexity.

Social and Economic Aspects

Social and economic aspects of forestry research -in relation with air pollution and climate change- is strongly related with the ecosystem services and their evaluation ([7]). Studies in this field lay between antropogenic influences, ecosystem functions, and ecosystem services concepts. Ecosystems functions are defined as the capacity of natural processes to perform ecosystem services ([7]) and can be classified as provisioning (wood, non-wood products etc.), regulating (air, water conservation etc.), and cultural (recreational, aesthetics etc.). Demand curve and cost based methods are used to evaluate the loss caused by decreased forest ecosystem services. The ecosystem services may be estimated by various methods (i.e., Biotope valuation method, Energy-water-vegetation method).

A research gap in this field is at the intersection of ecosystem structures-ecosystem services. For example ecosystem services of mixed forests may be quite different than monocultures ([8]). Another point that requires work is the effects of individual events. The dimension and frequency of extreme events are expected to increase particularly due to climate change ([3], [14]). Therefore, reliable methods are needed to identify social and economic aspects of individual damages towards forests.

Water Cycle

Air pollution and climate change will/may change availability, quality and regime of water resources and therefore forest ecosystems ([13] by affecting the water cycle components ([15], [10]). Water is a vital major component of ecosystems to shape them (climax vegetation) and to affect their health (drought, nutrient cycles, insects, etc.). The major research topics on the intersection of hydrology and forestry are: drought and floods and their effects; biodiversity affected by hydrologic diversity; evapotranspiration and its components; stream habitats and riparian ecosystems; nutrient cycle-water cycle interaction; precipitation-runoff; Erosion and sedimentation processes in forest ecosystems.

The hot topics of the water-climate change-forest ecosystems research triangle emphasized at the conference have been on the water stress and availability for the forest ecosystems in changing climatic conditions, management options for mitigating water deficit, water consumption of various stand types and tree species, hydrologic modelling of forested watersheds and water resources management options including hydropower plants.

On the other hand, evapotranspiration from forests has always been a major topic of hydrologic cycle ([30], [18]). Transpiration measurements on individual trees and stands should be incorporated with water budgets to be scaled up for large basins. Precision of watershed models should be increased in order to be used for climate change assessments which could be possible only with precise data on climate, soil, topography, water, and vegetation.

Studies on impacts of air pollution and climate change on aquatic and riparian ecosystems are very few in number ([9]) and remains as a research gap. In particular, urban forests including riparian corridors along the streams are under high risk of air pollution damage.

The topicality of this issue in air pollution and climate change research is so high that the generation of a new RG 7.01 working party about hydroecology was decided. The main aims of this WP will be encouraging studies more on: Developing Best Forest Management Practices towards mitigating the effects of air pollution and climate change. This includes water saving silviculture, Responses of ecosystems to extreme events like drought and floods (side effects of climate change), Biodiversity influenced by changing hydrologic conditions. Hydrologic diversity and biologic diversity are very closely related subjects and affected from air pollution and climate change, Evapotranspiration and its components in changing climatic conditions or air pollution damages, Stream habitats and riparian ecosystems. This is a very hot topic and number of papers on these subjects is growing huge. The air pollution and climate change part of it is very important, Nutrient cycle-water cycle interaction. This is sometimes ignored but water cycle is the driving mechanism in nutrient cycles, precipitation-runoff. A widely studied subject both by civil engineers and forest hydrologists. The climate change or forest damages affecting this coupling falls into the scope of suggested hydro-ecology WG, Erosion and sedimentation processes in forest ecosystems. Erosion is sometimes a major concern for forests because roads, logging, recreation and many other forestry treatments or activities are becoming sources of erosion. Besides, sedimentation is a mechanism that is shaping stream corridors. These natural or accelerated (by human impacts) processes are affected from changing climatic conditions as well as forest damages caused by air pollution. This in turn affects all stream habitats in a watershed system.

  Final recommendations 

Research results should be disseminated, integrated, and provided to the decision makers to ensure further support. IUFRO enables these three linkages through scientific meetings. The results of our last meeting in Antalya (Turkey) provided important insights on the research priorities on air pollution, climate change and forestry.

Monitoring of climate, soil, and water as well as vegetation is mandatory to enable sufficient amount of high-quality data for modelling and assessments. These data are vital to observe the responses of ecosystems to anthropogenic stressors particularly climate change. Being the major forestry research organization around the globe, IUFRO has a serious responsibility to provide scientific support for international issues like air pollution, climate change, biodiversity, and desertification.

Modelling techniques should be improved to get more reliable results and estimations. More sophisticated ecosystem models are developed and available but not applicable to many parts of the world due to data requirements. Simplified but reliable models are needed for widespread usage. The models should also have a linkage with management. Better management systems or options may be possible with a better understanding of ecological systems. And finally results should be available to public for taking actions. Public awareness can push decision makers to move.

  References