THE CONDITION OF FORESTS IN EUROPE 2013 EXECUTIVE REPORT 2013 THE CONDITION OF FORESTS IN EUROPE 2013 EXECUTIVE REPORT United Nations Economic Commission for Europe, Convention on Long-range Transboundary Air Pollution, International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) www.icp-forests.net ACKNOWLEDGEMENTS ICP Forests wishes to express its appreciation to all persons and institutions that have contribu- ted to the preparation of this report, in particular: - Johann Heinrich von Thünen Institute, Federal Research Institute for Rural Areas, Forestry and Fisheries, Institute of Forest Ecosystems and Institute of International Forestry and Forest Economics - National Focal Centres of ICP Forests AUTHORS Walter Seidling, Tanja Sanders, Cecilia Akselsson (Chap. 5), Nathalie Cools (Chap. 7), Alessandra De Marco (Chap. 9b), Bruno de Vos (Chap. 7), Wim de Vries (Chap. 9c), Sophia Etzold (Chap. 9c), Marco Ferretti (Chap. 9b), Uwe Fischer, Paolo Giordani (Chap. 2), Elisabeth Graf Pannatier (Chap. 5), Karin Hansen (Chap. 1), Mathieu Jonard (Chap. 5), Aldo Marchetto (Chap. 9b), Radovan Nevenic, Pasi Rautio (Chap. 9a), Gertjan Reinds (Chap. 9c), Mitja Skudnik (Chap. 3), Svein Solberg (Chap. 9c), Laura Martínez Suz (Chap. 4), Liisa Ukonmaanaho (Chap. 6), Elena Vangue- lova (Chap. 5), Stavros Veresoglou (Chap. 9b), Peter Waldner (Chap. 1, 9a, 9c), Esther Wattel- Koekkoek (Chap. 8), Daniel Žlindra (Chap. 3), Richard Fischer 1 2 PREFACE Perica Grbic Eng. Director – Directorate of Forests The need to protect and improve the management and monitoring of forest resources across Europe has become increasingly clear in recent years. Forests and their associated resources are immensely valuable to the economies and welfare of both developing and developed nations and there is worldwide concern over the impacts of global climate change on forests as well as the rate at which this change is taking place. Forests are one of the most important terrestrial ecosystems, of vital significance for sustaining the balance between oxygen and carbon in the atmosphere and they are under threat. Forests provide key ecosystem services – they regulate climate, sequester carbon, protect watersheds, and help conserve biodiversity. Many of our decisions are made without a full understanding of the value of these ecosystem services, or of the rate at which forests are being lost in the pursuit of more immediate economic gains. Sophisticated forest observation systems and methodologies are now available and the need for accurate information on change within forests is increasing. Thus, our common understanding of forest change and air pollution effects on forests will improve dramatically. Good and effective communication between scientists and forestry experts within the context of monitoring forest condition is a prerequisite for establishing the values, issues, risks, and challenges related to global change. Proposing measures for integrated sustainable land use of the key ecosystems on the planet is now possible and will help to limit the adverse impacts of air pollution and other anthro- pogenic impacts on forest condition. Ministry of Agriculture, Forestry and Water Management Republic of Serbia Perica Grbic Director – Directorate of Forests 3 ÜBERSCHRIFTCONTENT & SUMMARIES Just over three-quarters (78%) of the atmosphere 1. ATMOSPHERIC DEPOSITION comprises inert nitrogen which has very limited Nitrogen deposition largely originates from fossil availability for biological use. fuel combustion and animal husbandry. Deposition is highest in central Europe. Only a minor decrease All terrestrial ecosystems need reactive nitrogen in deposition has been measured on intensive mo- and historically this has been in short supply. Arti- nitoring plots over the past decade (see p. 6). ficial nitrogenous fertilizers and fossil fuel combus- tion are both sources of reactive nitrogen and their 2. LICHENS use has dramatically altered the global nitrogen cycle. Lichens are very sensitive indicators of nitrogen deposition. Deposition is high on 75% of the Euro- pean forest plots and this is reflected in the change in lichen species composition over time (see p. 8). 3. MOSSES Mosses absorb most of their nutrients and water across their surface. As a result, they are directly affected by atmospheric deposition. In a study car- ried out in Austria, Croatia, Italy, and Slovenia the nitrogen content in mosses significantly increased with increasing nitrogen deposition (see p. 10). 4. FUNGI Fungal species diversity and structure significantly decrease with increasing nitrogen deposition. On a European transect through nine countries, 393 mycorrhizal species were determined. These fungal types live in symbiosis with tree roots and play a major role in nutrient uptake by trees (see p. 12). 5. SOIL SOLUTION An analysis of trends on the Level II plots showed exceedances of critical limits for nitrogen in the subsoil on 50% of the plots. Leaching is mainly de- pendent on nitrogen deposition with other factors playing a relatively minor role (see p. 14). 004 Open field site with meteorological equipment and deposition samplers in Berchtesgaden (Germany), complementing the Level II plot within the forest. 6. LITTERFALL 9. EFFECTS ON TREES Litterfall and its decomposition are critical proces- 9A FOLIAGE NUTRIENT BALANCE ses for transferring nutrients from above-ground fo- Soil nitrogen generally stimulates plant growth. rest biomass to soils. Tree species composition (and How ever, excess nitrogen can cause other nu- thus foliar litter chemistry) affects nitrogen cycling trients such as magnesium to become deficient. rates at the scale of entire forest stands; for exam- This can affect forest health and enhance the ple, the scale of the nitrogen transfer in litterfall effects of additional stress factors. Nutrient im- determines the amount of nitrogen available for balances were detected in leaves and needles on tree growth (see p. 16). 10% of the nitrogen-saturated plots (see p. 24). 7. SOIL SOLID PHASE 9B CROWN CONDITION (TREE HEALTH) Soils play a key role in nitrogen cycling and storage Effects of nitrogen deposition on leaf and needle within ecosystems. They host nitrogen-fixing loss can be detected at a local level for some tree microorganisms, as well as those that release species. These impacts are compounded by the nitrogen back into the air. Mineralization of organi- effects of weather, insects and diseases, and soil cally-bound nitrogen takes place within soils and condition (see p. 26). converts nitrogen to a form available for tree growth. Loss of nitrogen from the soil is mainly 9C STEM GROWTH through harvesting and leaching. One of the key Nitrogen acts as fertilizer for trees. At sites with low questions concerns the saturation status of nitrogen soil levels, atmospheric nitrogen inputs in- European forest soils (see p. 18). crease growth. But on nitrogen-saturated plots, even high atmospheric nitrogen inputs have no im- 8. GROUNDWATER QUALITY pact on tree growth (see p. 30). Rain water containing dissolved nitrogen is pulled downwards through the soil by gravity, this is 10. CONCLUSIONS known as leaching. Leaching may affect the quality Assessing the input of nitrogen to forests and the of drinking water pumped up from groundwater. In direct and indirect responses of forest trees are forests on sandy soils in the Netherlands nitrogen- core activities of the large-scale and intensive leaching has decreased by 55% over the past 20 monitoring of forest ecosystems in Europe. ICP years, showing the success of emission reduction Forests provides policy makers with key informa- policies (see p. 22). tion for forest management, especially under the projected future climatic changes (see p. 33). 5 1. ATMOSPHERIC DEPOSITION LARGE REGIONAL VARIATION IN SLIGHT DECREASE IN NITROGEN NITROGEN DEPOSITION DEPOSITION ACROSS EUROPE Nitrogen deposition was measured on 219 ICP Fo- Trends in nitrogen deposition across Europe are rests Intensive ICP Forests Intensive Monitoring based on data from 83 plots with continuous mea- (Level II) plots in 24 countries across Europe in surements between 2002 and 2011 (Fig. 1-1). 2011. The mean combined throughfall deposition of High deposition levels were recorded in the forests nitrate (NO3) and ammonia (NH4) decreased from of central Europe, from Denmark to the Swiss Plain. ~13 to ~9 kg N ha-1 a-1 between 2002 and 2011 For ammonia the regions of high deposition also and the mean combined bulk deposition from ~10 extend further westward, to northern France, the to ~7 kg N ha-1 a-1 (Fig. 1-2). This is a decline of central UK and Ireland. In the Mediterranean area, around 30% and corresponds to a mean decrease relatively high values were only recorded at sites of about 3% per year. However, the situation on in- in Spain and southern France. dividual plots may differ from the mean trend. HIGH REGIONAL NITROGEN LOADS STILL LIKELY IN THE FUTURE Model results (not depicted) suggest that by 2020 critical deposition loads for nutrient nitrogen will still be exceeded on up to 50% of the land surface of the EU depending on the scenario used. Critical nitrogen deposition loads in Europe are generally widely exceeded. Collection of stem flow is important on trees with a smooth bark like Euro- pean beech (Fagus sylvatica) (Freising, Germany). 6 To minimise errors due to contamination, several deposition samplers are run in parallel at the open field site in Gronik, Slovakia. Throughfall nitrogen (NO3-N + NH4-N) 2002-2011 Figure