Science of the Total Environment 538 (2015) 703–711 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Pollution control enhanced spruce growth in the “Black Triangle” near the Czech–Polish border Tomáš Kolář a,b,⁎,PetrČermák c, Filip Oulehle b,d,MiroslavTrnkab,e,PetrŠtěpánek b,f,PavelCudlínb, Jakub Hruška b,d, Ulf Büntgen b,g,h,MichalRybníček a,b a Department of Wood Science, Faculty of Forestry and Wood Technology, Mendel University in Brno, Zemědělská 3, 613 00 Brno, Czech Republic b Global Change Research Centre, Academy of Science of the Czech Republic v.v.i, Bělidla 986/4a, 603 00 Brno, Czech Republic c Department of Forest Protection and Wildlife Management, Faculty of Forestry and Wood Technology, Mendel University in Brno, Zemědělská 3, 613 00 Brno, Czech Republic d Department of Biogeochemistry, Czech Geological Survey, Klárov 3, 118 21 Prague, Czech Republic e Department of Agrosystems and Bioclimatology, Faculty of Agronomy, Mendel University in Brno, Zemědělská 1, 613 00 Brno, Czech Republic f Czech Hydrometeorological Institute, Regional Office Brno, Brno, Czech Republic g Swiss Federal Research Institute WSL, Birmensdorf, Switzerland h Oeschger Centre for Climate Change Research, Bern, Switzerland HIGHLIGHTS GRAPHICAL ABSTRACT • Long-term growth changes of Norway spruce are evaluated for the “Black Tri- angle.” • The ring width variations of Norway spruce reflect May–July temperatures. • Acid deposition reduced the growth– temperature relationships of Norway spruce. • This study suggests a complex interplay of multiple factors on forest decline. • Our results prove a recovery of forest growth in the 1990s. article info abstract Article history: Norway spruce (Picea abies (L.) Karst.) stands in certain areas of Central Europe have experienced substantial Received 19 June 2015 dieback since the 1970s. Understanding the reasons for this decline and reexamining the response of forests to Received in revised form 17 August 2015 acid deposition reduction remains challenging because of a lack of long and well-replicated tree-ring width chro- Accepted 17 August 2015 nologies. Here, spruce from a subalpine area heavily affected by acid deposition (from both sulfur and nitrogen Available online 29 August 2015 compounds) is evaluated. Tree-ring width measurements from 98 trees between 1000 and 1350 m above sea fl fi – Editor: J. P. Bennett level (a.s.l.) re ected signi cant May July temperature signals. Since the 1970s, acid deposition has reduced the growth–climate relationship. Efficient pollution control together with a warmer but not drier climate most Keywords: likely caused the increased growth of spruce stands in this region, the so-called “Black Triangle,” in the 1990s. Air pollution © 2015 Elsevier B.V. All rights reserved. Central Europe Dendroecology Forest growth Norway spruce ⁎ Corresponding author at: Mendel University in Brno, Zemědělská 3, 613 00 Brno, Czech Republic. E-mail address: [email protected] (T. Kolář). http://dx.doi.org/10.1016/j.scitotenv.2015.08.105 0048-9697/© 2015 Elsevier B.V. All rights reserved. 704 T. Kolář et al. / Science of the Total Environment 538 (2015) 703–711 1. Introduction mostly associated with rapid reductions in SO2 emissions (e.g., Hauck et al., 2012; Elling et al., 2009), higher N availability (e.g., Laubhann In the second half of the 20th century, acidic air pollution was a seri- et al., 2009), the combined impact of rapid reductions in atmospheric ous concern across most of Europe (Stern, 2005). The increase in global SO2 and NOx, and significantly higher mean temperatures during the emissions, mainly sulfur dioxide (SO2) and nitrogen oxides (NOx), was growing season (e.g., Bošel'a et al., 2014a). Whether and how forest eco- unprecedented after World War II due to economic expansion systems responded to the drastic pollution controls initiated in the early (Grübler, 2002; Smith et al., 2011). The SO2 and NOx emissions in the 1990s has not been investigated yet. Czech Republic increased sharply after approximately 1950 (Dignon Here, TRW measurements are used to evaluate the long-term behav- and Hameed, 1989; Smil, 1990) until the 1980s (Kopáček and Veselý, ior of Norway spruce from the “Black Triangle,” the most polluted part of 2005). The emission loads were highest in the area known as the Central Europe. The aim of this study is to further investigate the forest “Black Triangle,” that is, the Czech–Polish–German border region decline beginning in the 1980s and the subsequent TRW recovery. Our (Grübler, 2002). This region was characterized by large coal resources, study is primarily motivated by the following two hypotheses: (1) The numerous power plants (Kopáček and Veselý, 2005), and topography combined effects of the extremely warm and dry summer in 1976 to- that favored the occurrence of prolonged inversion events. In view of gether with the exceptionally cold winter in 1978/1979 contributed to these ecological impacts, the United Nations Environment Programme the decreased growth of Central European Norway spruce from the (UNEP) officially designated this area as an “ecological disaster zone” late 1970s to the early 1980s. (2) The subsequent growth recovery (Grübler, 2002). was driven not only by reductions in SO2 and NOx emissions starting Desulfurization of brown coal power plants as well as the political in the late 1980s but also by the overall effects of increasing tempera- and economic changes in the early 1990s caused anthropogenic emis- tures. Our results may prove beneficial in determining the future forest sions to reduce considerably (Kopáček and Veselý, 2005). According to productivity under the predicted global climate change. Such informa- the Gothenburg Protocol, SO2 and NOx emissions in the Czech tion should be considered further in forest management strategies. Republic should have been reduced by 85% and 61%, respectively, in 2010 compared with the 1990 baseline. By 2007, SO2 emissions had al- 2. Materials and methods ready decreased by 88% and NOx emissions by 62% (Helliwell et al., 2014); therefore, the target emissions had been successfully surpassed. 2.1. Study area The reduction in SO2 emissions in the Czech Republic has been one of the most dramatic examples of pollution reduction in Europe During the second half of the last century, the Krkonoše mountain (Vestreng et al., 2007). range along the Czech–Polish border was one of the main foci of air pol- However, the high and persistent levels of sulfur dioxide pollution lution in Central Europe (Fig. 1). This region belongs to the Bohemian led to extensive forest decline (Vávrová et al., 2009), with most of the Massif. The main ridge of the mountains (35 km long) spreads from damage occurring in high-elevation conifer ecosystems (Vacek et al., east to west, forming a watershed between the North Sea and the Baltic 2013; Rydval and Wilson, 2012; Elling et al., 2009). Tree injury was typ- Sea. The biogeographic conditions, termed arctic–alpine tundra ically observed during the winter periods due to frequent episodes of (Soukupová et al., 1995), are characterized by frequent weather chang- harsh meteorological conditions and the high SO2 concentration in the es and long, extremely cold, and damp winters with abundant snow air (Lomský et al., 2012). One of the most common woody species grow- cover (Hejcman et al., 2006). The lowest mean temperatures are ing in high-elevation areas is Norway spruce (Picea abies (L.) Karst.), observed in January, and the warmest months are June and August. which covers an extremely broad ecological spectrum (Hertel and Annual precipitation totals vary from 1300 to 1450 mm (Table 1). Schöling, 2011), including many ecotones outside its natural range The highest precipitation totals occur in July and the lowest in spring, (Tollefsrud et al., 2008). In recent decades, spruce tree-ring width especially in April, when the highest peaks are still snow covered. A con- (TRW) reductions and poor crown condition during peak pollution tinuous snow cover persists from November to the beginning of May have been reported several times (e.g., Vacek et al., 2013; Rydval and (5–6 months), with a maximum snow depth observed in March or in Wilson, 2012; Akselsson et al., 2004; Kroupová, 2002; Kandler and the beginning of April. The mean snowpack thickness reaches values Innes, 1995; Sander et al., 1995). The decline in anthropogenic emis- of approximately 1.8 m (Hejcman et al., 2006). The main ridge is well sions led to Norway spruce growth recovery. However, the possible ex- exposed to wind. The predominant winds in Krkonoše blow from the planations for this phenomenon are unclear. These changes have been west or southwest (Kerzelová, 1983). Fig. 1. (A) Location of the study area in Europe and a detailed overview of the study sites in the Krkonoše Mountains. (B) Natural distribution of Norway spruce (Picea abies (L.) Karst.) (http://www.euforgen.org), together with the core region of sulfur deposition N2500 mg S m−2 a−1 in 1985 (hatched area reproduced from www.emep.int). T. Kolář et al. / Science of the Total Environment 538 (2015) 703–711 705 Table 1 Characteristics of the five tree-ring sampling sites (site codes: L, lower altitude below 1100 m a.s.l.; M, middle altitude between 1100 and 1300 m a.s.l.; and U, upper altitude above 1300 m a.s.l.). Site code Site Coordinates Altitude Aspect Slope Prevailing soil types Vegetation Edaphic category Avg. temp. Avg. prec. (m a.s.l.) (°) zone (°C) (mm) 1L Bílá Voda 50° 47′ 175″ N 15° 27′ 314″ E 1009 S 10 Podzolic soil Beech–Spruce Lapidosa 3.9 1401 acidophila 2M Mumlavská hora 50° 47′ 56″ N 15° 27′ 53″ E 1185 SW 5 Podzolic soil Spruce Paludosa 3.2 1421 oligotrophica 3M Alžbětinka 50° 45′ 34″ N 15° 31′ 15″ E 1192 NW 14 Leptosol, podzolic soil Spruce Humilis 3.3 1340 4M Modrý důl 50° 43′ 13″ N 15° 42′ 25″ E 1237 S 22 Leptosol, podzolic soil Spruce Humilis 3.5 1413 5U Pašerácký chodníček 50° 44′ 25″ N 15° 45′ 56″ E 1317 SW 18 Leptosol, podzolic soil Spruce Humilis 2.6 1414 Our study sites cover montane (800–1200-m) and subalpine quality control and homogenization using ProClimDB (Štěpánek, (1200–1450-m) vegetation zones.