Scots pine (Pinus sylvestris L.) is a widespread tolerant forest tree-species; however, its adaptability to environmental change differs among sites with various buffering capacity. In this study, we compared the spatial effects of aridity index (AI) and nitrogen deposition (ND) on biomass density in natural and man-made pine stands of differing soil fertility using geographically weighted multiple lag regression. Soil fertility was defined using soil series as zonal trophic (27.9%), acidic (48.2%), gleyed (15.2%) and as azonal exposed (2.5%), maple (2.4%), ash (0.8%), wet (2.1%) and peat (0.9%) under pine stands in the Czech Republic (Central Europe; 4290.5 km²; 130–1298 m a.s.l.). Annual AI and ND in every pine stand were estimated by intersection between raster and vector from 1 × 1 km grid for years 2000, 2003, 2007 and 2010 of severe non-specific forest damage spread. Biomass density was obtained from a MODIS 250 × 250 m raster using the enhanced vegetation index (EVI) for years 2000–2015, with a decrease in EVI indicating non-specific damage. Environmental change was assessed by comparing predictor values at EVI time t and t+λ. Non-specific damage was registered over 51.9% of total forest area. Less than 8.8% of damaged stands were natural and the rest (91.2%) of damaged stands were man-made. Pure pine stands were more damaged than mixed. The ND effect prevailed up to 2007, while AI dominated later. Temporal increasing ND effect under AI effectiveness led to the most significant pine stand damage in 2008 and 2014. Predictors from 2000 to 2007 afflicted 58.5% of non-specifically damaged stands at R² 0.09–0.76 (median 0.38), but from 2000 to 2010 afflicted 57.1% of the stands at R² 0.16–0.75 (median 0.40). The most damaged stands occurred on acidic sites. Mixed forest and sustainable management on natural sites seem as effective remediation reducing damage by ND.

Tree-ring width of Picea abies was studied along an altitudinal gradient in the Harz Mountains, Germany, in an area heavily affected by SO₂-related forest decline in the second half of the 20th century. Spruce trees of exposed high-elevation forests had earlier been shown to have reduced radial growth at high atmospheric SO₂ levels. After the recent reduction of the SO₂ load due to clean air acts, we tested the hypothesis that stem growth recovered rapidly from the SO₂ impact. Our results from two formerly damaged high-elevation spruce stands support this hypothesis suggesting that the former SO₂-related spruce decline was primarily due to foliar damage and not to soil acidification, as the deacidification of the (still acidic) soil would cause a slow growth response. Increasing temperatures and deposited N accumulated in the topsoil are likely additional growth-promoting factors of spruce at high elevations after the shortfall of SO₂ pollution.

The central mountainous area of Japan is affected by air pollutant emissions from nearby countries such as China and Korea. Sharp increases in the consumption of fossil fuels in the early 21st century, associated with rapid industrialization in China, resulted in long-range transport of pollutants from East Asia and increases in the harmful effects of pollution. However, the air pollutants emissions have decreased since 2006, when air pollution countermeasures were implemented in China. Furthermore, climatic patterns during 2008–2013 reduced tropospheric ozone concentrations around Japan. Such major changes in the social and climatic environment may have had a significant impact on forests. To investigate this, long-term forest monitoring data obtained at Buna-daira (1190 m a.s.l.), Buna-zaka (1090 m a.s.l.) and Arimine (1350 m a.s.l.) were analyzed. Buna-daira and Buna-zaka forests face the continental side of Mt. Tateyama in Toyama Prefecture. In both stands, the girth growth rate of Fagus crenata was found to have increased after 2008; however, such a tendency was not detected at Arimine, which is surrounded by mountains. The growth rates of Cryptomeria japonica, a conifer resistant to air pollution, were found to remain unchanged or decrease. Here, regional long-range transport of air pollution (including ozone and sulfur oxide) has been demonstrated to influence mountain forests in Japan. In particular, recent decreases in regional air pollution may be an important factor controlling increases in F. crenata, likely through changes in interspecific relationships between species sensitive to and tolerant of air pollution.

Over the past 20 years, the focus of forest science on air pollution has moved from forest decline to a holistic framework of forest health, and from the effects on forest production to the ecosystem services provided by forest ecosystems. Hence, future research should focus on the interacting factorial impacts and resulting antagonistic and synergistic responses of forest trees and ecosystems. The synergistic effects of air pollution and climatic changes, in particular elevated ozone, altered nitrogen, carbon and water availability, must be key issues for research. Present evidence suggests air pollution will become increasingly harmful to forests under climate change, which requires integration amongst various stressors (abiotic and biotic factors, including competition, parasites and fire), effects on forest services (production, biodiversity protection, soil protection, sustained water balance, socio-economical relevance) and assessment approaches (research, monitoring, modeling) to be fostered. Interactions between air pollution and climate change effects on forest services demand long-term research approaches that integrate multi-factorial field experiments, monitoring and modeling.

To investigate the effects of ambient-level gas-phase peroxides concurrent with O3 on foliar injury, photosynthesis, and biomass in herbaceous plants, we exposed Japanese radish (Raphanus sativus) to clean air, 50 ppb O3, 100 ppb O3, and 2-3 ppb peroxides + 50 ppb O3 in outdoor chambers. Compared with exposure to 100 ppb O3, exposure to 2-3 ppb peroxides + 50 ppb O3 induced greater damage in foliar injury, net photosynthetic rates and biomass; the pattern of foliar injury and the cause of net photosynthetic rate reduction also differed from those occurring with O3 exposure alone. These results indicate for the first time that sub-ppb peroxides + 50 ppb O3 can cause more severe damage to plants than 100 ppb O3, and that not only O3, but also peroxides, could be contributing to the herbaceous plant damage and forest decline observed in Japan's air-polluted urban and remote mountains areas.

Along the Upper Gulf of Thailand, coastal fences and breakwaters have been constructed using bamboo since 2005. Despite their potential benefits, bamboo structures disintegrate within seven years releasing floating debris which severely damages mangrove tree stems. The aim of the study was to investigate whether such stem damage resulted in the decline of Avicennia spp. stands along the Upper Gulf of Thailand. Tree health assessments were conducted to assess the probability of crown dieback in damaged and undamaged trees. Satellite-derived time-series of vegetation indices were used to detect long-term forest decline. In contrast to the unaffected landward mangroves, seaward mangroves were unable to recover from insect-induced defoliation events after the collapse of a nearby fence. Furthermore, there was a significantly higher probability that damaged trees showed signs of moderate-to-severe crown dieback. It is recommended that bamboo fences be secured by replacing individual stems before they become detached.

Fog is formed frequently in mountain areas and is apt to cause forest decline, because fog has highly concentrated air pollutants and is readily acidified. The elucidation of the fog characteristics in the areas has been limited because successive observation is difficult in mountains. We have observed wet depositions and meteorological conditions at Mt. Oyama, located about 56 km west–southwest of Tokyo. The mountain meteorology was observed with various devices and the fog frequencies dependent on the altitude were roughly estimated from the meteorology of the base of the mountain. The precipitation amount of the throughfall at the mountain is much larger than that of rainfall, and the large deposition on the canopy is caused by not only fog but also drizzle. Fog and drizzle sample was collected by string-type passive fog collector, PFC, and the meteorological data relating to the collecting rate of PFC sample were observed. PFC samples were affected by rainwater under windy condition and the contribution of the rain to the PFC sample volume was evaluated to be about 30% in average. The sampling rate of PFC was related to the precipitation intensity of throughfall, and it became possible to estimate the air pollutants deposition on the canopy via wet deposition by the analysis of the samples of PFC as well as rain. The fog and drizzle may cause several times larger deposition of air pollutants on the canopies than the deposition via rain at high mountain forest.

A dramatic increase in winter (December–February) temperature by 7.2 K (1.1 K per decade) since 1950 has occurred in the Ulan Bator basin, Mongolia. This increase in temperature strongly exceeds the global average of late twentieth century warming and even exceeds warming in most of the polar regions with pronounced increases in temperature. The exceptional warming is restricted to Ulan Bator within the Mongolian forest-steppe region and to wintertime. This suggests that the observed warming could result from radiative forcing by black carbon aerosols. In winter, Ulan Bator’s air is heavily polluted by particulate matter, including black carbon, originating from the combustion of low-quality fuel at low temperature. Winter smog has strongly increased in recent decades, concomitant to the increase in winter temperature, as the result of a strong increase in the city’s population. Exponential growth of Ulan Bator’s population started in the mid-twentieth century, but since 1990, altered socioeconomic frame conditions and a warming climate have driven more than 700,000 pastoralists from rural Mongolia to Ulan Bator where people live in provisional dwellings and cause Ulan Bator’s heavy air pollution. Tree-ring analysis from larch trees growing at the edge of the Ulan Bator basin shows negative correlation of stem increment with December temperature. This result suggests that milder winters promote herbivores and, thus, reduce the tree’s productivity. The negative impact of winter warming on the larch forests adds to adverse effects of summer drought and the impact of high sulfur dioxide emissions. Winter warming putatively associated with high atmospheric concentrations of black carbon aerosols in the Ulan Bator basin is an interesting example of a case where greenhouse gas-mediated climate warming in an area where people themselves hardly contribute to global greenhouse gas emissions affects both humans and ecosystems and causes additional local climate warming.

To determine the importance of Al-availability for soil micro-organisms 95 forest soils from Tyrol/Austria with comparable topography, vegetation, climatic conditions, soil type and with low soil pH (median = 3.9) were investigated for their physical (percentage of stable aggregates, water holding capacity), chemical (pH, electrical conductivity, contents of organic matter, concentrations of easily extractable aluminium, calcium, potassium, magnesium and phosphorus) and microbiological characteristics (microbial biomass and respiration, metabolic quotient, content of ATP, activities of protease and CM-cellulase, cfu-values of total and Al-tolerant bacteria and fungi). A highly significant negative correlation was detected between concentrations of KCl-extractable aluminium and soil pH. By the application of multivariate statistical methods, the effect of the concentration of KCl-extractable aluminium on abundance and activities of soil micro-organisms could be revealed. Al turned out to be of great importance for micro-organisms and often outmatched the significance of other well known soil properties like organic matter, pH or water holding capacity. However, due to very healthy trees at the sites under investigation no effect of Al or soil acidification on forest decline could be detected.

The historical Japanese city of Kyoto boasts a great many old Buddhist temples and Shinto shrines, many of which are surrounded by sizable forests that have long been preserved as sacred forests. However, acidic deposition has been fallen on the forests in Kyoto for many years. For this study, we conducted soil surveys and investigated the extent of decline of the trees in two Shinto shrines as historic monuments of ancient Kyoto. Our study revealed clear decline in two key tree species (Cryptomeria japonica (Japanese cedar) and Chamaecyparis obtusa (Japanese cypress)) in both shrines, with some trees showing signs of mortality. The soil was acidic, with an average pH of 4.35. Nutrient salt content too was only about one tenth the national average, with exchangeable Ca (0.52 cequiv./kg) and Mg (0.23 cequiv./kg) for 0-20 cm surface soil. The (Ca+Mg+K)/Al molar ratios were also very low, with 80% of all soil samples having a ratio of 10 or below. Such soil conditions are thought to hamper the sound growth of both Japanese cedar and Japanese cypress, and soil acidification is one of the most likely causes of the decline of temple and shrine forests in Kyoto.