Permission of the publisher is required for all other derivative works, including summaries and translations. The chapters in this book provide a snapshot of the state of knowledge about the effects of air pollution at the beginning of the 21st century.
Air pollution and global change
A double challenge to forest ecosystems
Introduction
Almost 70% of the water vapor passes through the stomata of forest trees and forests hold about 50% of the world's carbon stores. How will the world's forests respond to elevated CO2, a warming climate and increasing air pollution loads.
How will the world’s forests respond to elevated CO 2 , warming climate, and increasing air pollution loading?
On average, trees growing at elevated CO2 photosynthesize at about 60% higher rates than at background CO2 levels (Norby et al., 1999). Evidence suggests that our emissions of nitrogen oxides (NOx=NO+NO2) and volatile organic compounds (VOCs) have significantly increased O3 levels over large regions of the world (eg, Crutzen, 1988; Marenco et al., 1994).
Global warming
Ozone has been shown to reduce aboveground biomass accumulation by 20 to 40% or more for sensitive genotypes (Wang et al., 1986; The incidence and abundance of various insect and disease pests are generally predicted to increase under global warming. (Chakraborty et al., 2000; Bale et al., 2002).
Sulfur and nitrogen oxides and acidic deposition
This resulted in high mortality in the forest tent caterpillars, which were otherwise in peak cycle (Mattson, personal communication). While pollution control legislation in the United States (Furiness et al. Alewell et al., 2000) has resulted in reductions in sulfur emissions (Fig.
Other air pollutants
The classic example of this remains the forests of the San Bernardino Mountains in the Los Angeles air basin, which have received major impacts of nitrogen deposition over the past 60 years or more (Bytnerowicz and Fenn, 1996; Bytnerowicz et al. 2002a, 2002b ). Recent patterns of wet deposition before and after implementation of the 1990 Clean Air Act Amendments (CAAA) (from Driscoll et al., 2001).
Pollutant interactions
The cause was later found to be a synergistic interaction of moderately elevated levels of O3 and SO2 (Dochinger et al., 1970; Costonis, 1970). Atmospheric CO2 levels are expected to double above current levels by then (Stott et al., 2000; IPCC, 2001).
Management of genetic resources for future forests
Maintaining large amounts of genetic diversity will increase the probability that adequate fitness is maintained to meet rapidly changing environmental conditions (Gregorius, 1986; Müller-Starck, 1989; Koski, 1996; Rehfeldt et al., 1999). Alternative strategies are also needed to ensure that gene banks, clone banks, seed areas, seed collection areas and other in-situ conservation strategies are maintained in a multiplicative manner, so that change in contamination and/or or climatic scenarios do not result in the loss of these collections from single vulnerable test sites (Martin, 1996; Hannah et al., 2002).
Conclusions and knowledge gaps
Modeling changes in VOC emissions in response to climate change in the continental United States. Ed.), Effects of air pollution on forest health and biodiversity in the forests of the Carpathians.
What is the role of demographic factors in air pollution and forests?
- Analysis
- Future pollutant scenarios
- Research needs
- Summary
Over the next 50 years, 90% of population growth will come from racial and ethnic minorities. In the United States, there is a shift from the north and east to the south and west. Pressures to meet global standards of environmental quality, modeled after the Montreal Agreements and the Kyoto Protocol, will increase.
Changing atmospheric carbon dioxide: A threat or benefit?
Growth responses
1999a, 1999b), some studies reported a continuous increase in growth acceleration in their studies (Pokorný et al., 2001; Norby et al. 2002) and provided the first evidence of a sustained increase in forest productivity in closed-canopy forest. Others have found increased susceptibility to heat stress when trees are grown under elevated CO2 (Bassow et al., 1994).
Global warming: effects on forest ecosystems
As global warming continues, there will be more frequent occurrences of high temperature stress events (Mearns et al., 1984). Increased frequency of hot days under global warming is likely to significantly increase soil respiration (Atkin et al., 2000). However, it is less clear what effects elevated CO2 has on litter decomposition (Norby et al., 2000).
Afforestation and reforestation for carbon sequestration
Eddy current measurements of 10 EE from actual harvest site data are also shown (from Thornton et al., 2002). For example, currently more than 80% of the estimated C sink in Northern Hemisphere forests occurs in one third of the forest (Goodale et al., 2002). Potential contribution of afforestation/reforestation and agroforestry activities to global carbon sequestration (Brown et al., 1996).
Conclusions and knowledge gaps
Projected effects of climate change on patterns of vertebrate and tree species richness in the contiguous United States. Effects of elevated carbon dioxide and ozone on the genotypic response of aspen phytochemistry and the performance of a herbivore. Effects of elevated carbon dioxide and ozone on leaf chemical composition and dynamics in quaking aspen (Populus tremuloides) and paper birch (Betula papyrifera).
Tropospheric ozone: A continuing threat to global forests?
Ozone distribution at the surface and trends 1. Global ozone distribution
In the United States, trends in surface O3 are based on both 1-hour and 8-hour data. In contrast, recent O3 concentrations in the most unpolluted parts of Europe have averaged between 20 and 45 ppb (Volz and Kley, 1988; Janach, 1989). A typical mean tropospheric O3 concentration of 30-40 ppb is now found almost everywhere in the world (Finlayson-Pitts and Pitts, 2000; Dergoth et al., 2002).
Effects of ozone on forest trees
However, in many cases hourly ambient O3 concentrations do not exhibit a frequency distribution that is Gaussian (Nosal et al., 2000). The enzymatic response within the leaf is extremely rapid and can occur within minutes (Noormets et al., 2000). This work also provides important new field evidence for the previously described (McDonald et al., 2002) competitive interaction between genotypes in the presence of elevated O3.
Case studies of forest ecosystem response to ozone 1. North America
Other factors such as high nitrogen deposition (Bytnerowicz et al., 1999) and developmental stand changes due to fire suppression also contributed. Several of these species are moderately to very sensitive to O3 based on leaf damage (Miller et al., 2002). Despite concerns (Ferretti et al., 1999), annual canopy surveys remain the main tool for monitoring the status of European forests.
Ozone air quality standards in North America and critical levels in Europe Ambient air quality standards in North America are based on the best avail-
North American ozone air quality standards and critical levels in Europe North American ambient air quality standards are based on the best benefits. The recommendation is made that critical levels for O3 for forests, crops and semi-natural vegetation be based on the accumulated average hourly exposure of vegetation to ozone over an O3 concentration. It was concluded that a step-by-step procedure is needed to enable a Tier II assessment of critical ozone levels for forests.
Uncertainties in current scientific understanding on ozone and forests 1. Uncertainties due to experimental methodologies
Regardless of the different experimental methods used, there are a number of uncertainties associated with our current understanding. Modified from Percy et al. and Cornell, 1996; Myers Use of O3 treatments that do not simulate the stochasticity of the environmental fluxes and thus realism, (3) Use of uni- or bivariate systems and lack of emphasis on multivariate systems, and (4) Use of monocultures, thus eliminating competition between species. Such efforts cannot explain the dynamics of the atmosphere and associated plant physiology.
Conclusions
Oxidant exposure and effects on pine forests in the Mexico City and Los Angeles, California sky basins. Eds.), Urban Air Pollution and Forests: Resources at Risk in the Mexico City Air Basin. United States Environmental Protection Agency, Washington, D.C. Evaluation of the Montsouris series of ozone measurements in the nineteenth century.
Regional scale risk assessment of ozone and forests
Methods
AOT40 (accumulated exposure above the 40 ppb threshold) is defined as the sum of the differences between the hourly ozone concentrations and the deviation threshold of 40 ppb, calculated for all daytime hours (global radiation 50 W/m2) of the entire vegetative season, which is set conventionally. Finally, the AOT40 total daylight maps are obtained from the AOT40mixand Ratio maps by inverting Equation (3). 2, while the details of the semi-variogram functions used in the kriging procedure are given in Table 2.
Results and discussion 1. Level I risk assessment
The availability of groundwater was assessed by the Regional Agricultural Service (ERSAL) using a simple groundwater balance model based on climate data from the past 30 years (Mariani, 1997; Maracchi et al., 1992), taking into account and soil available water capacity, soil depth and covers obtained from the ERSAL pedological database, based on taxonomic unit distribution in the region, properly accomplished. Also, Scots pine forests in the natural parks located immediately north of Milan are subject to strong stress pressure. During the summer, the local insubric climate dictates frequent afternoon rainfall on the northern hills (Maracchi et al., 1992) and hot-and-humid conditions on the plains in the south.
Conclusions
Research campaigns have confirmed the presence of obvious symptoms of leaf damage in the field in forest populations of the mountain target of the photo-oxidant cloud generated in the lower urban and industrial lowlands. In: Air Pollution, Global Change and Forests in the New Millennium, 19th International Expert Meeting. Effects of outdoor ozone on common bean (Phaseolus vulgarisL.): results of an EDU antioxidant trial in the Po Valley (Italy) during the 1993 season.
Limitations and perspectives about scaling ozone impacts in trees
O 3 impacts on juvenile and mature trees
Percent response to O3 for solar leaves of young and mature trees of different tree species. Percent difference in stomatal conductance (GW) between sunlit leaves of mature trees and unshaded juveniles for different tree species. In this case, sun leaves from mature trees have much greater GW than leaves from shady juveniles.
Conclusions
Effects of short-term exposure to ozone on the carbon economy of mature and young Douglas firs [Pseudotsuga menziesii (Mirb) Franco]. Increased carbon dioxide enhances the effects of ozone on photosynthesis and growth Species respond in the same way regardless of the plant's photosynthetic pathway or functional group. Ozone uptake in the sun and shade of spruce trees: quantification of the physiological effects of ozone exposure.
Simulating the growth response of aspen to elevated ozone
A mechanistic approach from leaf-level photosynthesis to complex architecture
A meta-analysis, based on experimental results on young trees, indicates that tree growth rates can be expected to increase under elevated CO2 (Norby et al., 1999). However, the potential increase in forest biomass production and associated sequestration of carbon dioxide resulting from increased growth rates may be moderated by the interactive effects of other changing conditions, such as temperature (Long, 1991), nutrient scarcity soil nutrients (Stitt and Krapp, 1999). and increasing concentrations of phytotoxic ozone (Long, 1994; McKee et al., 1995; Schmieden and Wild, 1995). Increasing ozone concentrations threaten to reduce the potential production of forest dry matter as background concentrations are already close to harmful levels (PORG, 1993) and ozone, formed by a complex set of reactions between hydrocarbons and nitrogen oxides in the sun, can be transported long distances in relatively pristine environments (Chameides et al., 1994).
