**6. Effects of urban mesoclimate on soil physicochemical properties**

Temperature gradient between urban center and suburbs results in a local circulation of air. As air heated in urban center rises and relatively cool air of suburbs flows into urban center, a micro-current is formed. In this air circulation process, temperature inversion layer formed in the urban air inhibits the vertical movement of air, and thereby the polluted air from urban center comes down on the urban fringe [77]. Such an air circulation occurring through interaction of temperature differences between urban and suburban areas and temperature inversion can transport light gaseous air pollutants from the urban center to the urban fringe [74, 79].

Spatial distribution of soil properties reflected the effects of such an air circulation. Soil pH tended to be lower in grids in the urban fringe than in grids within the urban center (**Figure 5**). Ca2+ and Mg2+ concentrations of soil followed the pH

#### **Figure 5.**

*Spatial distribution of physicochemical properties of soil, such as pH, Ca2+, Mg2+, and Al3+, in the Seoul metropolitan area.*

**79**

**Figure 6.**

*Forest Decline Under Progress in the Urban Forest of Seoul, Central Korea*

trends (**Figure 4**), but Al3+ concentration was the vice versa as it was higher in the urban fringe than in the urban center (**Figure 4**). Most of these chemical properties

Soil acidification in those sites was due to deposition of acid precipitates, such as SOx and NOx [46]. Gaseous SOx and NOx are transformed to sulfuric acid (H2SO4) and nitric acid (HNO3) as they interact chemically with water in the air and soil and

Acidified soils of the urban periphery contained lower concentrations of basic cations, such as Ca2+ and Mg2+, than soils in the urban center, because they were leached through cation exchange mechanisms [82]. But higher concentrations of Ca2+ and Mg2+ in soils in the urban center are also related to deposition of heavy particulate probably from building materials (e.g., cement concrete; [83]) or to direct applications of calcium chloride (CaCl2) used for melting snow. In addition, acidified soil releases the Al3+ ion when soil is particularly acidified to below pH 4.5. Such an Al3+ ion inhibits plant cell division and consequently retards plant growth as a toxic ion [84]. These serial changes in soil chemistry are known to cause forest decline [82]. Changes of those soil properties tend to be intensified compared with the result

of soil are strongly related to soil acidification and to each other (**Figure 5**).

**7. Responses of urban forest on the changed mesoclimate and soil** 

*Stand ordination of the Mongolian oak forest established in urban and suburban areas around Seoul.*

Mongolian oak (*Quercus mongolica*) forests are the most widely distributed and dominant forest of the late successional stage in Korea [85]. The DCA ordination (**Figure 6**) showed that stands in the urban area (Mts. Nam, Acha, Daemo, Bulam,

*DOI: http://dx.doi.org/10.5772/intechopen.86248*

are deposited in dry and wet form on soil [80, 81].

of the former research [39].

**properties**

#### *Forest Decline Under Progress in the Urban Forest of Seoul, Central Korea DOI: http://dx.doi.org/10.5772/intechopen.86248*

*Forest Degradation Around the World*

ing countries [78].

Temperature inversions are frequently observed in most urban areas including Seoul. Temperature inversion results in poor dispersion of pollutants. Strong thermal inversion induces pollutant accumulation and thereby become a primary cause of the heavy air pollution. In addition, Seoul is backed by mountains, which intensified the accumulation of pollutants generated in the city itself and blown from other regions, particularly China, which is relatively closely located to Seoul. In recent decades, East Asia has been significantly industrialized and urbanized through its rapid economic growth. The industrialization and urbanization have resulted in adverse effect on air quality not only in this region but also in neighbor-

**6. Effects of urban mesoclimate on soil physicochemical properties**

Temperature gradient between urban center and suburbs results in a local circulation of air. As air heated in urban center rises and relatively cool air of suburbs flows into urban center, a micro-current is formed. In this air circulation process, temperature inversion layer formed in the urban air inhibits the vertical movement of air, and thereby the polluted air from urban center comes down on the urban fringe [77]. Such an air circulation occurring through interaction of temperature differences between urban and suburban areas and temperature inversion can transport light gaseous air pollutants from the urban center to the urban fringe [74, 79]. Spatial distribution of soil properties reflected the effects of such an air circulation. Soil pH tended to be lower in grids in the urban fringe than in grids within the urban center (**Figure 5**). Ca2+ and Mg2+ concentrations of soil followed the pH

**78**

**Figure 5.**

*metropolitan area.*

*Spatial distribution of physicochemical properties of soil, such as pH, Ca2+, Mg2+, and Al3+, in the Seoul* 

trends (**Figure 4**), but Al3+ concentration was the vice versa as it was higher in the urban fringe than in the urban center (**Figure 4**). Most of these chemical properties of soil are strongly related to soil acidification and to each other (**Figure 5**).

Soil acidification in those sites was due to deposition of acid precipitates, such as SOx and NOx [46]. Gaseous SOx and NOx are transformed to sulfuric acid (H2SO4) and nitric acid (HNO3) as they interact chemically with water in the air and soil and are deposited in dry and wet form on soil [80, 81].

Acidified soils of the urban periphery contained lower concentrations of basic cations, such as Ca2+ and Mg2+, than soils in the urban center, because they were leached through cation exchange mechanisms [82]. But higher concentrations of Ca2+ and Mg2+ in soils in the urban center are also related to deposition of heavy particulate probably from building materials (e.g., cement concrete; [83]) or to direct applications of calcium chloride (CaCl2) used for melting snow. In addition, acidified soil releases the Al3+ ion when soil is particularly acidified to below pH 4.5. Such an Al3+ ion inhibits plant cell division and consequently retards plant growth as a toxic ion [84]. These serial changes in soil chemistry are known to cause forest decline [82].

Changes of those soil properties tend to be intensified compared with the result of the former research [39].
