Effects of acidic desposition on forest soil and vegetation

Abstract

The paper concerns the potential effects of acidic deposition on the nutrient status of soil and forest and on the possible toxic effect of increased Al solubility. The nutrient status of trees may be influenced by pollutants interacting with the foliage and also by changing availability of nutrients in the soil. N compounds are often absorbed by the canopy whereas base cations are lost to the soil by foliar leaching. Cation leaching increases with increased acidity of precipitation. Throughfall acidity varies with tree species, season and distance from the emission areas. The impact of increased foliar leaching of base cations is not well known. In soil, acid deposition may have three effects: (i) a fertilizer effect caused by the deposition of N, and possibly, under specific conditions, also of S; (ii) an acidification effect caused by increased leaching of base cations; and (iii) an Al toxicity effect in cases where soil acidity is increased. Results of fertilizer experiments indicate that the atmospheric deposition of N is likely to increase forest growth especially in the northern parts of North America and Europe. At more southerly latitudes, nutrients in addition to N are often deficient. Therefore the N deposition is less likely to stimulate forest growth. Sulphur deposition is not likely to increase forest growth in most areas of the temperate zone. On the contrary, S deposition will mostly increase leaching of base cations such as Mg 2+ and Ca 2+ , and possibly K. Experiments with artificial acidification together with observations of increased Mg-deficiency in central Europe, indicate that Mg-deficiency might become a problem on sensitive soils exposed to acid deposition. The possibility of Al toxicity caused by increased soil acidity is discussed on the basis of experiments with seedlings of Norway spruce. It is concluded that Al toxicity appears to be unlikely unless the Al concentrations in the soil solution increase to about 20 mg l -1 .

Fine roots and ectomycorrhizas as indicators of environmental change

“…On the other hand, different authors reported variable responses of root growth of one species (Picea abies) to similar concentrations of Al (e.g. Rost-Siebert, 1983;Abrahamsen, 1984;Ingestad et al, 1985).…”

Responses of ground vegetation to prolonged simulated acid rain in sub‐arctic pine—birch forest

“…Evans, 1984;Jacobson et al, 1990;Back, Neuvonen & Huttunen, 1994). For example, long-term detrimental effects of acid deposition on plant growth have been reported, especially when sulphuric acid is applied and when rain has been allowed to reach the soil (Leith et al, 1989;Jacobson et al, 1990;Back et al, 1994), with a likely delayed negative growth response to acid application (Abrahamsen, 1984;Back et al, 1994). On the other hand, enhanced tree \igour and increased biomass growth observed, for instance, in Scandinavian trees (Kenttamies, 1991) are usually related to a possible fertilizing effect of nitrogen deposition during the earlier stages of acidification (Wood & Bormann, H 7;Kauppi, Mielikainen & Kuusela, 1992).…”

“…Little is known about the effects of acid rain on ground vegetation in boreal forests (Abrahamsen, 1984;Hutchinson, Dixon & Scott, 1986;Hutchinson et al, 1987;Hutchinson & Scott, 1988;Nygaard & Abrahamsen, 1991). However, it has been suggested that the dynamics of ground vegetation, especially of certain ericaceous understorey shrubs and the lichen-moss bottom layer, inter alia maintain the success of tree regeneration in northern forests (Mallik, 1995;Zacknsson et al, 1995) and are therefore of particular importance when considering long-term effects of acid precipitation on these ecosystems.…”

“…This approach does not allow comparison of vegetation changes with realistic control. The other factor which should be considered is that changes associated with acid rain are often slow and their direction can even change in different phases of acidification (Abrahamsen, 1984).…”

Soil acidification under the crown of oak trees I. Spatial distribution

“…During the last fifteen years soil acidification processes have attracted increased interest due to consequences of industrial pollution over forested areas, especially in North and Central Europe (Tamm, 1976;Abrahamsen, 1984;Van Breemen, 1985;Kauppi et al, 1986;Wittig, 1986;FalkengrenGrerup, 1986FalkengrenGrerup, , 1987Hallbäcken and Tamm, 1986;Tyler, 1987). Acidification markedly affects the area near the trunk base of trees, as has been assessed by soil pH and vegetation data (Zinke, 1962;Lane and Witcher, 1963;Wittig and Neite, 1985;Cloutier, 1985;Riha et al, 1986a,b;Wittig, 1986) and study of the mycorrhizal types (Kumpfer and Heyser, 1986).…”