Biogeochemical cycling in forests

Biogeochemical cycling in forests includes elemental inputs, exports, and a complex set of physical, chemical and biotic processes which comprise internal nutrient cycles (Fig. 1). Any disturbance, whether anthropogenic (i.e. 

The general scheme of biological and biogeochemical cycling in Forest ecosystems is shown in Figure 1. 

Figure 4. A model illustrating sulfur biogeochemical cycle in forest ecosystems (Bashkin, 2002).

There are significant differences between biogeochemical cycling in forest and swampy ecosystems of the Boreal climate zone. The annual growth (NPP) of moor vegetation is about 3.5 ton/ha, which is twice as small as that in a forest ecosystem. In the bog, the degradation of dead organic matter proceeds at a much smaller rate than in the forest. The mass of peat accumulated within a period of 100 years accounts for... 

Figure 4. The general nitrogen model for illuxtrating the microbial role in biogeochemical cycling in Forest ecosystems. Explanations for the fluxes 1. ammonia volatilization 2, forest fertilization 3, 2-fixation 4, denitrification 5, nitrate respiration 6, nitrification 7. immobilization 8, mineralization 9, assimilatory and dissimilatory nitrate reduction to ammonium 10, leaching II, plant uptake 12, deposition N input 13, residue composition, exudation 14, soil erosion 15, ammonium fixation and release by clay minerals 16, biomass combustion 17, forest har esting 18, litteifall (Nihkgard et al, 1994).

Woodmansee, R.G. Wallach, L.S. Effects of fire regimes on biogeochemical cycles In Fire Regimes and Ecosystem Properties, Proceedings. USDA, U.S. Forest Service, GTR-WO-26, 1981,... 

Table 3 presents the averaged data for the whole forest area of Boreal and Sub-Boreal zone. However, there are definite peculiarities of biological and biogeochemical cycles in the individual ecosystems. We will consider the Spruce Forest ecosystem of the Karelia region, Russia. These ecosystems occur in the wide area of the Karelia, south from 63° N. 

In the Mixed Forest ecosystems a soil fraction less than 1 pm contains most of the elements previously confined in the forest litter and gradually involved in the biogeochemical cycle. In this fraction Cu and Mo forms account for 60-70% of the total soil content. The metals, poorly absorbable by plants, for example, Cr and V, occur in finely dispersed soil fraction in smaller amounts, about 20-30%. 

We can see that the soluble and exchange forms of these metals are present in small amounts accounting merely for a few percent of the total metal content in soil. The content of organometal species is relatively high in the upper profile rich in humic species, whereas it drops sharply in the mineral horizons. Copper is extensively involved in the biogeochemical cycle in the Forest ecosystems and this is less profound for cobalt. It is noteworthy that a large part of metals (in particular, of copper) become bound to iron hydroxides. This is typical for various trace elements, including arsenic, zinc and other elements with variable valence. 

As abandoned pasture areas become increasingly invaded by shrubs and small trees, which in time lead to secondary forest formation, the biogeochemical cycles of plant nutrients and the hydrological cycle are expected, eventually, to resemble the cycles originally found in the primary forest. The rate of recuperation of biogeochemical cycles in secondary forests and the factors that influence those rates, however, deserve further attention. 

The flow of Amazon streams emerges directly from the extensive forests and savannas that compose the basin. Biogeochemical cycles in streams are thus intricately associated with processes operat-... 

The remarkable part of the forested area is swampy. In certain regions, like the vast West Siberian plain, swamp and waterlogged ecosystems occupy about 30% of the total area. The biogeochemical cycling in these ecosystems is very complex and specific. The slow rates of biogeochemical turnover, typical for all Boreal Forest ecosystems are more depressed in Swamp ecosystems. For instance, in the Sphagnum Swamp ecosystem, the most widespread type of Swamp ecosystems, the annual NPP... 

Figure 17. Biogeochemical cycle in Tropical rain Forest eco.syslem.s.

The main specificity of biogeochemical cycling in Tropical Rain Forest ecosystems is related to its almost closed character. This means that almost the total number of nutrients is re-circulating in biogeochemical cycles (Figure 17). 

Biogeochemical cycling in Seasonal Deciduous Tropical Forest and Woody Savanna ecosystems... 

The Seasonal Deciduous Tropical Forest and various Savanna ecosystems occupy 14.3 X lO km. The biogeochemical cycling in Seasonal Deciduous Tropical Forest and various Savanna ecosystems is similar to that in the Boreal and Sub-Boreal Deciduous Forest ecosystems. The clear distinction is relates to the reasons of periodical inhibition of biogeochemical activity. In the temporal climate it is connected with the winter temperature drop and in tropical areas it relates to the dry season with significant moisture deficit. 

Characterize the biogeochemical cycling in Seasonal Deciduous Tropical Forest and Woody Savanna ecosystems of Africa. Place attention on the differences in biogeochemical processes during wet and dry seasons. 

Discuss the geographic alterations of biogeochemical cycling in the Tropical Rain Forest ecosystems of Latin and South America. Describe the role of precipitation and soil types. 

Discuss acid rain problems in South East Asia. Emphasize your attention on acid deposition effects on biogeochemical cycling in Tropical Rain Forest ecosystems. 

Zou, X., Binkley, D. and Caldwell, B.A. (1995). Effects of dinitrogen-fixing trees on phosphorus biogeochemical cycling in contrasting forests. Soil Science Society of America Journal, 59, 1452-1458. 

Biomass Redistribution Associated with Deforestation and Fire. The influence of deforestation on biogeochemical cycles is dependent upon a number of factors associated with the unique characteristics of the ecosystem (climate, soils, topography, etc), the quantity of the total nutrient pool stored in aboveground biomass (Table II), and the level of disturbance (i.e. the degree of canopy removal, soil disturbance, and the quantity of wood or other forest products exported from the site). The quantity of biomass consumed by one or more slash fires following deforestation can also dramatically increase nutrient losses, influence post fire plant succession, and hence, postfire biogeochemical cycles. 

Aber, J. D. and Driscoll, C. T. (1997). Effects of land use, climate variation, and N deposition on N cycling and C storage in northern hardwood forests, Global Biogeochem. Cycles 11, 639-648. 

Heinrichs H., Mayer R. The role of forest vegetation in the biogeochemical cycle of heavy metals. J Environ Qual 1980 9 111-118. 

BIOGEOCHEMICAL CYCLING OF ELEMENTS AND POLLUTANTS EXPOSURE IN FOREST ECOSYSTEMS... 

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