Floristic composition

Measurement of total nutrient deposition requires studies integrating rainfall, through-fall, and stemflow in the wet component, as well as aerosol dry deposition. No studies in Amazonia have yet integrated all these components. Throughfall studies indicate a large enrichment of potassium, on the order of 2.7 to 10.2, leached from plant leaves (Holscher et al. 1998). This large variation in potassium enrichment could be caused by different floristic composition and precipitation patterns. 

Ratter and coworkers placed due emphasis on the influence of high calcium levels in the soil on the cerrado vegetation when they concluded that the floristic composition and phytosociological parameters of cerradoes and cerrados on more fertile soils can be quite different from those on dystrophic soils (Ratter 1971, 1992, Ratter et al. 1977, 1978). Many species occur only on dystrophic soils, others only on mesotrophic soils. Even when species indifferent to soil fertility occur in different communities their relative importance can vary to a great extent (Araujo and Haridasan 1988). Nutritional adaptations of such species and communities have received very little attention for any useful discussion at a community or ecosystem level (Haridasan 1992). 

Haridasan, M. 1992. Observations on soils, foliar nutrient concentrations and floristic composition of cerrado sensu stricto and cerradao communities in central Brazil. Pages 171-184. in P. A. Furley, J Proctor, and J. A. Ratter, editors. Nature and Dynamics of Forest-Savanna Boundaries. Chapman and Hall, London. 

Ratter, J. A., and T. C. D. Dargie. 1992. An analysis of the floristic composition of 26 cerrado areas in Brazil. Edinburgh Journal of Botany, 49 235-250. 

The floristic composition of floodplain forests is described by several forest inventories covering the complete Amazon basin. Detailed information is available from central Amazon forests in the vicinity of Manaus with inventories of about 17 ha of varzea forest from the Ilha de Marchantaria, Costa do Marrecao, and Costa do Barroso (Worbes 1983, 1986, Revilla 1991, Worbes et al. 1992, Klinge et al. 1995) and from igapo forests (Keel and Prance 1979, Revilla 1981, Worbes... 

We focus on temperate shelf seas because these are not only best studied, but also most subject to anthropogenic influence. Most of our examples are taken from studies in northwest European waters, because it is these that we know best. The aim of this chapter is to review recent improvements in knowledge of the sources and sinks of nutrients in the shelf seas of northwest Europe, and to consider, especially, the influence of ratios of nutrient elements on the floristic composition of the phytoplankton in these seas. We deal mainly with the macronutrient elements nitrogen, phosphorus and silicon, and to some extent with iron. The acronym DAIN (Dissolved Available /norganic Mtrogen) is a convenient way to refer to nitrate, nitrite and ammonium, excluding di-nitrogen which is not available to most phytoplankters. 

There are three broad explanations of phytoplankton floristic composition (Tilman etal., 1982). The first utilises differences in the capacity of species or lifeforms to grow in physical environments that differ especially in their vertical mixing intensity. Although nutrients are part of the argument, the explanations focus simply on the supply of the most limiting nutrient. The second type of... 

The three classes of explanation essentially deal with local matters. This is because the abundance of populations of microplankters can potentially change rapidly, at rates of the order of 10 1d 1, whereas water movement is slow in coastal seas, typically, a few kilometres a day even in regions of relatively high flow (Hill Simpson, 1988). For example, water flowing through the Sound of Jura in western Scotland seems to adjust its floristic composition quickly to the local intensity of vertical mixing (Jones etal., 1984). 

Biogeochemical explanations of variations in phytoplankton floristic composition work at two levels. The first level is qualitative, and concerns the crude distinctions between algae that require silicon (diatoms and some others) and those that don t, or between cynaobacteria able to assimilate N2 and all other pelagic photoautotrophs. The second level is quantitative, and concerns the idea that optimum ratios of the nutrient elements required for growth may... 

Verity and Smetacek (1996) have argued that predation or top-down trophic effects are as important as resource-driven or bottom-up factors in structuring planktonic ecosystems. However, grazing control of phytoplankton floristic composition will only occur if secondary consumers are selective for particular algal types. Initial evidence was against such selection. Marshall (1973) reviewed the evidence for dietary restriction in copepods ... 

Organisms themselves do not experience ambient nutrient ratios directly. The ratios are modified by assimilatory and internal storage mechanisms. Thus, there are especial difficulties in relating floristic composition to ambient ratios under low-nutrient, rapid-cycling, summer conditions. For the sake of simplicity, we therefore emphasise the ratio of elements in new nutrients. In the case of the temperate seas of northwest Europe, these ratios are winter values and those in external enrichments including river discharges and experimental additions to mesocosms. 

On the basis of variations in the habitat characteristics (landform and soil characteristics), the floristic composition and the dominant species, Omar [9] suggested six ecosystems coastal plain and lowland ecosystem desert plain ecosystem alluvial fan ecosystem escarpment, ridge and hilly ecosystem wadi and depression ecosystem and burchan sand dune ecosystem. Each of these ecosystems is characterized by a dominant plant community and associated with several other species. 

It is the purpose of the present communication to asses the diverse properties of biogeocenoses from a system approach perspective and to identify cause-effect relationships in the d5mamics of their floristic composition under the influence of external and internal factors. 

FLORISTIC COMPOSITION OF NEOTROPICAL SAVANNAS AND SEASONALLY DRY FORESTS... 

Floristic Composition, Species Distribution and Endemism IN Neotropical Savannas... 

Evidence from floristic composition, macrofossils, microfossils, molecular phylogenetics and molecular population genetics can be used to answer these questions. 

Gentry, A. H., Diversity and floristic composition of lowland tropical forest in Africa and South America, in Biological Relationships Between Africa and South America, Goldblatt, R, Ed, New Haven, Yale University Press, 1993, 500. 

Gentry, A.H., Diversity and floristic composition of neotropical dry forests, in Seasonally Dry Tropical Forests, Bullock, S.H., Mooney, H.A. and Medina, E., Eds, Cambridge University Press, Cambridge, 1995,146. 

FIGURE 2.2 Species occurrence vs. percentage of sites in the cerrado core area (e.g. 38 species occur at >50% of sites, while 300 species occur at >2.5%). Reprinted with permission of Cambridge University Press Ratter, J.A., Bridgewater, S., and Ribeiro, J.F. 2003. Analysis of the floristic composition of the Brazdian cerrado vegetation. Ill Comparison of the woody vegetation of 376 areas. Edinburgh J. Bot. 60 57-109. 

Ratter, J.A. et al., Analysis of the floristic composition of the Brazilian cerrado vegetation n. Comparison of the woody vegetation of 98 areas, Edinburgh J. Bot., 53, 153, 1996. 

FACTORS DETERMINING VEGETATION STRUCTURE (PHYSIOGNOMY) AND FLORISTIC COMPOSITION... 

In the southern cerrados, areas covered by two major physiognonfies can be recognized, each with its own distinct floristic composition 1) cerradao, in the west of the region (associated with more fertile soils) and 2) cerrado sensu stricto in the eastern part of the region (associated with very poor, sandy soils). 

Recent studies in Sao Paulo state (Toppa, 2004) have demonstrated a strong correlation between cerrado biomass, floristic composition and soil-water capacity (sand/clay proportion), the last of which was shown to be a more important factor than fertility, acidity or aluminium saturation of the soil. This is a revival of the ideas of more than a hundred years ago (Warming, 1892), when water availability was considered to be the main constraint to the occurrence of forest vegetation in the cerrado domain. 

More recently, fire frequency and soil chemical properties have been considered the main factors conditioiflng cerrado distribution, structure and floristic composition, water availability being disregarded, since forests and cerrado can occur under the same annual rainfall. However, in a region... 

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