Showing papers on "Ecosystem published in 1985"

Ecosystem Behavior Under Stress

Abstract: The behavior of ecosystems under stress can be shown to be analogous to Selye's characterization (1973, 1974) of the response of higher organisms to stress. The ecosystem-level distress syndrome is manifest through changes in nutrient cycling, productivity, the size of dominant species, species diversity, and a shift in species dominance to opportunistic shorter-lived forms. These symptoms of ecosystem dysfunction are common in both terrestrial and aquatic systems under various stress impacts including harvesting, physical restructuring, pollutant discharges, introductions of exotic species, and extreme natural events (such as disastrous storms or volcanic activity). The progression of appearance of symptoms under intensifying stress levels may be interrupted temporarily as ecosystem homeostasis and homeorhetic mechanisms intercede. Inability to cope leads to further dysfunctions and, perhaps, to irreversible ecosystem breakdown.

Developments in Stream Ecosystem Theory

Abstract: Four significant areas of thought, (1) the holistic approach, (2) the linkage between streams and their terrestrial setting, (3) material cycling in open systems, and (4) biotic interactions and in...

Long-Term Ecosystem Stress: The Effects of Years of Experimental Acidification on a Small Lake

Abstract: Experimental acidification of a small lake from an original pH value of 6.8 to 5.0 over an 8-year period caused a number of dramatic changes in the lake's food web. Changes in phytoplankton species, cessation of fish reproduction, disappearance of the benthic crustaceans, and appearance of filamentous algae in the littoral zone were consistent with deductions from synoptic surveys of lakes in regions of high acid deposition. Contrary to what had been expected from synoptic surveys, acidification of Lake 223 did not cause decreases in primary production, rates of decomposition, or nutrient concentrations. Key organisms in the food web leading to lake trout, including Mysis relicta and Pimephales promelas, were eliminated from the lake at pH values as high as 5.8, an indication that irreversible stresses on aquatic ecosystems occur earlier in the acidification process than was heretofore believed. These changes are caused by hydrogen ion alone, and not by the secondary effect of aluminum toxicity. Since no species of fish reproduced at pH values below 5.4, the lake would become fishless within about a decade on the basis of the natural mortalities of the most long-lived species.

An Ecosystem approach to aquatic ecology: Mirror Lake and its environment

Abstract: I: An Ecosystem Approach.- A. Ecosystem Analysis.- 1. The Hubbard Brook Ecosystem Study.- 2. Other Interactions Between Ecosystems.- II: The Hubbard Brook Valley.- A. Environmental Parameters.- B. Biogeochemistry.- III: Mirror Lake and Its Watershed.- A. Physiographic Setting and Geologic Origin of Mirror Lake.- Location and General Physiographic Setting.- Geology.- Glacial History and Origin of Lake Basin.- Topography and Drainage Basin Characteristics.- Comparison of Mirror Lake and Hubbard Brook Drainage Basins.- B. Historical Considerations.- 1. History of the Vegetation on the Mirror Lake Watershed.- 2. Catastrophic Disturbance and Regional Land Use.- 3. Mirror Lake: Cultural History.- IV: Mirror Lake-Physical and Chemical Characteristics.- A. Importance of Perspective in Limnology.- B. Physical and Chemical Environment.- C. Stability, Circulation and Energy Flux in Mirror Lake.- D. Approaches to the Study of Lake Hydrology.- E. Flux and Balance of Water and Chemicals.- V: Mirror Lake-Biologic Considerations.- A. Species Composition, Distribution, Population, Biomass and Behavior.- 1. Bacteria.- 2. Phytoplankton.- 3. Periphyton.- 4. Macrophytes.- 5. Zooplankton.- 6. Benthic Macroinvertebrates.- 7. Benthic Microinvertebrates.- 8. Salamanders.- 9. Fishes.- B. Production and Limiting Factors.- 1. Bacteria.- 2. Phytoplankton.- 3. Macrophytes.- 4. Periphyton Production.- 5. Zooplankton.- 6. Benthic Macroinvertebrates.- 7. Vertebrates.- C. Organic Carbon Budget.- D. Decomposition.- VI: Mirror Lake-Ecologic Interactions.- A. The Littoral Region.- B. The Profundal Region.- C. The Pelagic Region.- D. The Lake-Ecosystem.- VII: Paleolimnology.- A. Sedimentation.- 1. Late-Glacial and Holocene Sedimentation.- 2. Contemporary Sedimentation.- B. Diatoms.- C. Animal Microfossils.- D. Fossil Pigments.- E. Chemistry.- F. Paleoecology of Mirror Lake and Its Watershed.- VIII: The Aquatic Ecosystem and Air-Land-Water Interactions.- A. Direct Atmospheric Input to Lakes.- B. Fluvial Input to Lakes.- C. Effects of Disturbance on the Land-Water Linkage.- D. Atmospheric Inputs to Watersheds Affecting Inputs to Lakes.- IX: Air and Watershed Management and the Aquatic Ecosystem.- A. Developmental State of the Forested Watershed-Ecosystem.- B. Forest Harvesting.- C. Highway Construction and Maintenance.- D. Air and Water Pollution.- E. Eutrophication Trends in Mirror Lake.- References.- Index of Genera and Species.- Index of Lakes and Streams.- General Index.

Development of a linked forest productivity-soil process model

Abstract: A general model of linked carbon-nitrogen cycles in forest ecosystems as constrained by climate and geology is described. The model, written in FORTRAN, is based on the JABOWA model of Botkin et al. (1972) as revised by Solomon et al. (1984). The birth, growth, and death of all trees greater than 1.43-cm dbh in a 1/12-ha plot are simulated. The return of litter and its decomposition are also simulated. Sunlight is the driving variable. Growing season degree days, soil water availability, and actual annual evapotranspiration are calculated from monthly rainfalls and temperatures as well as soil field moisture capacity and wilting point. Decomposition and soil nitrogen availability are calculated from organic matter quantity and carbon chemistry, evapotranspiration, and degree of canopy closure. Light availability to each tree is a function of leaf biomass of all taller trees. Degree days and the availabilities of light and water constrain species reproduction. These, along with soil nitrogen availability, constrain tree growth and hence carbon accumulation in biomass. The probability of a tree's dying increases with age and slow growth. Leaf, root, and woody litter are returned to the soil at the end of each year to decay the following year. Parameters for 72more » upland species of eastern North America are taken from literature data. The model simulates species composition and ecosystem processes for most upland forests of eastern North America. 6 figs., 6 tabs.« less

Major world ecosystem complexes ranked by carbon in live vegetation: a database

Abstract: Estimation of the inventory of carbon in major world ecosystems and of the exchanges with the atmosphere and other major reservoirs has thus been approached in two ways. In the major reservoirs has thus been approached in two ways. In the first approach, development of broad global patterns uses potential vegetation maps, or associates vegetation types with climatic or other environmental factors independent of local disturbance. In the second approach, development of modern regional or stand-type estimates is based on analyses of current vegetation and land-use practices. This method uses updated resource maps of natural vegetation, forestry surveys, agricultural yields, and human and economic as well as geopolitical considerations. Both approaches were applied in the development of the ecosystem map. The personal judgment of experts about ecosystem types, their locations and extent, and likely biomass or carbon in landscape complexes representative of different parts of the world is crucial in either approach.

Functional Groups in the Protozoa: Roles in Differing Ecosystems1,2

Abstract: Feeding habits of freshwater protozoa were used to group species into functional, trophic groups. Community structure in differing ecosystems was examined in relation to the number of species occumng in the functional group categories. Six wetland ecosystems and a large river ecosystem were studied. Changes in community structure during the colonization of artificial substrates were also examined. Changes during colonization were studied in a mesotrophic lake, in low-order streams, and in laboratory micro- ecosystems. In the latter case, the response of colonizing communities to a heavy metal toxicant was studied. All communities studied were dominated by bactivorous-detritivorous species and, to a lesser extent, by photosynthetic species. The chief functional role of substrate-associated protozoans appears to be the processing of dead organic matter and its associated bacterial flora. Functional groups utilizing resources other than detntal or mineral nutrients (saprotrophs, algivores, omnivores, and predators) were always minor community components. Colonizing communities were often dominated by photosynthetic species during early colonization stages but were again dominated by bactivorous-detntivorous species at species equilibrium. Low levels of toxicant (Cd) reduced numbers of both photosynthetic and bactivorous-detritivorous species. Higher toxicant levels virtually eliminated photosynthetic species and reduced bacterial detritivores by over one-half. Roles of protozoan species in ecosystems are closely tied to the processing of detritus and the recycling of mineral nutrients. Enumeration of individuals in functional categories is proposed as a simplified method for studying the abundance and activity of protozoa in ecosystems. Examination of changes in functional group composition and the relationship of functional group abundances to rates of carbon processing are suggested for studies of the importance of protozoa to the flow of energy and materials in ecosystems. OST ecosystems are not fragile, random associations of M species but are composed of species associations with multiple redundancies that act to maintain system function even when a few or many component parts may be changing or miss- ing. Species patterns in aquatic ecosystems often appear ran- dom, and the probability of collecting a given taxon at a given site is frequently not great. Understanding large species arrays

Adaptive strategies of woody species in neotropical savannas

Abstract: Summary 1. In this review we discuss the adaptive strategy of woody species in tropical savannas. The low, evergreen, broadleaved, sclerophyllous tree is considered as the typical woody representative in these ecosystems. The discussion is largely based on data concerning four widespread neotropical species: Curatella americana, Byrsonima crassifolia, Bowdichia virgilioides and Casearia sylvestris, together with more fragmentary information available on other American and African savanna woody species. 2. Several types of savanna ecosystems with contrasting ecological features have to be distinguished. Our discussion refers to tree species in one of these types: seasonal savannas, that occur in a tropical wet and dry climate, with constantly high temperature, and on well-drained soils. Most of these savannas are normally burned once a year, towards the end of the dry season. 3. Woody species in seasonal savannas exhibit a quite distinctive morphology. They have low, tortuous trunks, deep and extensive root systems, relatively high R/S and L/S ratios, and large, highly scleromorphic leaves. Their annual phenodynamics appears somewhat puzzling since leaf renewal and expansion, as well as blooming, take place during the dry, apparently less favourable, part of the year. 4. Savanna trees maintain high leaf conductance throughout the year. Some species show a moderate midday decrease in leaf conductance suggesting partial stomatal closure, particularly under very high atmospheric water demands, or in young, developing leaves. However, given the steep vapour density gradient, transpiration flux density tends to be high, especially on clear dry-season days. 5. There is no drastic drop in leaf water potential, as might be expected with a high transpiration rate. The most negative values attained in either season only rarely exceed the leaf turgor loss point. This moderate fall in ψ permits leaf expansion in the dry season. Variable hydraulic resistance contributes to maintain high water flow when steep ψ gradients between soil and leaves are produced. 6. When all factors are taken into account, it seems that savanna trees maintain a favourable water budget all the year, thanks to their extensive root systems that may extract soil water from deep layers, thus allowing the maintenance of a high water flux through the soil-plant-atmosphere system even during the dry season. In this way, these trees have the least seasonal behaviour of all plant components in the seasonal savanna ecosystem. 7. Seasonal savannas occur on extremely poor, nutrient-deficient soils. As an apparent consequence of this nutrient stress, the concentration of nitrogen, phosphorus, potassium, calcium and magnesium in leaves tends to be significantly lower than in forest trees or in drought-deciduous species. 8. Two mechanisms contribute to improve the nutrient economy. One is the reallocation of absorbed nutrients between old and young tissues; the other, the minimization of nutrient losses due to low leaf wettability, low leaf cuticular conductance, and leaf renewal in the rainless season. 9. Savanna trees have low photosynthetic capacity. This is probably due to high internal resistance of leaves induced by their low nitrogen concentration. However, under field conditions rates of CO2 uptake may be maintained near their optimum because leaf conductance is high all day, and leaf temperature closely matches air temperature, remaining therefore within the optimal range for photosynthesis. 10. All in all, it appears that the physiological behaviour of savanna trees favours a continuously high water flux through the plant that, even if it lowers water-use efficiency, maintains leaf temperatures near optimum for CO2 uptake, prevents sharp drops in leaf water potential, and induces a high passive uptake of soil nutrients. In this way, the close interaction between water, carbon and nutrient economies leads to the increased fitness of these populations in the seasonal savanna environment.

Sensitivity of boreal forests to possible climatic warming.

Abstract: General circulation models indicate substantial CO2 warming in high latitudes In these regions, which include the boreal coniferous forests, the activity of ecosystems is largely controlled by temperature The effective temperature sum (degree-days) is used in this study for describing the regional variability in the productivity of boreal ecosystems Although the concept is simple, it takes into account two basic factors: the length of the growing season and the day-to-day level of activity of the ecosystem This study examines which areas in the boreal coniferous forests would be most sensitive to a possible climatic warming The data used in the study are for Finland A regression is estimated between regional forest growth rate and effective temperature sum A climatic warming is assumed and the corresponding growth response is calculated, using the regression, for northern and southern areas, and for maritime and continental areas The response is expressed in terms of (i) absolute increase in growth (grams per m2 per year) and (ii) relative increase in growth The results indicate that a given climatic warming would yield the greatest absolute increase in growth in warm (ie southern) and maritime parts of the biome In terms of the relative growth response the sensitivity would increase northward and toward maritime areas

Lake Chad : ecology and productivity of a shallow tropical ecosystem

Abstract: Historical background.- I. The lacustrine environment and its evolution.- 1. Paleolimnology of an upper quaternary endorheic lake in Chad Basin.- 2. The lacustrine environment.- 3. Physical and chemical characteristics of the waters.- 4. Hydrochemical regulation of the lake.- II. The main types of communities and their evolution during a drought period.- 5. The aquatic vegetation of Lake Chad.- 6. The phytoplankton.- 7. The zooplankton.- 8. The benthic fauna: ecology, biomass and communities.- 9. The fauna associated with the aquatic vegetation.- 10. Fish communities of Lake Chad and associated rivers and flood-plains.- III. The balance of a lacustrine ecosystem during `Normal Chad' and a period of drought.- 11. Phytoplankton production.- 12. Secondary production (zooplankton and benthos).- 13. The exploitation of fish stocks in the Lake Chad region.- IV. Trophic relations.- 14. Trophic relations between the phytoplankton and the zooplankton.- 15. Trophic relations of fishes in Lake Chad.- 16. The impact of birds on the lacustrine ecosystem.- V.- 17. The lacustrine ecosystem during the `Normal Chad' period and the drying phase.- Systematic index.- General index.

Interactions between Invertebrates and Microfungi in Freshwater Ecosystems

Abstract: The importance of detritus metabolism in aquatic ecosystems has been stressed by various authors since at least the 1930s. There is evidence now that detritivorous species feed on the microfungi attached to the leaf detritus rather than the detritus itself and that these are a high quality food. Moreover, the numerous species of microfungi colonizing leaf detritus are important in making it a heterogeneous food resource for coexisting detritivores. The fungi present on leaf detritus in low abundance constitutes many different niche refuges shared among coexisting animal species. On the other hand, the abundance of fungi can be affected by foraging strategy of animals. Trophic niche plasticity of each animal population mediates the resource partitioning in detritus systems. The population niche width depends on the genotype arrangement of generalists and specialists. This arrangement seems established by predation pressure as well as competition. Thus, abundance of microfungi, niche width of detritivores and species packing in freshwater detritus communities are interdepedent aspects of a complex ecological system.

A multifactor ecological classification of the northern hardwood and conifer ecosystems of Sylvania Recreation Area, Upper Peninsula, Michigan

Abstract: An ecological method of multifactor ecosystem classification was applied in the Sylvania Recreation Area, an 8500-ha tract of old-growth northern hardwood – conifer forests in upper Michigan. The u...

Long-term estuarine variability and associated biological response

Abstract: Corpus Christi Bay, one of seven major Texas estuaries, is characterized by low freshwater inflow, small tidal flushing, low annual rainfall, and high evaporation rates. Minimal exchange of water makes this estuary sensitive to episodic environmental variation caused by sudden surges of freshwater from flooding rains or hurricanes. It is suggested that this episodic variability stimulates estuarine production. For the last 11 years, detailed data have been collected on benthic community structure, primary and secondary productivity, and sediment nutrient regeneration which are combined with other information, such as fishery yields, into a reconstructed long-term data set. During this same period significant environmental changes in the estuary have been documented. In 1979 the lowest salinity recorded over the 11-year record was related to a short-term, high intensity rainfall. The benthos responded with abundance and biomass levels far greater than any other year during the study interval. Correlated with increased benthic production were large increases in shrimp yields. During more subtle changes with respect to freshwater input in 1981, significant alterations in primary productivity were quantified. Primary, secondary, and tertiary carbon production estimates derived from the reconstructed long-term data base indicated the benthos as a major link between primary producers and other consumers. Carbon flow from primary producers, however, appeared inadequate to support benthic production. Nutrient recycling was judged to provide more than 90% of nitrogen needed to support phytoplankton production and was considered a major factor influencing ecosystem function. The matching of biological responses to significant environmental changes in this estuary provided insight into ecosystem function and stressed the importance of short-term variability. Although recycling was identified as a major source of nutrients supporting primary production, it was concluded that episodic environmental change from freshwater input provided a much needed stimulus to productivity. These episodic changes replaced materials lost through recycling and sustained productivity over the long term.

Fate and effect of allochthonous organic material in aquatic microbial ecosystems An analysis based on chemostat theory

Abstract: Two mathematical descriptions of a microbial ecosystem with external input of organic material were formulated. Included in these descriptions are only those parts of the ecosystem which are thought to be of key importance in the linkage between flows of organic material and mineral nutrients. The slmplest model, based upon Monod-hnetics of growth and constant cell composition, is amenable to graphical analysis. It was used to explore 2 complementary aspects: How does organic load alter the equilibirum state of the ecosystem, and how do the mechanisms of mineral cycling between bacteria, algae and protozoans influence degradation of the organic material? The other model is based on an extension of Droop's model for algal growth which allows for variations in cell composition. By simulation techniques, the effects of this refinement were explored.

Water filtration through reflective microtidal beaches and shallow sublittoral sands and its implications for an inshore ecosystem in Western Australia

Abstract: Volumes of seawater filtered through the intertidal zone were measured on three modally reflective microtidal beaches in Western Australia. The filtered volumes were large, 19 m3 m−1 day−1 and 73 m3 m−1 day−1 on two ‘clean’ beaches but only 0·4 m3 m−1 per tidal cycle on a beach covered in kelp and seagrass wrack. The mean residence times of this water in the interstitial system and its percolation paths were both short, 1–7 h and 2–5 m respectively. Water input was greater across a beach cusp horn than across a cusp embayment. Most input occurred in the upper swash zone where the water table was less than 20 cm deep. Tidal variations in input volumes were evident even with tide ranges of only 20 cm. The inshore zone off these beaches filters on average 0·07 m3 m−2 day−1 at an average depth of 5·5 m under 0·4 m waves of 6·5 s duration. The importance of these procedures in the mineralization of organic materials and the regeneration of nutrients for an inshore ‘lagoon ecosystem’ is estimated and discused.

Physiological and ecological controls on carbon sequestering in terrestrial ecosystems

Abstract: Carbon cycling processes in ecosystems are generally believed to be well understood. Carbon, hydrogen, oxygen and other essential elements are chemically converted from inorganic to organic compounds primarily in the process of photosynthesis. Secondary metabolic processes cycle carbon in and among organisms and carbon is ultimately released back to the environment as CO2 by respiratory processes. Unfortunately, our understanding of this cycle was determined under the assumption that the primary inorganic form of C (CO2 in the atmosphere) was relatively constant. With the emerging concensus that atmospheric carbon concentration is increasing, we must now reassess our understanding of the carbon cycle. How will plants, animals and decomposers respond to a doubling of carbon supply? Will biological productivity be accelerated? If plant productivity increases will a predictable percentage of the increase be accumulated as increased standing crop? Or, is it possible that doubling the availability of CO2 will increase metabolic activity at all trophic levels resulting in no net increase in system standing crop? The purpose of this paper is to review evidence for physiological and growth responses of plants to carbon dioxide enhancement. Essentially no research has been completed on the ecological aspects of these questions. From this review, I conclude that accurate predictions of future ecosystem responses to increasing atmospheric carbon dioxide concentration are not possible without additional understanding of physiological and ecological mechanisms.

Microfloral and faunal interactions in natural and agro-ecosystems.

Abstract: 1. Introduction.- 2. Nutrient cycling and decompoisition in natural terrestrial ecosystems.- 3. Decomposition and nutrient cycling in agro-ecosystems.- 4. Biodegradation of organic residues in soil.- 5. Root and soil microbial interactions which influence the availability of photoassimilate carbon in the rhizosphere.- 6. The role of microorganisms in the soil nitrogen cycle.- 7. Role of microflora in terrestrial sulfur cycling.- 8. The role of microfloral and faunal interactions in affecting soil processes.- 9. Effects of management on soil decomposers and decomposition processes in grasslands and croplands.- 10. Recent advances in quantitative soil biology.- 11. The role of modeling in research on microfloral and faunal interactions in natural and agroecosystems.

The factor of scale in ecosystem mapping

Abstract: Ecosystems come in many scales or relative sizes. The relationships between an ecosystem at one scale and ecosystems at smaller or larger scales must be examined in order to predict the effects of management prescriptions on resource outputs. A disturbance to an ecosystem may affect smaller component ecosystems, which are encompassed in larger systems that control the operation of the smaller systems. Environmental factors important in controlling ecosystem size change in nature with the scale of observation. This article reviews those environmental factors that are thought to be useful in recognizing and mapping ecosystems at various scales.

Nutrient Cycles in Antarctic Marine Ecosystems

Abstract: Studies of mineral cycling in the marine environment can be very informative in regard to understanding food web dynamics and general functioning of the ecosystem. Although emphasis is placed on the essential macro-and micro-elements, other mineral elements are also valuable tracers for various processes involving chemical transformations. Most chemical elements show a unique distribution pattern in the water column which reflects their biological and chemical reactivities and the rates at which they are resolubilized. Antarctic waters can be visualized as a giant chemostat, with nutrient rich water upwelling at the Divergence at high latitudes and the water ultimately downwelling at the Polar Front or the Sub-Tropical Convergence. In comparison with other major up-welling areas of the world, one would expect to find almost complete stripping of plant nutrients with time in the upper 50–100 m due to growth of phytoplankton. This condition of nutrient depletion would also be suggested by abundant data on rates of primary production in all sections of the Southern Ocean. Nitrate and phosphate, however, show only slight decreases in concentration in sections from close to the continent to close to the Sub-Tropical Convergence. This apparent contradiction has been explained by recent data which show that N is re-cycled 6–7 times in the euphotic zone before it settles out to deeper water as particulate organic N. These findings have focused attention on the nature of the food web which results in such very high rates of nutrient re-cycling in surface waters. Microbial populations seem to be the dominant organisms responsible for these transformations. With the exception of studies dealing with the distribution of silicon and related elements in the water column and sediments, little attention has been paid to questions of mineral cycling in Antarctic waters. Our understanding of the interaction between biological-physical-geochemical processes in the Antarctic is thus meagre in comparison with temperate and tropical waters.

Leaf litter disappearance rates in Puerto Rican montane rain forest

Abstract: The time course of leaf litter disappearance of six rain forest tree species was monitored for 32 weeks at the El Verde lower montane rain forest study site in northeastern Puerto Rico. Dacryodes excelsa, Sloanea berteriana, and Drypetes glauca were chosen to represent primary climax species, while Cecropia peltata, Inga vera, and Ixora ferrea were selected to represent secondary successional species in this forest. The study was designed to elucidate differences in nutrient release associated with the successional position of different tree species to determine what properties of leaf structure influenced the observed rates of nutrient disappearance. The string, nonconfined, tethered leaf method was employed. Dry weights and concentrations of nitrogen, phosphorus, potassium, calcium, and magnesium were determined over a period of 32 weeks. The secondary canopy species exhibited slower decay rates than did the primary species. The same pattern emerged between the secondary and primary understory species. The interacting effects of the leaf structural characteristics such as percentage lignin and percentage fiber correlated most strongly with observed decay rates. Nutrients were considered important in establishing organic matter resource quality but did not appear to influence decay rates; instead, nutrient dynamics reflected intervals of element immobilization, mineralization, and importation. Secondary species exhibiting specific combinations of structural properties may act to conserve nutrients by their slower rates of leaf litter disappearance. THE BREAKDOWN AND MINERALIZATION OF DEAD ORGANIC MATTER through the actions of decomposer organisms and fluctuating environmental conditions results in the progressive disappearance of litter from the forest floor. Mineralization and the subsequent translocation of biologically important elements among the various ecosystem components insures maximal reutilization and minimal cycling loss. The study of this process, particularly as it pertains to evergreen tropical forests, contributes to the understanding of nutrient relations in these ecosystems. The present study determined the time course of leaf litter disappearance from six different tropical forest tree species and discusses properties of leaf structure that influence the observed rates. Prior research has centered on specific aspects of nutrient release and the factors affecting the overall rate of litter disappearance. Such contributing factors have included differences among species, season, and location (Wiegert & Murphy 1970), plant material (Jenny et al. 1959, Shanks & Olson 1961, Olson 1963, Cornforth 1970), environmental conditions (Bocock & Gilbert 1957, Nye 1961, Hopkins 1966, John 1973), or microflora and -fauna (Witkamp 1963, 1966, 1969; Witkamp & Crossley 1966; Edwards et al. 1970). Other efforts have considered nutrient release in terms of the structural properties of the decaying substrate. These studies have concentrated on the structural effects and modifications of organic materials during the disappearance process and on the influences that individual substrate constituents might have on decomposer communities and overall decay rates (King & Heath 1967, Bailey et al. 1968, Minderman 1968). Disappearance dynamics provide an insight into the mechanism of nutrient release. Rainfall and temperature in tropical rain forest ecosystems do not affect the decomposition rate of leaf litter (La Caro 1974). Constant rapid rates exist because the biological activity of decomposer organisms is never hindered or inhibited. The rate of disappearance is ultimately dependent on the nature of the organic matter resource. Each plant part, due to differences in chemical and physical properties, will yield different disappearance rates (Odum 1970). Litter resources can be further subdivided to distinguish between different species or forest types. Categorizations distinguishing species by successional life-support strategies may help identify physiological mechanisms in specific ecosystems. Identification of some specific nutrient cycling mechanisms may shed light on the dynamics of nutrient maintenance in tropical rain forest ecosystems. Secondary successional vegetation is characterized as having the ability to live in disturbed forest sites under widely ranging environmental conditions. Secondary species live comparatively short lives, are fast growers, good seed disp rsers, and generally shade tolerant. Secondary vegetation has also been reported to decay at a faster rate than primary because of the differing structural characteristics of their decaying materials (Ewel 1976). In contrast, climax species generally exhibit opposite properties (Richards 1952, Smith 1970). Leaf litter exhibiting a specific combination of structural characteristics that tends to imI Received 8 September 1983, revision accepted 20 August 1984. BIOTROPICA 17(4): 269-276 1985 269 This content downloaded from 207.46.13.149 on Mon, 03 Oct 2016 06:15:48 UTC All use subject to http://about.jstor.org/terms mobilize nutrients for longer periods of time in disturbed forest sites may provide a valuable nutrient conservation function.

Floodplain forest ecosystem.

Abstract: 1. Natural conditions of floodplain forests. 2. Basic environmental factors. 3. Primary Production. 4. Some physiological processes in the ecosystem of a floodplain forest. 5. Secondary Production. 6. Decomposition. 7. Cycling of mineral nutrients. Plates. Index.

Nutrient Cycling in Relation to Biological Productivity in Antarctic and Sub-Antarctic Terrestrial and Freshwater Ecosystems

Abstract: Many terrestrial and freshwater ecosystems and their component ecological units in the Antarctic and Sub-Antarctic have been characterized in terms of single sets of chemical data. The biota and their growth, production and life cycles are often then related directly to the nutrient status of the system. However, such extensive studies provide no indication of the nutrient dynamics of the system. At only a few sites has intensive research involving frequent sampling and analysis on a seasonal or year-round basis been undertaken, mainly within the past 10–15 yr. Major advances have been made in recent years in investigating and understanding the processes involved in biogeochemical cycling, particularly of the major elements responsible for growth and production. Nutrient pathways through mineral and organic substrata, and contributions by precipitation, seaspray, fauna, etc., are gradually being quantified. The herbivore cycle in these relatively simple ecosystems is almost absent in terrestrial environments and much reduced in freshwater environments compared with corresponding ecosystems in other biomes. Food chains are short and virtually cease at the invertebrate herbivore level. Consequently, the decomposer cycle assumes the dominant role in the biological cycling of nutrients. The seasonal activity of critical groups of micro-organisms in relation to nutrient uptake and release is being studied experimentally both in the field and in the laboratory. The present state of this rapidly expanding area of research in the Antarctic and Sub-Antarctic is discussed, highlighting some of the more important findings. The need to develop more intensive long-term research programmes integrating geological, pedological, hydrological, micro-climatological and biological studies at selected ecologically important sites is emphasized. These regions offer ideal simple environments in which to test fundamental hypotheses concerning the functioning of ecosystems. The complex processes involved in nutrient cycling and their influence on the productivity of the associated biota may be more easily investigated in these south polar biomes than in most others.

Invertebrate Colonization of Submerged Wood in a Cypress-Tupelo Swamp and Blackwater Stream

Abstract: We examined the effects of location within a swamp-stream ecosystem on colonization rate and community structure of the macroinvertebrate assemblages of submerged wood. Uniform-sized sections of freshly cut wood from water tupelo trees (Nyssa aquatica L.) were suspended below floating platforms at swamp and stream sites for periods of 1-8 weeks. The location of wood substratum affected community structure to a large degree and patterns of colonization to a slight extent. Logs in the swamp-tributary site held almost three times as many individuals and twice as many taxa as did logs in the swamp and outflow stream sites. Stream sites, however, were similar in proportions of various functional and taxonomic groups. Except for the abundance of true midges (Chironomidae), the densities of most major taxonomic groups were significantly affected by location within the swamp-stream ecosystem. Recruitment of individuals and species were extremely rapid and reached a rough steady state at most sites within 1 week. Filter-feeding taxa were numerically dominant early but soon were subordinate to gatherer and scraper functional feeding groups. This trend resulted primarily from the progressive increase in abundances of riffle beetles and mayflies. Current velocity, seston particle size, dispersal capacity and competition for space may be important factors affecting community structure and colonization patterns in this aquatic ecosystem.