Ecosystem

About: Ecosystem is a research topic. Over the lifetime, 25460 publications have been published within this topic receiving 1291375 citations. The topic is also known as: ecological system & Ecosystem.

Epiphyte biomass and nutrient capital of a neotropical Elfin forest

Abstract: The epiphyte communities of a Costa Rican cloud forest make up a conspicuous portion of the canopy, especially on large canopy dominants. Non-destructive sampling methods were used to assess the composition, biomass, and nutrient concentration of live and dead epiphytes on representative host trees to determine the mineral capital contained in the epiphyte components of the standing vegetation. Epiphyte standing crop on a single large Clusia alata (Guttiferae) tree is 141.9 kg. The nutrient capital (in g) is: N = 3062; P = 97; K = 678; Ca = 460; Mg = 126; Na = 207. Using information on forest structure and epiphyte distribution, stand-level estimates of epiphyte mat nutrient capital were made. Although epiphyte biomass constitutes less than 2 percent of total elfin forest ecosystem dry weight, the nutrients they contain are equivalent to up to 45 percent of nutrients contained in ecosystem foliage of similar ecosystems. Assessment of epiphyte nutrient capital gives a more complete and accurate idea of the aboveground vegetation pools, and supports the idea that epiphytes may play a greater role in ecosystem nutrient dynamics than has been previously considered. ALTHOUGH THE IMPORTANCE OF MINERAL NUTRITION for plants and animals has been recognized for centuries, only recently has there been a systematic approach to mineral element cycling in entire ecosystems (Pomeroy 1970, Jordan et al. 1972, Golley et al. 1975). Estimates of the total amount of mineral elements and the rate of elemental cyding within a complete landscape unit during a period of time have resulted in the formulation of several basic mineral cycling concepts (Rodin and Bazilevich 1967, Jordan and Kline 1972, Bormann and Likens 1979). The general approach has been to divide the ecosystem into a series of compartments, or pools, and to measure the quantity and chemical composition of each pool and the pathways and rates of flux between each component in as great detail as possible. A small number of ecosystemlevel studies (e.g., Ovington and Madgwick 1959, Cole et al. 1968, Woodwell and Whittaker 1968, Duvigneaud and Denaeyer-DeSmet (1975), an even smaller number of which were tropical (e.g., Nye 1961, Odum and Pigeon 1970, Golley et al. 1975, Grubb 1977, Cole and Johnson 1978, Jordan 1982), have been important in the development of theories of community stability, nutrient use efficiency, and ecosystem resilience. Because of the greater diversity and complexity of tropical forests, and the greater logistical problems encountered there, the sizes of many of the compartments that make up tropical ecosystems remain poorly known. In most whole-ecosystem studies, epiphytes-plants deriving support but not nutrients directly from their host trees-have been discounted or ignored, as their biomass was considered insignificant in proportion to other forest components. However, vascular and non-vascular epiphytes make up a conspicuous portion of many rain forest canopies, reaching their greatest diversity and abundance in neotropical cloud and elfin forests, which are regularly enshrouded in mist and lack a prolonged dry season (Richards 1964, Sanford 1968, Madison 1977, Sugden and Robins 1979). Although the epiphytic flora of these forests has attracted a good deal of botanical attention, most of it has been focused on aspects of taxonomy (Dressler 1979, Benzing 1981a), phytosociology (Eggeling 1947, Sanford 1968, Johnson and Awan 1972, Russell and Miller 1977, Madison 1979, Sugden 1981, Yeaton and Gladstone 1982), and physiology (Hosokawa and Odani 1957, Medina 1972, Benzing and Ott 1981, Huber 1978). These canopy-dwelling plants must overcome greater extremes of insolation, temperature, humidity, and wind than their terrestrial counterparts. They lack organic connection to the bank of nutrients and water stored in forest soils. Resources are pulse-supplied from atmospheric sources, and canopy surfaces may be characterized by frequent and/or prolonged deprivations of moisture and nutrients (Benzing 198 1b). Many aspects of epiphyte morphology, physiology, and life history contribute to their efficiency at garnering and retaining airborne nutrients (Benzing 198 1b, 1982). By virtue of their powers of mineral accretion and their location along primary nutrient flux routes, epiphytes can be major participants in the impoundment and movements of mineral elements in a forest ecosystem (Nadkarni 1983). The effects of epiphytes on ecosystem-level interactions have been investigated in only a few studies, all in temperate forests (Denison et al. 1972, Pike 1972, 1978, Lang et al. 1976, 1980, Schlesinger and Marks 1977, Benzing and Seeman 1978). Assessing the mineral IReceived 3 November 1983, revised 3 February 1984, accepted 7 February 1984. BIOTROPICA 16(4): 249-256 1984 249 This content downloaded from 157.55.39.104 on Sun, 19 Jun 2016 06:38:59 UTC All use subject to http://about.jstor.org/terms capital contained in epiphytes is an important first step in determining their role in rain forest nutrient dynamics and in obtaining a more complete and accurate picture of all aboveground components. Minerals contained in their living and dead tissues constitute a nutrient pool, distinct from host tree minerals, which are immobilized for some span of time within the canopy. These can be transferred to other ecosystem pools via litterfall, crown wash, and in some cases, by host tree canopy root systems (Nadkarni 1981). In this paper, as part of a comparative study of within-canopy nutrient dynamics in temperate and tropical rain forests, I assess the composition, biomass, and nutrient content of epiphyte communities on large canopy trees in a neotropical elfin forest, compare the nutrient capital contained in epiphytes with other ecosystem components of similar forests, and discuss some of the processes by which epiphytes accrue and retain their nutrient capital. Some of the terms used in this paper have multiple or ambiguous meanings and are defined here: biomassthe dry weight of living matter present in a given plant community; standing crop-the dry weight of living and dead components of a given plant community; epiphyte mat-the composite unit of living arboreal plants and their associated detrital matter found within host tree

An integrated model of soil, hydrology, and vegetation for carbon dynamics in wetland ecosystems

Abstract: [1] Wetland ecosystems are an important component in global carbon (C) cycles and may exert a large influence on global climate change. Predictions of C dynamics require us to consider interactions among many critical factors of soil, hydrology, and vegetation. However, few such integrated C models exist for wetland ecosystems. In this paper, we report a simulation model, Wetland-DNDC, for C dynamics and methane (CH4) emissions in wetland ecosystems. The general structure of Wetland-DNDC was adopted from PnET-N-DNDC, a process-oriented biogeochemical model that simulates C and N dynamics in upland forest ecosystems. Several new functions and algorithms were developed for Wetland-DNDC to capture the unique features of wetland ecosystems, such as water table dynamics, growth of mosses and herbaceous plants, and soil biogeochemical processes under anaerobic conditions. The model has been validated against various observations from three wetland sites in Northern America. The validation results are in agreement with the measurements of water table dynamics, soil temperature, CH4 fluxes, net ecosystem productivity (NEP), and annual C budgets. Sensitivity analysis indicates that the most critical input factors for C dynamics in the wetland ecosystems are air temperature, water outflow parameters, initial soil C content, and plant photosynthesis capacity. NEP and CH4 emissions are sensitive to many of the tested input variables. By integrating the primary drivers of climate, hydrology, soil and vegetation, the Wetland-DNDC model is capable of predicting C biogeochemical cycles in wetland ecosystems.

Terrestrial carbon and intraspecific size-variation shape lake ecosystems

Abstract: Conceptual models of lake ecosystem structure and function have generally assumed that energy in pelagic systems is derived from in situ photosynthesis and that its use by higher trophic levels depends on the average properties of individuals in consumer populations. These views are challenged by evidence that allochthonous subsidies of organic carbon greatly influence energy mobilization and transfer and the trophic structure of pelagic food webs, and that size variation within consumer species has major ramifications for lake community dynamics and structure. These discoveries represent conceptual shifts that have yet to be integrated into current views on lake ecosystems. Here, we assess key aspects of energy mobilization and size-structured community dynamics, and show how these processes are intertwined in pelagic food webs.

An ecosystem-level perspective of allelopathy

Abstract: Allelopathy is an interference mechanism by which plants release chemicals which affect other plants; while it has often been proposed as a mechanism for influencing plant populations and communities, its acceptance by plant ecologists has been limited because of methodological problems as well as difficulties of relating the results of bioassays used for testing allelopathy to vegetation patterns in the field. Here we argue that the concept of allelopathy is more appropriately applied at the ecosystem-level, rather than the traditional population/community level of resolution. Firstly, we consider the wide ranging effects of secondary metabolites (widely regarded as allelochemicals) on organisms and processes which regulate ecosystem function, including herbivory, decomposition and nutrient mineralization. It is apparent that plants with allelopathic potential against other organisms induce net changes in ecosystem properties, which may in turn impact upon the plant community in the longer term. We then illustrate these concepts using two contrasting examples of how invasive plant species with allelopathic potential may alter ecosystem properties through the production of secondary metabolites, i.e. Carduus nutans (nodding thistle) in New Zealand pastures and Empetrum hermaphroditum (crowberry) in Swedish boreal forests. In both cases the production of secondary metabolites by the invasive species induces important effects on other organisms and key processes, which help determine how the ecosystem functions and ultimately the structure of the plant community. These examples help demonstrate that the concept of allelopathy is most effectively applied at the ecosystem-level of resolution, rather than at the population-level (i.e. plant-plant interference).