Aspects Of Ecosystem Function Research Articles

Modeling forest harvesting effects on landscape pattern in the Northwest Wisconsin Pine Barrens

Forest management shapes landscape patterns, and these patterns often differ significantly from those typical for natural disturbance regimes. This may affect wildlife habitat and other aspects of ecosystem function. Our objective was to examine the effects of different forest management decisions on landscape pattern in a fire adapted ecosystem. We used a factorial design experiment in LANDIS (a forest landscape simulation model) to test the effects of: (a) cut unit size, (b) minimum harvest age and (c) target species for management. Our study area was the Pine Barrens of northwest Wisconsin, an area where fire suppression has caused a lack of large open areas important for wildlife. Our results show that all three management choices under investigation (cut unit size, minimum harvest age and target species for management) have strong effects on forest composition and landscape patterns. Cut unit size is the most important factor influencing landscape pattern, followed by target species for management (either jack pine or red pine) and then minimum harvest age. Open areas are more abundant, and their average size is larger, when cut units are larger, target species is jack pine, and minimum harvest age is lower. Such information can assist forest managers to relate stand level management decision to landscape patterns.

Public Health Emergency on Planet Earth: Insights from the Millennium Ecosystem Assessment

Human health is related to ecosystem functioning in complex ways. Human societies are fundamentally dependent upon ecosystem services—most obviously, the provision of food and clean water supplies. Less tangibly, but no less importantly, other aspects of ecosystem function that underpin human health include: soil formation; recycling of wastes; some degree of regulation of infectious diseases; and stabilization (buffering) of local environments against catastrophic physical disruption. These benefits that humankind derives from well functioning ecosystems have largely been taken for granted in the past. Increasingly, however, it is recognized that the human impacts on Earth’s natural systems threaten the ecosystem services on which we depend. Three overlapping categories of causal mechanisms linking human well-being and ecosystem status can be described (Table 1).

Effects of organism size and community composition on ecosystem functioning

AbstractWe tested (1) if the size of dominant species influenced ecosystem functioning in food webs consisting of bacteria, algae, and protozoa; (2) whether those effects changed in importance through time; and (3) how those effects compared with differences in diversity among experimental food webs. We constructed food webs using two size fractions of organisms that differed in individual mass by approximately two orders of magnitude. We measured total biomass and respiration (total CO2production) as two aspects of ecosystem functioning. We also compared these size‐dependent patterns in functioning across two levels of species richness. Initially, organism size strongly influenced total community biomass. With time, however, biomass and respiration eventually converged in communities dominated by large or small species. We conclude that after sufficient time for community development any differences in ecosystem functioning resulted from differences in community composition, including species richness, but not the size of the dominant organisms.

Non‐random species extinction and plant production: implications for ecosystem functioning

SummaryUnderstanding ecosystem responses to plant species loss is essential for the optimal management of grasslands. Recent studies have examined the effects of simulated random species loss in experimental plant communities but not those of realistic non‐random species loss resulting from transient extinction pressures in semi‐natural grasslands.To investigate the potential effects of non‐random species loss on grassland productivity, we established mesocosms with mixed communities comprising 15 plant species, and exposed them to 2 years of high‐intensity management (an extinction phase) followed by 2 years of low‐intensity management (a restoration phase) allowing recolonization from differentially managed neighbouring plots. In addition, monocultures of each component species were subject to the same extinction–restoration phases.During the extinction phase, species with high monoculture biomass had lower extinction probabilities in the mixed community than species with low monoculture biomass, but there was also species‐specific variation. The species that were most productive or most persistent during the extinction phase were not the same as those performing best in the restoration phase.No consistent effects of spontaneous recolonization from neighbouring communities on species richness or productivity of the focal communities were observed during the restoration phase.We estimated that extinction of all but the species with the lowest extinction risk reduced biomass productivity by 42–49%; loss of all but the four species with the lowest extinction risk reduced it by 2–35%. Identical calculations for a random extinction scenario yielded reductions of 52% and 26–54%, respectively.Synthesis and applications. Prediction of the effects of species loss on plant production and on other aspects of ecosystem functioning in semi‐natural grasslands must account for both specific non‐random extinction processes and post‐extinction conditions. For European mesic grasslands experiencing a shift from high‐intensity to low‐intensity management, our results suggest that recolonization by ‘missing’ species must be actively assisted if high production is a management objective.

Biodiversity and ecosystem functioning in aquatic microbial systems: a new analysis of temporal variation and species richness‐predictability relations

Studies of microbial communities from aquatic ecosystems provide important insights into relations between various aspects of ecosystem functioning and changes in biodiversity. Aquatic microbial systems provide a valuable counterpoint to studies of terrestrial systems, because patterns reflect consequences of interactions occurring over many generations of community development, and are unlikely to represent artifacts of the initial conditions established in experimental communities. In this paper we re‐analyse our previously published data to separate the contributions of temporal and spatial variation to overall variation in ecosystem functioning. A new analysis based on re‐sampling confirms a negative relationship between richness and the variability of one ecosystem process, carbon dioxide flux. The negative relationship reflects high variation among communities of low species richness, rather than high temporal variation within communities of low richness. We also review the various transformations and summary statistics proposed as alternate measures of variability in ecosystem functioning, to point out that different measures are often appropriate for different kinds of data. Finally, we conclude that arguments about the cosmopolitan distribution of microbes do not preclude the existence of important relations between microbial species richness and ecosystem functioning.

Responses of leaf processing to impacts in streams in Atlantic rain forest, Rio de Janeiro, Brazil--a test of the biodiversity-ecosystem functioning relationship?

The relationship between biodiversity and ecosystem functioning has been intensely debated and researched in recent times. It is generally agreed that there is redundancy of species in ecosystems such that loss of species does not necessarily result in change in the functioning of the ecosystem in which they occur. However the state of our knowledge does not allow prediction of sensitivity or specificity of this relationship for any particular ecosystem. A widely-held opinion is that ecosystem functioning is relatively stable to environmental impact, whereas biodiversity is more sensitive. We tested this in streams of the Atlantic forest using leaf decomposition as an aspect of ecosystem functioning and measuring the diversity of the associated fauna. In lightly impacted streams of the urban park Parque Estadual da Pedra Branca, RJ, leaf processing rate of a hard-leaf species, Myrcia rostrata (Myrtaceae) was more than 50% slower than in "intact" streams at the biological reserve of Ilha Grande, RJ. Taxon diversity of fauna of the leaves was not significantly lower in the impacted than the intact streams. We construe this as preliminary evidence contrary to the notion that ecosystem functioning is less sensitive than biodiversity to impacts in this system.

Production of N(2) through anaerobic ammonium oxidation coupled to nitrate reduction in marine sediments.

In the global nitrogen cycle, bacterial denitrification is recognized as the only quantitatively important process that converts fixed nitrogen to atmospheric nitrogen gas, N(2), thereby influencing many aspects of ecosystem function and global biogeochemistry. However, we have found that a process novel to the marine nitrogen cycle, anaerobic oxidation of ammonium coupled to nitrate reduction, contributes substantially to N(2) production in marine sediments. Incubations with (15)N-labeled nitrate or ammonium demonstrated that during this process, N(2) is formed through one-to-one pairing of nitrogen from nitrate and ammonium, which clearly separates the process from denitrification. Nitrite, which accumulated transiently, was likely the oxidant for ammonium, and the process is thus similar to the anammox process known from wastewater bioreactors. Anaerobic ammonium oxidation accounted for 24 and 67% of the total N(2) production at two typical continental shelf sites, whereas it was detectable but insignificant relative to denitrification in a eutrophic coastal bay. However, rates of anaerobic ammonium oxidation were higher in the coastal sediment than at the deepest site and the variability in the relative contribution to N(2) production between sites was related to large differences in rates of denitrification. Thus, the relative importance of anaerobic ammonium oxidation and denitrification in N(2) production appears to be regulated by the availability of their reduced substrates. By shunting nitrogen directly from ammonium to N(2), anaerobic ammonium oxidation promotes the removal of fixed nitrogen in the oceans. The process can explain ammonium deficiencies in anoxic waters and sediments, and it may contribute significantly to oceanic nitrogen budgets.

Applications of biogeochemical modelling in southern Africa

Biogeochemical modelling is largely concerned with the cycling of carbon, nitrogen, phosphorus and sulphur in the biosphere. It offers a robust approach to modelling many aspects of ecosystem function at the regional scale, since it is not highly dependent on a detailed know ledge of species or organism-level processes. In southern Africa biogeochemical modelling has been used to provide new insight into the geographical distribution and underlying mechanisms of palatable (sweetveld) and unpalatable (sourveld) grasslands and high-herbivory and low- herbivory savannas. It has also been applied to the problem of estimating the emissions of trace gases and smoke particles from vegetation fires in the region, and suggests that the emissions are much lower than previously believed. Work in progress relates to the modelling of tropospheric ozone precursors produced by the soil and plants. Biogeochemical modelling has the potential to be an integrating tool, drawing together data collected at widely different scales in a way that allows hypotheses about the working of the biosphere to be rigorously tested.

Islands: Biological Diversity and Ecosystem Function.

Oceanic islands represent a set of systems in which biological diversity varies as a consequence of remoteness or size, not environment; they are also generally simpler than continental ecosystems. Islands therefore provide an opportunity to determine the direct effects of biological diversity on ecosystem function. This volume addresses the following topics: components of biological diversity on islands and their patterns of variation; the modern threats to the maintenance of biological diversity on islands; the consequences of island biology and its modification by humanity regarding aspects of ecosystem function; the global implications of islands for conservation; and how islands can help one to understand the processes inducing changes throughout the world.

Fate and effects of the insecticide Dursban® 4E in indoor Elodea-dominated and macrophyte-free freshwater model ecosystems: III. Aspects of ecosystem functioning

The effects of the insecticide Dursban® 4E (active ingredient chlorpyrifos) on aspects of water chemistry, community metabolism, and decomposition of particulate organic matter were studied in indoor freshwater microcosms intended to mimic drainage ditches. To several of these systems, a single dose (simulating aerial drift) was applied to achieve nominal chlorpyrifos concentrations of 5 or 35 μg/L. Two experiments were performed; one, in which all model ecosystems were dominated by the macrophyte Elodea nuttallii, and one, using systems devoid of macrophytes. The response of ecosystem functioning is discussed in relation to the shifts in community structure observed. Treatment effects on community metabolism, as signaled by a decrease in dissolved oxygen and pH and an increase in alkalinity and conductivity, could be observed in the high-dose Elodea-dominated microcosms only. In addition, Dursban 4E application in these systems resulted in a more persistent decrease in the decay rate of macrophyte material present in litter bags than in open water microcosms. Concentrations of inorganic nitrogen and orthophosphate in the water column of both types of model ecosystem were hardly affected by insecticide application. It is concluded that the impact of Dursban 4E on ecosystem functioning differed considerably between the two types of model ecosystems, and that functional endpoints were more robust than structural properties.