Ecological yield

Ecological yield is the harvestable population growth of an ecosystem. It is most commonly measured in forestry: sustainable forestry is defined as that which does not harvest more wood in a year than has grown in that year, within a given patch of forest.

However, the concept is also applicable to water, soil, and any other aspect of an ecosystem which can be both harvested and renewed—called renewable resources. The carrying capacity of an ecosystem is reduced over time if more than the amount which is "renewed" (refreshed or regrown or rebuilt) is consumed.

Ecosystem services analysis calculates the global yield of the Earth's biosphere to humans as a whole. This is said to be greater in size than the entire human economy. However, it is more than just yield, but also the natural processes that increase biodiversity and conserve habitat which result in the total value of these services. "Yield" of ecological commodities like wood or water, useful to humans, is only a part of it.

Very often an ecological yield in one place offsets an ecological load in another. Greenhouse gas released in one place, for instance, is fairly evenly distributed in the atmosphere, and so greenhouse gas control can be achieved by creating a carbon sink literally anywhere else.

History

Some of the earliest academic papers on the subject were researching methods of sustainable fishing. Work of Russel et al. in 1931 observed in particular that ”it appears that the ideal of a stabilised fishery yielding a constant maximum value is impractical.”[1] This work was mostly theoretical. Practical work would begin later, performed by industry and government agencies.

Motivation

Ecological yield is a theoretical construct which aggregates information from several physically measurable quantities. It can be used to reason about other ecological indicators such as the footprint. It can also be used as a decision-making tool for governments and corporations.

Ecological footprint

The idea of ecological footprints is to measure the cost of economic activity in terms of the amount of ecologically productive land required to sustain it. Doing this accurately requires estimating how productive the land is; in other words, it requires measuring ecological yield. Conversely, one can extract ecological yield estimates from ecological footprint estimates.

Avoiding overexploitation

Corporations take out loans to buy equipment and land use rights. In order to pay back these loans, they must extract and sell resources from the land. If the corporation is ignorant of the yield of the land in question, then the debt instruments may demand a yield greater than the ecological capacity to renew. Green economics links this process with ecocide and poses solutions through monetary reform.

Even well-meaning corporations may systematically overestimate the yield of an ecosystem. In the case of multiple corporations bidding for land rights, an economic phenomenon known as the winner's curse causes the winning party to systematically overestimate the economic value of the land. Typically the economic value comes mostly from the ecological yield, in which case the corporation will overestimate that as well.

Another form of overestimation may come from generalizing data from other ecosystems. For example, the same species of fish in two different systems may have significantly different diets. If its diet in one region consists mostly of algae but in another region consists largely of smaller fish, then it will be more expensive for the latter ecosystem to produce the fish. Yield will be correspondingly lower in the second region. This example illustrates the need for ecosystem-specific study and monitoring in order to reason about ecological yield.

Definition and properties

One may define yearly ecological yield for a fixed ecological product as follows: the yield is the amount of the product which may be removed from the ecosystem so that it is capable of recovering in one year. As a theoretical property of ecosystems, it cannot be measured directly but only estimated. Note that definition is sensitive to the time period which is allowed for recovery: the amount of product one can remove which regenerates over 3 years is not necessarily 3 times that which one can remove and regenerate over 1 year. The yearly ecological yield is most useful because of the cycle of seasons and the commercial notion of the fiscal year. The seasons affect growth through temperature, sunlight, and rain, especially at the lowest trophic level. The fiscal year affects decisions by corporations to harvest resources: they may choose to harvest at or above ideal levels based on their need for short-term cash flow.

Calculation techniques

Yield of the whole biosphere

In 1986, Vitousek et al.[2] estimated that humans made use of 50 petagrams (50 billion tons) per year of biomass produced from photosynthesis. They also estimated that these 50 billion tons comprised between 20% and 40% of photosynthetic activity on earth. Separately, the Global Footprint Network estimates the total human footprint as 1.6 times the total biosphere. [3] This implies that ecosystems are overexploited by a factor of 1.6 on average.

Theoretical prediction

In most biomes, the only form of primary production is photosynthesis. In other words, all new biomass can be traced back to photosynthetic plants and algae by a chain of predation. Therefore, one can predict the yield of one organism in an ecosystem as a function of the yield of its primary producers. When the biomass from prey is converted into biomass in its predator, some losses occur due to biological and thermodynamic inefficiency. The conversion rate is typically about 10%. In other words, 100 kg of plant matter may be converted into 10 kg of herbivores, which then may be converted to 1 kg of carnivores who exclusively eat herbivores. One can compute the trophic level of an organism as the weighted average of length of the predation chain from the organism to a primary producer. This trophic level determines an exponential multiplier to convert from primary producer biomass to the organism's biomass.

Measurement techniques

Measuring forests

One can measure the amount of wood removed from a forest by asking the company who removed it; typically only one company has the logging rights to any given plot of land. In order to measure the regrowth of the forest in the coming year, typically one picks a representative subsample of the region and tracks every single tree in the subsample.

One such study measured growth in a section of the Tapajós National Forest for 13 years after logging activity.[4] The loggers intended to harvest on a 30-year cycle. Logging in this region is restricted to mature trees measuring at least 45 cm DBH. Before logging, the region had somewhere between 150 m³ and 200 m³ of mature tree volume per hectare. Loggers removed about 75 m³ of tree per hectare, between 40% and 50% of the standing mass.

The authors show that growth rates in the region were elevated for up to 3 years after logging. After 13 years of growth, the basal area reached 75% of its original volume. They also show that logging makes substantial changes to the species composition and canopy structure of the forest. This introduces subjectivity into the notion of "recovery" for an ecosystem.

See also

References

  1. ^ Russell, E. S. (1931-03-01). "Some theoretical Considerations on the "Overfishing" Problem". ICES Journal of Marine Science. 6 (1): 3–20. doi:10.1093/icesjms/6.1.3. ISSN 1054-3139.
  2. ^ Vitousek; Ehrlich, P. R.; Ehrlich, A. H.; Matson, P. A. (1986). "Human appropriation of the products of photosynthesis". Bioscience. 36 (6): 368–373. doi:10.2307/1310258. JSTOR 1310258.
  3. ^ "Open Data Platform". data.footprintnetwork.org. Retrieved 2018-06-08.
  4. ^ Silva, J.N.M.; De Carvalho, J.O.P.; Lopes, J.do C.A.; De Almeida, B.F.; Costa, D.H.M.; De Oliveira, L.C.; Vanclay, J.K.; Skovsgaard, J.P. (1995-02-01). "Growth and yield of a tropical rain forest in the Brazilian Amazon 13 years after logging". Forest Ecology and Management. 71 (3): 267–274. CiteSeerX 10.1.1.61.9227. doi:10.1016/0378-1127(94)06106-S. ISSN 0378-1127.
Abiotic component

In biology and ecology, abiotic components or abiotic factors are non-living chemical and physical parts of the environment that affect living organisms and the functioning of ecosystems. Abiotic factors and the phenomena associated with them underpin all biology.

Abiotic components include physical conditions and non-living resources that affect living organisms in terms of growth, maintenance, and reproduction. Resources are distinguished as substances or objects in the environment required by one organism and consumed or otherwise made unavailable for use by other organisms.

Component degradation of a substance occurs by chemical or physical processes, e.g. hydrolysis. All non-living components of an ecosystem, such as atmospheric conditions and water resources, are called abiotic components.

Bacterivore

Bacterivores are free-living, generally heterotrophic organisms, exclusively microscopic, which obtain energy and nutrients primarily or entirely from the consumption of bacteria. Many species of amoeba are bacterivores, as well as other types of protozoans. Commonly, all species of bacteria will be prey, but spores of some species, such as Clostridium perfringens, will never be prey, because of their cellular attributes.

Copiotroph

A copiotroph is an organism found in environments rich in nutrients, particularly carbon. They are the opposite to oligotrophs, which survive in much lower carbon concentrations.

Copiotrophic organisms tend to grow in high organic substrate conditions. For example, copiotrophic organisms grow in Sewage lagoons. They grow in organic substrate conditions up to 100x higher than oligotrophs.

Decomposer

Decomposers are organisms that break down dead or decaying organisms, and in doing so, they carry out the natural process of decomposition. Like herbivores and predators, decomposers are heterotrophic, meaning that they use organic substrates to get their energy, carbon and nutrients for growth and development. While the terms decomposer and detritivore are often interchangeably used, detritivores must ingest and digest dead matter via internal processes while decomposers can directly absorb nutrients through chemical and biological processes hence breaking down matter without ingesting it. Thus, invertebrates such as earthworms, woodlice, and sea cucumbers are technically detritivores, not decomposers, since they must ingest nutrients and are unable to absorb them externally.

Dominance (ecology)

Ecological dominance is the degree to which a taxon is more numerous than its competitors in an ecological community, or makes up more of the biomass.

Most ecological communities are defined by their dominant species.

In many examples of wet woodland in western Europe, the dominant tree is alder (Alnus glutinosa).

In temperate bogs, the dominant vegetation is usually species of Sphagnum moss.

Tidal swamps in the tropics are usually dominated by species of mangrove (Rhizophoraceae)

Some sea floor communities are dominated by brittle stars.

Exposed rocky shorelines are dominated by sessile organisms such as barnacles and limpets.

Eco-capitalism

Eco-capitalism, also known as environmental capitalism or green capitalism, is the view that capital exists in nature as "natural capital" (ecosystems that have ecological yield) on which all wealth depends, and therefore, market-based government policy instruments (such as a carbon tax) should be used to resolve environmental problems.The term "Blue Greens" is often applied to those who espouse eco-capitalism. It is considered as the right-wing equivalent to Red Greens.

Energy Systems Language

The Energy Systems Language, also referred to as Energese, Energy Circuit Language, or Generic Systems Symbols, was developed by the ecologist Howard T. Odum and colleagues in the 1950s during studies of the tropical forests funded by the United States Atomic Energy Commission. They are used to compose energy flow diagrams in the field of systems ecology.

Feeding frenzy

In ecology, a feeding frenzy occurs when predators are overwhelmed by the amount of prey available. For example, a large school of fish can cause nearby sharks, such as the lemon shark, to enter into a feeding frenzy. This can cause the sharks to go wild, biting anything that moves, including each other or anything else within biting range. Another functional explanation for feeding frenzy is competition amongst predators. This term is most often used when referring to sharks or piranhas. It has also been used as a term within journalism.

Lithoautotroph

A lithoautotroph or chemolithoautotroph is a microbe which derives energy from reduced compounds of mineral origin. Lithoautotrophs are a type of lithotrophs with autotrophic metabolic pathways. Lithoautotrophs are exclusively microbes; macrofauna do not possess the capability to use mineral sources of energy. Most lithoautotrophs belong to the domain Bacteria, while some belong to the domain Archaea. For lithoautotrophic bacteria, only inorganic molecules can be used as energy sources. The term "Lithotroph" is from Greek lithos (λίθος) meaning "rock" and trōphos (τροφοσ) meaning "consumer"; literally, it may be read "eaters of rock". Many lithoautotrophs are extremophiles, but this is not universally so.

Lithoautotrophs are extremely specific in using their energy source. Thus, despite the diversity in using inorganic molecules in order to obtain energy that lithoautotrophs exhibit as a group, one particular lithoautotroph would use only one type of inorganic molecule to get its energy.

Mesotrophic soil

Mesotrophic soils are soils with a moderate inherent fertility. An indicator of soil fertility is its base status, which is expressed as a ratio relating the major nutrient cations (calcium, magnesium, potassium and sodium) found there to the soil's clay percentage. This is commonly expressed in hundredths of a mole of cations per kilogram of clay, i.e. cmol (+) kg−1 clay.

Mycotroph

A mycotroph is a plant that gets all or part of its carbon, water, or nutrient supply through symbiotic association with fungi. The term can refer to plants that engage in either of two distinct symbioses with fungi:

Many mycotrophs have a mutualistic association with fungi in any of several forms of mycorrhiza. The majority of plant species are mycotrophic in this sense. Examples include Burmanniaceae.

Some mycotrophs are parasitic upon fungi in an association known as myco-heterotrophy.

Organotroph

An organotroph is an organism that obtains hydrogen or electrons from organic substrates. This term is used in microbiology to classify and describe organisms based on how they obtain electrons for their respiration processes. Some organotrophs such as animals and many bacteria, are also heterotrophs. Organotrophs can be either anaerobic or aerobic.

Antonym: Lithotroph, Adjective: Organotrophic.

Overpopulation

Overpopulation occurs when a species' population exceeds the carrying capacity of its ecological niche. It can result from an increase in births (fertility rate), a decline in the mortality rate, an increase in immigration, or an unsustainable biome and depletion of resources. When overpopulation occurs, individuals limit available resources to survive.

The change in number of individuals per unit area in a given locality is an important variable that has a significant impact on the entire ecosystem.

Planktivore

A planktivore is an aquatic organism that feeds on planktonic food, including zooplankton and phytoplankton.

Recruitment (biology)

In biology, especially marine biology, recruitment occurs when a juvenile organism joins a population, whether by birth or immigration, usually at a stage whereby the organisms are settled and able to be detected by an observer.There are two types of recruitment: closed and open.In the study of fisheries, recruitment is "the number of fish surviving to enter the fishery or to some life history stage such as settlement or maturity".

Relative abundance distribution

In the field of ecology, the relative abundance distribution (RAD) or species abundance distribution describes the relationship between the number of species observed in a field study as a function of their observed abundance. The graphs obtained in this manner are typically fitted to a Zipf–Mandelbrot law, the exponent of which serves as an index of biodiversity in the ecosystem under study.

Species homogeneity

In ecology, species homogeneity is a lack of biodiversity. Species richness is the fundamental unit in which to assess the homogeneity of an environment. Therefore, any reduction in species richness, especially endemic species, could be argued as advocating the production of a homogenous environment.

Sustainable yield

The sustainable yield of natural capital is the ecological yield that can be extracted without reducing the base of capital itself, i.e. the surplus required to maintain ecosystem services at the same or increasing level over time. This yield usually varies over time with the needs of the ecosystem to maintain itself, e.g. a forest that has recently suffered a blight or flooding or fire will require more of its own ecological yield to sustain and re-establish a mature forest. While doing so, the sustainable yield may be much less.

In forestry terms it is the largest amount of harvest activity that can occur without degrading the productivity of the stock.

This concept is important in fishery management, in which sustainable yield is defined as the number of fish that can be extracted without reducing the base of fish stock, and the maximum sustainable yield is defined as the amount of fish that can be extracted under given environmental conditions. In fisheries, the basic natural capital or virgin population, must decrease with extraction. At the same time productivity increases. Hence, sustainable yield would be within the range in which the natural capital together with its production are able to provide satisfactory yield. It may be very difficult to quantify sustainable yield, because every dynamic ecological conditions and other factors not related to harvesting induce changes and fluctuations in both, the natural capital and its productivity.

In the case of groundwater there is a safe yield of water extraction per unit time, beyond which the aquifer risks the state of overdrafting or even depletion.

Sustainable yield in fisheries

The sustainable yield of natural capital is the ecological yield that can be extracted without reducing the base of capital itself, i.e. the surplus required to maintain ecosystem services at the same or increasing level over time. This yield usually varies over time with the needs of the ecosystem to maintain itself, e.g. a forest that has recently suffered a blight or flooding or fire will require more of its own ecological yield to sustain and re-establish a mature forest. While doing so, the sustainable yield may be much less.

In fisheries, the basic natural capital, or virgin population, must decrease with extraction. At the same time productivity increases. Hence, sustainable yield would be within the range in which the natural capital together with its production are able to provide satisfactory yield. It may be very difficult to quantify sustainable yield, because dynamic ecological conditions and other factors not related to harvesting induce changes and fluctuations in both the natural capital and its productivity.

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Example webs
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