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.
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.
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.
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.
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.
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.
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.
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.
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.
An ecosystem consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the system through photosynthesis and is incorporated into plant tissue. By feeding on plants and on one another, animals play an important role in the movement of matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and microbes.
Natural capital is the world's stock of natural resources, which includes geology, soils, air, water and all living organisms. Some natural capital assets provide people with free goods and services, often called ecosystem services. All of these underpin our economy and society, and thus make human life possible.
The carrying capacity of an environment is the maximum population size of a biological species that can be sustained by that specific environment, given the food, habitat, water, and other resources available. The carrying capacity is defined as the environment's maximal load, which in population ecology corresponds to the population equilibrium, when the number of deaths in a population equals the number of births. The effect of carrying capacity on population dynamics is modelled with a logistic function. Carrying capacity is applied to the maximum population an environment can support in ecology, agriculture and fisheries. The term carrying capacity has been applied to a few different processes in the past before finally being applied to population limits in the 1950s. The notion of carrying capacity for humans is covered by the notion of sustainable population.
Logging is the process of cutting, processing, and moving trees to a location for transport. It may include skidding, on-site processing, and loading of trees or logs onto trucks or skeleton cars. In forestry, the term logging is sometimes used narrowly to describe the logistics of moving wood from the stump to somewhere outside the forest, usually a sawmill or a lumber yard. In common usage, however, the term may cover a range of forestry or silviculture activities.
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through chemosynthesis, which uses the oxidation or reduction of inorganic chemical compounds as its source of energy. Almost all life on Earth relies directly or indirectly on primary production. The organisms responsible for primary production are known as primary producers or autotrophs, and form the base of the food chain. In terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae predominate in this role. Ecologists distinguish primary production as either net or gross, the former accounting for losses to processes such as cellular respiration, the latter not.
In population ecology and economics, maximum sustainable yield (MSY) is theoretically, the largest yield that can be taken from a species' stock over an indefinite period. Fundamental to the notion of sustainable harvest, the concept of MSY aims to maintain the population size at the point of maximum growth rate by harvesting the individuals that would normally be added to the population, allowing the population to continue to be productive indefinitely. Under the assumption of logistic growth, resource limitation does not constrain individuals' reproductive rates when populations are small, but because there are few individuals, the overall yield is small. At intermediate population densities, also represented by half the carrying capacity, individuals are able to breed to their maximum rate. At this point, called the maximum sustainable yield, there is a surplus of individuals that can be harvested because growth of the population is at its maximum point due to the large number of reproducing individuals. Above this point, density dependent factors increasingly limit breeding until the population reaches carrying capacity. At this point, there are no surplus individuals to be harvested and yield drops to zero. The maximum sustainable yield is usually higher than the optimum sustainable yield and maximum economic yield.
Ecosystem diversity deals with the variations in ecosystems within a geographical location and its overall impact on human existence and the environment.
An old-growth forest is a forest that has developed over a long period of time without disturbance. Due to this, old-growth forests exhibit unique ecological features. The Food and Agriculture Organization of the United Nations defines primary forests as naturally regenerated forests of native tree species where there are no clearly visible indications of human activity and the ecological processes are not significantly disturbed. Barely one-third of the world's forests are primary forests. Old-growth features include diverse tree-related structures that provide diverse wildlife habitats that increases the biodiversity of the forested ecosystem. Virgin or first-growth forests are old-growth forests that have never been logged. The concept of diverse tree structure includes multi-layered canopies and canopy gaps, greatly varying tree heights and diameters, and diverse tree species and classes and sizes of woody debris.
Population ecology is a sub-field of ecology that deals with the dynamics of species populations and how these populations interact with the environment, such as birth and death rates, and by immigration and emigration.
Ecosystem ecology is the integrated study of living (biotic) and non-living (abiotic) components of ecosystems and their interactions within an ecosystem framework. This science examines how ecosystems work and relates this to their components such as chemicals, bedrock, soil, plants, and animals.
Ecoforestry has been defined as selection forestry or restoration forestry. The main idea of ecoforestry is to maintain or restore the forest to standards where the forest may still be harvested for products on a sustainable basis. Ecoforestry is forestry that emphasizes holistic practices which strive to protect and restore ecosystems rather than maximize economic productivity. Sustainability of the forest also comes with uncertainties. There are other factors that may affect the forest furthermore than that of the harvesting. There are internal conditions such as effects of soil compaction, tree damage, disease, fire, and blow down that also directly affect the ecosystem. These factors have to be taken into account when determining the sustainability of a forest. If these factors are added to the harvesting and production that comes out of the forest, then the forest will become less likely to survive, and will then become less sustainable.
Algal mats are one of many types of microbial mat that forms on the surface of water or rocks. They are typically composed of blue-green cyanobacteria and sediments. Formation occurs when alternating layers of blue-green bacteria and sediments are deposited or grow in place, creating dark-laminated layers. Stromatolites are prime examples of algal mats. Algal mats played an important role in the Great Oxidation Event on Earth some 2.3 billion years ago. Algal mats can become a significant ecological problem, if the mats grow so expansive or thick as to disrupt the other underwater marine life by blocking the sunlight or producing toxic chemicals.
An ecological pyramid is a graphical representation designed to show the biomass or bioproductivity at each trophic level in an ecosystem.
The following outline is provided as an overview of and guide to forestry:
This is a glossary of environmental science.
Ecological efficiency describes the efficiency with which energy is transferred from one trophic level to the next. It is determined by a combination of efficiencies relating to organismic resource acquisition and assimilation in an ecosystem.
Earth Overshoot Day (EOD) is the calculated illustrative calendar date on which humanity's resource consumption for the year exceeds Earth’s capacity to regenerate those resources that year. The term "overshoot" represents the level by which human population's demand overshoots the sustainable amount of biological resources regenerated on Earth. When viewed through an economic perspective, the annual EOD represents the day by which the planet's annual regenerative budget is spent, and humanity enters environmental deficit spending. EOD is calculated by dividing the world biocapacity, by the world ecological footprint, and multiplying by 365, the number of days in a year:
Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term applies to natural resources such as water aquifers, grazing pastures and forests, wild medicinal plants, fish stocks and other wildlife.
The biocapacity or biological capacity of an ecosystem is an estimate of its production of certain biological materials such as natural resources, and its absorption and filtering of other materials such as carbon dioxide from the atmosphere.
FORECAST is a management-oriented, stand-level, forest-growth and ecosystem-dynamics model. The model was designed to accommodate a wide variety of silvicultural and harvesting systems and natural disturbance events in order to compare and contrast their effect on forest productivity, stand dynamics, and a series of biophysical indicators of non-timber values.
