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Wednesday, May 31, 2023

Attenuation

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Attenuation

In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates.

Hearing protectors help reduce acoustic flux from flowing into the ears. This phenomenon is called acoustic attenuation and is measured in decibels (dBs).

In electrical engineering and telecommunications, attenuation affects the propagation of waves and signals in electrical circuits, in optical fibers, and in air. Electrical attenuators and optical attenuators are commonly manufactured components in this field.

Background

Frequency-dependent attenuation of electromagnetic radiation in standard atmosphere.

In many cases, attenuation is an exponential function of the path length through the medium. In optics and in chemical spectroscopy, this is known as the Beer–Lambert law. In engineering, attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc.) and is represented by the attenuation coefficient of the medium in question. Attenuation also occurs in earthquakes; when the seismic waves move farther away from the hypocenter, they grow smaller as they are attenuated by the ground.

Ultrasound

One area of research in which attenuation plays a prominent role, is in ultrasound physics. Attenuation in ultrasound is the reduction in amplitude of the ultrasound beam as a function of distance through the imaging medium. Accounting for attenuation effects in ultrasound is important because a reduced signal amplitude can affect the quality of the image produced. By knowing the attenuation that an ultrasound beam experiences traveling through a medium, one can adjust the input signal amplitude to compensate for any loss of energy at the desired imaging depth.

Wave equations which take acoustic attenuation into account can be written on a fractional derivative form.

In homogeneous media, the main physical properties contributing to sound attenuation are viscosity  and thermal conductivity.

Attenuation coefficient

Attenuation coefficients are used to quantify different media according to how strongly the transmitted ultrasound amplitude decreases as a function of frequency. The attenuation coefficient () can be used to determine total attenuation in dB in the medium using the following formula:

Attenuation is linearly dependent on the medium length and attenuation coefficient, as well as – approximately – the frequency of the incident ultrasound beam for biological tissue (while for simpler media, such as air, the relationship is quadratic). Attenuation coefficients vary widely for different media. In biomedical ultrasound imaging however, biological materials and water are the most commonly used media. The attenuation coefficients of common biological materials at a frequency of 1 MHz are listed below:


Material
Air, at 20 °C 1.64
Blood 0.2
Bone, cortical 6.9
Bone, trabecular 9.94
Brain 0.6
Breast 0.75
Cardiac 0.52
Connective tissue 1.57
Dentin 80
Enamel 120
Fat 0.48
Liver 0.5
Marrow 0.5
Muscle 1.09
Tendon 4.7
Soft tissue (average) 0.54
Water 0.0022

There are two general ways of acoustic energy losses: absorption and scattering. Ultrasound propagation through homogeneous media is associated only with absorption and can be characterized with absorption coefficient only. Propagation through heterogeneous media requires taking into account scattering.

Light attenuation in water

Shortwave radiation emitted from the Sun have wavelengths in the visible spectrum of light that range from 360 nm (violet) to 750 nm (red). When the Sun's radiation reaches the sea surface, the shortwave radiation is attenuated by the water, and the intensity of light decreases exponentially with water depth. The intensity of light at depth can be calculated using the Beer-Lambert Law.

In clear mid-ocean waters, visible light is absorbed most strongly at the longest wavelengths. Thus, red, orange, and yellow wavelengths are totally absorbed at shallower depths, while blue and violet wavelengths reach deeper in the water column. Because the blue and violet wavelengths are absorbed least compared to the other wavelengths, open-ocean waters appear deep blue to the eye.

Near the shore, coastal water contains more phytoplankton than the very clear mid-ocean waters. Chlorophyll-a pigments in the phytoplankton absorb light, and the plants themselves scatter light, making coastal waters less clear than mid-ocean waters. Chlorophyll-a absorbs light most strongly in the shortest wavelengths (blue and violet) of the visible spectrum. In coastal waters where high concentrations of phytoplankton occur, the green wavelength reaches the deepest in the water column and the color of water appears blue-green or green.

Seismic

The energy with which an earthquake affects a location depends on the running distance. The attenuation in the signal of ground motion intensity plays an important role in the assessment of possible strong groundshaking. A seismic wave loses energy as it propagates through the earth (seismic attenuation). This phenomenon is tied into the dispersion of the seismic energy with the distance. There are two types of dissipated energy:

  • geometric dispersion caused by distribution of the seismic energy to greater volumes
  • dispersion as heat, also called intrinsic attenuation or anelastic attenuation.

In porous fluid—saturated sedimentary rocks such as sandstones, intrinsic attenuation of seismic waves is primarily caused by the wave-induced flow of the pore fluid relative to the solid frame. 

Electromagnetic

Attenuation decreases the intensity of electromagnetic radiation due to absorption or scattering of photons. Attenuation does not include the decrease in intensity due to inverse-square law geometric spreading. Therefore, calculation of the total change in intensity involves both the inverse-square law and an estimation of attenuation over the path.

The primary causes of attenuation in matter are the photoelectric effect, compton scattering, and, for photon energies of above 1.022 MeV, pair production.

Coaxial and general RF cables

The attenuation of RF cables is defined by:

where is the input power into a 100 m long cable terminated with the nominal value of its characteristic impedance, and is the output power at the far end of this cable.

Attenuation in a coaxial cable is a function of the materials and the construction.

Radiography

The beam of X-ray is attenuated when photons are absorbed when the x-ray beam passes through the tissue. Interaction with matter varies between high energy photons and low energy photons. Photons travelling at higher energy are more capable of travelling through a tissue specimen as they have less chances of interacting with matter. This is mainly due to the photoelectric effect which states that "the probability of photoelectric absorption is approximately proportional to (Z/E)3, where Z is the atomic number of the tissue atom and E is the photon energy. In context of this, an increase in photon energy (E) will result in a rapid decrease in the interaction with matter.

Optics

Attenuation in fiber optics, also known as transmission loss, is the reduction in intensity of the light beam (or signal) with respect to distance travelled through a transmission medium. Attenuation coefficients in fiber optics usually use units of dB/km through the medium due to the relatively high quality of transparency of modern optical transmission . The medium is typically a fiber of silica glass that confines the incident light beam to the inside. Attenuation is an important factor limiting the transmission of a digital signal across large distances. Thus, much research has gone into both limiting the attenuation and maximizing the amplification of the optical signal. Empirical research has shown that attenuation in optical fiber is caused primarily by both scattering and absorption.

Attenuation in fiber optics can be quantified using the following equation:

Light scattering

 
Specular reflection
 
Diffuse reflection

The propagation of light through the core of an optical fiber is based on total internal reflection of the lightwave. Rough and irregular surfaces, even at the molecular level of the glass, can cause light rays to be reflected in many random directions. This type of reflection is referred to as "diffuse reflection", and it is typically characterized by wide variety of reflection angles. Most objects that can be seen with the naked eye are visible due to diffuse reflection. Another term commonly used for this type of reflection is "light scattering". Light scattering from the surfaces of objects is our primary mechanism of physical observation. Light scattering from many common surfaces can be modelled by reflectance.

Light scattering depends on the wavelength of the light being scattered. Thus, limits to spatial scales of visibility arise, depending on the frequency of the incident lightwave and the physical dimension (or spatial scale) of the scattering center, which is typically in the form of some specific microstructural feature. For example, since visible light has a wavelength scale on the order of one micrometer, scattering centers will have dimensions on a similar spatial scale.

Thus, attenuation results from the incoherent scattering of light at internal surfaces and interfaces. In (poly)crystalline materials such as metals and ceramics, in addition to pores, most of the internal surfaces or interfaces are in the form of grain boundaries that separate tiny regions of crystalline order. It has recently been shown that, when the size of the scattering center (or grain boundary) is reduced below the size of the wavelength of the light being scattered, the scattering no longer occurs to any significant extent. This phenomenon has given rise to the production of transparent ceramic materials.

Likewise, the scattering of light in optical quality glass fiber is caused by molecular-level irregularities (compositional fluctuations) in the glass structure. Indeed, one emerging school of thought is that a glass is simply the limiting case of a polycrystalline solid. Within this framework, "domains" exhibiting various degrees of short-range order become the building-blocks of both metals and alloys, as well as glasses and ceramics. Distributed both between and within these domains are microstructural defects that will provide the most ideal locations for the occurrence of light scattering. This same phenomenon is seen as one of the limiting factors in the transparency of IR missile domes.

UV-Vis-IR absorption

In addition to light scattering, attenuation or signal loss can also occur due to selective absorption of specific wavelengths, in a manner similar to that responsible for the appearance of color. Primary material considerations include both electrons and molecules as follows:

  • At the electronic level, it depends on whether the electron orbitals are spaced (or "quantized") such that they can absorb a quantum of light (or photon) of a specific wavelength or frequency in the ultraviolet (UV) or visible ranges. This is what gives rise to color.
  • At the atomic or molecular level, it depends on the frequencies of atomic or molecular vibrations or chemical bonds, how close-packed its atoms or molecules are, and whether or not the atoms or molecules exhibit long-range order. These factors will determine the capacity of the material transmitting longer wavelengths in the infrared (IR), far IR, radio and microwave ranges.

The selective absorption of infrared (IR) light by a particular material occurs because the selected frequency of the light wave matches the frequency (or an integral multiple of the frequency) at which the particles of that material vibrate. Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies (or portions of the spectrum) of infrared (IR) light.

Applications

In optical fibers, attenuation is the rate at which the signal light decreases in intensity. For this reason, glass fiber (which has a low attenuation) is used for long-distance fiber optic cables; plastic fiber has a higher attenuation and, hence, shorter range. There also exist optical attenuators that decrease the signal in a fiber optic cable intentionally.

Attenuation of light is also important in physical oceanography. This same effect is an important consideration in weather radar, as raindrops absorb a part of the emitted beam that is more or less significant, depending on the wavelength used.

Due to the damaging effects of high-energy photons, it is necessary to know how much energy is deposited in tissue during diagnostic treatments involving such radiation. In addition, gamma radiation is used in cancer treatments where it is important to know how much energy will be deposited in healthy and in tumorous tissue.

In computer graphics attenuation defines the local or global influence of light sources and force fields.

In CT imaging, attenuation describes the density or darkness of the image.

Radio

Attenuation is an important consideration in the modern world of wireless telecommunication. Attenuation limits the range of radio signals and is affected by the materials a signal must travel through (e.g., air, wood, concrete, rain). See the article on path loss for more information on signal loss in wireless communication.

Trillion Tree Campaign

From Wikipedia, the free encyclopedia
 
Trillion Tree Campaign
Formation2018
Founded atGrimaldi Forum, Monaco
Fields
Official language
English, German, Spanish, French, Portuguese
Parent organization
Plant-for-the-Planet
AffiliationsUNEP
Websitetrilliontreecampaign.org
Formerly called
Billion Tree Campaign

The Trillion Tree Campaign is a project which aims to plant one trillion trees worldwide. It seeks to repopulate the world's trees and combat climate change as a nature-based solution. The project was launched at PlantAhead 2018 in Monaco by Plant-for-the-Planet. In the fall of 2018, the project's official website was published in order to register, monitor, and donate trees to reforestation projects around the world. The campaign is a continuation of the activities of the earlier Billion Tree Campaign, instigated by Wangari Maathai, who founded the Green Belt Movement in Africa in 1977.

As of 30 May 2021, 164 restoration projects participate in the campaign and 13.96 billion (1.396% of the goal) trees have been planted worldwide.

History

Billion Tree Campaign

The Green Belt Movement began its activity in Africa in 1977, eventually planting more than 30 million trees. The Billion Tree Campaign was inspired by Nobel Peace Prize laureate Wangari Maathai, founder of the Green Belt Movement. When an executive in the United States told Maathai their corporation was planning to plant a million trees, her response was: "That's great, but what we really need is to plant a billion trees."

The project was launched in 2006 by the United Nations Environment Programme (UNEP) under the patronage of Prince Albert II of Monaco and the World Agroforestry Centre-ICRAF as a response to the challenges of climate change, as well as to a wider array of sustainability challenges from water supply to biodiversity loss, and achieved the initial target of planting a billion trees in 2007. The billionth tree, commonly known as an African olive, was planted in Ethiopia in November 2007. In 2008, the campaign's objective was raised to 7 billion trees, a goal which was surpassed three months before its target of the climate change conference that was held in Copenhagen, Denmark, in December 2009.

The 2-billionth tree took root as part of the United Nation's World Food Programme agroforestry initiative. The campaign's target was then raised to seven billion trees. In 2009, UNEP mobilized action across the globe through the "Twitter for Trees" campaign. UNEP pledged to plant one tree to feed into the Billion Tree Campaign for every follower who joined from 5 May 2009 to World Environment Day on 5 June 2009. The campaign was a success, with 10,300 people following the page by World Environment Day.

The World Organization of the Scout Movement also planted trees under the campaign, in line with its mandate to study and protect nature across several countries. United Nations Peacekeeping missions also joined the campaign and planted trees within their field missions in East Timor, Ivory Coast, Darfur, Lebanon, Haiti, Congo, and Liberia, among others.

After the campaign

Felix Finkbeiner addressed the United Nations in a  speech to open the International Year of Forests 2011, saying: "It is now time that we work together. We combine our forces, old and young, rich and poor; and together, we can plant a trillion trees. We can start the Trillion Tree Campaign." In December 2011, after more than 12 billion trees had been planted, UNEP formally handed management of the program to the youth-led not-for-profit Plant-for-the-Planet Foundation (an organisation that had been participating in the Billion Tree Campaign since 2007), based in Tutzing, Germany. Momentum has since continued, with 40,000 young ambassadors spreading the message in over 100 countries.

In 2015, researcher Tom Crowther found that about 3 trillion trees exist in the world and later it was also estimated that planting 1.2 trillion more trees would counteract 10 years of anthropogenic CO2 emissions.

In 2017, Pakistan's Billion Tree Tsunami restored 350,000 hectares of forests.

On 9 March 2018, the Trillion Tree Declaration was signed at the Grimaldi Forum in Monaco. Signatories include Prince Albert II of Monaco, Gyalwang Drukpa, Patricia Espinosa in collaboration with the WWF, WCS, and BirdLife International.

In September 2019, the Plant-for-the-Planet app was released under an open-source license. It allowed users to register planted trees or to plant trees by donating to different tree-planting organizations around the world. The foundation does not take any commissions for donations made through the campaign.

One Trillion Tree initiative

The 2020 World Economic Forum, held in Davos, announced the creation of the One Trillion Tree initiative platform for governments, businesses, and civil society to provide support to the UN Decade on Ecosystem Restoration (2020–2030), led by UNEP and FAO. Forum participant Donald Trump, then-president of the United States, announced that the government of the U.S. would commit to the initiative.

Principles

  • Reducing fossil fuel emissions
  • Conserving existing ecosystems
  • Restoration must be socially and ecologically responsible

By country

China

In the years 2011—2022, China restored more than 70 million hectares (700,000 km2) of forests. The nation committed to plant and conserve 70 billion trees by the year 2030 as part of the Trillion Tree Campaign.

US

The United States has pledged to plant, grow, and restore around 51 billion trees by the year 2030. Currently, forests in the country absorb 15% of its carbon emissions. This can rise to 27% with responsible reforestation.

Green retrofit

From Wikipedia, the free encyclopedia

A green retrofit is any refurbishment of an existing building that aims to reduce the carbon emissions and environmental impact of the building. This can include improving the energy efficiency of the HVAC and other mechanical systems, increasing the quality of insulation in the building envelope, implementing sustainable energy generation, and aiming to improve occupant comfort and health.

Green retrofits have become increasingly prominent with their inclusion in a number of building rating systems, such as the USGBC's LEED for Existing Buildings: Operations & Maintenance, Passive House EnerPHit, and Green Globes for Existing Buildings. Some governments offer funding towards green retrofits as existing buildings make up a majority of operational buildings and have been identified as a growing area of consideration in the fight against climate change.

Overview

Most retrofits can be considered somewhat "green" because rather than constructing a new building, an existing one is improved. This saves resources that would otherwise be used to build an entirely new structure. A green retrofit typically aims to incorporate sustainability and save energy costs with each design decision.

Retrofitting a building inherently carries the constraints of the existing building and site. For example, the orientation of a building in regard to the sun has a great impact on its energy performance, but it's generally not within the scope of a retrofit to rotate the building. Budgetary constraints also often impact the energy conservation measures proposed.

Until recently, green retrofits have generally been considered as one-off projects for specific buildings or clients, but given the increased emphasis on improving the energy efficiency of existing building stock in the face of climate change, they are beginning to be reviewed systematically and at scale. The main challenge this presents for governments and advocacy groups is that the existing building stock is characterized by different uses, located in disparate climatic areas, and uses different construction traditions and system technologies. Because of these disparities, it is difficult to characterize strategies that apply to all buildings.

Green retrofits have recently garnered considerable research attention due to government emphasis on retrofitting old building stock to address climate change. It is estimated that up to half of building stock is always over 40 years old. Older buildings have significantly worse energy performance than their modern counterparts due to shortcomings in their design, deterioration in mechanical system efficiency, and increases in envelope permeability. The energy use intensity of houses in the United States dropped 9% from 1985 to 2004 due to improvements in end-use energy efficiency and code improvements. Unfortunately, this is offset by the overall increase in the total number of houses.

Components of a green retrofit

Integrated design

Green retrofits utilize an integrated design strategy. This is in opposition to the traditional waterfall design strategy, in which architects, engineers, and contractors operate independently from one another. In an integrated design strategy, these teams work together to leverage their areas of expertise and solve design problems while also considering the building as a whole. This is imperative for a green retrofit, where the design solutions are often constrained by the existing site. This could relate to the orientation and geometry of the existing building form, the size of the site, or the installation requirements of the existing and proposed mechanical systems. Because these constraints affect all aspects of building design, the only way sustainable, effective, and cost-efficient solutions can be synthesized is when project teams consider all these aspects from the project start.

Occupant behavior

Many sustainable building practices are passive and can be automated, like insulation or light controls. Others depend on the behavior of the building's occupants to realize their full energy efficiency potential. An energy efficient heating system does very little good if the windows are left open in winter. Per Ascione et al., "the first lever of energy efficiency is a proper energy-education of users". Green retrofits can involve training building occupants in sustainable practices and building systems that they'll interact with, which helps ensure that any energy conservation measures used will reach their full design potential. Training can be handled by system manufacturers or the project design team.

LED bulbs are a popular and effective choice for green lighting retrofits.

Lighting retrofits

One of the most common forms of a green retrofit is a full or partial lighting retrofit. A lighting retrofit usually consists of replacing all or some of the lightbulbs in a building with newer, more efficient models. This can also include changing light fixtures, ballasts, and drivers. LED bulbs are generally the preferred choice in a lighting retrofit because of their greatly increased efficiency compared to incandescent bulbs, but other types of bulbs like compact fluorescent or metal halides may be used as well.

Lighting retrofits are a popular form of green retrofit because, compared to other methods of improving energy efficiency, they are relatively straightforward to plan and execute, and the energy savings often provide a quick return on investment. Most modern LED and compact fluorescent bulbs are designed to work with existing light fixtures and rarely involve any additional work than removing and screwing in a new lightbulb. The installation is also relatively quick compared to more invasive energy conservation measures.

Lighting retrofits can also include implementing new lighting controls like occupancy sensors, daylight sensors, and timers. When correctly implemented, these controls can reduce the demand for lighting. However, due to the complicated nature of lighting controls, there is debate as to whether or not they are an effective energy conserving measure because of the prevalence of over-optimistic energy usage reduction estimates and the difficulty in predicting the actions of human occupants.

HVAC retrofits

Heating, ventilation, and air conditioning (HVAC) account for around 50% of a building's operating energy consumption, and HVAC retrofits can account for 40-70% of energy savings. Reducing this consumption can provide both energy and cost savings, so it is the main focus of many green retrofits, especially in colder climates where heating accounts for over 60% of energy use. The heating system, cooling system, air handling systems, humidification systems, and ductwork in the building are often considered.

Heat recovery ventilation is recommended for newly air-sealed homes as it uses the heat from the warm, moist, stale air that is being vented from the home to warm the cool, fresh, and filtered air that is entering the home. This allows for minimal heat loss while mitigating concerns of carbon monoxide poisoning, radon gas, or harmful particulates accumulating in the home.

Other green HVAC retrofits can include implementing a newer, more efficient model of the same type as the existing system, such as replacing an old water boiler with a more efficient one to feed a hydronic heating system. Sometimes a larger system overhaul is merited—for example, exchanging an old boiler for a newer ground or air source heat pump system.

A blower door test can locate leaks in a building envelope.

Building envelope retrofits

Thermal insulation and building envelope performance are key to the overall energy performance of any building. Many older buildings are not insulated up to current standards, let alone up to the standards recommended in many green building rating systems. Many of these buildings spend energy and money heating, cooling, or conditioning the air inside them only to see it seep out through leaks in the building envelope or through poorly insulated windows.

During many green retrofits, the first step towards improving the building's envelope is to evaluate its current shortcomings. Air-sealing is an easily accessible and cost-efficient way to improve the energy efficiency of a home that is mechanically heated or cooled. Caulking can be used to fill gaps in immobile areas like window and door frames and or poorly sealed appliances. Weather stripping can be used where moving parts meet, such as the area between the door and the doorframe or windows that can open. These drafty areas can be found by feeling for temperature differences and drafts on days when the temperature inside the house is dramatically different than the temperature outside the house, burning incense and watching how the smoke moves to detect drafts, or hiring a professional to perform a blower door test. In a blower door test, a door with a fan and a gauge is installed into one of the doorways and the house is depressurized. The gauge can then measure the air changes per hour (ACH), or how many times the volume of air in the house is completely replaced in one hour. The draftier a house is, the higher the air changes per hour will be.

Window retrofits

Windows are the weakest point of insulation in a building's envelope and contribute greatly to how thermally effective that envelope is. Because of this, windows are another common area of focus for a green retrofit. Similar to a lighting retrofit, windows are a relatively straightforward aspect of a building to retrofit, with easy-to-calculate payback periods. Modern, efficient windows are generally sized for existing window openings and can usually be installed without much additional work on the building envelope.

Most green retrofits will replace older single-pane windows with more efficient triple-paned varieties that are filled with an inert gas such as argon or krypton. These windows have greater R-values, so they insulate a space far better than single-pane windows. Some windows have low-e coatings to control the solar heat gain coefficient.

Green roof retrofits

The Chicago City Hall retrofitted a semi-intensive green roof in 2001.

Green roofs, also called living roofs, have a number of major benefits, including reducing stormwater runoff and urban heat island effect, increasing roof insulation, improving building acoustics, and providing biodiversity.

There are many factors to account for when considering a green roof for a green retrofit. Extensive green roofs use a thin substrate layer for the often shorter vegetation that needs less room for roots to grow. Intensive green roofs use a thicker growing substrate to accommodate larger plant species that require more space for their roots. Semi-intensive green roofs fall somewhere in between the two. The strength of the existing structure must be considered; many existing structures were not designed for an intensive green roof, which can carry a considerable structural load. The existing roof also needs to be evaluated for stripping or re-waterproofing. Some roofs can simply be laid over with sedum mats, while others require additional work to prepare. A peaked or sloped roof does not preclude the installation of a green roofing system but can influence the installation costs and product choices available.

In general, older buildings with lower existing insulation values benefit the most from green roof retrofits, and where there are no modifications necessary to install one, green roofs have been shown to have many benefits.

Passive design

Passive design is a design strategy that uses the shape and placement of the architecture and landscaping to heat, cool, light, ventilate, and sometimes provide power to the building. Often, this impacts the shape of the building envelope, the orientation of the building, and the placement of the building. The shape of the building can also create microclimates in which the building is designed to trap heat or funnel breezes for warming in the winter or cooling in the summer. While these passive design elements are more often applied in newly built green buildings, passive design can still be a consideration in green retrofits. For example, if there are windows that receive very little sunlight in the winter or a large amount of sunlight in the summer, those may be replaced first to reduce an undesirable amount of heat lost in the winter or gained in the summer. Using landscaping, such as planting a deciduous tree in front of south-facing windows to maximize solar heat gain in the winter while shading the windows in the summer, is also an example of passive design.

Costs, barriers, and benefits

Possible benefits of green retrofits include:

  • Improved energy security
  • Reduced air pollution
  • Reduced greenhouse gas emissions and impact on climate change
  • Increased thermal comfort
  • Enhanced indoor air quality and occupant health
  • Generation of local jobs
  • Reduction of peak electrical demand

Possible barriers to green retrofits include:

  • Initial cost and financing
  • Lack of knowledge and experience of the designers, architects, construction workers, inspectors, and financial institutions involved in the project
  • Building code regulations
  • Lack of consumer interest

The scope of a green retrofit can vary widely. It can involve specific building systems, like the lighting, or can be a full renovation of all non-structural components. While a lighting retrofit is straightforward to execute and relatively unobtrusive to building occupants, it won't generally carry as much of a benefit or cost as an insulation retrofit. When weighing the benefits and costs of a green retrofit, each of these components must be considered towards the project as a whole.

While green retrofits do have an up-front cost, the amount depends on how extensive the retrofits are. Likewise, the kind of retrofit that is implemented will also impact how fast the investment is returned in savings. The economic feasibility of a green retrofit depends on the state of installed systems of the existing building, the proposed design, the energy costs of the local utility grid, and the climatic conditions of the site. Any economic incentives granted will depend on what country or state the project is in. These incentives differ regionally and can affect the total project feasibility. In Ireland, for example, "shallow" green retrofits have been found to be economically feasible, but "deep" retrofits are often not feasible without government grant aid to offset the initial capital costs.

The EU has found that implementing green retrofit programs comes with the benefit of "energy security, job creation, fuel poverty alleviation, health and indoor comfort".

Green retrofits can carry benefits such as the re-use of existing building material. Concrete and steel have some of the highest embodied energy impacts of any building material and can account for up to 60% of the carbon used in the construction of a building. They are primarily used in the structure of a building, which usually remains untouched in retrofits.

Most types of green retrofit introduce new building materials into the space which can themselves emit harmful indoor air pollutants. The amount, type, and exposure to these pollutants will depend on the material itself, what it is used for, and how it is installed. Often, green retrofits call for sealing leaks in the building envelope to prevent the escape of conditioned air, but if this is not offset by an increase in ventilation, it can contribute to higher concentrations of indoor air pollutants in the building.

Reforestation

From Wikipedia, the free encyclopedia
Tropical tree nursery at Planeta Verde Reforestación S.A.'s plantation in Vichada Department, Colombia
 
A 15-year-old reforested plot of land
 
A 21-year-old plantation of red pine in southern Ontario

Reforestation (occasionally, reafforestation) is the natural or intentional restocking of existing forests and woodlands (forestation) that have been depleted, usually through deforestation but also after clearcutting.

Management

A debated issue in managed reforestation is whether the succeeding forest will have the same biodiversity as the original forest. If the forest is replaced with only one species of tree and all other vegetation is prevented from growing back, a monoculture forest similar to agricultural crops would be the result. However, most reforestation involves the planting of different selections of seedlings taken from the area, often of multiple species. Another important factor is the natural regeneration of a wide variety of plant and animal species that can occur on a clear cut. In some areas the suppression of forest fires for hundreds of years has resulted in large single aged and single species forest stands. The logging of small clear cuts, and/or prescribed burning, actually increases the biodiversity in these areas by creating a greater variety of tree stand ages and species.

Over 90% of the world's forests regenerate organically, and more than half are covered by forest management plans or equivalents.

For harvesting

Reforestation is not only used for recovery of accidentally destroyed forests. In some countries, such as Finland, many of the forests are managed by the wood products and pulp and paper industry. In such an arrangement, like other crops, trees are planted to replace those that have been cut. The Finnish Forest Act from 1996 obliges the forest to be replanted after felling. In such circumstances, the industry can cut the trees in a way to allow easier reforestation. The wood products industry systematically replaces many of the trees it cuts, employing large numbers of summer workers for tree planting work. For example, in 2010, Weyerhaeuser reported planting 50 million seedlings. However replanting an old-growth forest with a plantation is not replacing the old with the same characteristics in the new.

In just 20 years, a teak plantation in Costa Rica can produce up to about 400 m³ of wood per hectare. As the natural teak forests of Asia become more scarce or difficult to obtain, the prices commanded by plantation-grown teak grows higher every year. Other species, such as mahogany, grow more slowly than teak in Tropical America but are also extremely valuable. Faster growers include pine, eucalyptus, and Gmelina.

Reforestation, if several indigenous species are used, can provide other benefits in addition to financial returns, including restoration of the soil, rejuvenation of local flora and fauna, and the capturing and sequestering of 38 tons of carbon dioxide per hectare per year.

The reestablishment of forests is not just simple tree planting. Forests are made up of a community of species and they build dead organic matter into soils over time. A major tree-planting program could enhance the local climate and reduce the demands of burning large amounts of fossil fuels for cooling in the summer.

For climate change mitigation

Forests are an important part of the global carbon cycle because trees and plants absorb carbon dioxide through photosynthesis. Therefore, they play an important role in climate change mitigation. By removing the greenhouse gas carbon dioxide from the air, forests function as terrestrial carbon sinks, meaning they store large amounts of carbon. At any time, forests account for as much as double the amount of carbon in the atmosphere. Forests remove around three billion tons of carbon every year. This amounts to about 30% of anthropogenic all carbon dioxide emissions. Therefore, an increase in the overall forest cover around the world would mitigate global warming.

At the beginning of the 21st century, interest in reforestation grew over its potential to mitigate climate change. Even without displacing agriculture and cities, earth can sustain almost one billion hectares of new forests. This would remove 25% of carbon dioxide from the atmosphere and reduce its concentration to levels that existed in the early 20th century. A temperature rise of 1.5 degrees would reduce the area suitable for forests by 20% by the year 2050, because some tropical areas will become too hot. The countries that have the most forest-ready land are: Russia, Canada, Brazil, Australia, the United States and China.

The four major strategies are:

  • Increase the amount of forested land through reforestation
  • Increase density of existing forests at a stand and landscape scale
  • Expand the use of forest products that sustainably replace fossil-fuel emissions
  • Reduce carbon emissions caused by deforestation and degradation

Implementing the first strategy is supported by many organizations around the world. For example, in China, the Jane Goodall Institute, through their Shanghai Roots & Shoots division, launched the Million Tree Project in Kulun Qi, Inner Mongolia to plant one million trees. China used 24 million hectares of new forest to offset 21% of Chinese fossil fuel emissions in 2000. In Java, Indonesia newlywed couples give whoever is conducting their wedding 5 seedlings. Each divorcing couple gives 25 seedlings to whoever divorces them. Costa Rica doubled its forest cover in 30 years using its system of grants and other payments for environmental services, including compensation for landowners. These payments are funded through international donations and nationwide taxes.

The second strategy has to do with selecting species for tree-planting. In theory, planting any kind of tree to produce more forest cover would absorb more carbon dioxide from the atmosphere. However, a genetically modified variant might grow much faster than unmodified specimens. Some of these cultivars are under development. Such fast-growing trees would be planted for harvest and can absorb carbon dioxide faster than slower-growing trees.

Impacts on temperature are affected by the location of the forest. For example, reforestation in boreal or subarctic regions has less impact on climate. This is because it substitutes a high-albedo, snow-dominated region with a lower-albedo forest canopy. By contrast, tropical reforestation projects lead to a positive change such as the formation of clouds. These clouds then reflect the sunlight, lowering temperatures.

Planting trees in tropical climates with wet seasons has another advantage. In such a setting, trees grow more quickly (fixing more carbon) because they can grow year-round. Trees in tropical climates have, on average, larger, brighter, and more abundant leaves than non-tropical climates. A study of the girth of 70,000 trees across Africa has shown that tropical forests fix more carbon dioxide pollution than previously realized. The research suggested almost one fifth of fossil fuel emissions are absorbed by forests across Africa, Amazonia and Asia. Simon Lewis stated, "Tropical forest trees are absorbing about 18% of the carbon dioxide added to the atmosphere each year from burning fossil fuels, substantially buffering the rate of change."

As of 2008 1.3 billion hectares of tropical regions were deforested every year. Reducing this would reduce the amount of planting needed to achieve a given degree of mitigation.

Methods

A study finds that almost 300 million people live on tropical forest restoration opportunity land in the Global South, constituting a large share of low-income countries' populations, and argues for prioritized inclusion of "local communities" in forest restoration projects.

Using existing trees and roots

Planting new trees often leads to up to 90% of seedlings failing. However, even in deforested areas, existing root systems often exist. Growth can be accelerated by pruning and coppicing where a few branches of new shoots are cut and often used for charcoal, itself a major driver of deforestation. Since new seeds are not planted, it is cheaper. Additionally, they are much more likely to survive as their root systems already exist and can tap into groundwater during harsher seasons with no rain. While this method has existed for centuries, it is now sometimes referred to as farmer-managed natural regeneration.

Financial incentives

Policy that promote reforestation for incentives in return have shown promising results of being an effective and motivative concept to re-plant globally on a mass scale. Some incentives for reforestation can be as simple as a financial compensation. Streck and Scholz (2006) explain how a group of scientists from various institutions have developed a compensated reduction of deforestation approach which would reward developing countries that disrupt any further act of deforestation. Countries that participate and take the option to reduce their emissions from deforestation during a committed period of time would receive financial compensation for the carbon dioxide emissions that they avoided. To raise the payments, the host country would issue government bonds or negotiate some kind of loan with a financial institution that would want to take part in the compensation promised to the other country. The funds received by the country could be invested to help find alternatives to the extensive cutdown of forests. This whole process of cutting emissions would be voluntary, but once the country has agreed to lower their emissions they would be obligated to reduce their emissions. However, if a country was not able to meet their obligation, their target would get added to their next commitment period. The authors of these proposals see this as a solely government-to-government agreement; private entities would not participate in the compensation trades.

Another emerging revenue source to fund reforestation projects deals with the sale of carbon sequestration credits, which can be sold to companies and individuals looking to compensate their carbon footprint. This approach allows for private landowners and farmers to gain a revenue from the reforestation of their lands, while simultaneously benefiting from improved soil health and increased productivity.

Alongside past financial incentive strategies, reforestation tax benefits have been another way the government has encouraged companies to promote reforestation tactics through the promises of a tax break.

As many landholders seek to earn carbon credits through sequestration, their participation also encourages biodiversity and provides ecosystem services for crops and livestock. 

Implementation

Forest regrowth in Mount Baker-Snoqualmie National Forest, Washington state, US

Global

The 2020 World Economic Forum, held in Davos, announced the creation of the Trillion Tree Campaign, which is an initiative aiming to plant 1 trillion trees across the globe. The implementation can have big environmental and societal benefits but needs to be tailored to local conditions.

The forest landscape restoration strategy seeks to rehabilitate landscapes and repair marginal and degraded areas in order to generate productive forest landscapes that are resilient and long-term. It aims to guarantee that diverse ecological and land-use functions are restored, safeguarded, and preserved over time.

Asia

China

In China, extensive replanting programs have existed since the 1970s, which have had overall success. The forest cover has increased from 12% of China's land area to 16%. However, specific programs have had limited success. The "Green Wall of China", an attempt to limit the expansion of the Gobi Desert, is planned to be 2,800 miles (4,500 km) long and to be completed in 2050. In 2015 China announced a plan to plant 26 billion trees by the year 2025; that is, two trees for every Chinese citizen per year. China requires that students older than 11 years old plant one tree a year until their high school graduation.

Between 2013 and 2018, China planted 338,000 square kilometres of forests, at a cost of $82.88 billion. By 2018, 21.7% of China's territory was covered by forests, a figure the government wants to increase to 26% by 2035. The total area of China is 9,596,961 square kilometres (see China), so 412,669 square kilometres more needs to be planted. According to the government's plan, by 2050, 30% of China’s territory should be covered by forests.

In 2017, the Saihanba Afforestation Community won the UN Champions of the Earth Award in the Inspiration and Action category for their successful reforestation efforts, which began upon discovering the survival of a single tree.

From 2016 to 2021, 3976 square kilometers of forests were planted in the Tibet Autonomous Region, with plans for 20 million trees to be planted before 2023.

In the years 2012-2022 China restored more than 70 million hectares (700,000 km2) of forests. China committed to plant and conserve 70 billion trees by the year 2030 as part of the Trillion Tree Campaign.

Launched in 1978 and scheduled to last until 2050, the Three Northern Protected Forest Development Program - informally known as the "Great Green Wall" - aims to eventually plant nearly 90 million acres of new forest in a 2,800-mile stretch of northern China.

India

Jadav Payeng had received national awards for reforestation efforts, known as the "Molai forest". He planted 1400 hectares of forest on the bank of river Brahmaputra alone. There are active reforestation efforts throughout the country. In 2016, India had more than 50 million trees planted in Uttar Pradesh and in 2017, more than 66 million trees planted in Madhya Pradesh. In addition to this and individual efforts, there are startup companies, such as Afforest, that are being created over the country working on reforestation. Lots of plantation are being carried out in the Indian continent but the survivability is very poor especially for massive plantations, with less than 20% survivability rate. To improve the forest cover and to achieve the national mission of forest cover of 33%, there is a need to improve the methods of plantation. Rather than mass planting, there is a need to work on performance measurement & tracking of trees growth. Taking this into consideration, a non-profit organisation Ek Kadam Sansthan in Jaipur is leading the development of a module of mass tracking for plantations. The pilot has been done successfully and the organisation is hoping to implement nationwide by the end of 2021.

Japan

The Ministry of Agriculture, Forestry and Fishery explain that about two-thirds of Japanese land is covered with forests, and it was almost unchanged from 1966 to 2012. Japan needs to reduce 26% of green house gas emission from 2013 by 2030 to accomplish Paris Agreement and is trying to reduce 2% of them by forestry.

Mass environmental and human-body pollution along with relating deforestation, water pollution, smoke damage, and loss of soils caused by mining operations in Ashio, Tochigi became the first environmental social issue in Japan, efforts by Shōzō Tanaka had grown to large campaigns against copper operation. This led to the creation of 'Watarase Yusuichi Pond', to settle the pollution which is a Ramsar site today. Reforestation was conducted as a part of afforestation due to inabilities of self-recovering by the natural land itself due to serious soil pollution and loss of woods consequence in loss of soils for plants to grow, thus needing artificial efforts involving introducing of healthy soils from outside. Starting from around 1897, about 50% of once bald mountains are now back to green.

Pakistan

The Billion Tree Tsunami was launched in 2014 by planting 10 billion trees, by the provincial government of Khyber Pakhtunkhwa (KPK) and Imran Khan, as a response to the challenge of global warming. Pakistan's Billion Tree Tsunami restored 350,000 hectares of forests and degraded land to surpass its Bonn Challenge commitment.

In 2018, Pakistan's prime minister Imran Khan declared that the country will plant 10 billion trees in the next five years.

In 2020, the Pakistani government launched an initiative to hire 63,600 laborers to plant trees in the northern Punjab region, with indigenous species such as acacia, mulberry and moringa. This initiative was meant to alleviate unemployment caused by lockdowns to mitigate the spread of COVID-19.

Philippines

In 2011, the Philippines established the National Greening Program as a priority program to help reduce poverty, promote food security, environmental stability, and biodiversity conservation, as well as enhance climate change mitigation and adaptation in the country. The program paved the way for the planting of almost 1.4 billion seedlings in about 1.66 million hectares nationwide during the 2011-2016 period. The Food and Agriculture Organization of the United Nations ranked the Philippines fifth among countries reporting the greatest annual forest area gain, which reached 240,000 hectares during the 2010–2015 period.

Europe

Armenia

The Armenia Tree Project was founded in 1994 to address environmental and economic concerns related to Armenia's dwindling forests. Since its founding, the organization has planted more than 6.5 million trees in communities throughout Armenia.

Ireland

In 2019 the government of Ireland decided to plant 440 million trees by 2040. The decision is part of the government's plan to make Ireland carbon neutral by 2050 with renewable energy, land use change and carbon tax.

Ireland is also driven to increase sustainable timber consumption while also adding more eco friendly work positions. They also have taken efforts to limit the use of methane emissions by signing a pledge to draw back methane use by 30%.

Germany

By the 14th century, forests in heavily populated areas had been devastated by industry, many of which required wood for their activities. Peter Stromer (1310-1388), lord of the Stromer trading and commercial company, was spurred by this shortage to "conduct forest culture experiments". In 1368 he successfully sowed fir and pine seeds in the Nuremberg Reichswald, which over time ended the wood shortage and established the "triumph of the pine in the Nuremberg Reichswald" (at the expense of other deciduous trees). The "doctrine of coniferous sowing" spread widely through forestry regulations and other writing at the time.


Reforestation is required as part of the federal forest law. 31% of Germany is forested, according to the second forest inventory of 2001–2003. The size of the forest area in Germany increased between the first and the second forest inventory due to forestation of degenerated bogs and agricultural areas.

United Kingdom

Since the 1980s, 8.5 million trees have been planted in the United Kingdom in an area of the Midlands around the villages of Moira and Donisthorpe, close to Leicester. The area is called The National Forest. An even larger reforestation project, called The Northern Forest, is beginning in South Yorkshire. It aims to plant 50 million trees. Despite this, the UK government has been criticized for not achieving its tree planting goals. There have also been concerns of non-native tree planting disturbing the ecological integrity and processes of what would be a native habitat restoration.

Middle East

Israel

Since 1948, large reforestation and afforestation projects were accomplished in Israel. 240 million trees have been planted. The carbon sequestration rate in these forests is similar to the European temperate forests.

Israel and only one other country was documented to have a net increase of forestation in the 2000's. This type of progress could be attributed to the social practices that Israel incorporates into their society.

Lebanon

For thousands of years Lebanon was covered by forests; one particular species of interest, Cedrus libani was exceptionally valuable and was almost eliminated due to lumbering operations. Many ancient cultures along the Mediterranean Sea harvested these trees including the Phoenicians who used cedar, pine and juniper for boat building, the Romans, who cut them down for lime-burning kilns, and the Ottomans, who used much of the remaining cedar forests of Lebanon as fuel in steam trains in the early 20th century. Despite two millennia of deforestation, forests in Lebanon still cover 13.6% of the country, and other wooded lands represent 11%.

Law No. 558, which was ratified by the Lebanese Parliament on April 19, 1996, aims to protect and expand existing forests, classifying all forests of cedar, fir, high juniper, evergreen cypress and other trees, whether diverse or homogeneous, whether state-owned or not as conserved forests.

Since 2011 more than 600,000 trees, including cedars and other native species, have been planted throughout Lebanon as part of the Lebanon Reforestation Initiative, which aims to restore Lebanon's native forests. Projects financed locally and by international charity are performing extensive reforestation of cedar being carried out in the Mediterranean region, particularly in Lebanon and Turkey, where over 50 million young cedars are being planted annually.

The Lebanon Reforestation Initiative has been working with tree nurseries throughout Lebanon since 2012 to grow stronger seedlings with higher survival rates.

Turkey

Of the country's 78 million hectares of land in total the Ministry of Agriculture and Forestry aims to increase Turkey's forest cover to 30% by 2023.

4000 years ago Anatolia was 60% to 70% forested. Although the flora of Turkey remains more biodiverse than many European countries deforestation occurred during both prehistoric and historic times, including the Roman and Ottoman periods.

Since the first forest code of 1937 the official government definition of 'forest' has varied. According to the current definition 21 million hectares are forested, an increase of about 1 million hectares over the past 30 years, but only about half is 'productive'. However, according to the United Nations Food and Agriculture Organization definition of forest about 12 million hectares was forested in 2015, about 15% of the land surface.

The amount of greenhouse gas emissions by Turkey removed by forests is very uncertain. As of 2019 however a new assessment is being made with the help of satellites and new soil measurements and better information should be available by 2020.

According to the World Resources Institute "Atlas of Forest Landscape Restoration Opportunities" 50 million hectares are potential forest land, a similar area to the ancient Anatolian forest mentioned above. This could help limit climate change in Turkey. To help preserve the biodiversity of Turkey more sustainable forestry has been suggested. Improved rangeland management is also needed.

National Forestation Day is on 11 November but, according to the agriculture and forestry trade union although volunteers planted a record number of trees in 2019, most had died by 2020 in part due to lack of rainfall.

North America

Canada

Natural Resources Canada (The Department of Natural Resources) states that the national forest cover was decreased by 0.34% from 1990 to 2015, and Canada has the lowest deforestation rate in the world. The forest industry is one of the main industries in Canada, which contributes about 7% of Canadian economy, and about 9% of the forests on earth are in Canada. Therefore, Canada has many policies and laws to commit to sustainable forest management. For example, 94% of Canadian forests are public land, and the government obligates planting trees after harvesting to public forests.

United States

Direct-sowing of seed in a burned area by the USFS, Idaho Panhandle National Forest

It is the stated goal of the US Forest Service (USFS) to manage forest resources sustainably. This includes reforestation after timber harvest, among other programs.

United States Department of Agriculture (USDA) data shows that forest occupied about 46% of total U.S. land in 1630 (when European settlers began to arrive in large numbers), but had decreased to 34% by 1910. After 1910, forest area has remained almost constant although U.S. population has increased substantially. In the late 19th century the U.S. Forest Service was established in part to address the concern of natural disasters due to deforestation, and new reforestation programs and federal laws such as the Knutson-Vandenberg Act (1930) were implemented. The U.S. Forest Service states that human-directed reforestation is required to support natural regeneration and the agency engages in ongoing research into effective ways to restore forests.

As for the year 2020, United States of America planted 2.5 billion trees per year. At the beginning of the year 2020, a bill that will increase the number to 3.3 billion, was proposed by the Republican Party, after President Donald Trump joined the Trillion Tree Campaign.

South America

Costa Rica

Through reforestation and environmental conservation, Costa Rica doubled its forest cover in 30 years.

Costa Rica has a long-standing commitment to the environment. The country is now one of the leaders of sustainability, biodiversity, and other protections. It wants to be completely fossil fuel free by 2050. The country has generated all of its electric power from renewable sources for three years as of 2019. It has committed to be carbon-free and plastic-free by 2021.

As of 2019, half of the country's land surface is covered with forests. They absorb a huge amount of carbon dioxide, combating climate change.

In the 1940s, more than 75% of the country was covered in mostly tropical rainforests and other indigenous woodlands. Between the 1940s and 1980s, extensive, uncontrolled logging led to severe deforestation. By 1983, only 26% of the country had forest cover. Realizing the devastation, policymakers took a stand. Through a continued environmental focus they were able to turn things around to the point that today forest cover has increased to 52%, two times more than 1983 levels.

An honorable world leader for ecotourism and conservation, Costa Rica has pioneered the development of payments for environmental services. Costa Rica's extensive system of environmental protection has been encouraging conservation and reforestation of the land by providing grants for environmental services. The system is not just advanced for its time but is also unparalleled in the world. It received great international attention.

The country has established programs to compensate landowners for reforestation. One of the main programs established in Costa Rica was the Forest Promotion Certificate in 1979 and is funded by international donations and nationwide taxes. The initiative is helping to protect the forests in the country, and is now helped pass both the Forest Law in 1986 and FONAFIFO in 1990 which insures the continuity of the conservation programs.

Peru

Approximately 59% of Peru is covered by forest. A history of political turmoil and the government's inability to enforce environmental regulations has led to the degradation of the forest and environment in Peru. A military coup in 1968 caused a loss of economic mobility in the Talara region and sparked a boom in illegal logging due to the lack of alternative economic opportunities. Illegal mining and logging operations are responsible for a great deal of Peru's deforestation and environmental damage. The Peruvian government has not been able to enforce an environmentally conscious mining formalization plan to protect the Amazon forest in the Madre de Dios region. The 1980s were known in Peru as the “lost decade” due to a nationwide internal conflict and severe economic crisis almost destroying the country and resulting in the state losing control over several regions. Many areas in Peru, including Madre de Dios, had no state presence until the government initiated a movement to ‘conquer and populate the Amazon,’ with the hopes of minimizing illegal and informal mining operations that had expanded in the region and were polluting the Amazonian rivers and the destroying of its forests.

Reforestation initiatives have expanded in the country since. In Peru, reforestation is essential to preserving the livelihoods of rural communities because much of the population relies on the forest in some way. Deforestation also disproportionally affects indigenous communities in Peru, which is why reforestation efforts are essential for the protection of many communities' livelihoods.

Sub-Saharan Africa

One plan in this region involves planting a nine-mile width of trees on the Southern Border of the Sahara Desert for stopping its expansion to the south. The Great Green Wall initiative is a pan-African proposal to "green" the continent from west to east in order to battle desertification. It aims at tackling poverty (through employment of workers required for the project) and the degradation of soils in the Sahel-Saharan region, focusing on a strip of land that is 15 km (9 mi) wide and 7,500 km (4,750 mi) long from Dakar to Djibouti. As of May 2020, 21 countries joined the project, many of them are directly affected by the expansion of the Sahara desert. It should create 10 millions green jobs by 2030.

In 2019, Ethiopia begun a massive tree planting campaign "Green Legacy" with a target to plant 4 billion trees in one year. In one day only, over 350 million trees were planted.

Organizations

Ecosia is a non-profit organisation based in Berlin, Germany, that has planted over 100 million trees worldwide as of July 2020.

Trees for the Future has assisted more than 170,000 families, in 6,800 villages of Asia, Africa and the Americas, to plant over 35 million trees.

Ecologi is an organisation that offers its members ways to support climate change solutions. This includes offsetting their carbon emissions and tree planting. So far over 50 million trees have been planted through Ecologi, as well a more than 2.2 million tonnes of CO2e reduced.

Wangari Maathai, 2004 Nobel Peace Prize recipient, founded the Green Belt Movement which planted over 47 million trees to restore the Kenyan environment.

Shanghai Roots & Shoots, a division of the Jane Goodall Institute, launched The Million Tree Project in Kulun Qi, Inner Mongolia to plant one million trees to stop desertification and alleviate global warming.

Team Trees was a 2019 fundraiser with an initiative to plant 20 million trees. The initiative was started by American YouTubers MrBeast and Mark Rober, and was mostly supported by YouTubers. The Arbor Day Foundation will work with its local partners around the world to plant one tree for each dollar they raise.

Trees For Life (Brooklyn Park) is a state based organisation, which was established back in 1981 and delivers conservation, revegetation and community training programs. It now has thousands of active supporters and energizes activity within communities.

Many companies are trying to achieve carbon offsets by nature-based solutions like reforestation, including mangrove forests and soil restoration. Among them are Microsoft and Eni. Increasing the forest cover of Earth by 25% will offset the human emissions in the last 20 years. In any case it will be necessary to pull from the atmosphere the CO2 that already have been emitted. However, this can work only if the companies will stop new emissions and stop deforestation.

Related concepts

A similar concept, afforestation, refers to the process of restoring and recreating areas of woodlands or forests that may have existed long ago but were deforested or otherwise removed at some point in the past or lacked it naturally (e.g., natural grasslands). Sometimes the term "re-afforestation" is used to distinguish between the original forest cover and the later re-growth of forest to an area. Special tools, e.g. tree planting bars, are used to make planting of trees easier and faster.

Another alternative strategy, proforestation, is similar as it can be used to counteract the negative environmental and ecological effects of deforestation through growing an existing forest intact to its full ecological potential.

Criticism

Competition with other land uses

Reforestation competes with other land uses, such as food production, livestock grazing, and living space, for further economic growth. Reforestation can divert large amounts of water from other activities. A map created by the World Resources Institute in collaboration with the IUCN identifies 2 billion hectares for potential forest restoration. It is criticised for including 900 million hectares of grasslands.

Environmental risks

Reforestation often has the tendency to create large fuel loads, resulting in significantly hotter combustion than fires involving low brush or grasses. Reduced harvesting rates and fire suppression have caused an increase in the forest biomass in the western United States over the past century. This causes an increase of about a factor of four in the frequency of fires due to longer and hotter dry seasons.

Effects on biodiversity

Reforesting sometimes results in extensive canopy creation that prevents growth of diverse vegetation in the shadowed areas and generating soil conditions that hamper other types of vegetation. Trees used in some reforesting efforts (e.g., Eucalyptus globulus) tend to extract large amounts of moisture from the soil, preventing the growth of other plants. The European Commission found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the former leads to irreversible effects in terms of biodiversity loss and soil degradation.

The effects reforestation has on biodiversity is not limited to just other forms of vegetation, it can affect all forms of living organisms all contained in the present ecosystem. Due to the major role trees have on ecosystems it is important to better understand components like the ecosystem, waterways, and species present in areas that are being re-planted. Prior research helps limit the depletion of biodiversity which can hinder medicinal discoveries, and alter gene flow in organisms.

Carbon stocks

There is also the risk that, through a forest fire or insect outbreak, much of the stored carbon in a reforested area could make its way back to the atmosphere. Furthermore, the probability that legacy carbon will be released from soil is higher in younger boreal forest. An example of this can be seen in the peatlands in Central Africa, which house an abundance of carbon in the mud called peat. Much like the forest fire or insect outbreak which can harm tropical rainforests, money can also be seen an incentive to harm forests and be paid off to protect it. The mudGlobal greenhouse gas emissions caused by damage to tropical rainforests may be underestimated by a factor of six. Additionally the effects of af- or reforestation will be farther in the future than those of proforestation. It takes much longer − several decades − for the benefits for global warming to manifest to the same carbon sequestration benefits from mature trees in tropical forests and hence from limiting deforestation. Some researchers note that instead of planting entirely new areas, reconnecting forested areas and restoring the edges of forest, to protect their mature core and make them more resilient and longer-lasting, should be prioritized.

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