What a tree is for.
Shade on a sidewalk, a city that is survivable in August, a planet that keeps its rain. The case for trees is usually made with adjectives. Here it is made with numbers, each one traceable, and with the figures for where you live first.
Or use my location (we think you're around Columbus, OH).
Where you live: Columbus, OH
Figures for your city, then your state or province, then your country. Each links to the report it came from.
Ohio
- Air
Trees in Ohio's urban areas removed about 24,500 tonnes of air pollution in 2010, with human health benefits valued at $205 million.
Nowak et al. 2014, Tree and forest effects on air quality and human health in the United States, Environmental Pollution, 2010 · i-Tree Eco modeling with BenMAP health valuation, urban land only
- Carbon
Trees in Ohio's urban areas store about 22.9 million tonnes of carbon and take up roughly 739,000 tonnes more each year; counting all urban and community land, storage rises to 32.3 million tonnes.
Nowak et al. 2013, Carbon storage and sequestration by trees in urban and community areas of the United States, Environmental Pollution, 2013 · Carbon density per unit tree cover applied to statewide urban tree cover, c. 2005; gross sequestration
- Energy
Ohio's urban and community trees save residents about $335 million a year in building energy costs ($92.3 million in electricity and $243 million in heating).
Nowak et al. 2017, Residential building energy conservation and avoided power plant emissions by urban and community trees in the United States, Urban Forestry & Urban Greening 21, 2017 · Statewide modeling of tree shade, wind and temperature effects on residential buildings
United States
- Air
Trees in US urban areas alone removed about 651,000 tonnes of air pollution in 2010, worth $4.7 billion in avoided health costs.
Nowak et al. 2014, Tree and forest effects on air quality and human health in the United States, Environmental Pollution, 2010 · i-Tree Eco modeling; most health value accrues in urban areas
- Canopy
The United States has about 5.5 billion urban trees, and tree canopy covers 39.4% of the nation's urban land.
Nowak & Greenfield 2018, US Urban Forest Statistics, Values, and Projections, Journal of Forestry 116(2), 2018 · Photo-interpreted tree cover combined with field-plot tree densities
- Canopy
US urban land is projected to grow by 95.5 million acres between 2010 and 2060, from 68.0 million to 163.1 million acres (8.6% of the country), putting more forest and farmland under pavement.
- Canopy
US urban and community tree cover fell by about 175,000 acres a year between roughly 2009 and 2014, a loss of some 36 million trees a year and $96 million a year in lost benefits, while impervious cover rose.
Nowak & Greenfield 2018, Declining urban and community tree cover in the United States, Urban Forestry & Urban Greening 32 (USDA Forest Service Treesearch), 2018 · Paired aerial photo interpretation, c. 2009 to 2014
- Canopy
Urban land in the lower 48 states grew from 2.5% of the land area in 1990 to 3.1% in 2000 and is projected to reach 8.1% by 2050, an increase larger than Montana.
Nowak et al. 2010, Sustaining America's Urban Trees and Forests, USDA Forest Service GTR-NRS-62, 2010
- Carbon
Trees in US urban areas store about 643 million tonnes of carbon, valued at $50.5 billion, and sequester another 25.6 million tonnes a year worth $2.0 billion.
Nowak et al. 2013, Carbon storage and sequestration by trees in urban and community areas of the United States, Environmental Pollution, 2013 · Field data from 28 cities and 6 states applied to statewide urban tree cover, c. 2005
- Cooling
US urban areas run about 1 to 7°F warmer than outlying areas during the day and 2 to 5°F warmer at night, and air-conditioning demand rises 1 to 9% for every 2°F of warming.
- Cooling
Tree shade lowered wall and roof surface temperatures by 20 to 45°F in a multi-month EPA-cited study, and suburbs with mature trees are 4 to 6°F cooler than new suburbs without trees.
US EPA, Reducing Urban Heat Islands: Compendium of Strategies, Trees and Vegetation chapter, 2008
- Money
US urban forests deliver about $18.3 billion a year in benefits: $5.4 billion from air pollution removal, $5.4 billion from reduced building energy use, $4.8 billion from carbon sequestration and $2.7 billion from avoided power-plant emissions.
Nowak & Greenfield 2018, US Urban Forest Statistics, Values, and Projections, Journal of Forestry 116(2), 2018 · i-Tree based national estimates
- Energy
Urban and community trees in the lower 48 states cut residential energy bills by about $7.8 billion a year ($4.7 billion in electricity, $3.1 billion in heating), a 7.2% reduction in residential energy use, plus $3.9 billion a year in avoided power-plant emissions.
Nowak et al. 2017, Residential building energy conservation and avoided power plant emissions by urban and community trees in the United States, Urban Forestry & Urban Greening 21, 2017 · Modeled shade, wind and air-temperature effects of trees near buildings
- Health
The CDC recorded an average of 702 heat-related deaths a year in the United States from 2004 to 2018.
- Health
Trees and forests in the lower 48 states removed 17.4 million tonnes of air pollution in 2010, avoiding more than 850 deaths and 670,000 cases of acute respiratory symptoms, with health benefits valued at $6.8 billion.
Nowak et al. 2014, Tree and forest effects on air quality and human health in the United States, Environmental Pollution, 2010 · i-Tree Eco dry-deposition modeling with EPA BenMAP health valuation
- Survival
A review of 56 urban tree mortality studies found median annual mortality of 6.6% to 7% in the first five years after planting, and about 2.5% a year for established street trees across all study designs.
Hilbert et al. 2019, Urban Tree Mortality: A Literature Review, Arboriculture & Urban Forestry 45(5), 2019
- Survival
A meta-analysis of US street tree studies found annual survival rates of 94.9% to 96.5%, meaning a planted street tree population loses half its trees in 13 to 20 years and a street tree's mean life expectancy is 19 to 28 years.
Roman & Scatena 2011, Street tree survival rates: meta-analysis and Philadelphia field survey, Urban Forestry & Urban Greening, 2011 · Meta-analysis of 16 studies assuming constant annual mortality
What one tree does for a house and a block
The benefits closest to home are the ones you can feel in July.
Shade matters more than air temperature. Surfaces under tree canopy can run 11 to 25 °C (20 to 45 °F) cooler than the same material in full sun, which is why a shaded sidewalk is walkable and a bare one is not.
Trees placed on the west and south of a house cut summer cooling energy; US studies put the saving between 7 and 47 percent depending on climate and placement.
US EPA, Reducing Urban Heat Islands: Compendium of Strategies, Trees and Vegetation chapter
A large tree moves a lot of water. A mature oak can transpire more than 40,000 gallons (150,000 liters) a year, water that would otherwise run off streets or sit in the ground.
USGS Water Science School, Evapotranspiration and the Water Cycle
Street trees are tied to how people feel. In Toronto, ten more trees on a city block was associated with health perception comparable to being seven years younger or earning $10,000 more a year.
Losing trees shows up in the death statistics. Across 15 US states, the arrival of the emerald ash borer and the loss of ash trees was associated with an additional 6,113 deaths from lower-respiratory illness and 15,080 from cardiovascular disease over 18 years.
Donovan et al. 2013, American Journal of Preventive Medicine
What a canopy does for a city, a watershed and a farm belt
At the scale of a city the effects stop being comfort and start being infrastructure.
US urban trees remove about 17.4 million tonnes of air pollution a year, with health benefits valued at $6.8 billion, including roughly 850 avoided deaths and 670,000 avoided cases of acute respiratory symptoms.
The US is losing urban tree cover: about 175,000 acres (71,000 hectares) a year between 2009 and 2014, replaced mostly by impervious surface, at an estimated cost of $96 million a year in lost benefits.
Nowak and Greenfield 2018, Urban Forestry and Urban Greening
Across 93 European cities, raising tree cover to 30 percent would have cooled summers by about 0.4 °C and prevented roughly a third of heat-attributable deaths in 2015, 2,644 of 6,700.
Land under urban trees in European cities runs 8 to 12 °C cooler than treeless urban land in Central Europe in summer, two to four times the cooling that grass gives.
Trees in fields are agriculture, not decoration. Maize grown under Faidherbia albida in African parklands yields two to three times more than maize in the open, because the tree drops nitrogen-rich leaves at planting time.
Mangroves protect more than 15 million people a year from flooding and avert $65 billion in property damage worldwide; coastal cities and farms sit behind them.
What forests do for everyone
The global numbers are large and worth stating plainly, with the arguments attached.
Forests cover 4.06 billion hectares, 31 percent of the world's land. The world lost a net 4.7 million hectares a year in the 2010s, down from 7.8 million a year in the 1990s, because planting and natural regrowth offset some of the clearing.
The world's forests take up about 2.4 billion tonnes of carbon a year, around a quarter of what people emit, and hold roughly 860 billion tonnes in trees and soil.
Forests are a net sink of about 7.6 billion tonnes of CO2 a year once clearing is subtracted, roughly 1.5 times the annual emissions of the United States.
Restoration potential is real and contested. A 2019 estimate found room for 0.9 billion hectares of extra canopy outside farms and cities; later responses argued it overstated carbon gains and risked treating grasslands and savannas as empty. Where you plant matters as much as how much.
Forests make rain downwind. Moisture transpired by trees falls again as precipitation over land; in the Amazon, Congo and East Asia, 30 to 50 percent of rainfall is recycled through vegetation.
Forests hold most of the world's land-based species: more than 80 percent of amphibians, 75 percent of birds and 68 percent of mammals that live on land.
Why planting is the easy part
A tree that dies in its second summer delivered none of the above. Maintenance is where the benefits are decided.
About half of newly planted urban trees do not survive their first decade or two; a review of 16 studies found annual mortality highest in the first five years, driven by water, soil and neglect rather than species.
Street trees live short lives: a synthesis of US studies found a mean life expectancy of 19 to 28 years for street trees, with a 3.5 to 5.1 percent annual mortality rate.
Watering is the whole job early on. Most municipal guidance converges on 15 to 20 gallons (55 to 75 liters) a week in the first two growing seasons, applied slowly at the root zone.
USDA Forest Service, Urban and Community Forestry guidance, summarized across city programs
The benefits scale with size. A large healthy tree provides many times the shade, interception and pollution removal of a sapling, so keeping a 40-year-old tree alive is worth more than planting a dozen new ones in its place.
More figures
From the facts table, which grows as we add places. Browse all facts.
- Air
Investing about US$4 per urban resident a year in street trees across 245 of the world's largest cities could save tens of thousands of lives a year through cleaner, cooler air.
- Wildlife
At least 1.11 billion hectares of primary forest remained in 2020, 81 million hectares less than in 1990.
- Wildlife
About 726 million hectares of forest were inside protected areas in 2020, 191 million hectares more than in 1990.
- Wildlife
Forests are home to about 80% of amphibian species, 75% of bird species and 68% of mammal species, plus 60,082 known tree species.
- Canopy
Forests are still being lost to deforestation at nearly 11 million hectares a year, while legally protected forests now cover one-fifth of all forest area (FRA 2025).
- Canopy
Tropical primary forest loss hit 6.7 million hectares in 2024, nearly double 2023 and equal to 18 soccer fields every minute.
World Resources Institute / Global Forest Watch (University of Maryland GLAD data), 2024
- Canopy
The world had about 4.06 billion hectares of forest in 2020, nearly one-third of all land and about 0.52 hectares per person.
- Canopy
The world lost a net 4.7 million hectares of forest a year in 2010-2020, down from 7.8 million hectares a year in the 1990s.
- Canopy
About 10 million hectares of forest were cleared each year in 2015-2020, down from 12 million hectares a year in 2010-2015.
- Canopy
An estimated 420 million hectares of forest were converted to other land uses between 1990 and 2020.
- Canopy
Earth has about 3.04 trillion trees, over 15 billion are cut down each year, and the total has fallen roughly 46% since the start of human civilization.
Crowther et al. 2015, Nature, 'Mapping tree density at a global scale', 2015
- Carbon
For the first time on record, fire was the leading cause of tropical primary forest loss in 2024 (nearly 50% of it), and forest fires worldwide emitted 4.1 gigatonnes of greenhouse gases.