Tree Planting CO₂ Sequestration Calculator

Frequently Asked Questions

• How much CO₂ does a tree absorb?+
  Less certainly than most planting websites suggest, and the honest answer is a range that spans a factor of five. The US EPA equivalencies calculator credits a medium-growth urban tree with 0.060 tonnes — 60 kg — of CO₂ per tree per year, an average taken across the first ten years after planting and already weighted for the chance the tree dies (EPA assumes 59 per cent survival at ten years). That figure describes a dispersed street or garden tree with no competition, which grows faster than a tree in a stand. The widely quoted 21–22 kg (48 lb) a year is an Arbor Day Foundation and US Forest Service figure with no primary publication behind it. National inventories avoid per-tree numbers altogether: the IPCC 2006 Guidelines give above-ground growth per hectare — for a young tropical rain forest stand in continental Asia 7.0 tonnes of dry matter per hectare a year (Table 4.9), which at the default 0.47 carbon fraction (Table 4.3) is about 12 tonnes of CO₂ per hectare, or roughly 12 kg per tree at 1,000 stems a hectare and 30 kg at 400. The species presets on this page, 13 to 30 kg a year at maturity, sit inside that per-hectare band and deliberately below the open-grown urban figure; they are planning estimates, not measurements of your trees.
• Why do young trees absorb so little at first?+
  A newly planted sapling has very little leaf area and woody mass, so it captures only a fraction of what it will at maturity. Uptake ramps up as the tree grows, reaching its full rate after several years. The calculator models this with a growth ramp over roughly five years, so the cumulative curve starts shallow and steepens.
• Which species absorbs the most?+
  Fast-growing tropical species generally sequester carbon quickest in their early decades, followed by dense hardwoods, with slower conifers and fruit trees lower. Mangroves are remarkable for the carbon they lock into waterlogged soils. Pick the species group that matches your planting to get a representative rate.
• How long to offset a flight or my footprint?+
  Enter a footprint in kilograms of CO₂ — or arrive here from the flight or commute calculators, which pass the figure across automatically — and the tool shows two things: roughly how many of your chosen trees, working for a year at maturity, would absorb it, and how many years your actual planting would take to absorb it, marked on the growth curve.
• Does the calculator account for trees growing over time?+
  Yes. Rather than assuming every tree absorbs at its full mature rate from day one, it ramps young trees up over their first years, so the cumulative-absorption curve is an S-shape: slow at first, then steady. This gives a more honest picture than a flat annual rate.
• Is planting trees a reliable way to offset carbon?+
  It is valuable but imperfect. A tree only holds its carbon while it lives and stands; fire, disease, drought or felling can release it again, and the absorption takes years to decades. That makes tree planting a slow, somewhat reversible offset best seen as a complement to cutting emissions at the source rather than a substitute for it.
• Does soil carbon count?+
  Forests store substantial carbon in soil and roots as well as in the trunk and branches, and over the long term that can rival the above-ground store. The rates used here are broad whole-tree averages; detailed projects account for soil separately. Treat the figure as an estimate of the tree’s overall contribution.
• Should I protect existing forest or plant new trees?+
  Both matter, but protecting mature, intact forest usually delivers faster and more certain climate benefit, because those trees are already absorbing and storing large amounts of carbon that would be released if cleared. New planting is a long-term investment whose benefit builds over decades, as the growth curve shows.
• How accurate are these numbers?+
  They are broad estimates for understanding scale, not a certified carbon credit. Real sequestration varies widely with species, climate, soil, spacing, survival rate and management. Use the tool to grasp orders of magnitude and the time involved, and rely on verified project data for any formal offsetting.
• Why are these numbers lower than some tree-planting websites quote?+
  Three reasons, all deliberate. First, the growth ramp: this tool scales a sapling up to its full rate over five years instead of crediting a mature rate from the day it is planted, which alone cuts the first decade’s total by about a fifth. Second, it uses per-tree rates that sit inside the range implied by the IPCC per-hectare defaults rather than the most generous figure in circulation. Third, it counts nothing for survival — every tree is assumed to live — so if anything it still errs high: field studies of planting programmes routinely report losses of a quarter or more in the first years. A certified carbon project would model species, site, spacing, mortality and soil carbon explicitly; this page is for grasping scale and time.