Find your biggest tree

Why this matters

Every region on Earth has a champion-class size for each of its forest tree species — the maximum size that species reaches under near-ideal conditions, given centuries of relative quiet. Most champion-class trees on public land have already been catalogued; on private land, in less-visited corners of public forests, and in heavily-fragmented temperate-deciduous forest, plenty of large old trees are unmeasured and undocumented. Adding one is real work that real registries accept.

The four registries you can submit to:

• The American Forests Champion Trees National Register (United States) — tracks the largest specimen of each native and naturalised tree species nationally and by state^[1].
• The Ancient Tree Inventory (United Kingdom; Woodland Trust) — volunteer-collected register of large, ancient, and notable trees across the UK^[2].
• The BC Big Tree Registry (British Columbia, Canada; UBC Faculty of Forestry) — provincial register of large trees by species^[3].
• Monumental Trees — international, multilingual database covering most of Europe, parts of Asia, Australasia, and the Americas^[4].

If you live somewhere none of these covers, iNaturalist is the universal fallback: a geotagged photograph with a confirmed species ID is a permanent observation that will outlast every individual database^[6].

Step 1 — Choose your area

Pick a forested area you can reach within an hour: a local nature reserve, a corner of a national or provincial park, a wood at the edge of a town, a creek-line on private land you have permission to walk, an old farm boundary that was never cleared. Larger old trees often survive on edges, riparian corridors, and former field boundaries because those locations were skipped in past clearing.

Step 2 — Walk and look

Walk slowly through the chosen area. Look up. Compare crown sizes against your eye-line. The biggest crowns are visible above the surrounding canopy from a distance — they break the otherwise-even tree-tops in a way that draws the eye once you know to look. Pick the largest tree you can find.

If you have time, identify two or three candidates from the canopy view, then walk to each and inspect the trunk. The trunk is what you measure.

Step 3 — Measure DBH

DBH is “diameter at breast height,” the standard tree-size metric. The convention is the diameter of the trunk at 1.37 m (4 feet 6 inches) above the ground on the uphill side of the tree.

1. Stand on the uphill side of the trunk if the ground is sloped.
2. Mark a point on the trunk 1.37 m above the ground using your tape held vertically.
3. At that height, wrap your tape horizontally all the way around the trunk and read the circumference in centimetres.
4. DBH = circumference ÷ π (3.1416). Or use a phone calculator: a 314 cm circumference is a 100 cm DBH.

If the tree forks below 1.37 m, treat each fork as a separate tree and measure the larger one above the fork. If the trunk has a buttress or root flare extending above 1.37 m (large old redwoods, old cedars, fig trees, baobabs), measure above the buttress, and note that you did so.

The Native Tree Society has a thorough open guide to all the edge cases^[5].

Step 4 — Estimate height (optional)

Height is harder to measure accurately and is genuinely optional for a first submission. The simplest method, accurate to within a few metres on most trees:

1. Use a clinometer app on your phone to measure the angle from your eye to the top of the tree.
2. Measure your distance from the trunk with the same tape you used for DBH.
3. Height ≈ (distance × tan(angle)) + your eye height.

For ambitious teenagers, the “sine method” described in the Native Tree Society guide is more accurate but requires three measurements and a bit of trigonometry^[5].

Step 5 — Identify the species

If you do not already know the species:

1. Photograph the bark, a leaf or needle (collect a fallen one; do not pick), and any cones, flowers, or fruit.
2. Use the Seek app (free, on-device, no account) for an instant suggestion.
3. Verify against an authoritative reference for your country — the project card on reading the forest lists the references that count.

Step 6 — Photograph the tree

1. One wide photograph: the whole tree, with you or another person standing at the base for scale.
2. One trunk close-up at chest height showing bark texture clearly.
3. One foliage close-up of a single representative leaf, needle, or twig.
4. One ground-level photograph showing the root flare, if visible.

Step 7 — Record the location

Record GPS coordinates from your phone (any compass or maps app). Round to two decimal places (about 1 km precision) for any registry submission you are uncertain about — trees small enough to be poached or photographed unsafely should never have their precise coordinates published. Larger old trees on managed public land can be submitted at full precision.

Step 8 — Submit

Pick the registry that fits. Submit:

• Species (scientific name, with common name if known)
• DBH in centimetres
• Height in metres (if measured)
• Approximate location (round coordinates if appropriate)
• Date measured
• Your name (or anonymous, depending on the registry)
• The four photographs

If the registry has nothing close to your size, congratulations: you have just contributed a real data point to the long-term record. If the registry already has a larger one nearby, congratulations: you now know what the regional champion-class size is for that species, and you have a personal benchmark for the next one.

Why this is real work

Tree registries are largely volunteer-collected. Champion trees are taken down by storms, fire, and disease. Old champions die; new ones need to be found and measured to update the record. Your single afternoon is one observation. The aggregate of these observations across one country is the only way the record stays current. The American Forests register has been updated continuously since the 1940s by the same kind of volunteer measurement^[1]; nobody else does it for them.