Reading the forest

If you remember three things from this primer, take these: most forests have only a handful of dominant tree species; you can usually name them after a few weekends of attention; and the difference between a young plantation and an old-growth stand is something you can learn to see, not something only a specialist can.

Identify the species first

Pick a single forested area near you and treat it as your home patch. Spend three or four walks just looking at the dominant trees. In any temperate forest there are usually three to seven species that account for 80 to 95% of the canopy — once you can name those, the forest stops being green wallpaper and becomes a place with structure.

The fastest free tool for this in 2026 is Seek, made by iNaturalist. It runs entirely on your phone, requires no account, no signup, no data sharing, and uses on-device computer vision to suggest species IDs from a photograph^[2]. Aim it at a leaf, a piece of bark, or a fallen seed pod, wait a moment, and it gives a confidence-rated identification you can verify against photographs. It is not perfect — especially for closely related conifers and ambiguous broadleaves — but it is right far more often than not, and on a 30-minute walk you can ID most of what you see.

Once you have a candidate, verify against a real botanical reference. The Royal Botanic Gardens at Kew publishes Plants of the World Online (POWO) as a fully free authoritative species database for the entire global flora^[4]. In the U.S., the USDA NRCS PLANTS database is the federal reference for native and naturalised species^[3]. In the UK, Forest Research publishes downloadable identification field guides^[5]. For most other countries the national arboriculture or forestry research body publishes something equivalent.

If you want to upgrade beyond Seek, install the full iNaturalist app and submit your observations research-grade — that is, with confirmed species ID by another user. Your observations then become part of an open dataset used by ecologists everywhere^[1]. The library’s project card on becoming an iNaturalist contributor walks through how.

Read the structure

Once you can name the trees, look for the structural indicators of forest age. The five from the foundational primer are the ones that matter:

1. Big living trees, near the regional maximum. Learn the regional “champion-class” size for your dominant species and look for individuals approaching it. In Pacific Northwest old growth Douglas-fir reaches 200 cm DBH; in Appalachian eastern hemlock 100 cm; in Mediterranean cork oak 70 cm. The number is regional but the principle is universal.
2. Standing dead trees of every size and decay class. A working forest gets snags removed; old growth keeps them. Count the snags on a 100 m walk; the number is diagnostic.
3. Coarse woody debris on the floor. Big logs at multiple stages of decay, often with seedlings growing from their tops. Plantation forest is conspicuously clean of these; mature natural forest is not.
4. Multi-layered canopy. Look up. If you see one continuous layer with no emergent giants, no mid-canopy, no suppressed understory, you are in plantation. If you see five or six distinct vertical layers including mosses and lichens, you are in old or near-old forest.
5. Mixed-age structure. Are there trees of multiple generations on the same hectare, with younger cohorts filling gaps where bigger trees fell? That mixed-age structure is what continuous old growth looks like; even-aged stands of one cohort are typically post-clearcut or post-fire.

Read the age (without coring)

Field-coring a tree to count its growth rings is the precise way to age it; it is also invasive (a small wound the tree has to heal) and most readers should not do it. Three non-invasive proxies get you most of the way:

Bark texture. Most temperate species change bark texture in characteristic ways with age. Young Douglas-fir has smooth grey bark; mature trees have deeply furrowed reddish-brown bark with corky plates an inch or more thick. Young oak has smoother bark; old oak has the classic deep-ridged bark with deep fissures. Learn the bark stages of one or two of your dominant species first.

Crown shape and architecture. Young conifers have a single dominant leader and a clean conical shape. Mature conifers have a more rounded or flattened crown, often with multiple dominant leaders, broken or dead-topped tops, and visibly weathered branches. Young broadleaves grow into the canopy; mature broadleaves spread laterally and have characteristically heavier limbs.

Diameter at breast height (DBH). Tree species in a given climate have known approximate growth-rate curves. A 60 cm DBH eastern hemlock in upstate New York is roughly 150 to 200 years old; a 60 cm DBH Douglas-fir on the BC coast is roughly 100 years old. The International Society of Arboriculture publishes regional growth-rate references that let you back into approximate ages from DBH^[5].

Read the decay

Trees are not either “healthy” or “dying” — they are constantly doing both. The signs to learn:

Healthy: dense crown of foliage at expected density, complete bark coverage, no large dead branches in the lower crown, no wounds with active discharge, no fungal fruiting bodies on the trunk except small ones in normal locations.

In decline: patchy or thin crown, multiple large dead branches, peeling or sloughing bark, conks (large mushroom-like fungi) growing from the trunk, deep fissures or wounds in the trunk, lean toward the prevailing wind direction.

Decline is not necessarily bad — declining trees become snags, snags become standing dead, standing dead falls and becomes coarse woody debris, and that material feeds the next generation of forest. The presence of trees in active decline is a signal of health at the stand level, even when the individual tree itself is dying.

What this turns into

Once you can do the four tasks above — name the species, read the structure, estimate the age, recognise the decay class — a walk in the woods stops being passive. You can tell whether the forest you are in is plantation, second-growth, mature, or old growth. You can tell whether it is recovering or being degraded. You can have a real conversation with anyone managing the land about what is or is not appropriate.

And, more selfishly: every walk afterwards is better. You stop missing things.