Record it so it survives the winter

The five things worth writing down

• Position, precisely. Not "the park" — a grid reference, or a what3words, or the nearest gate plus a bearing and a distance. A tree you cannot find again is a tree you cannot check when it fruits.
• Which tree. In a stand of forty birches, mark the one you mean. A strip of surveyor's tape on the trunk, photographed, costs nothing and settles the question later.
• The characters you actually saw. Leaf, bark, fruit — and note which of them you had and which you did not. "Bark only" is a legitimate record and tells the next reader exactly how much weight to put on it.
• Height and girth as measurements, not adjectives. "Tall" means nothing. A clinometer or a laser gives a height; a tape around the trunk at 1.3 m gives a girth. Two numbers, six months apart, are a growth record.
• What was on the tree. Galls, mines, cankers, bleeding patches, dieback. These are half of what a species record is worth — and a bleeding canker photographed in June is a diagnosis you can act on, where a note saying "looked poorly" is not.

Photograph the right four things

One leaf, flat, on a plain background with something for scale. One patch of bark at chest height, in flat light rather than direct sun — sunlight on bark hides the surface texture that the whole bark character depends on. One fruit or seed, whole and in cross-section if it is a cone or a nut. And one shot of the whole tree from far enough back that its shape reads. Nothing else is needed, and a hundred shots of foliage will not replace these four.

Measure the leaf properly, once

The plates in this library are drawn from five numbers: the number of teeth along the margin, the depth of those teeth as a fraction of the blade's half-width, the number of vein pairs, the aspect ratio of length to width, and petiole length as a fraction of blade length. You do not need all five to make an identification. But you do need to measure the same leaf you photographed, and to say which leaf it was — sun leaf, shade leaf, or one from a stump sprout, because those three can differ by a factor of two in every one of those numbers.

Two trees that get confused for the wrong reason

The most common error in the field is not a mistaken species, it is a mistaken tree. Two people standing in the same wood, arguing about whether a leaf is sessile oak or English oak, are usually describing two different trees. Measure the petiole on the same leaf you looked at the acorn from, and the argument ends. The second most common error is ignoring the rootstock: a grafted ornamental in a park carries the foliage of one species on the trunk of another, and a record that reads the trunk and the leaf as one organism will be wrong in a way that is very hard to see from the note alone.

Worked examples

Each dossier on this site ends with a field-notes panel giving the specific thing to check for that species — what to measure, which symptom is diagnostic, and which lookalike to rule out first. Four to start with:

• Sycamore maple — Sycamore seedlings establish in deep shade, which oak and ash seedlings cannot, so a wood with sycamore saplings under a closed canopy is quietly converting to sycamore.
• Silver birch — A birch with a forked twin trunk or a bushy 'witches broom' in the crown is worth recording.
• English oak — Sudden oak death and acute oak decline both show first as black bleeding patches on the trunk with a dark fluid seeping out.
• Eastern white cedar — In the far north this tree can be far older than its size suggests: a 15 cm trunk has been aged at over 400 years on cliff faces.

Then file it

A record you keep is worth more than a record you make. Put the same five things in the same order every time, whether that is a notebook, a spreadsheet or a national recording scheme — the format matters far less than the repetition. And revisit: an identification you can check in a different season is the only one that ever becomes certain.

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