Why the Trees Are Telling You Something

Stand still beside an old oak for a minute and look properly at the bark. Chances are you will see more texture than wood: soft green cushions, feathery grey tufts, flat crusty patches in mustard and chalk-white. Mosses and lichens are the quiet tenants of British woodland, and once you can name a few of them you gain a sixth sense for the health and history of a wood.

Neither group is a parasite in the way people often fear. Lichens are partnerships between fungi and algae, and mosses are simple plants without proper roots or a water-carrying plumbing system. They take their water and nutrients from the air, which is why they are so revealing. A wood rich in leafy lichens is usually a wood with clean air and a long continuity of trees. A wood with mostly crusty, pollution-tolerant species tells a different story.

Getting Your Eye In Before You Get Your Key Out

Identification starts with honest looking, not with a book. Take a hand lens of 10x to 20x, a small soft brush, and a notebook. Dress for the weather and remember that many species are only identifiable when damp, so a misty morning or a light spray from a water bottle is your friend.

Work through a simple sequence on each tree:

• Where is it growing? Base of the trunk, mid-trunk, upper branches, twigs, exposed roots, or on the sheltered side? Many species are strict about this.
• What shape is it? Leafy and shrubby, flat and scaly, crusty and painted-on, or gelatinous and jelly-like.
• What colour? Note whether it is grey-green, yellow-green, orange, white, or dark grey-black.
• How does it attach? Crusty lichens cannot be lifted without taking bark with them. Leafy ones peel away. Shrubby ones hang or stand out in tufts.
• Any fruit bodies? Look for cups, discs, or pinheads. A 10x lens turns a plain grey patch into a map of tiny saucers.

Record the tree species too. Ash, oak, willow, and elder all carry recognisably different communities, and a species that is common on one may never appear on another.

Common Mosses on UK Bark

Mosses are the easier starting point. You can usually identify four or five characteristic species without a keying headache.

• Common Feather-moss (Kindbergia praelonga) forms loose, feathery green mats on tree bases and damp soil. The stems look like tiny fern fronds held flat.
• Rough-stalked Feather-moss (Brachythecium rutabulum) is the default green moss on many trunks. It is robust, slightly glossy, and the shoot tips curve like small hooks.
• Common Tamarisk-moss (Thuidium tamariscinum) is unmistakable when you see it: fern-like, neatly divided, and arranged in flat tiers of yellow-green.
• Silver-moss (Bryum argenteum) looks like tiny silver-green beads and thrives on exposed bark and stone in drier, dustier spots.
• Common Haircap (Polytrichum commune) is more often on the woodland floor, but its stiff, starry rosettes turn up on stumps and rotting roots.

If a moss is growing on a trunk in a low, dense, dark-green cushion, look for the tiny sporophytes. The shape and angle of the capsule, and whether it nods or stands straight, is often the deciding feature.

Lichens That Reward a Second Look

Lichens divide usefully into three growth forms: crusty, leafy, and shrubby. Learn a couple from each and you have a working framework for any British wood.

• Common Greenshield (Flavoparmelia caperata) is a large, leafy, yellow-green lichen with a wrinkled, slightly lobed edge. It is a good sign of cleaner air and older trees.
• Parmotrema species look similar but often have grey-green lobes edged with fine hairs or cilia. Use your lens along the margins.
• Oakmoss (Evernia prunastri) is the classic shrubby, strap-like lichen, grey-green above, paler beneath, soft and thong-like. It drapes over branches and releases a faintly sweet, woodland smell when damp.
• Ramalina species have stiff, hollow, branching thalli, usually grey-green and growing upright from bark and twigs.
• Physcia and Xanthoria are orange or grey foliose lichens typical of nutrient-enriched bark, so expect them on roadside trees and elder.
• Crustose species such as Lecanora and Pertusaria paint the bark in grey, white, or ochre. Their spot-like fruiting bodies need a steady hand and good light to see.

Reading the Wood Through Its Species List

The real pleasure is in what the list means. Shrubby lichens such as oakmoss and the hair lichens require long, clean, damp air, and they are often absent from woods that have been around for only a century or that sit in polluted valleys. A trunk covered in Evernia, Ramalina, and leafy Parmelia species is usually the sign of a genuinely old site with a continuous canopy.

Mosses tell you about moisture and structure. Deep, damp, shaded ravines and north-facing trunks carry the richest communities, while exposed ridges and dry bark support only the toughest pioneers. Neither mosses nor lichens should be harvested from trees casually, and if you do take a small sample for study, take it from windblown material or loose bark rather than living wood.

Building a Simple Practice

Choose one tree you can visit often and follow it through the seasons. Photograph the same patch of bark each month, note the weather, and sketch what has changed.

• Start with four species only: a feather-moss, a leafy lichen, oakmoss, and a crusty patch.
• Learn one new species each outing rather than chasing ten at once.
• Keep a small card of key features in your pocket and write the tree species beside every record.
• Use a x10 hand lens in the field and check tricky material at home with a x20.

Within a year you will read a trunk the way you read a field margin: not as a blank surface, but as a record of air, age, water, and time. That is woodcraft of a quietly useful kind, and it costs nothing but attention.