There is a maximum height for a tree
A REDWOOD has to lift water from its roots to its topmost needles, and it has no pump. The water is pulled up in unbroken threads by evaporation from the leaves at the top, with the whole column hanging together by the stickiness of water to itself.
That only works up to a point. Climbers who measured the tallest redwoods found the summit needles small, stiff and short of water compared with those lower down, and calculated a ceiling around 130 metres — above which the pull simply breaks. The tallest tree ever reliably measured comes in just under that. It is not a coincidence, and it applies to every tree on Earth.
Holly only grows prickles where it is bitten
Look up at a HOLLY tree rather than at the branch in front of you. The leaves within reach of a deer or a cow are armed with spines; the leaves higher up the same tree are often smooth-edged ovals with barely a point on them.
The tree is responding to being eaten. Damage to the lower leaves triggers the prickly form in the leaves grown afterwards, and the change involves chemical tags on the DNA rather than any change to the genes themselves. It is one of the easiest pieces of plant behaviour to see on an ordinary walk, and one of the strangest: a tree that remembers being bitten and builds armour at the right height.
An oak is a block of flats
A mature OAK supports more forms of life than any other tree in Britain — surveys put the number of associated species at well over two thousand, several hundred of which are found on oak and nowhere else. Caterpillars, beetles, gall wasps, lichens, fungi, bats in the splits, birds in the holes, and a layer of things eating all of those.
Age is part of it. An oak may take 300 years to grow, spend 300 years mature and 300 years slowly dying, and the dying stretch is the busiest, because rot holes and dead limbs are exactly what most of those species need. A tidy tree surgeon removing the dead wood from a veteran oak can empty it out.
The tree that vanished from the paintings
The ELM in this grid is largely a historical entry. Tall elms lined English hedgerows and fill nineteenth-century landscape paintings; then a beetle carrying a fungus arrived in infected timber, and between the late 1960s and the 1980s something like twenty-five million of them died.
The species is not extinct — roots survive and throw up saplings, which grow to hedge height and then get found by the beetle again. Anyone who remembers the trees remembers them; anyone born since has mostly never seen a full-grown one. The ASH is now going through its own version with a different fungus, and is worth a look before it too becomes a tree that used to be everywhere.
Reading the grid, and the rings
The broadleaves are here — OAK, MAPLE, BIRCH, BEECH, ELM, ASH, WILLOW, POPLAR, ASPEN, SYCAMORE, CHESTNUT, WALNUT, HAZEL, HAWTHORN and ROWAN — with the evergreen PINE, SPRUCE, FIR, CEDAR, CYPRESS, JUNIPER and HOLLY, plus the REDWOOD and the PALM.
Cut any of them through and the rings record the weather: wide in a kind year, narrow in a hard one. Because every tree in a region shares that pattern, overlapping samples from living trees, old beams and bog timber can be chained backwards thousands of years — which is how a roof is dated to a particular decade, and how radiocarbon dating was itself checked against something countable.