For an ecologist, fieldwork is a pleasure. In autumn it is a bittersweet pleasure. The day itself will be a quiet joy like other field days, but the weakening sun, lengthening shadows and changing colours remind us that such pleasures will soon be curtailed, until spring, when buds will start bursting forth once more.

It was in search of such bittersweet pleasure that, some years ago, I set out with a colleague, Victoria, on a research trip to survey some lime trees. We were studying two British species of limes that grow in close proximity in the same wood, trying to understand how separate they were. Did they co-exist as two distinct species, small-leaved lime and large-leaved lime? Or did they take advantage of this proximity, of overlapping flowering times and shared pollinators, to cross-fertilise and merge into one?

A line of isolated magical woods, roughly situated on the English–Welsh border from Shropshire down to the lower reaches of the Wye Valley, is where this question is best answered and hence our destination. On this day we were in Worcestershire. Bordered by hills to the east and west, split by two of the great English rivers, the Severn and the Avon, and retaining a mixture of grassland, arable fields, orchards and woodland, it is perhaps the quintessential English lowland county. Its patchwork would still be recognised by Piers Plowman as the one he viewed from the Malverns in the fourteenth century. Travelling through the narrow lanes, autumn had clearly begun to show its hand. Late morning and there was still dew on the vegetation, while in the hedgerows green was beginning to retreat from the leaves.

The Knapp and Papermill Nature Reserve is a microcosm of the county. It is entered via a narrow path that ascends up a short rise to reveal an old orchard, where burnished apples are starting to fall from the boughs. This gives way to grassland, untouched by the intrusion of late twentieth-century agriculture, although the season was leaving its mark. The straw-coloured grass dropped its seed as we walked through it to admire more closely the purple-red of the knapweed flowers. To the left is a narrow stream. To the right is a steep slope, bearing a wood that is a relic of the virtually continuous verdant cover that once sprawled over the land. It is this wood, or rather its limes and their sexuality, that we had come to study.

The English have a confused relationship with woodlands. Plans to limit public access or to grub out parts of them for development are seen as an outrage, evoking strong resistance. At the same time, we see them as sources of danger; from childhood we are warned of them, through fairy stories, as places where people are easily lost or abducted. Nature resides there, but a nature that is wild and sometimes life-threatening.

Individual trees also elicit a strong emotional response, and limes are among the most beloved. When I first started to study them, I thought this was a product of their rarity. They are invariably found in special, secretive places; a relic of pre-human Britain, when such trees covered most of the land. Thus to find limes is to briefly glimpse the world as it appeared to our ancestors.

This cannot be the full story, however. Lime-lovers abound even without this historical ecological perspective. Perhaps it is the trees themselves: typically immense structures with dense canopies of abundant foliage, supported by huge, stout trunks, that in turn rely upon rock-grasping roots. These trees continue to exist as they have done for centuries, roots and leaves miraculously extracting the chemicals for life; they have broken time’s arrow and to encounter them is to gain a brief glimpse of immortality.

Perhaps our affection is an echo of the folklore that surrounds them. Across various parts of Europe the tree represents justice, health, fertility and romance. In Germany, the romantic association inspired the famous medieval poem Unter der Linden by Walter von der Vogelweide, which tells of the secret tryst between a knight and a peasant girl. Perhaps that connection lies in the shape of the leaves themselves – photosynthetic hearts suspended overhead.

It is these hearts we had come to collect, to extract DNA and thus determine the relationship between the trees. We also mapped their locations, measure trunk size and growth form to help form a fuller picture. A picture of past unions and tangled relationships. We carefully paced out our survey area. The steep rocky slope made movement through the wood difficult, but once we found our targets we fell to work quickly. Although we had never been in the field together previously, we fell into an easy rhythm. Taking each tree in turn, we swiftly, almost wordlessly took on our roles. Find the tree, number it, slip the tape around it, measure, record, take a trowel full of soil, place in bag, seal, label, match the leaves to the trunk, collect, place in bag, seal, breathe deeply and move on to the next one.

We continued to work in this way, slipping through the wood and gradually losing sense of time or, indeed, of anything beyond the trees themselves, until we had a full set of samples. Collecting done, we sat and rested under one of our trees. A couple of cast-off leaves spiralled down in front of us and the day slowly came back into focus.

Paul Ashton, 2016