The day started with rain, lots of it, clouds stubbornly low, with mist predicted for late afternoon. A perfect time to go out.

It doesn’t take long for our feet to become wet through. The Troutbeck Valley is a wet place – just the right kind of habitat, in fact, for alders, and this is what we’ve come to see. We wanted to spend some time with the Trout Beck Alder as it turns itself, slowly, brown.

There are no far-reaching views today; in this thick mist vision is reduced to metres. At my feet, droplets of water balance on every head of grass, each rush, and the last of the flowers offering up their colours before winter. I’m drawn in by a scabious and kneel down low, getting wetter still. There’s something beautifully contradictory about the scabious – its form is like an explosion, yet it is subtle and gentle. Its violet seems the most unlikely thing today, when all around is grey and softened brown, and it holds mist in single droplets, like jewels.

It does feel as if today is all about water. Trout Beck is tumbling, peat-white and noisy, and water seeps into my shoes and into my hair, face and hands. No rain but around me is a constant fine spray. In the river, it is, of course, even wetter. Rob has abandoned all thoughts of staying dry and waded in beyond the tops of his boots. I am already wet, so wade in too. The eager flow of the river is a contrast to the trees, which when seen from a distance, seem completely still.

When I reach the tree I see that its leaves are becoming dry and brown. An alder doesn’t step into autumn with the glorious gold of a beech or the fresh yellow of a birch – alders are fairly understated trees and their slide into autumn is far from showy.

There’s a serenity and peace about this particular tree. I climb in and with my feet off the ground I am held safely as if on an island, and I have a sense of its peaceful certainty. It’s almost buzzing with calm. All around me is water: the beck is on one side and the tree’s trunk is sitting in a deep puddle covering grass and moss. Drops of water fall from the leaves and branches into my hair, roll into my eyebrows, gloss my eyes, and track down my cheeks. I lean into the wet bark.

Alders love to have their feet wet and it’s not surprising to find so many of them here, where the earth seldom seems dry, and almost all the paths are rivulets, channelling the flow of rain and the steady seep of water from the fells that act like sponges. We measure the girth of the tree to be 159cm. There are other alders far wider than this, as well as spindly trees, and some are growing in the middle of the river – they will never have their feet dry.

We head back in the gloaming, following the curve of the river and then crossing the stone clapper bridge. There the fell is taken over by alders and as we walk through them something happens to the light: it is fading and blending with mist and the colour seems to leach from the trees, transforming the place into what feels like an old hand-printed monochrome photograph, softened by time. This woodland, this alder carr, has become an inbetween space, between day and night, between here and there, between real and imagined. There’s no breeze and we are held in the midst of a shimmering gathering of trunks and the rising scent of moisture on leaves and earth. The only noise is the tumbling river. We fall silent.

When we emerge from the trees we’re a little lower down in the fields at the back of Troutbeck Park Farm, which was once owned by Beatrix Potter. Most people know BP as the writer of the Peter Rabbit series of books, but she was also a keen naturalist and a revered sheep breeder. As a breeder, she used the name Mrs Heelis, and it was as Mrs Heelis that she bequeathed this farm and much of the land around it to the National Trust as part of her legacy to them. It was also largely thanks to her that the National Trust made a pledge that each one of its Lake District farms would maintain a flock of herdwick sheep, hefted to the land around them so that their knowledge of the fells would be passed down from one generation to the next. The herdwick ewes we’ve passed today, many of them connected through their bloodlines to the flock of Beatrix Potter’s time, are looking slender, having had their summer coats clipped. Their lambs are more chunky, and dark fleeced. They look at us quizzically as we pass through the lush inbye land, as if passing through history.

The trunk of the Trout Beck Alder holds some strands of wool, left-overs from sheep rubbing themselves here while wandering past. We don’t know how old this tree is but it’s old enough, for sure, to have witnessed the comings and goings of many generations of herdwicks whose numbers have risen and fallen from decade to decade. Who else might have taken the time to get to know it over the decades? I wonder. Perhaps it has gone largely unnoticed, as seems the way with most trees that are accepted and loved as part of a wider scene but unacknowledged as individuals, until, perhaps, such time as they buckle and fall under the influence of man, weather or time.

When we arrived back home, we looked closely at the leaves we collected, making their slow but sure transition from summer into autumn.