David Nash, Yorkshire Sculpture Park

Wood is a mysterious substance. We do not make it, it makes itself. It is useful to us, alive and dead. Without it, our history would not be the same. But it is so ever-present, so much a part of that history, that we rarely see the wood for the trees. David Nash has seen both the wood and the trees for years. To him, wood is life.

The opening of this show says it all. Outside the first gallery is a huge eucalyptus, split into three by the sculptor. (Nash only works with “found” wood – from dead or dying trees, offcuts from tree-surgeons, or from wood yards – "wood quarries", he calls them.) Inside, the regular information desk has been replaced by a huge chunk of the same tree, and is surrounded by more raw wood which will crack and change over the year of the exhibition: it has been a thousand years growing; now it will alter as the visitors watch. Wood is a process, not a product.

Inside the gallery, the mammoth trunk is countered by Oculus Block (pictured above right), a huge bole of a tree-root and trunk, some 12 tons,  2.4 metres across and three metres high, four trees that grew and, at some point over their centuries of life, fused together. This is framed by pieces of bark, shaped and leaning against the wall, framing the trunk as they framed and protected it in life. Two Vessels, two long canoe-shaped pieces of oak, scorched black along the prows and the hollowed interiors  - blade-sharp in their forward motion - are transporters of living wood, thrusting into space.

Outside, the totemic Red Column (pictured left), satisfyingly rounded and lush despite its towering upward thrust, sits next to Black Dome, a series of graduated black pyramids lurking by a hedge, vanishing and reappearing as the light changes. Black Ball (main picture), at the top of the hill, looks like an alien spaceship entirely at home in Yorkshire. Almost visible across the valley is the extraordinary permanent piece commissioned by the park: Oxley Bank Black Steps (pictured below right) carves gently into the hillside, 71 charred oak steps embedded in a coal drift that echoes a drift of bluebells alongside. The dual organic nature of the steps, wood and coal, recapitulates the history of the local countryside and man’s dependency on the natural world: “man-made” could not exist without “nature-made” first.

There are also drawings (Nash combines elegant, precise draughtsmanship with lush, saturated colours) of projects such as Ash Dome, a circle of ashes planted in Wales in the 1970s. A video shows Nash through the decades pruning and shaping the circle to create the dome, aging as the trees grow, the two living constructs, man and trees, changing and maturing, together.

One vast gallery is filled with shapes and shadows to recreate the feel of his North Wales workshop. On entering, the room seems overstuffed; walk around, however, and shapes speak to each other across decades and across the space. Branch Cube, an ash outline of a box with branches “growing” out of it, is placed above a glass wall. The branches creep outwards, like ivy, and like ivy are curiously ambiguous, both ominous and delicate. On the other side of the wall, the huge Elm Ball sits, charred and brooding, and our view of the branches changes again, as next to the glass Cracking Box, a small, Dalek-shaped work, wonky and endearing, squats gently in the sunlight. Each new work immediately changes our perception of the last.

Nearby some of Nash’s “family tree” drawings are on display, mapping diagrammatically how ideas have flowed from one piece to the next, or how one tree has given itself to several sculptures, which in turn have transformed themselves into other pieces. In one, his early “towers”, wildly complex constructions of wavering purpose - sort of David-Smith-meets-Calder - progressively simplify in one strand, to the ladders of the 1970s, simple shapes simply held together, complexity into simplicity. In another, an early piece, Nine Cracked Balls, balls roughly hewn and left to shape themselves by cracking, develop into Three Clams on a Rack, a more interventionist piece, then into Cracking Box, where the path divides, one strand going on to Crack and Warp columns, delicately layered towers that also reshape themselves over time, while another moves to a new planted earthwork.

These schema bring Nash into focus, showing him as a serious thinker: about shape, about density, flux, transition and time. And it is hard to think of any place other than Yorkshire Sculpture Park where a retrospective of this sculptor’s career could be so satisfyingly displayed. Nash’s 40-year preoccupation with his material changes the way we look at wood, at not only its own shape, but the shapes it makes as it surrounds space, the shapes of voids and vacuums. Yorkshire Sculpture Park’s fine retrospective displays Nash as a sculptor of serious thought and, in equal measure, serious beauty.

• David Nash is at Yorkshire Sculpture Park, West Bretton, Wakefield until 27 February 2011