Surprising shapes and strange statues are, once again, scattered among the trees and ponds of Stone Lane Gardens this summer. This five acre plot was developed and nurtured by Kenneth Ashburner from the early 1970s until his death in 2010. It holds the National Collection of Birch (Betula) and Alder (Alnus) and has had a sculpture exhibition every summer since 1992. Twenty years ago, when we lived in Liverpool, I remember a Tate Gallery exhibition focused on sculpture ‘Breaking the Rules’- there are plenty of examples at Stone Lane.

Trees themselves have a sculptural quality. The bright white and deep orange bark of the birches is not just a backdrop to the art on display. The trees have been shaped over the seasons by the light, and the weather, together with the more direct intervention of gardeners with pruning saws.

One striking sculpture this year is Excalibur by Andrew Logan. It feeds off our shared inheritance of Arthurian legend as it emerges from the Lower pond. What are the limits of this sculpture? How much is hidden from view in the murky waters; and are those waters part of the sculpture? The pond is surely more than a frame for the work. Similarly the rust-coloured Hares by Christine Baxter create the perfect frame for themselves in the long grass under the trees.

Now and then you also come across sculptures hanging from branches, clay figures or abstract concoctions of woven silver wire. This is another example of the sculpture depending on the trees. These sculpture directs the gaze in new ways, breaking the rule that sculpture needs to be static on a plinth

Even though Stone Lane is only a few miles from Meldon Hill and many of the high tors of northern Dartmoor, the gardens enclose you in a separate world. The pictures of the garden as it was in 1992 show just how the Birch and Alder trees have grown to create the garden, but exclude the view. This can be understood as a loss or a gain as the visitor is forced to focus on the immediate surroundings.