Caeau Tan y Bwlch (“the fields below the mountain pass”) on the northern slopes of Bwlch Mawr represent some of the last remaining unaltered fields on the Llŷn Peninsula with clawdd (earth and stone) walls still in place. The area is a Site of Special Scientific Interest attributed to its biological features and untouched status.
Owned by Plantlife, the site is now protected thanks to a partnership involving the North Wales Wildlife Trust, the National Trust and the Countryside Council for Wales.
The unfertilised fields have lead to thriving flower-rich meadows with a variety of plants. In particular, the site is renowned for its population of rare Greater Butterfly Orchids. Their delicate white flowers can be seen carpeting the fields during late June and most of July. Other noteworthy plants include Yellow Rattle, Meadow Vetchling, Intermediate Lady’s Mantle and Adder’s Tongue. The upper fields of neutral grassland give way to a mire dominated by rushes, especially Sharp-flowered Rush. Large cushions of Bog Moss occur, supporting delicate stems of Cranberry. Wood Horsetail is particularly abundant in this habitat.
Breeding birds include Grasshopper Warbler. Butterflies include Small Pearl-bordered Fritillary and Ringlet. The best time to visit the site to see the plants and butterflies is during June and July. However, to make the most of the bird song such as Whitethroat, Grasshopper, Willow and Garden Warblers, May is the ideal time of year.
The meadows are grazed from September to April every year. Some of the drier meadows are cut for hay in late summer. Limited parking is available at the reserve.