Resilience of biodiversity to habitat change in the marginal uplands or 'ffridd' of Wales
Tree planting or abandonment will damage distinctive and important biodiversity in 'ffridd' that lays between enclosed land and mountain pasture.
- Resurvey birds and habitats in 50 ffridd plots last surveyed in the in 1980s and collect new data on butterfly abundance.
- Understand how habitat composition and change influence biodiversity.
- Estimate carbon storage in different habitat components of ffridd mosaics, and ffridd plots overall.
- Predict biodiversity change and carbon storage potential for three future land use scenarios: cessation of grazing, farming for wildlife and tree planting.
Habitat composition changed significantly, with increased Molinia (+3 per cent) and scattered tree density (+6 per cent), and reduced bracken (-14 per cent) matching other data and climate predictions for Wales.
Of 18 birds, 14 had increased, particularly resident insectivores of lowland woodland (robin +2,407 per cent, wren +1,939 per cent), but also some ffridd specialists (dunnock +887 per cent, stonechat +737 per cent) which is likely a response to locally less-severe winters. However, three significant decliners: resident yellowhammer (-53 per cent) and migrant wheatear (-66 per cent) and whinchat (-67 per cent) indicate other drivers of change such as low winter or passage survival. These changes have led to reduced bird community distinctiveness.
Ffridd carbon was mostly in soil and litter and was most sensitive to tree and wet habitat cover. Modelling the three scenarios showed carbon storage is doubled by allowing ffridd to be replaced by woodland, and natural regeneration by cessation of grazing stores marginally more carbon than tree planting. Changes in biodiversity will be greatest and most rapid under tree planting (particularly commercial conifers) and smallest under Farming for Wildlife.
Bird species characteristic of open habitats and ffridd will be lost following canopy closure, but are likely to be most resilient in places where inherently variable responses to cessation of grazing take place.