Memory of Trees, The (F. G. Cottam)

Billionaire Saul Abercrombie owns a vast tract of land on the Pembrokeshire coast.  His plan is to restore the ancient forest that covered the area before medieval times, and he employs young arboreal expert Tom Curtis to oversee this massively ambitious project. 
Saul believes that restoring the land to its original state will rekindle those spirits that folklore insists once inhabited his domain. But the re-planting of the forest will revive an altogether darker and more dangerous entity – and Saul’s employee Tom will find himself engaging in an epic, ancient battle between good and evil.  A battle in which there can be only one survivor.