In February 1917 he granted a 500-year lease of almost 8,000 acres of the picturesque and virtually pristine Holnicote Estate on Exmoor, one of the most beautiful pieces of wild country to be found in England to the National Trust, in order to preserve it from future development. This more than doubled the extent of the lands controlled by the National Trust, then only recently created. His brother and successor Arthur and nephew Francis, 13th & 14th Baronets respectively, co-operated in the negotiations concerning the gift. The lease was converted into an outright gift 35 years later by his great-nephew Sir Richard Thomas Dyke Acland, 15th Baronet (1906-1990), who also donated Killerton.