This week I visited the Great Fen project, an extraordinarily ambitious plan to restore 9,000 acres of wetland near Huntingdon. Walking through the nature reserve which will lie at its heart, we saw dragonflies and water deer (a threatened species in their native China), and sniffed water mint. It's hard not to be captivated by the project. Yet its very scale draws us into a debate about how land should be managed in future.