deer populations have 'irrupted' (undergone explosive population growth) in Scotland and across the world wherever their predators have been exterminated. by contrast, persistent irruptions have never been documented in areas with healthy predator populations (thread)

its no exaggeration to say that these irruptions have been catastrophic for the ecosystems where they've taken place - heavy browsing pressure prevents trees from regenerating successfully, so woodlands fall apart over time as dying trees are not replaced

in Scotland, selective browsing and grazing knocks out most wildflowers and berry-producing plants, replacing them with huge expanses of purple moor grass in the west and heather in the east. this deer-resistant vegetation supports only a tiny fraction of the life possible

excessive grazing and trampling causes ancient peatlands to break down, polluting freshwater ecosystems and releasing millennia of accumulated carbon

in the absence of predation or sufficient culling, deer are the ultimate losers - having stripped away all the tasty vegetation (as well as shelter), they're forced to subsist on poor quality forage, which often isn't enough to get them through the winter. many starve to death

restoring balance to depleted ecosystems through predator reintroductions is probably the long term solution, but in the mean time culling needs to be significantly stepped up - the benefits are recovering ecosystems, healthier deer and reestablishment of carbon sinks @scotgov