The tall conifers of America's Pacific Northwest are experiencing a peculiarly heavy cone-harvest. Ken Bible of the University of Washington in Seattle, who investigates the phenomenon, says: ?In normal mast years [when most Douglas-fir cones are produced], we would see four or five cones per branch. Now we are seeing 30.?

The cone-production cycle is thought to be driven in part by weather events during the development of tree buds and cones. Bible says that his team is looking closely at temperature, rain, humidity and wind data at several development stages to see if they can work out what caused the super mast.

It seems to be confined to that region. For example, white spruce in Canada are masting normally in Edmonton, Calgary and Banff, reports Jalene LaMontagne, at the University of Calgary in Alberta.