Bumper beech seed triggers pest plague

The heaviest beech forest seedfall in more than a decade is predicted this year. It is expected the increased seedfall will lead to an explosion in the numbers of rats, mice and stoats, who will turn to our native birds for food once the seeds disappear.

Beech trees generally seed every four to five years but weather conditions over the last two summers—a cool summer followed by a warm one—appear to have triggered a bumper seed or “beech mast” event. Intense and widespread flowering was witnessed throughout North and South Island beech forests during spring and early summer, prompting the need for urgent action.

Past experience has shown that when a beech mast occurs, it leads to a dramatic rise in mice and rat populations, who feast on the plentiful seed all winter. To give you an idea of how quickly they can multiply, a single female rat can potentially produce 10 offspring every eight weeks—that’s a lot of rats!

An explosion in rodent numbers leads to a sharp rise in the number of stoats, which also pose a lethal threat to many species.

Rat eating fantail chicks at nest

In spring, when the seed runs out, germinates and rots, these predators will then prey on native birds and their eggs, as well as other critically endangered critters such as native bats and snails.

This will put some of our most threatened species at risk of extinction including:

– mōhua/yellowhead
– kākāriki karaka/orange-fronted parakeet
– pekapeka/short-tailed bat
– whio/blue duck
– Powelliphanta snails

Kea and tākahe are also at risk of being preyed on by stoats.

Yellowhead/mōhua

Landcare Research estimates that 25 million native birds die through predation every year in New Zealand and the beech mast is expected to make the situation much worse. For example, there are only 200–400 wild orange-fronted parakeet left and during the beech mast that occurred in 2000, 85% of the southern population was wiped out due to the rat plague.

85% of the southern population of orange-fronted parakeets were wiped out during the beech mast that occurred in 2000

DOC staff will monitor the amount of seed produced this summer and seedfall in the autumn. Rat tracking will also take place in February and May.

DOC scientist Graeme Elliott says, “So far we’ve only been able to get a visual idea of the issue. We’ve seen lots of flowering during the spring, which caused huge clouds of pollen above the forests.

“The seeds are developing at the moment but in February we’ll be able to start counting them to get a better idea of the scale of the mast. We do this by shooting down branches at the top of the tree, where they’re exposed to the sun and produce the most seeds.

“The best indicator will be the rat tracking. If the numbers dramatically increase or are already high in February, we’ll know we’ve got a big problem to deal with.”

Last night the Minster of Conservation, Dr Nick Smith, announced DOC’s plans to respond and launched our largest-ever species protection programme called ‘Battle for our Birds’. We’ll talk about this in more detail over the coming weeks. For now, you can learn more about it on the DOC website: www.doc.govt.nz/battleforourbirds.