A mast year occurs when the climate is warmer than the previous year, causing native flora to fruit more.
Forest and Bird are projecting 2019 to be the biggest mast year in decades.
Some plants are deeply influenced by mast years, with trees such as Rimu fruiting in abundance.
This year, Rimu trees at Whenua Hou, south of Invercargill, have fruited for the first time in 17 years.
With flora fruiting in abundance, many native species, such as the endangered kākāpō, are expected to have a record-breaking breeding season.
Spokesperson for the Department of Conservation, Bridget Railton, said kākāpō breeding seasons are strongly linked to mast years.
But, Forest and Bird have said mast years can lead to an increase in pest populations.
Spokesperson Caitlin Carew said once the pests have stopped eating all the native fruit, they will turn to the native species instead.
Carew said DOC will need additional funding if they want to prevent pest populations from getting out of hand this year.
She said they need to prevent another species from going extinct like the Mohua population in the Marlborough Sounds.
