Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Predicting mast seeding and the ensuing predator problems

A new model has been developed to help predict ‘mast seeding’ in some New Zealand plants to allow land managers to prepare for the likely predator population explosions that follow.

Mast seeding is the production of unusually high quantities of seed that occurs in some plants in some years. It is quite common in New Zealand plants including beech trees, and also occurs in Northern Hemisphere trees such as oaks, beeches, pines and spruce. These occasional large flower and seed crops usually lead to big increases in populations of seed consumers (e.g., mice and rats) and consequently predator populations (e.g., stoats, feral cats).

Unfortunately when the introduced predators in New Zealand ecosystems increase they generally consume more native birds and insects.

Scientists have been trying to understand what triggers mast seeding to provide land managers with at least a one-year advance warning of a ‘predator pulse’. Previous research suggested that synchronizing flowering cues are almost always weather-related, with warm temperature in the previous summer most often cited . But this prediction method has proved inconsistent.

In an internationally-significant discovery, a team led by University of Canterbury and Landcare Research scientists has found that the climate signal that triggers masting is the change in mean (average) summer temperature between the preceding two years, not simply temperature in the previous summer.

The researchers analysed 26 very long mast-seeding datasets from New Zealand spanning 15 species in five plant families. The length of time seed production and/or flowering was measured ranged from 15 to 43 years, and the data covered a range of different habitats (alpine to lowland) and plant life forms (trees, grasses, daisies). They also compared the results from the New Zealand datasets with 20 of the longest-running Northern Hemisphere datasets, covering 17 species from North America, Japan and Europe.

The findings consistently showed that a wide range of mast-seeding species respond to the difference in temperature from one growing season to the next, i.e. the change in mean summer temperature between the two preceding years.

The temperature-difference model was also a much better predictor of the rare phenomenon of consecutive high-seed events (double masts), which occur only after a specific sequence of cold/warm absolute summer temperatures. Double masts in beech forests in 1999/2000 led to increased predation of threatened endemic birds from Fiordland to the Marlborough Sounds.

The model, which uses existing climate information, is of “considerable importance” to the Department of Conservation, according to Threats Science & Technical Manager (Central), Susan Timmins. “As it predicts mast seeding events a year in advance it gives conservation managers time to plan aerial 1080 operations that target seed-fuelled mouse, rat and stoat irruptions before they cause significant ecological harm.”