Pest impacts on indigenous trees

  • Image, Pest impacts on indigenous trees.

    Deer, goats, and possums are animal pests in New Zealand. The species of trees they prefer to eat may become locally extinct and nationally much rarer than less palatable species. Resulting changes in forest composition may have profound effects on other plant and animal species. The pest impacts on a particular tree species may affect the available habitat for and food source of those other plants and animals.

    We classified Pest impacts on indigenous trees as a national indicator.

    Key findings

     Trend not assessed

    Between two surveys (taking place between 2002 and 2014), goats and possums had a strong effect on the mortality rates of their preferred trees and deer had a moderate effect on the mortality rates of their preferred trees.

    • For indigenous tree species that goats and possums prefer to eat, the number of trees that died exceeded the number of newly-established trees.
    • For tree species that goats and possums tend to avoid eating, the number of newly established trees exceeded the number of trees that died.
    • For tree species that deer prefer to eat, the number of trees that died was similar to the number of newly established trees.
    • For tree species that deer tend to avoid eating, the number of newly established trees exceeded the number of trees that died.

    Figure 1

    pest-impact-goats

    Figure 2

    pest-impact-possums

    Figure 3

    pest-impact-deer

    Definition and methodology

    Information about the impact of pests on indigenous trees records the difference in mortality and recruitment of tree species that are either preferred or avoided by three herbivorous pests (goats, possums, and deer) in forests across New Zealand.

    This information comes from 874 survey plots (20m x 20m) distributed across forests on both public conservation land and private land around New Zealand. Each of these plots was first surveyed between 2002 and 2007. All trees with trunk diameters greater than or equal to 2.5cm when measured at 1.35m height (called ‘diameter at breast height’ or DBH) were tagged and identified. The same plots were resurveyed between 2009 and 2014. Any trees present in the first survey but missing from the second were recorded as dead. Any trees not recorded in the first survey but were in the second as having a trunk greater than or equal to 2.5cm DBH were recorded as newly established trees.

    This indicator does not include information on seedlings and saplings that might have been removed by herbivores before reaching the height and size requirements of a new tree as defined above.

    Data quality

    We classified Pest impacts on indigenous trees as a national indicator.

    Relevance

    relevance-direct This national indicator is a direct measure of the ‘Impacts on biodiversity’ topic.

    Accuracy

    accuracy-high The accuracy of the data source is of high quality.

     

    See Data quality information for more detail.

     

    Published 21 October 2015

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