Maintaining forest health and vitality is the foundation of sustainable forest management. Decline in forest ecosystem health may have significant economic and ecological consequences for society. Diseases, wind, wild fires and deforestation are the main threats to forest ecosystems in New Zealand.
To stay healthy, forest ecosystems must be able to recover from, or adapt to, disturbances. Many disturbance and stress events occur naturally. Some may overwhelm ecosystem functions, fundamentally altering their patterns and processes and reducing ecological function.
In both 2003 and 2008, Cyclaneusma needle cast and Dothistroma needle blight caused the most loss. Outbreaks of these diseases have been less extensive in recent years. Drier conditions and more effective copper spray formulations have reduced Dothistroma incidence. The reduction in forest areas in the central North Island through land conversions has diminished the spray requirement.
The production of resistant clones has helped to reduce Cyclaneusma incidence.
Wind is the main abiotic factor affecting planted forests in New Zealand. Some 63 000 hectares of forest were damaged over a period from 1945 to 2008.Three main storm events contributed two-thirds of the total damage over the 50-year period.
In the six-year period from 2007 to 2013, wildfire incidents affected about 4000 hectares of planted forest and about 500 hectares of indigenous forest.
Controlled fire is no longer widely used as a site preparation tool in New Zealand forest management. Controlling wildfire in forests during droughts remains a management challenge.
Deforestation in planted forests increased significantly after 2002, rising to a peak just before the ETS policy started in 2008. This rise was due in part to forest landowners anticipating deforestation liabilities under the ETS, the price of emission units and the relative attractiveness of alternative land uses, such as dairy farming.
The 2013 annual deforestation survey reported that forest owners’ intentions to deforest in future years (2014–2020) were lower than in 2012.