This indicator identifies the impact of abiotic processes and agents on forests. Where change due to these agents and processes occurs beyond a critical threshold, forest ecosystem health and vitality may be significantly altered and a forest’s ability to recover could be reduced or lost. Monitoring and measuring the effects of these processes provide information helpful in the formulation of management strategies to mitigate risk.
Recent work on analysis of wind damage records of planted forests shows an average of 0.21 percent of the national net stocked area affected by wind annually, across a range of 0.98 in the most affected to 0.03 percent in the least, affected wood supply regions. By modelling wind event data, it has been estimated that 500 hectares of damage nationally would occur every five years, with a 95 percent expectation of such damage occurring between 4.5 and 6.2 years. Similarly, 1000 hectares of damage might be expected every 6.4 years, with the 95 percent expectation of this happening between 4.8 and 9.9 years.
Periodic severe seasonal needle cast of radiata pine of unknown origin has been recorded in a number of locations throughout New Zealand since the early 1980s. This has been termed physiological needle blight (PNB) and is considered a disturbance caused by abiotic factors. The disorder affects trees 15 years and older and causes foliage to turn red brown and die, while still attached to the tree. To date, the precise cause of PNB is unknown, but investigation has focused on both the mechanisms that promote the symptoms and the subsequent pathogen infection causing needle death. PNB occurs in radiata pine planted forests in late winter or early spring and is associated with high water availability, in winter (in particular high mid-winter rainfall) and high canopy humidity. PNB outbreaks have often been associated with non-porous soils.
The incidence of PNB is relatively high in the northern part of the North Island compared with lower incidence at sites further south.
Controlled fire is no longer widely used as a site preparation tool in New Zealand forest management, although controlled fire is used as part of fire management training. Controlling wildfire in forests, during drought periods, remains a management issue.
Wind is the main abiotic factor affecting planted forests in New Zealand. Records of wind damage indicate that a total of 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.
PNB incidence remains sporadic and is estimated to have affected about 15 000 hectares of planted forest per year on average in the 2009–2013 period.
The National Rural Fire Authority gathers information on fire incidence. 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.
Information on deforestation (permanent clearance of forest) is obtained from time-series mapping of land-use change and through annually updated forest owner surveys of deforestation intentions; these sources provide information about historical clearance as well as likely clearance in future. Both these sources are primarily for assessing current and future forest carbon levels used to monitor the Government’s international climate change commitments and New Zealand Emissions Trading Scheme (ETS). They will also assist with future climate change policy development.
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. Forest owners’ intentions to deforest in future years (2014–2020) are reportedly declining.