Stand Replacement Return Intervals in the Northern Forests in 2000-2013

The periodic replacement of old forest stands by young ones is characteristic to the majority of forests in northern countries. This replacement may happen as the result of spontaneous disturbances (such as fires, windthrows, insect outbreaks and forest diseases) as well as the result of forest management (particularly clearcuts). In these cases natural and semi-natural disturbances and forest industry compete for the same resource – productive forest stands. Even if logging alone does not exceed the annual allowable cut level and the scale of spontaneous stand replacement events does not exceed historical averages, the cumulative impact of all these factors may lead to quick depletion of forests. Considering this when evaluating whether forest management may in fact lead to forest depletion, it is important to take into account the impact of both logging and actual forest loss due to various natural or semi-natural factors. Under a clearcut system to account for all these factors we suggest the uniform indicator, based on spatial forest characteristics – stand replacement return interval (SRRI). SRRI is an estimated (using the “moving window” method, see methodology) average period of time during which each particular site (within the area under consideration or “moving window”) would undergo a complete replacement of old forest stands by young ones, under the condition that the rate of tree cover change would be the same as recently: during the period of time with reliable and suitable data records available for calculation. SRRI is an analogue of the rotation period average for all forests within a clearcut system, but it is calculated by taking into account clearcuts as well as other remotely detectable stand-replacing events.