Photos: Metla/Erkki Oksanen, Matti Koivula

Ecological background of the disturbance dynamics model

The goal of ecologically sustainable forest management is to secure natural environments at different scales and, in turn, the viability of native species. The aim is to maintain biological diversity as a whole, not just certain charismatic species with well-known ecology. If this aim is adopted, then the only realistic option for developing ecologically sustainable management protocols is to try to maintain natural types of habitats and their diversity in the landscape (Hunter 1999, Lindenmayer & Franklin 2002).

Forest disturbances are crucial for the maintenance of the diversity of habitat types and species. The term 'disturbance' refers to events that relatively quickly change forest structure so that space and resources are released and the micro-climate is altered. In natural forests, variability in disturbance dynamics profoundly affect diversity by producing a variety of habitat types to which the native species have evolved and adapted (Gromtsev 2002, Angelstam & Kuuluvainen 2004).

From the point of view of biodiversity conservation and sustainable forest management, clear-cut harvesting appears problematic because it creates landscape and stand structures that crucially differ from structures resulting from natural processes (Kuuluvainen 2009). The principal goal of traditional forest management has been the minimization of timber loss, caused by natural disturbance forces such as wildfire, windstorms, plant diseases and pest insects. This economically viable goal has been to a large extent achieved in the Nordic countries, but simultaneously many naturally-developed habitat types have become less abundant and of lower quality. From an economic point of view, disturbances can be considered detrimental damaging forces, but in the forest ecosystem they are key factors in maintaining and renewing biodiversity (Attiwill 1994, Esseen ym. 1997, Kuuluvainen 2002).

Natural disturbances, and habitat types resulting from them, are thus vital for the maintenance of diversity in natural forests. To maintain diversity characteristic of natural conditions, forest management should aim at promoting such disturbance dynamics that produce environments that resemble comparable environments of natural forests (Attiwill 1994, Hunter 1999). Disturbances caused by forest management, however, always differ from natural disturbances. The most important and obvious difference is that in managed forests, most of the wood material is removed whereas in natural forests dead trees are retained. The aim of ecologically sustainable forestry is to apply knowledge obtained from natural forests to ensure both the maintenance of natural diversity and the other management goals in the best possible way (Lindenmayer & Franklin 2002).

Mimicking natural disturbance dynamics is becoming an important approach to maintain diversity in managed forests (Hunter 1999, Lindenmayer & Franklin 2002, Perera et al. 2004). Management models, based on natural disturbance dynamics, have recently been developed for several regions in the boreal zone (Angelstam & Rosenberg 1993, Angelstam 1998, Bergeron et al. 1999, 2002). A common feature for these models is the use of techniques creating both large open areas and the preservation of forest cover and continuity using partial harvesting methods.

Disturbance dynamics in managed and natural forests

Coarse and fine filter

Applications of disturbance model

Literature