Disturbances in deciduous temperate forest ecosystems of the northern hemisphere: their effects on both recent and future forest development

Disturbances in forests can kill mature trees, but also create the conditions necessary for the establishment of new tree cohorts and create micro-habitats for new plant and animal species, thereby increasing the species diversity compared to undisturbed stands. We review the types and intensities of disturbances on forests in three regions of the temperate zone of the northern hemisphere: northeastern North America, Central Europe, and East Asia. We focus on (1) the ways in which disturbances affect forest stand development; (2) the differences among the three areas in this regard; (3) the consequences for future forest management. In both northeastern North America and East Asia, hurricanes and typhoons represent the major mode of natural disturbance, while in Central Europe winter windstorms occur after deciduous trees have lost their leaves. Tornadoes can have even greater destructive power (but affect relatively narrow strips of land), and the more severe of these mainly occur in North America. The general disturbance patch system therefore is relatively large in northeastern North America, small in Central Europe, and of intermediate size in temperate East Asia. In addition to wholly natural disturbance factors, human commerce and globalization have enabled new disturbance types by introducing pests and diseases from one region to another. In North America especially, several of the most important foundation species in temperate forests are strongly affected, so that not just the species composition but also the whole forest structure is changing fundamentally. In all three areas in the past the change in land use by growing human populations strongly affected the structure as well as the species composition of forests. Nearly all the recent forest stands of the temperate zone had been used in the past in a particular way, and many of today's forests had previously been converted into agricultural land. Finally climate change is superimposing itself on forest development worldwide. Nevertheless, climate change is not a new phenomenon, so forest ecosystems in all time periods have been exposed to changing climatic conditions and have had to adapt. Each forest stand therefore represents a unique recent expression of the interaction of environmental conditions and plant species, a snapshot of the relevant abiotic and biotic factors, including human impact.