Assessing the naturalness of boreal forests in eastern Fennoscandia

This study aims to define the level of naturalness in the protected forests of eastern Fennoscandia, i.e. to determine how natural or semi-natural are the currently protected and unmanaged forests, and the extent to which the past human influence has affected the current forest structure. The plots used in the study represent both currently unmanaged and managed forests. The unmanaged forests are located in nature protection areas. We have used data from earlier forest inventories, determined by the visual estimation of compartments, together with the measured stand variables. The data cover detailed analysis of 79 forest sites or stands in both in mesic and sub-xeric forests. The whole successional gradient is included in the data. In unmanaged forests, fellings have occurred on 39% of the sample plots in sub-xeric areas, and on 28% of the sample plots in mesic areas. According to the historical records 33% of all the unmanaged forests have definitely been (selectively) felled, 21% possibly, and 46% show no signs of fellings. In general, the unmanaged forests in eastern Finland bear ample evidence of light selection felling, Thus, these stands could better be regarded as semi-natural rather than natural forests. Mesic old-growth stands are less affected (73% are completely untouched), but the tree volume data, number of tree storeys and the signs of slash-and-burn cultivation are nevertheless clear evidence of the impact of human activities. The growing intensity of human activities since the 1950s can also be seen in semi-natural succession forests as the presence of cut stumps and the probability of felling in young stages. Real natural/semi-natural sapling and young forests are very rare and occur only in Russia. The diameter distribution in semi-natural sapling and young forests with reverse J-shaped distributions showed considerably greater variation. Also the mature and old-growth, semi-natural forests were characterised by the decrease in reverse J-shaped distributions. The timber volume in stands was generally lower at the beginning of the 20th century. Overall, the forests in nature reserves axe structurally rather different to those growing at the beginning of the 20th century, and show patterns not typical of natural forests. The slash-and-burn agriculture practised during the 1800s and earlier has profoundly affected the natural spatial and temporal disturbance regimes, with clear consequences for the current tree species and age composition. More recent deviations from the natural forest structures are, however, largely due to the absence of natural and anthropogenic forest fires during the 1900s. (C) 2002 Elsevier Science B.V. All rights reserved.