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Coarse woody debris (CWD) was studied in old Pinus sylvestris L. dominated forests in three geographic regions in the middle boreal vegetation zone: (i) in Häme in southwestern Finland, characterized by a long history of forest utilization, (ii) in Kuhmo in northeastern Finland, with a more recent history of forest utilization, and (iii) in the Vienansalo wilderness area in northwestern Russia, characterized by large areas of almost natural forest. Within the geographic regions the measured 0.2-ha plots were divided into three stand types according to the degree of human impact: (i) natural stands, (ii) selectively logged stands, and (iii) managed stands. The results showed that compared with natural forests, forest management has strongly reduced both the amount and diversity of CWD. The highest total CWD volumes were found in the natural stands in Häme (mean 67 m3·ha–1) and Kuhmo (92 m3·ha–1) and in the selective logged stands in Vienansalo (80 m3·ha–1), while the lowest CWD volumes were found in the managed stands in Häme (7 m3·ha–1) and Kuhmo (22 m3·ha–1). The duration of forest utilization also plays a role, as forests with short management histories (Kuhmo region) still carried structural legacies from earlier more natural stages of the forest. In addition to lower total CWD volumes, managed stands also largely lacked certain dead wood characteristics, particularly large dead trees and standing dead trees with structural diversity characteristics (such as stem breakage, leaning stems, and fire scars) when compared with natural and selectively logged stands. The CWD characteristics of stands selectively logged in the past were often comparable with those of natural stands, suggesting that old selectively logged stands can be of high value from the nature conservation point of view.

This study examined the effect of local competition, as determined by the number, size, and spatial distribution of neighboring trees, on crown base height, crown width, and crown asymmetry of trees growing in a natural mature Scots pine (Pinus sylvestris L.) forest in eastern Finland. Local competition was described with competition indices. Crown asymmetry was characterized as the distance and direction from the stem center to the visually estimated crown mass center. Nonspatial and spatial models for crown base height and crown width were derived, as well as a spatial model for the horizontal distance from the crown mass center to stem base position. The effect of neighbors on the direction of crown mass center from stem base position was studied using the center of competition and the widest free angle free of competitors closer than 5 m. The derived spatial models for crown base height and crown width, taking local competition into account, were only slightly better than the nonspatial models. This was because diameter at breast height and tree height, the independent variables used in the nonspatial models, described quite well the conditions of local competition for a tree. The spatial model for crown base height was 2.22% units (adjusted R 2) better than the nonspatial model. Correspondingly, the spatial model for crown width was 1.77% units better than the nonspatial model. Crown asymmetry characteristics were measured for 57% of the trees. The spatial model for the distance to the crown mass center could only explain about 10% of the total variation of the dependent variable. The model for the direction of the crown mass center from stem base position showed that the variables describing direction of local competition, i.e., the competition center and the widest free angle, could not adequately explain the direction of asymmetry. One reason for this was that tree crowns showed plastic responses to the prevailing asymmetry of solar radiation geometry. Therefore, the directional distribution of the crown asymmetry was strongly weighted toward southern and southwestern directions, i.e., the directions of most abundant incoming solar radiation. We suggest that the detected developmental plasticity in crown asymmetry was affected both by the directionality of solar radiation geometry and by that of local competition, which is influenced by the number, size, and spatial distribution of close competitors. Résumé : Cette étude examine l'effet de la compétition locale déterminée par le nombre, la taille et la distribution spatiale des arbres voisins sur la hauteur de la base du houppier, ainsi que la largeur et l'asymétrie du houppier des arbres poussant dans une forêt naturelle mature de pin sylvestre (Pinus sylvestris L.) dans l'est de la Finlande. La compétition locale est décrite par des indices de compétition. L'asymétrie du houppier est caractérisée par la direction et la distance entre le centre de la tige et le centre de gravité du houppier estimé visuellement. Des modèles non spatiaux et spatiaux pour l...

Tree mortality and its causes and spatial pattern were examined along four transects (width 40 m, length 2550-3960 m), with a total length of 12 190 m and area of 48.8 ha, in a Pinus sylvestris L. dominated, boreal forest landscape. Tree mortality was determined within a time window of 3 years by identifying those trees (dbh ≥ 10 cm) along the transects that fi tted into one of the three categories: 1) current mortality: trees that had died during the year of survey (1998), 2) recent mortality: trees that had died during the year (1997) before the survey year, and 3) predicted mortality: trees that were expected to die during the year (1999) following the survey year. Long-term tree mortality was studied on 10 plots (20 m × 100 m) by dating 87 dead trees using dendrochronological methods. The mean current mortality was 1.4 m 3 ha -1 (3.7 trees ha -1 ). Both the recent and predicted mortalities were also 1.4 m 3 ha -1 . Mortality was, on the average, higher on peatlands than on mineral soils. The highest mortality was found within an area recently fl ooded by beavers. Over half of the examined trees (52%) were judged to die without any visible signs of an external abiotic cause. At the landscape scale, tree mortality was continuous although somewhat aggregated in space. Of the 66 dated standing dead Pinus trees, 23 (35%) had died during the 19th century and two during the 18th century, demonstrating that dead Pinus can remain standing for long periods of time before falling. Our results show that autogenic mortality of individual trees or small groups of trees was the predominant mode of disturbance in this Pinus dominated landscape.

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