To estimate the age of Norway spruce (Picea abies (L.) Karst.) logs by means of decay classes, and to assess how long it takes for downed logs to decompose, we dated logs dendrochronologically by applying 5-and 8-grade decay classification systems. Study sites were chosen in old-growth and previously selectively cut forest stands in boreal south-central Scandinavia; 113 logs were dated to the number of years since death, 120 were dated to the number of years since fall, and 61 logs were dated to both. The number of years from death to fall showed a negative exponential distribution, with a mean of 22 years and a range of 0-91 years. Decay classes of logs (8-grade scale) reflected time since fall (R 2 = 0.58) better than time since death (R 2 = 0.27) in a linear regression model. This result is due to the lower decomposition rate of standing snags. Therefore, the decomposition time of logs should be divided into two periods: time from death to fall, which varies considerably, and time after fall, which appears to follow a linear relationship with decay class. The model predicted that it takes 100 years after fall for downed logs to decompose completely (reaching decay class 8) in old-growth stands. Logs in selectively cut stands appeared to decompose faster (64 years), which is explained by a sample shortage of old logs resulting from previous cuttings. We conclude that the decomposition time of downed logs may be severely underestimated when data is retrospectively compiled from previously logged forest stands.Résumé : Pour estimer l'âge des billes d'épicéa commun (Picea abies (L.) Karst.) au moyen de classes de décomposi-tion et évaluer le temps requis pour que les billes au sol se décomposent, nous avons daté des billes dendrochronologiquement en appliquant des systèmes de classification comportant cinq et huit degrés de décomposition. Les sites d'étude ont été choisis dans des peuplements de forêt ancienne et des peuplements où avait déjà été effectuée une coupe sélective dans la zone boréale du Centre-Sud de la Scandinavie. Le nombre d'années écoulées depuis la mort de l'arbre a été déterminé chez 113 billes, le nombre d'années écoulées depuis la chute de l'arbre au sol chez 120 billes et les deux chez 61 billes. Le nombre d'années écoulées entre la mort de l'arbre et sa chute au sol suit une distribution exponentielle négative avec une moyenne de 22 ans et une étendue de 0-91 ans. Les classes de décomposition des billes (échelle à huit degrés) reflètent davantage le temps écoulé depuis la chute de l'arbre au sol (R 2 = 0,58) que depuis la mort de l'arbre (R 2 = 0,27) selon un modèle de régression linéaire. Ceci est dû au fait que le taux de décomposition des chicots encore debout est plus faible. Par conséquent, le temps de décomposition des billes devrait être divisé en deux périodes : le temps écoulé entre la mort de l'arbre et sa chute au sol qui varie considérablement et le temps écoulé depuis sa chute au sol, lequel semble relié de façon linéaire aux classes de décomposition. Dans les peuplements de for...
Distribution and size of 38 capercaillie Tetrao urogallus leks were related to amount and configuration of old forest patches in two south-east Norwegian coniferous forests. The smallest occupied patch was 48 ha containing a solitary displaying cock. All patches larger than 1 km contained leks. Number of cocks per lek increased with increasing patch size. Number of leks per patch increased in a step-wise manner with one lek added for each 2.5-3 km increase in patch size. In large patches there was one lek per 3-5 km old forest, and density of lekking cocks was 2-2.5 per km. In small patches density of cocks varied considerably. Density of cocks was not related to patch isolation or patch shape. However, among leks surrounded by 50-60% old forest within a 1 km radius, number of cocks increased with increasing old forest fine-graininess. We argue that when old forests cover more than 50%, a fine-grained mosaic may support higher densities of lekking cocks than a coarse-grained mosaic. Conversely, when old forests cover less than 50%, a fine-grained mosaic is unfavourable, because each old forest patch becomes too small and isolated. Finally, we present a predictive model of how old forest fragmentation influences density of leks, number of cocks per lek, and total density of cocks.
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