Wood In Boreal Forests Research Articles

Scale-specific responses of saproxylic beetles: combining dead wood surveys with data from satellite imagery

We investigate relevant scales and cost-efficient methods for measurements of habitat for saproxylic, aspen-associated beetles, in two boreal forest landscapes in south-eastern Norway. We sampled saproxylic beetles with window traps on fresh aspen dead wood and conducted field surveys of dead wood in the surroundings (1, 2 and 3 km radius). In addition, we used maps derived from satellite imagery to extract data on forest age and volume for the same surroundings. We found that species richness of saproxylic beetles was related to dead wood volume estimated by field survey within 1 or 2 km radius from the trapping points. However, the map-derived variable describing area of forest with high levels of deciduous wood volume was the overall best predictor of species richness. The scale of response to this variable differed; species richness of all saproxylic beetles was best predicted by estimates for the 2 km radius whereas richness of species more strongly associated with aspen was best predicted by estimates for the 3 km radius. This might indicate that aspen-associated beetles disperse over larger distances than many other beetles; possibly an adaptation to the scattered distribution and ephemeral nature of aspen dead wood in boreal forests. Our results show that substrate variables must be measured at the scale that is ecologically relevant for the study organism to elicit a response. We also show that remote sensing data -often easy to obtain for large scales—can be used to complement studies of scale-specific responses and thus improve conservation measures for saproxylic beetle species.

Trophic levels and habitat specialization of beetles caught on experimentally added aspen wood: Does trap type really matter?

Saproxylic (wood living) beetles make up an important part of forest biodiversity and are of importance for conservation practices. The beetles are commonly surveyed on various dead wood resources by use of flight interception traps (window traps), catching both species depending on the resource and vagrant (irrelevant) species. Enclosed traps have been suggested as an alternative sampling method, as they sample only the beetles utilizing the dead wood resource. This is the first study to compare the two trap types based on catches from experimentally added identical wood units. Our main aim was to test whether enclosed window traps catch a higher proportion of specialized species and species of a lower trophic level than open window traps, and whether proportions of vagrant species decrease with habitat specialization and trophic level in both trap types. The study was carried out during two summers with traps mounted on replicated, identical units of fresh aspen dead wood in boreal forest in south-eastern Norway. Contrary to our expectations and earlier findings, the enclosed window traps did not catch a higher proportion of habitat specialists (aspen-associated species) or species at the lowest trophic level (wood feeding) compared to the open traps. Rather, the proportion of predators was higher and fungivores lower in enclosed versus open window traps, and no difference was found between different categories of habitat specialization. The proportion of vagrant species was lowest among the beetles with the strongest specialization (aspen-associated) whereas there was no difference with trophic levels. We suggest that keeping vagrants but selecting species based on host tree affinity is the best way to use catches from open window traps on dead wood units. Studies of predators and fungivores should be interpreted with care.

The choice of definition has a large effect on reported quantities of dead wood in boreal forest

A survey was conducted to assess the impact of the choice of definition on reported quantities of dead wood in Swedish forests, which to more than 90% are located in the boreal zone. The data collection was made on a subsample of the permanent plots of the Swedish national forest inventory. The objects included were standing dead trees and snags down to 5-cm diameter at breast height, dead lying stems and branches down to a threshold diameter of 1 cm and stumps down to a threshold diameter of 5-cm at normal stump height. Standing trees, snags and stumps were inventoried on 10-m radius circular plots while the downed objects were inventoried using both circular plots and line intersect sampling; thin objects (diameter 1–5 cm) were assessed only through line intersect sampling. The results showed that the estimated volume of dead wood was as high as 25 m3 ha−1 when all components were included. With the standard Swedish definition, the corresponding estimate was only 10.9 m3 ha−1, or 43% of the total value. Since definitions of dead wood vary greatly between countries we conclude that great caution must be exercised when figures are compared in connection with international reporting. For example, adding stumps to the Swedish definition would increase the amounts of dead wood from 10.9 to 15.7 m3 ha−1, i.e. with 44%.

Discovery of the Epixylic LiverwortLophozia ciliataDamsh., L. Söderstr. & H.Weibull in Canada

Abstract. Lophozia ciliata Damsh., L.Soderstr. & H.Weibull is one of a number of liverworts that grow on dead wood in boreal forests. The species is widely distributed in Scandinavia but until now has not been reported from Canada. This article documents the occurrence of the species from the boreal forest of northwestern Alberta, Canada.