On the spider population (Arachnida: Aranei) of the brushwood of marsh labrador tea (Ledum palustre L.) in larch taiga forest of the boreal-forest zone of the Bureinski Reserve (Russian Federation)

Long term studies of the spider population of the brushwood of Marsh Labrador tea, the most important edificator of dwarf shrub layer in the larch taiga forest predominating in the Bureinski Reserve, have been conducted. During the course of research, 54 spider species belonging to 12 families occurring on shoots of the Marsh Labrador were recorded. This number demonstrates a rather high level of taxonomic diversity comparable to those of the entire spider population of poplar forests (58 species) or valley spruce forests (56 species) of the Bureinski Reserve. The majority of spiders occurring on the Marsh Labrador tea belong to small- or medium-sized species. Web-building and wandering spider groups are equally represented (29 and 25 species correspondingly), yet almost the entire spectrum of ecological groups is represented. The crab-spiders (Thomisidae, Philodromidae) were most diverse (13 species). Spider densities were rather high, for instance, reaching 36 specimens per m in one of the best studied larch taiga forests. A similar index for a poplar forest was about 5 specimens per m [5]. No differences have been found between the spider assemblages of the brush wood of Marsh Labrador tea in different parts of the Bureinski Reserve; the dominating complex usually consisted of 13 species (viz., 20% of the entire quantity). The Marsh Labrador tea seems to be attractive to spiders because it is an evergreen dwarf shrub forming dense brushwood with a particular microclimate and comparatively homogeneous physical environment regardless of the place of growing, such as river terrace or slopes of variable exposure and altitude. Due to permafrost the Marsh Labrador tea usually grows in marshy plots. The dwarf shrub layer formed by the Marsh Labrador tea exists all year round. Its projective cover degree only insignificantly decreased during autumn periods due to partial leaf fall and dying off superterrene parts of sedges. Therefore, the environment formed by the Marsh Labrador tea is notable for its stability during season changes. The Marsh Labrador tea is also a richly blooming plant pollinated by insects, with an extended period of flowering (from June to August). Its large inflorescences attract lots of insect-pollinators, many of which serve the main prey for crab-spiders. The leaf underside of the Marsh Labrador tea is covered with reddish hairs and is actively used by spiders for attaching their egg sacs. Rigid leaves give a good protection for egg sacs against bad weather and serve a reliable retreat for spiders at different stages of their life cycle. Another important characteristic of the Marsh Labrador tea, which is responsible for its wide distribution and dominating role, is an ability to successfully survive fires that are common in the area at hand. This makes the environment formed by the Marsh Labrador tea one of the most stable and quickly recovering.

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