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Abstract

Community assembly is the trajectory exhibited over time regarding species composition and community structure as species colonize an empty patch. Chase (2007) distinguish two basic types of assembly where a niche-assembled community is constrained by species interactions and competitive hierarchies whereas a dispersal-assembled community is unaffected by competition. The first wood-living (saproxylic) beetles to colonize a dead tree are sub-cortical, cambial-living species with a larval development-time of one year or less. Important community assembly events could therefore take place the first summer after tree death. Community assembly was studied during the eight weeks immediately after tree death. By exposing 0.5 m long stem sections (bolts) of Norway spruce, Picea abies, to colonization for increasingly longer times (0.5, 1, 2, 4, and 8 weeks) a temporal sequence was created. A total of 140 bolts at four forest sites in central Sweden were studied with six to eight replicates per site. Two of the sites were old-growth forest and the other two were forest sites subjected to burning right before the experiment started. I used community ecology measures to describe assembly patterns and emphasize findings that would have gone unnoticed in an analysis confined to the 8-week final state. In total 8802 beetles of 56 species were reared from the bolts. Two fire-dependent species were found in burnt forest, this is noteworthy since unburnt bolts were used in both forest types. The total number of emerged beetles per bolt was similar in the two forest types in early assembly but later this density was higher in the old-growth forest. During assembly the community-level carrying capacity was reached in old-growth forest but not in burnt forest. During assembly, community evenness and taxonomic richness was higher in the burnt forest than in old-growth forest but at eight weeks these community measures had converged. The two forest types became more dissimilar regarding species composition as the community assembly progressed. Old-growth forest also had a lower bolt-to-bolt variation in species composition than burnt forest. Cambivores was the functional group that made up the largest proportion of individuals in both forest types but the proportion was highest in old-growth forest. The proportion fungivores was highest in burnt forest. The proportion predators peaked early in both forest types and then decreased during assembly. In old-growth forest, 74 % of the bolts were numerically dominated by the cambivorous scolytine Dryocoetes autographus. In burnt forest only 33 % of the bolts were dominated by that species. Furthermore, burnt forest also had fungivores as bolt dominants, for example the fire-favoured corticarid Corticara rubripes, whereas old-growth forest bolts were always dominated by cambivores. In conclusion, the beetle assemblages in the two forest types followed different assembly trajectories. The beetle assemblage in burnt forest conforms to a dispersal-assembled community whereas that in old-growth forest conforms to a niche-assembled community (sensu Chase 2007). The biology of fire-adapted beetles is discussed in light of these findings.

Published in

Title: Beetles: Biodiversity, Ecology and Role in the Environment
Publisher: Nova Science Publishers

SLU Authors

UKÄ Subject classification

Ecology

Publication identifier

  • ISBN: 978-1-63463-380-2

Permanent link to this page (URI)

https://res.slu.se/id/publ/64401