Abstract
In the black-spruce clay-belt region of Western Québec, soil nutrients are limited due to paludification. Under paludified conditions, nutrient subsidies from decomposing surface coarse woody material (CWM) may be important particularly during the later stages of ecosystem development when deadwood from senescent trees has accumulated. For soil organisms, CWM can alter microclimatic conditions and resource availability. We compared abundance and species richness of oribatid mites below or adjacent to CWM across a chronosequence which spans ca. 700 years of stand development. We hypothesized that oribatid abundance and richness would be greater under the logs, particularly in later stages of forest development when logs may act as localized sources of carbon and nutrients in the paludified substrate. However, oribatid density was lower directly under CWM than adjacent to CWM but these differences were attenuated with time. We suggest that oribatids may be affected by soil compaction and also that such microarthropods are most likely feeding on recently fallen leaf litter, which may be rendered inaccessible by the presence of overlying CWM. This may also explain the progressive decline in oribatid density and diversity with time, which are presumably caused by decreases in litter availability due to self-thinning and Sphagnum growth. This is also supported by changes of different oribatid trophic groups, as litter feeders maintain different numbers relative to CWM with time while more generalist fungi feeders only show differences related to position in the beginning of the succession.
Highlights
In the prolonged absence of major disturbance, forest ecosystems may pass through a retrogressive phase whereby overall productivity declines in response to a long-term net loss of nutrients such as phosphorus (P) [1,2]
We collected 1180 Acari (824 Oribatida including immature stages), 292 Collembola, and 83 other microarthropods composed of Thysanoptera, Homoptera (Aphidae), and larval stages of Coleoptera and Diptera
1841), which feeds on plant tissues, and Eniochthonius minutissimus (Berlese, 1903), a typical fungi feeder, were very abundant
Summary
In the prolonged absence of major disturbance, forest ecosystems may pass through a retrogressive phase whereby overall productivity declines in response to a long-term net loss of nutrients such as phosphorus (P) [1,2]. 1000 years) [6,7] In these ecosystems, growth of Sphagnum combined with rising water tables and cold temperatures result in an increasing proportion of nutrients immobilized in poorly decomposing organic matter as stands age [8]. Mill.) B.S.P) feathermoss forests of the clay-belt region of Western Québec are often prone to paludification in the absence of fire [9] and are some of the most nutrient limited forests known [10]. In this region, surface deadwood decreases radically after 260 years after fire (unpublished results). Buried wood resulting from paludification increases steadily as stands progress to old-growth
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