How Sphagnum bogs down other plants
A review in Trends in Ecology and Evolution arguing that Sphagnum, the peat moss that often dominates bogs in temperate and cold climates, succeeds because it creates a habitat in which few other plants can flourish. Van Breemen holds that the traditional view of Sphagnum as simply well adapted to wet, nutrient-poor mires needs adjusting to recognise its active role in creating those conditions: it builds acidic, nutrient-poor, cold and anoxic peat bogs, and the bog helps it outcompete other plants for light. The review works through water-holding hyaline cells, carboxylic acid groups that give a high cation exchange capacity and largely account for its acidity, chemically protected litter that decomposes slowly, efficient interception of atmospheric nutrients, and peat that conducts heat poorly. It concludes that some direct and much circumstantial evidence points to four factors mainly responsible for adverse conditions for vascular plants on raised bogs: low nutrient availability, anoxia, low temperatures and high acidity.
The synthesis uses Jones, Lawton and Shachak's terms; niche construction does not appear. Sphagnum combines autogenic ecosystem engineering, building bogs out of its own dead tissue, with allogenic engineering, as iron pans and clogged pores make the mineral soil beneath less permeable. Like trees it uses dead tissue to outcompete others for light, but by attacking competitors at the root. A clonal patch and its bog can be regarded as an extended phenotype, and because these properties also benefit the individual plant in the short term, this may have aided the genus's evolution. Few studies have set out to test the adverse factors, evidence on nutrient limitation differs between regions, and raised bogs can form without Sphagnum, as in the tropics. Drainage, he notes, irreversibly increases the permeability of peat, which then becomes unsuitable for Sphagnum. The bridge to psychological safety is ours. Tom's Organisational Substrate article argues that people in a substrate that suits them often unconsciously reinforce it, potentially to the detriment of others; we read Sphagnum as that pattern with no intent at all, and the conditions for speaking up as part of ground built this way.
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