Present status for Cephalanthera rubra and Chimaphila umbellata in Sweden.
The results of the Flora Guardians' national monitoring of the threatened Cephalanthera rubra (VU) and Chimaphila umbellata (EN) are presented. Both species produce dust seeds, are partial or initial myco-heterotrophs and occur mainly in semi-open, dry to mesic, pine-dominated coniferous forests in the southern half of Sweden, with the highest frequencies on the island of Gotland. There are 119 and 677 registered Flora Guardian sites being surveyed during 1990-2015 for C. rubra and C. umbellata, respectively (sites on Gotland not included). In both species, there has been a steady increase in the number of revisited sites per year since 1990, in line with the increasing efforts by the Flora Guardians overall. Cephalanthera rubra is one of the more intensively monitored species on the Swedish mainland with 6.3 visits per site during an average time span of 17 yr. The species was absent from half of its sites during the last survey, but since C. rubra may be dormant underground for some years, this figure is an exaggeration of local extinctions. From 15 sites (13%) the species is presumably extinct, since it has not been found again during the last four surveys. A population decline is seen in 4.5 times as many sites as those that are increasing. Main reasons for the loss of C. rubra are denser canopies and field-layer vegetation as well as clear-felling of the forest, while mild thinning of the canopy, especially of Norway spruce, may favour the species. Figures from the last counts indicate a current population of 600 plants on the mainland, with an addition of at least 13 000 plants on Gotland. The Swedish population is estimated to contain 20 000-25 000 plants. Chimaphila umbellata had 3.3 visits per site during an average time span of 10 yr. The species was absent from 28% of its sites during the last survey, which nearly represents the local extinctions. Site half-life is estimated at 19 yr while mainly small populations disappear. A population decline is seen in 2.7 times as many sites as those that are increasing. Main reasons for the loss of C. umbellata are clear-felling of the forest habitats as well as denser canopies and field-layer vegetation. Sums from the last counts give 68 000 shoots, but since many sites have not been quantified, a coarse estimate of 100 000-200 000 shoots is more probable. However, C. umbellata is probably one of the most overlooked species in the South Swedish flora because it inhabits a very common habitat that botanists visit relatively seldom, and the species is also difficult to detect during most of the year. Active search would definitely yield new sites. The figures on site loss (and population decline) in both species are probably exaggerated due to the fact that they are based on already known sites (which inexorably will go extinct with time) and do not include possible establishments. This is an inevitable effect of monitoring rare phenomena, when not sampling the whole population (of possible habitats), which should be taken account of. Active search for new sites in suitable habitats may partly compensate for this statistical bias, by comparing the number of new sites with current and extinct sites. In both C. rubra and C. umbellata site loss is more marked towards the south of their distributions, correlating with nitrogen deposition intensity and possible subsequent effects on competing vegetation and associated fungi. There is at least one example in which an invasive alien species, Lupinus polyphyllus, has contributed to the local extinction of C. rubra.