Estimation of Population Trends

As fungi are rarely included in monitoring programmes, there is often a shortage of data that can document an actual decrease in population size. A sudden decline may also be difficult to detect, because the production of fruit bodies is strongly influenced by climatic factors (Chapter 5). A species fruiting in summer may not be observed for several years if the summers are hot and dry, and then, when favourable conditions again occur, it may fruit in abundance. Luckily there are few examples, if any, of common fungi which have been documented to decrease very rapidly during the recent years. In The Netherlands substantial work has been carried out to investigate changes in the frequency of macro-mycetes, based on foray reports, mapping projects and repeated analyses of permanent plots, and a strong decrease, mainly for ectomycorrhizal taxa, has been documented (e.g. Arnolds, 1991; Nauta and Vellinga, 1993). In most other countries similar data are lacking and gradual changes in population sizes of particular species have to be estimated on a more uncertain basis. In many cases however, negative population trends can be assumed with reference to overall changes in habitat quality, land use or forestry practices, which may strengthen the understanding of former, present and even future population changes.

Short-term fluctuations in population levels are also evaluated under some of the IUCN criteria. Fluctuations in fruit body production, caused by climatic factors, make it almost impossible to detect if fluctuation at the population level takes place. Strongly fluctuating population sizes may be an obvious threat for other groups of organisms, but are probably less relevant for fungi.

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