Individual study: Effects of harvesting and trampling on the sustainability of edible mushroom harvests at Moosboden fungus reserve, Genève, Switzerland
Egli S., Peter M., Buser C., Stahel W. & Ayer F. (2006) Mushroom picking does not impair future harvests – results of a long-term study in Switzerland. Biological Conservation, 129, 271-276
Forest fungi have important ecosystem functions, such as decomposing organic matter and improving pathogen resistance of their host trees. Picking mushroom fruiting bodies for food is a popular past-time in many countries, and sometimes commercially important. The expansion of commercial harvesting has led to widespread concern about possible damage to fungi populations through over-harvesting.
Fungi harvesting, in addition to potentially reducing the availability of spores needed for dispersal and reproduction, may be detrimental through physical damage from picking and trampling. Several countries have introduced legal restrictions on harvesting. In Switzerland there are weight limits on harvest, a measure which has proved controversial due the lack of scientific evidence regarding the effectiveness of such restrictions. In this case, the effects of trampling and mushroom harvesting on future mushroom harvests are described.
Study site: The study was carried out in Moosboden, a 3 ha fungus reserve (1,250 m.a.s.l.) in southwestern Switzerland. The area is a uniform Norway spruce Picea abies woodland, reforested in the late 19th century.
Fourteen 13 m × 13 m blocks were divided into four 6.5 m × 6.5 m plots with the following four treatments distributed randomly:
1) picking with trampling;
2) picking without trampling;
3) no picking with trampling;
4) no picking without trampling.
The study commenced in 1990 and ended in 2000. In the plots in which picking occurred, all edible mushrooms were plucked or cut weekly throughout every fruiting season (May – December). Plucking mushrooms entailed removing the cap (or pileus) and stem (stipe) from the soil in a manner emulating mushroom harvesters. The treatments in which trampling occurred, corresponded to normal walking associated with mushroom harvesting, emulating that of a mushroom picker. On the 'without trampling' plots, catwalks were installed prior to starting the experiment, to avoid trampling while picking or counting the mushroom fruiting bodies.
Sampling: All fruiting bodies of soil-inhabiting macromycetes species were identified and counted at weekly intervals from May to December. When first recorded, a fruit body was marked with a harmless dye (methylene blue) on the cap to avoid double counting. Thirty-nine species within the wood that form large quantities of very small fruiting bodies (but which are edible and collected) were excluded to avoid counting difficulties, as were 12 taxonomically indistinct species, to avoid possible irregularities due to unclear identification. All observation plots were surrounded by fences to avoid disturbance by mushroom pickers.
Effects of harvesting: A total of 250 species were counted, comprising 50,222 fruiting bodies. Of these, 10,173 fruiting bodies of 51 species were edible. The results of the study suggest that the production of fruiting bodies was unaffected by harvesting. Although large inter-annual variations occurred (e.g. due to weather conditions), both species richness and the number of fruiting bodies were similar in harvested and non-harvested plots (average of treatments 1 and 2 versus average of treatments 3 and 4, see Table 1, attached).
Effects of trampling: Trampling significantly reduced the number of fruiting bodies produced (average of treatments 1 and 3 versus average of treatments 2 and 4). Whilst the values given in Table 1 (attached), indicate that there was a large variation in average numbers over the course of the 10 year study, perhaps suggesting that differences were not significant, these variations were due to inter-annual differences. In every year, the number of fruiting bodies produced was lower in trampled plots, and data analyses suggests that trampling reduces fruiting body production by 30%. The average number of species was also lower in trampled compared with untrampled plots. However, contrary to expectations, the total number of fungi species that fruited was marginally higher in the trampled than in the non-trampled plots (195 and 189, respectively).
Conclusions: Since harvesting mushroom and toadstool fruiting bodies effectively removes the spores, evidence from this study suggests that either fungi regenerated through mycelial spread, or that there was recruitment of spores from elsewhere. Whilst the results suggest that fungi harvesting per se is not detrimental, larger-scale studies are needed before this can be established with certainty. Harvesting generally occurs over large areas and may thus have a greater detrimental effect on spore availability than would experimental harvesting in small plots. Trampling reduced the number of fruiting-bodies and average number of species, but not the total number of species. It appears likely that trampling destroys mushrooms and toadstools during the early stages of growth prior to fruiting, but does little or no damage to the mycelia.
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