Mushroom picking does not impair future harvests – results of a long-term study in Switzerland

Summary

Study 1

Forest fungi have important ecosystem functions, such as decomposing organic matter and and pathogen resistance of their host trees. Picking their fruiting bodies for food is a popular past time in many countries, and is sometimes commercially important. The expansion of commercial harvesting has led to widespread concern about over-harvesting and possible damage to fungi populations. Several countries have introduced legal restrictions on harvesting. In Switzerland there are weight limits on harvests, a measure, which has proved controversial due the lack of scientific evidence regarding the effectiveness of such restrictions. In this case, the long-term effects of picking or cutting mushrooms on future mushroom harvests are described.

Experimental design: The study was carried out in Chanéaz, a 74 ha fungus reserve in southwestern Switzerland. The area comprises mixed old-growth forest dominated by beech Fagus sylvatica, pedunculate oak Quercus robur, Norway spruce Picea abies, silver fir Abies alba, Scots pine Pinus sylvestris, Eastern white pine Pinus strobus and European larch Larix decidua.

Experimental design: The study was conducted over a 27-year period (1977-2003). Five 300 m² blocks were divided into three 10 m × 10 m plots containing three treatments:

1) harvesting by picking
2) harvesting by cutting
3) a control

In treatment plots, all edible mushrooms were plucked or cut weekly throughout every fruiting season (May – December) in a manner mimicking that of a mushroom harvester. Plucking mushrooms entailed removing the cap and stipe (stem) from the soil with some damage to the mycelium. Cutting mushrooms entailed slicing the stipe with a knife close to the ground, thus avoiding damage to the mycelium. All observation plots were surrounded by fences to avoid disturbance by mushroom pickers.

Sampling: All fruiting bodies (i.e. cap and stipe) of soil-inhabiting macromycete fungi were identified and counted at weekly intervals from May to December. When first recorded, the fruiting bodies were marked with a harmelss dye (methylene blue) on the cap to avoid double counting. Thirty-nine species that form large quantities of very small fruiting bodies (but which are still harvested) were excluded to avoid counting difficulties, as were 12 taxonomically indistinct species to avoid possible irregularities due to uncertain identification.

A total of 436 species were counted, comprising 97,700 fruiting bodies. Of these, 53,863 fruit bodies of 103 species belonged to edible fungi.

Selective harvesting of ground-dwelling, edible macromycete fungi did not decrease relative to unharvested non-edible ones with respect to either the abundance of fruiting bodies or species richness. Over the 27-year duration of the study, no different trends in fruting body production were detected between the harvested and non-harvested sites, irrespective of the harvesting technique deployed. Furthermore, average species richnes and average abundance of fruiting bodies over the entire 27-year period did not differ significantly between treatments (see Table 1, attached).

Conclusions: In this study, no difference in species richness or abundance of species of edible fungi (that are collected by mushroompickers) was evident in the harvested compared with the non-harvested sites. Since harvesting fungal fruiting bodies effectively removes the spores, either adequate numbers of spores were recruited from neighbouring areas or fungi reproduced asexually through the spread of mycelium. The results raise questions about the usefulness of harvest quotas. However, as widescale harvesting fungi may deplete the availability of spores over large areas, further information about spore dispersal is needed before the impacts of such harvesting on fungi populations can be determined.

Study 2

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.

Experimental design:

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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