During a 5-year period, the effects of thinning, final-felling and fertilizing with ammonium nitrate (150 kg N per hectare) on the production of edible mushrooms were studied on 23 separate sites located over the whole of Sweden. Approximately 2.500 mushroom surveys were conducted on these sites. These were non-repetitive, and the whole analysis is based on a comparison between a control (no forestry operations) and treated sites. The following results were obtained: 1. The method we used suffers from some obvious drawbacks. It is probably not possible to study the effects on the amount and species composition of the mushroom flora using traditional sample-plot techniques. To those who plan similar studies in the future, we recommended a careful survey of the mushroom flora present on the trial area over at least five years before any forestry treatments are carried out. Other factors to note are the size of the parcels and the length of the observation periods. Studies of species composition probably require sample plots of at least 2000 - 2500 m2, while half of that would be sufficient if one is simply measuring biomass. Furthermore, repetition is necessary. The reason that we did not follow this practice here was that the main purpose at the outset of our experiment was to study changes in the vegetation on a larger number of sample plots, randomly laid out on the parcels. 2. The annual mean productin of edible mushrooms on the control plots in the 23 trials was approximately 40 kg per year and hectare. Based on these figures, the production of edible mushrooms on forest land can be calculated to at least 800 million kg per year, or about 100 kg per capita. Picking and consuming the most attractive edible mushrooms amounts to only a small fraction of this total. The collected amounts of chanterelles and edible boletes averaged only about 1.4 kg per year and hectare or about 5% of the total amount of edible mushrooms. Edible gyromitra morels (false morels) can be found on the clear-cut parcels during a 3-5 years period, with an average production of 0.5-1.0 kg per hectare and year. 3. The effects of final- felling on edible mushroom production depend on whether or not seed trees are left on the site. On eight plots with seed trees the average mushroom productin was 13.3 kg per year and hectare, as opposed 2.3 kg on 13 plots with no remaining seed trees. The corresponding value for the control parcels averaged 44.1 kg per hectare. During the first five years clear-cut areas produce only 5% of the amount of mushrooms found in untreated stands. If seed trees are left, however, this corresponding value jumps to 30. 4. Thinning has very little effect on the production of edible mushrooms. However a 5-year program of combined thinning and fertilizing resulted in an average reduction of 30%. The average productin during the studied 5-year ........
