Partial restoration of fungal and plant species diversity by removal of litter and humus layers in stands of Scots pine in the Netherlands

Published source details De Vries B.W.L., Jansen E., Van Dobben H.F. & (1995) Partial restoration of fungal and plant species diversity by removal of litter and humus layers in stands of Scots pine in the Netherlands. Biodiversity and Conservation, 4, 156-164.
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Summary

Due to high atmospheric acid and nitrogenous deposition, the vegetation in Scots pine Pinus sylvestris forests on originally poor, dry sandy soils in the Netherlands has dramatically changed. Formerly there was a sparse undergrowth of higher plants, mainly heather Calluna vulgaris and/or crowberry Empetrum nigrum and a dense cover of bryophytes and lichens, and abundant ectomycorrhizal fungi. The undergrowth in these forests is now usually dominated by wavy hair-grass Deschampsia flexuosa together with a number of other nitrophilous vascular plants, whilst ectomycorrhizal fungi and terricolous lichens have dramatically declined.

Periodic removal of litter and humus layers has been suggested as a way to help restore the previous species diversity. A field experiment was carried out in which humus and litter layers were completely removed by sod-cutting. As removal of these layers with a surplus of cations may have an acidifying effect, the application of lime (crushed limestone) as a countermeasure was also investigated.

Study sites: Five P.sylvestris stands, on formerly nutrient-poor acidic sands, ranging from 40 to 80 years old were selected: three (Appelscha, Smilde and Dwingeloo) in the northeast Netherlands (Drenthe province): and two (Ugchelen and Leuvenum) in the central Netherlands (Gelderland province).

Experimental design: A factorial experiment was set up with sod-cutting and liming as variables. In each stand, eight plots (each 50 mÂ²) were assigned the following treatments: control without liming; control with liming; sod-cutting without liming; sod-cutting with liming.

Sod-cutting consisting of manual removal of the litter and humus layers, including the vegetation, during the spring of 1985. At this time, 5 kg of Dolokal (crushed limestone) equivalent to 1 ton/ha, was applied to liming treatments.

Fungi and plant monitoring: Ectomycorrhizal fungi were recorded monthly during the summer and autumn from 1986-1989. Fruit bodies were counted and then removed in order to avoid recounting.

Vegetation was recorded in the summer of 1985 immediately before the start of the experiment, and at the end of the experiment in the summer of 1989. The abundance of all species (except those in the tree layer) was estimated as percent cover.

Ectomycorrhizal fungi: A total of 27 taxa was observed. Liming did not have any significant effects on species richness or fruit body abundance.

In the first year after sod-cutting, no effects on species richness and fruit body abundance were noted, but the number of fruit bodies was significantly higher in the sod-cut plots in 1987. This effect became less in subsequent years and by the fourth year the differences compared with the control were no longer significant. The effects of sod-cutting on fruit body abundance were not significant for most species, however, there was a significant positive effect for Laccaria bicolor, Inocybe lacera and Cortinarius fusisporus, and a significant negative effect for Lactarius hepaticus.

The majority of fruit bodies (80%) were observed in the sod-cut plots. However, this effect is mainly due to only one species, L.bicolor, which comprised 68% of the total number of fruit bodies and showed a very clear preference for sod-cut plots. Differences in fruit body abundance for the remaining species were small between control and sod-cut plots. There was clearly a major effect of sod-cutting in reversion of ectomycorrhizal succession to earlier stages.

Vegetation: Sod-cutting resulted in a dcrease of species of later successional stages (shrubs, broadleaf tree saplings, pleurocarpous bryophytes), whilst pioneer species (mostly acrocarpous bryophytes, but also P.sylvestris saplings) increased. Significant effects of liming were found for a few species only: rosebay willow-herb Chamerion angustifolium and dandelion Taraxacum officinale increased significantly with liming, whilst heather Calluna vulgaris decreased.

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