De Levende Natuur nummer 1 van 2011 (English summary)

Does soil biodiversity matter for nature rehabilitation?

R.H. Kemmers, E.P. Brinkman, J. Bloem, J. Faber & W.H. van der Putten

Both natural and restored oligotrophic (Nardo-Galion) and mesotrophic haylands (Cirsio-Molinietum) with different floristic qualities were investigated on soil chemical, soil biological and vegetational parameters to test the hypothesis that floristic diversity depends on soil biological diversity. Direct mutualistic and antagonistic relationships as well as indirect relationships through nutrient cycling were studied by feed back experiments in the laboratory and field surveys. Pots with sterile soils were inoculated with soils from the different hayland types and conditioned with seedlings of disturbance species, common accompanying species and characteristic species. For the Cirsio-Molinietum haylands it appeared that characteristic species produced less biomass if they were grown on soils conditioned by disturbance species, specifically if the soils originated from sites with a bad floristic quality. For Nardo-Galion haylands it appeared that characteristic species produce little biomass when grown on sterilized soils. On unsterilized soil from the same sites the productivity of characteristic species was variable probably due to the occasional presence of ecto-mycorrhizae.

Nardo-Galion haylands with a good quality appeared to be bound to an active microbial community functioning as an nitrogen sink by N-immobilization, so that only little nitrogen remains available for plant growth. There is an insignificant flux of nitrogen to higher trophic levels in the soil food web. In Cirsio-Molinietum haylands a high base saturation appeared to be an important prerequisite for an active soil life. Through the soil food web important nitrogen fluxes flow from microbes, to nematodes and earthworms finally. Bacteria, protozoa and especially earthworms represent the most important nitrogen sink. In both hayland types environmental stress, like acidification, is likely to cause a shift in the soils nitrogen balance from nitrogen immobilization to net nitrogen mineralization in favor of crop productivity and decreased floristic diversity.

We got sufficient evidence from our study that the soil food web seriously affects plant species performance. We not only recommend a follow up of this exploratory study but also a serious consideration of restoration measures focused on rehabilitation of soil life as a boundary condition for the maintenance of floristic diversity.

Flora of the Meuse floodplain: 15 years of change by ecological restoration

G. Kurstjens & B. Peters

Between 1990 and 2006 the area of protected nature reserve in the floodplain of the Meuse has increased from less than 100 ha to more than 1.500 ha. Extensive field research and literature study (Maas in Beeld project) has been carried out to reveal changes in flora which can be related to ecological restoration projects.

More than 50% of indicative plant species of river ecosystems showed a positive trend; one seventh of the species has decreased by comparising the period 1980 t/m 1993 and 1994 t/m 2009. When classified into ecological groups, plant species of open water, pioneer situations, open woodland and edges of scrub, showed a positive trend. Characteristic plant species of seepage situations, wet forests and dry grasslands neither showed a positive nor negative trend.

Important factors for success are changing agricultural land into nature reserve and increasing river dynamics. During floods, (sandy) soils are deposited and seeds are transported. Man-made pioneer situations created by gravel mining and global warming contribute to success, but to a lesser extent. The decrease in some species abundancy is caused by a lack of source populations, ongoing habitat destruction and the lack of river dynamics.

We advise to focus on increasing the area of nature reserves along the Meuse valley and to  improve the quality of floodplain projects. Along the Zandmaas section more attention should be paid to seepage water as an important ecological factor. Other important themes are stimulation of natural flooding by removing dams that drive up the water and uncovering sandy and gravel soils.         

Fifty years of growth of a drift sand bog in the Kootwijk-forestry (Veluwe area, the Netherlands)

R.J. Bijlsma, H.N. Leys & I.S. Zonneveld

The drift sand bog phenomenon was discovered by the last two authors in 1959 in the afforested drift sands near Kootwijk (foto 1). In 2009 the first author rediscovered this remarkable site (foto 2). The bog consists of Sphagnum capillifolium and appeared even larger in size than in 1959. The phenomenon occurs in other Scots pine afforestations in former drift sands of the Veluwe as well. The bogs are situated in north-facing slopes on very nutrient poor drift sand and often border on more or less isolated blown-out areas that accumulate cold air at nights with calm weather and clear skies. Usually a gap in the Scots pine canopy is present over the bog. These features together cause relatively cool and humid microclimatic conditions which are apparently sufficient to sustain peatmoss establishment and persistence. The high precipitation values (850-900 mm per year) of the Veluwe-area along with the relatively high grazing pressure by red deer (slowing down succession) further facilitate this process. The suggestion that water stagnating properties of blown-over soil profiles may explain the occurrence of drift sand bogs could not be confirmed. Up till now 9 peatmoss species have been found in more than 50 bogs in the Veluwe-area (figure 1). Surprisingly, no other moisture indicating vascular plants or bryophytes have been found. The rich liverwort communities that occurred in north-facing slopes in drift sand afforestations disappeared in the early 1980s caused by the encroachment of Deschampsia flexuosa. Apparently, peatmoss carpets are able to outcompete this grass species. Due to succession towards deciduous forest, drift sand bogs will eventually disappear due to litter accumulation and shading, especially on blown-over soil prolies. Slopes on very humus poor drift sand without soil profiles are the most promising for managing drift sand bogs in the future.

By students/PhD: Sexual reproduction of Pussy Toes: fertile or futile?

T.S. Slagter & M. Wolma

Pussy toes (Antennaria dioica) on Schiermonnikoog is pollen-limited, with a fragmented population. None of the insect orders foraging on Pussy Toes appeared to transfer pollen better than any of the other insect orders, suggesting that the species is a generalist. Flowering periods of male and female plants of twelve individual subpopulations were compared. There were only six patches with both male and female flower heads. Three of these showed a significantly different, albeit overlapping, difference in flowering period between males and females. For all subpopulations together, flowering periods of male and female plants on Schiermonnikoog were significantly asynchronized as well. A fluorescent dye experiment, as well as observations on the pollen load on visitors, suggested limited pollen dispersal between subpopulations. We conclude that successful pollen transfer from male to female flowers of Pussy Toes on Schiermonnikoog is limited, because in only three subpopulations the flowering periods of male and female flowers were synchronized, and other patches comprised one gender only. The general asynchronization of male and female flowering times also reduces the likelihood of pollen dispersal between patches. This means that the series of very small patches of flowering plants on the island is only poorly connected by pollination, and thus do not function as a single, larger population. Effectively, the population size of Pussy Toes on Schiermonnikoog is thus much smaller than the total number of individuals suggests.

The underground metamorphose of Stag beetles

P. Hendriks

In recent years, several studies in relation to behavioural aspects and conservation of populations of Stag beetles (Lucanus cervus) have been done. At the moment collaboration on a European scale is taking place. Several documents with measures for conservation purposes have been published. While studying the larval growth of this beetle, interesting information about cocoon building and pupation was gathered as well. It was possible to follow and photograph the metamorphose of a Stag beetle larva to pupa and beetle, a very fragile and invisible stage in a Stag beetle life. The larvae, as well as the pupae are found under the surface in and near decayed hard wood. It is getting more and more evident that maintenance of underground decaying hardwood is essential for the conservation of populations of Stag beetles.  

Restoring the coexistence of plant species of ancient forest, forest edges and Nardion grassland in a former seed orchard

L. De Keersmaeker, K. Vandekerkhove, E. De Crop, H. Demolder, B. Opstaele & L. Martens

Vroenenbos is a 47 ha part of the ancient forest of Halle (560 ha) in Flanders (northern Belgium). Most of the forest of Halle was converted from a grazed coppice with standards to a high forest where light-demanding plant species are scarce. By contrast, plant species of nutrient-poor grassland, heathland, forest edges, and ancient forest still coexist in Vroenenbos. This is the consequence of a quick succession of clear-felling of coniferous stands (1850-1960), followed by a specific management as seed orchard of coniferous tree species (1960-1990). The seed orchards were left unmanaged from 1990 onwards and the area was protected in 2006 to restore the floristic diversity. For this purpose, we studied the emergence of 28 target species, present in Vroenenbos but rare or declining in Flanders, after sod-cutting of 18 experimental sites. Emergence was higher on sites that were not, or only prior to 1870, managed as arable land, than on sites managed as arable land after that time. Furthermore, the former are characterised by a low soil content of plant-available phosphorous, whereas the latter are eutrofied. Based on these results we present a management plan, that includes clear-felling of the remaining seed orchards. This conversion will be followed by mowing of sites with high potentials for restoration of species-rich Nardion grassland, that are located at the foot of the slope, and by grazing of higher sites, that are more or less eutrophicated. The valley itself, much of which is covered by spring wood, is left unmanaged.