De Levende Natuur nummer 6 van 2015 (English summary)

The restoration of matgrass sward-vegetation in Southern Limburg (The Netherlands)

M.J. Weijters, N.A.C. Smits & R. Bobbink

The biodiversity of calcareous grasslands and matgrass swards on hillsides in Southern Limburg is still declining, despite the great commitment of the local site-managers and long-term research input. Both communities are Natura-2000 habitat types for which The Netherlands has a European conservation responsibility. Both grassland types are part of a gradient in soil pH, with low pH at the top and high pH at the bottom of the slope. This gradient in pH results in different grassland types along the slope, with acid grassland at the top, matgrass sward in the middle part and calcareous grassland at the bottom of the slope. This article summarizes the research conducted from 2005-2013 to identify the cause of the deterioration of the matgrass sward parts of these unique slopes, funded by the Dutch national research programme on restoration (OBN). 

The soil of the matgrass vegetation had significantly higher ammonium concentrations and a higher ammonium to nitrate ratio, compared to the calcareous grassland vegetation. This might be one of the major causes of the still declining species richness of these sites. By measuring the PAA (potential ammonium oxidizing activity) it was clearly shown that the nitrification in the matgrass swards was hampered compared to both the acid and calcareous parts of the hilly gradient. Study of the DNA of the soil  bacteria showed that there was no difference in bacterial composition over the gradient with the three vegetation types. The hampered nitrification rates in the matgrass swards were thus not caused by the absence of typical nitrifying bacteria. In addition, the soil pH was much too high,  between 4.8-6.0, to be the cause of the reduced rate of nitrification. In order to study the potential effect of the vegetation, a greenhouse experiment was conducted in which characteristic plant species of the matgrass vegetation and of calcareous grassland both were grown at soil sampled from underneath matgrass sward and calcareous grassland. The PAA indicated that the plant species of matgrass swards hampered the nitrification process. In a climate chamber study with intact soil cores it was clearly shown that the soil pore-water showed high concentrations of nitrate while only ammonium was added in the artificial rain, and the PAA measured at the end of the experiment showed much higher nitrification-rates than measured at the same sites in field conditions. This experiment showed that after removal of the matgrass-sward vegetation a strong increase in nitrification activity occurred. 

The hampering of the nitrification rate by the matgrass vegetation could be considered as an advantage for these plants under N-poor conditions by preventing the transition of ammonium to nitrate, and thus reducing the leaching of mobile nitrate. However,  the slopes in Southern Limburg are currently coping with high atmospheric inputs of N, especially in its reduced form (NHy). This high N deposition, combined with hampered nitrification caused by the vegetation itself, have led to an accumulation of ammonium and a high ammonium to nitrate ratio in the soil of the matgrass vegetation. Two things are crucial for the restoration of these unique slopes, namely the reduction of the atmospheric N inputs and the removal of the accumulated ammonium. To reach the latter, it is a possibility to remove ca. 5 cm of topsoil – with vegetation - at strongly degraded sites. After restoring the abiotic conditions, green hay from an intact species-rich  donor-site should be added and also disappeared species can be reintroduced as seeds. Small-scale field experiments are being conducted at this moment to test this method.

Restoration of species rich fauna communities on calcareous grasslands

M.E. Nijssen & C.G.E. van Noordwijk

Calcareous grasslands are well known for their high biodiversity of plants and invertebrate species. In The Netherlands only around 20 small grasslands patches remain, most of them smaller than 2 hectares. These grasslands suffered from fragmentation, nitrogen deposition and lack of management for decades until renewed autumn grazing was introduced around 1980. Composition and structure of the vegetation improved, but populations of characteristic invertebrate species failed to recover. To gain insight into the bottlenecks preventing further restoration we analysed the life-cycles and traits of characteristic butterflies, ants and carabid beetles in relation to the chalk grassland habitat. This analyse revealed four main bottlenecks for chalk grassland fauna: 1) increased grass encroachment due to high N-deposition, leading to a cooler microclimate in summer and more intensive grazing in autumn; 2) small and isolated grasslands leading to small and vulnerable populations and low chances of (re)colonisation; 3) disturbance through intensive management in autumn; 4) climate change leading to larger fluctuations in population size and increased chances of local extinction. Restoration and conservation of rich fauna communities in calcareous grasslands therefore requires an expansion and connection of existing calcareous grasslands, further reduction of nitrogen deposition and a change in management timing and intensity. Trials are currently taking place to investigate whether rotational summer grazing has a positive impact on calcareous grassland plant and animal communities.

The story and restoration steps of the ‘Montagne Saint-Pierre’ nature reserve in Wallonia

R. Vanherck & T. Ory vertaald door M. Lejeune

The ‘ Montagne Saint-Pierre’ is a Walloon nature reserve located at the north-east of the city of Visé. This mediterranean like area is composed of more than 35 hectares of calcareous grasslands and is well known as the home for many rare species of plants (i.e. wild orchids) and insects. The reserve was widely dominated by large open areas but reforested rapidly following the abandonment of grazing in the early 20th century. Only small areas of dry grasslands remained at that time. Thanks to budgets accorded by the European commission through two LIFE projects (named ‘hélianthème’ and ‘pays mosan’) major restoration work has taken place since 2011. Deforestation of large areas occurred and those areas were bounded with fences that permitted pasture with sheeps and goats. Restoration work will still continue in the coming years looking for the most appropriate long term management plan taking into account new possible management techniques and cost control.

Altenbroek: a nature reserve in the valleys of Noor and Voer, Belgium

J. Dewyspelaere & R. Palmans

Since its acquisition in 1995, Natuurpunt performs a management in the nature reserve Altenbroek (Voeren (B)) focused at restoration of habitats that had been deteriorated by the expansion of agriculture and forestry. Especially calcareous grasslands and heathlands should take advantage of it. Besides the traditional restoration management by grazing and mowing, also removal of phosphate-rich topsoil and phosphate-extraction are applied.

Irregular high forest: an alternative for the traditional coppice-with-standards forest management of the slope forests of Zuid-Limburg?

J. den Ouden, P.W.F.M. Hommel, K.A.O. Eichhorn & F.S. van Westreenen

The slope forests of Zuid-Limburg, particularly with chalk bedrock close to the soil surface, are renowned for their diverse flora, but this diversity has decreased dramatically in the last decades. This decrease has been attributed to several environmental factors, but the main cause appears to be the prolonged dark phase persisting under a dense tree canopy. Traditionally, these slope forests were managed under a coppice-with-standards silvicultural system, frequently bringing light and disturbance to the forest floor and thus promoting the maintenance of a highly diverse vegetation. Around World War II, this traditional system was abandoned, leading to the development of high forest, a long-term closure of the forest canopy and consequently the demise of the characteristic flora.

Several restoration projects have demonstrated that reversion to traditional coppice-with-standard management greatly benefits the restoration of the typical slope-forest flora. This type of management is extremely costly, however, and thus not appropriate to be installed over larger areas. This article describes the first results of an alternative approach with the application of an irregular high forest system. 

The irregular high forest may best be characterised as a selection forest with light-demanding species. Within a 15-20 year cycle, all undergrowth is removed, except for a selection of young trees that are added to the reserve. The reserve consists of a population of trees of different ages, and are selected for stem form and species. The system also resembles the traditional coppice-with-standards in the frequent disturbance and clearance of the undergrowth, but differs from it in the lower frequencies of the coupes and the larger canopy cover of the reserve. Harvest of larger diameter trees of intended high stem quality will reduce harvesting costs and increase revenue.

The irregular high forest system was established a two experimental sites, each with a control treatment, and a 35% and 55% residual canopy treatment. Results of the first three years after harvest show a strong increase in botanical diversity. Species of high light and forest edge habitats have re-established from the seed bank or from seed dispersed into the sites. Typical forest herb species increased in abundance or re-established on the site. 

The irregular high forest systems appears a promising alternative to the traditional coppice-with-standards system to restore the characteristic flora of the slope forests in Zuid-Limburg. Yet, it will take a number of cutting cycles before the entire system can be evaluated in terms of ecological and economic sustainability.

Effects of increasing canopy heterogeneity in calcareous woodlands on the Lepidopteran fauna

M.F. Wallis de Vries & M.J.M. Prick

We investigated the short-term impacts of restoring management on butterflies and moths in two ancient woodland sites on calcareous slopes. At both sites an untreated control plot was compared to two plots where crown cover was reduced to 55 % and 35 %, respectively. Surveys were conducted prior and after the felling between 2011 and 2014. Butterfly numbers increased and witnessed to the reestablishment of the endangered Silver-washed fritillary Argynnis paphia. In contrast moth numbers and species richness fell dramatically in both cutting treatments. This especially concerned species with woody host plants from woodlands and woodland edges. The decline was less strong on the northwesterly exposed site than on the south-exposed site. We argue that the changes in the Lepidopteran fauna are strongly determined by changes in vegetation structure and microclimate, with contrasting effects for butterflies and moths. To promote both species groups, rotational management at a sufficient scale to prevent detrimental edge effects seems advisable.

Lessons taken from dead wood beetle research in hollow trees of the Voerstreek

A.A.M. Thomaes & L. Crevecoeur

A study was performed on the saproxylic beetles present in hollow trees in Voeren and surrounding. We found 23 species listed on the German Red List, Crepidophorus mutilatus was found as a new species of the Belgian fauna and Gnorimus variabilis was rediscovered since the last observation in 1932. Elater ferrugineus, an indicator of landscapes rich in saproxylic species was found in 13 of the 16 studied sites. Based on this research we can conclude that the region of Voeren is still very rich in saproxylic beetles of hollow trees. Management guidelines are given to prioritise, protect and restore landscapes with hollow trees in order to protect the associated fauna.

Nitrate pollution of spring fed fens in South Limburg (NL)

H. de Mars, S.P.J. van Delft, E.J. Weeda & J.H.J. Schaminee

Stream valleys in South Limburg are known for their many springs and spring fed fens. Their importance is recognized by the designation of six Natura 2000 areas.  

However, South Limburg groundwater is struggling with high nitrate levels, up to 200 mg/l from 1975 onwards, due to intensive fertilization. So far little progress has been made to reduce this surplus substantially. Therefore the quality and biodiversity of springs and the spring fed fens are supposedly under pressure. Although the situation regarding the water quality of the springs is relatively well documented, until recently a clear picture of the situation for the spring fed fens was missing. Research in the context of OBN fills that knowledge gap now. The results so far seem to imply that most of the nitrate entering these fens is immobilized into microbial biomass or is eliminated during the pyrite formation in the shallow organic soil layers. Although in most cases active tufa formation takes place, the fen vegetation is not limited by P as was expected. The fen vegetation tends to be a high productive tall sedge fen instead of a low productive small sedge fen. This is probably related to a (regular) degradation of the superficial organic layers in dry periods or by drainage allowing the previously immobilized nutrients to become available eventually causing eutrophication.

Within the spring fed fens due to spatial variation nitrate and sulfate concentrations may locally differ significantly from the concentrations in groundwater. It is therefore advised to focus on the springs within these fens when monitoring the nitrate load of the fens.

The future of wet meadows in Southern Limburg

E.J. Weeda, H. de Mars & J.H.J. Schaminee

The floristic composition of wet meadows in Southern Limburg has considerably changed during the last century. Cirsium oleraceum, Colchicum autumnale, Primula veris and several orchids have almost vanished from this habitat, but many common grassland species have strongly declined as well. A succession towards either rough or poor grassland vegetation is observed. To maintain eutrophic wet Calthion meadows slight manuring and after-grazing seem appropriate measures.

Limestone quarries:  start, development and management of non-Dutch nature

M.E. Nijssen, M.C. Scherpenisse, P.J.M. Verbeek, H. de Mars, E. van Rijsselt & B. Possen

All open calcareous habitats in The Netherlands are manmade. Over 300 small (<0.1 ha) to very large (144 ha) opencast limestone quarries in province Limburg domiciliate a wide variety of plant and animal species of which many are on the Dutch red-lists and protected under European Natura 2000 regulation. Although these species are often considered pioneers, most belong to stress-tolerators with low reproductive and dispersal power. To protect these species management of limestone quarries should be focussed on keeping an open landscape, rather than stimulating erosion processes. Grazing with goats and sheep, cutting of shrubs and trees and topsoil removal on cliffs are the most promising measures. Limestone quarries can be treated as part of the cultural landscape and play an important role in conservation of a biodiverse calcareous nature in The Netherlands.

Perspectives for nature in South-Limburg

B.F. van Tooren, O.P.J.H. Op den Kamp, M. Lejeune, A.H. Ovaa & H.L. Schimmel-ten Kate

The papers in this issue give a broad overview of the threats and the perspectives for nature in the (calcareous) hills in the South of Limburg and near Belgium. The biodiversity decreased strongly the last century. However, the last decades we can also observe some recovery, mainly due to an intensified nature management as well as more knowledge about the relevant processes that influence for example the woodlands, the chalk grasslands or the wet grasslands. Relevant issues for the coming decades are the improvement of the quality of the seepage water in springs. The nitrogen load in this water is too high, due to intensive farming on the plateaus. Also needed is a strong decrease of the nitrogen deposition. Improvement of the cooperation between the governments on both sides of the border needs also attention. However, the most important issue for the next decades is the recovery of the quality of the landscape. Even common plant species or butterflies have disappeared from the roadsides, the hedges or from other elements in the landscape. The former function of these elements in connecting the reserves has been gone and also the attractiveness of the landscape has strongly diminished. There is still a lot of work to do.