De Levende Natuur nummer 3 van 2015 (English summary)


50 jaar Drentsche Aa


DLN 2015-3

Case history of the plan for the brook landscape reserve Drentsche Aa

B. Hanskamp & J.C. Smittenberg

In 2015, 50 years has passed since the publication of a report about the idea to start a nature– and landscape reserve ‘Stroomdallandschap Drentsche Aa’. In the time before and after, the realization of this idea has met several incidental pieces of good luck and disappointments. In 1924, the plan to canalize brook and brooklets on behalf of a better water discharge was not realized because the farmers estimated this plan to expensive. Between 1940-1960 existed another threat of nature and landscape values: intensification of agriculture practices. This caused in 1960 that new plans for the water discharge and agriculture development by re-allotment and reclamation were made. Nature conservationists and rural planners of different governmental and provincial authorities co-operated intensively, resulting in the publication of the report ‘Gedachtenplan’  in 1965. This plan concerned about 2.200 ha agricultural land. The destination of agricultural land toward nature areas was a new development in The Netherlands. Farmers offered resistance, but after about 3 years of negotiations and promises of good prices for their land they agreed. For the realization a special land use plan was made, finally established by the regional parliament in 1973.  In the following 50 years the nature- and landscape reserve has been steadily enlarged to about 6.000 ha. This reserve is still unique and not only important as a reserve for nature and landscape but it has also a great touristic value.

The Drentsche Aa area, 50 years looking for public support, common grounds and expertise

H.J. van der Windt & S. van Bommel

In this article it is described and analyzed how during the period 1965-2015 the inhabitants of the Drentsche Aa region were involved in the decision-making process and activities of the National Park and National Landscape, compared to the influence of others: governmental agencies, NGO’s and experts. Around 1965, two different coalitions developed, each existing of inhabitants, agencies, NGO’s and experts, one in favor of agricultural modernization and one in favor of nature protection. Several times heavy conflicts arose. From 1990 onwards, the government tried to involve citizens, cso’s, NGO’s and communities  in the decision-making processes and management of the area. In 2002, these efforts resulted in a special co-ordination institution, the ‘Overlegorgaan’ of the National Park, in which they all are represented. Furthermore, the area was labelled as a National Park ‘with extended objectives’, including agriculture, and a larger area as National Landscape. The Overlegorgaan has some power and responsibility for the management of the park, and is headed by an independent chairman. In addition it is tried to develop a common frame and common activities. This approach seems to be rather successful, given the fact that after 2002, serious conflicts hardly occurred. New ideas and practices developed, such as a system of regional hosts and hostesses, developing plans for villages, a special festival and experiments with nature friendly agriculture. On the other hand, there is still not really a true Drentsche Aa identity which is recognized and accepted by all inhabitants. So, in future it will be challenging to combine different objectives such as nature conservation, modern agriculture and recreation and to align the aims of different policy levels.

The Drentsche Aa-landscape : a continuous challenge for nature management

E.J. Lammerts, H. Offringa, R. Postma & W. Winter

In the last fifty years, in the Drentsche Aa-area, nature management measures evolved from very local and small scale activities to dominant forms of land use. During this period the goals and strategies have changed considerably. In the early years nature management consisted of haymaking, sometimes succeeded by grazing in late summer and autumn. This strategy was applied, first in only a few and later in a fast increasing number of small nature reserves. The newly emerging scientific discipline ecohydrology in the 80’s of last century stressed the importance of thinking and acting on a landscape level in nature management. Large scale restoration of the hydrological system more and more was considered to be an important precondition to improve the quality of wet ecosystems. Monitoring shows that this approach has been quite succesfull. For the near future in the Drentsche Aa-area a new management strategy in nature management is adopted by distinguishing areas with a natural from those with a semi-natural way of nature management. This will furthermore improve the ecological quality of the Drentsche Aa nature reserve.

Water management as important factor for nature conservation in the Drentsche Aa area

C.J.S. Aggenbach, A.P. Grootjans, P.P. Schollema, P. Hendriks & H.R. Jager

During the last century the water management in the Drentsche Aa area has changed considerably.  The brook valleys with peat soils had desiccated, mainly as a result of agricultural drainage in the whole catchment area, but also by gradual deepening of the stream bed in the valleys. Also groundwater extraction had locally caused some desiccation of peat areas. Since 1990 the brook valleys in the middle reaches have been rewetted on a large scale, mostly by filling up of numerous local ditches. In some trajectories of the brooks experiments were carried out to lower the drainage effect of these brooks on adjacent peatlands. The measures consisted of less intensive mowing in the water courses, input of dead trees, and re-profiling of the streambed. These measures had a variable, and often limited effect on the water table rise in the brook. For further rewetting strong re-profiling of brooks is needed. Furthermore attention is needed for the influence of strong drainage in the recharge areas on the dynamics of groundwater levels in the brook valleys.

From open sewer to a liveable stream, a big step in the right direction

P.P. Schollema, M. van Dongen, H. van Dam, H.V. Winter, A.B. Griffioen & A.I. de Vroome

This article provides a historical overview of the development of water quality and ecology in the Drentsche Aa, a small stream in the northern part of The Netherlands. Available water quality data for the period 1933-2013 show increasing pressure on parameters like Chloride, Oxygen and Biological Oxygen Demand (BOD) until the 50’s. After the 60’s and 70’s water quality started to improve, but it took until the 90’s before it applied to the target values. More recently there is an increasing pressure of plant protection agents on the aquatic ecosystem. Beside chemical data it is also described how organisms like fish and diatoms reacted on the developments in water quality and the measures that will be taken in order to establish further water quality improvements and river restoration.

Vegetation development Drentsche Aa from 1982 to 2012

F.H. Everts, N.P.J. de Vries, B. Hoentjen, A.P. Grootjans & C.J.S. Aggenbach

The spatial distribution of vegetation types has been monitored three times in the Drentsche Aa Nature Reserve in The Netherlands in the period between 1982 to 2012. The vegetation mainly consists of meadows, which are managed by Staatsbosbeheer (the State Nature Conservation agency). Analysis of three vegetation surveys show a gradual increase in vegetation types that are characteristic of lowland brook valleys. The restoration success of brook valley meadows differs between sub-areas. In some areas (middle reaches) the restoration success was much higher than in other areas (upper- and lower reaches). In the middle reaches the restoration was much quicker than in the upper and lower reaches, mainly because of the large scale rewetting of the meadows in the middle reaches.  A restored hydrological system is, therefore, equally important for the restoration of brook valley meadows as traditional management techniques, such as grazing and mowing without fertilization.  Despite these positive findings, several problems have remained. For instance, the spread of characteristic species of peat forming vegetation types (fens), such as Carex appropinquata, Carex diandra, Carex lasiocarpa and Menyanthes trifoliata, is stagnating. Possible limiting factors are: (1) the high iron concentrations in the (top)soil water, which can be toxic for fen species, (2) the (still) high productivity of the wetlands or (3) the limited dispersal capabilities of these species.

Recovery of Primula vulgaris in Drenthe, The Netherlands

S.H. Luijten, A.C. Vos-Smit, H.P. Offringa & J.G.B. Oostermeijer

In 2012 a project was started to restore metapopulation viability of the Common primrose in the province of Drenthe. To increase genetic diversity, mitigate inbreeding depression and balance pin-thrum ratios of the reintroduced populations, offspring was greenhouse-grown from seeds obtained from manually outcrossing plants in the three remaining populations in 2012. The adult offspring were outcrossed among populations in 2014. The resulting >50.000 seeds were sown in autumn 2014 at ten reintroduction sites in the National Park Drentsche Aa. Prior to the reintroduction, a sowing experiment was performed to test habitat suitability and evaluate our selection of potential new sites. The coming years, the reintroduction success will be monitored and evaluated.

Black Rampion in nature reserve ‘Stroomdallandschap Drentsche Aa’

J.E. Dijkhuis, M.M. Kwak & J.C. Smittenberg

Black Rampion (Phyteuma spicatum ssp. nigrum), a hemicryptophytic perennial herb, is rare in The Netherlands. It is one of the beauties of the nature reserve “Stroomdallandschap Drentsche Aa”, due to the unusual colour of the flowers. Despite the fact that the species occurs in the nature reserve, in meadows and along road verges and ditches, the number and size of populations are decreasing, especially in the meadows. The most likely explanation for the decrease in the past 20 years is the increasing wetness of the meadows. This is due to discontinuations of ditch management in combination with the implementation of hydrological restoration measures resulting in rising of the groundwater table. The limited dispersal of the Black Rampion through roots and / or seeds may also play a role. Populations in road verges and along ditches also met problems like complete removal of the vegetation, cover with materials from cleaning the ditches, too early mowing etc. The possibilities to conserve the remaining populations exist of careful management of the locations and increase the number of habitats for germination, by stimulating seed production and increasing the population size (whether or not by actions like hand pollination or manual sowing ). The groundwater level in the remaining Black Rampion meadows should not increase in the future.

Half a century of breeding birds in the river valley of the Drentsche Aa

W. van Manen, B. Dijkstra & Y. de Vries

Based on reports from the 1960s and 1970s, and standardized mapping of breeding birds from the 1980s onwards, the composition, distribution and abundance of breeding birds in the valley of Drentsche Aa in the northern Netherlands is reconstructed. Overall, the number of breeding bird species has increased since the 1960s (partly a methodological artefact, as studies in the 1960s and 1970s were much less intensive than later on) and more species increased than declined: however, species turnover was rather high (fig. 3). Initially species of woodland and scrubland increased, whereas species characteristic of farmland in open river valleys (except Snipe) declined (fig. 2). After hydrological restoration species of marshes settled or increased, but a more or less similar increase was for some of these species observed in parts of the area that were not hydrologically restored, but showed the same increase in shrub-cover (table 1). The species characteristic for open river valleys (waders) did not recover after hydrological restoration. In general, the breeding bird population showed the same trends as recorded country-wide.

Scenes from a marriage: fifty years of nature and heritage management in the Dutch National Landscape Drentsche Aa

J.N.H. Elerie & Th. Spek

The paper discusses landscape and heritage management in the Dutch National Landscape Drentsche Aa (Northern Netherlands) during the past five decades. Since 1965 there has always been a certain tension between the goals and methods of modern nature management and its effects on archaeological sites and historical landscapes. This culminated in the 1990s when large-scale nature restoration projects seriously threatened cultural landscape values. In the past decade much of this tension has been harmonized by new integral landscape management methods, public participation and interdisciplinary research projects aimed at the integration of nature and culture.

European nature at its best in the Drentsche Aa area

E.B. Adema & H. Dekker

Natura 2000 is a network of important nature protection areas in the European Union. The Drentsche Aa area is one of the biggest areas in The Netherlands. The Drentsche Aa is one of the most complete stream systems in Europe. Besides the stream and valley also infiltration areas are part of the protected system. Therefore hydrological processes on landscape scale take place or can be restored. The habitat directive of Natura 2000 consists of eight primary goals for the Natura 2000 area (table 3). For species-rich Nardus grasslands and Molinia meadows on calcareous soils a ‘sense of urgency’ is administered. Measures must secure these habitat types within 10 years. It is an omission that Calthion meadows an important grassland type in the Drentsche Aa region are lacking in the habitat directive. As a part of Natura 2000 the PAS (The Integrated Approach to Nitrogen) aims on two goals. Stop the decline in biodiversity and make room for economic development. A set of measures that mitigates the effects of nitrogen must achieve these goals. Sometimes measures outside the Natura 2000 area are necessary. In other cases more research is needed to analyze the landscape ecological system and address solutions to protect habitat types. Cultural historical values and conflicting goals are limiting factors by formulating measures. The approach in the Drentsche Aa is restoring the ecological system, but also heritage and interest of other stakeholders have to be taken into account. However this may not lead to irreversible loss of natural values in the Drentsche Aa area.

A long-term view on the area

P.C. Schipper, J.N.H. Elerie, E. Takman, J.A. Wolf & U. Vegter

During the past fifty years the views how to protect and develop the Drentsche Aa area have varied significantly. In this paper Staatsbosbeheer presents a long-term view on the area. For that three zones are distinguished with different accents: preservation of historical patterns, development of a new wilderness and multifunctional. In the central zone, heart of the National Park where the historical patterns prevail, there are several suggestions to improve the landscape quality. It is argued that the restoration to a single historical period cannot be the aim. All different historical periods should be visible. In this way the wilderness, projected in the southern zone, presents the supposed image of pre-historical times. The rewilding is carried out in three steps: reinforcing the hydrological conditions, introduction and stimulation of deciduous woodland species like Lime (Tilia spec.) and finally introduction of large herbivores as Red deer.

Fifty years protection of the Drentsche Aa, what is the outlook?

P.C. Schipper, J.P. Bakker, J.C. Smittenberg, U. Vegter, J.C.E.W. Hooijmeijer & H.L. Schimmel-ten Kate

Fifty years of protection in the Drentsche Aa area has been very successful. It is the best preserved stream valley of the lowlands of Northwest Europe, but the adjustment of the management to new insights demands a constant effort. Decision-making in the area has also changed: from top-down to bottom-up , and  as a result, residents and nature - and landscape conservationists get along much better. Unfortunately, the Government retreats and seems to undervalue the goods and services the National Landscape provides.