De Levende Natuur nummer 6 van 2010 (English summary)


DLN 2010-6

Desmids in moorland pools near Oisterwijk

B.F. van Tooren & E. Brouwer

The moorland pools near Oisterwijk were famous for the presence of many rare desmid species. However, due to changes in the water management and increasing air pollution, the number of species rapidly decreased, and most rare species disappeared. Several of those species, e.g. Micrasterias mahabuleshwarensis, are nowadays extinct in The Netherlands.

In the winter of 1995/1996 all mud was removed from three moorland pools, Voorste Goorven, Witven and Van Esschenven. Starting in 1996 the Voorste Goorven, with a connection to Witven and Van Esschenven, was supplied with buffered ground water that is pumped up. Surprisingly, several Potamogeton species and Characeae, e.g. Nitella translucens, were found in large amounts during the first years. However, already in 1999 their cover diminished. The number of desmid species increased, reaching its highest numbers in 1999. Several species that are rare nowadays in the Netherlands were recorded. However, none of the extremely rare species from the beginning of the 20th century, was found again. Since 1999, the number of desmid species is decreasing again, including most rare species. Although in the first years the number of species and the species composition of the three pools was different, these differences are disappaearing. In total almost 150 desmid species are found in these three pools during the last 15 years, but nowadays the number of species is about 70 due to a combination of limited amounts of CO2, brown water and steep margins.
The limited amounts of CO2 is the result of the removal of all organic materials and the reduced acification. A relevant option to recover flora and vgetation, including higher numbers of desmid species, is to remove trees near the pools, to secure sunny margins that can promote the development of vegetation.

Revision and update of empirical N critical loads for Europe

R. Bobbink, H.B.M. Tomassen, M.J. Weijters & J.-P. Hettelingh

The increased emissions of ammonia (NH3) and nitrogen oxides (NOx have not sufficiently been reduced  in the last decades to avoid adverse effects on terrestrial ecosystems. Because of short- and long-range transport of these compounds, atmospheric nitrogen (N) deposition is too high in many (semi-) natural ecosystems in Europe. The series of events which occurs when N inputs are excessive in an area with originally low background deposition rates is highly complex. Many ecological processes interact and operate at different temporal and spatial scales. The most obvious effects of increased N inputs are eutrophication, soil or water acidification, negative impacts of reduced N, and/or increased sensitivities for stress and pests. Therefore,  significant changes in vegetation composition and diversity, and in nitrogen economy may occur.

UNECE procedures have been developed to set empirical critical loads for atmospheric N deposition since the late 1980s. Primarily based on significant changes in the structure and function of ecosystems in N-addition studies, these N critical loads have been established for European natural and semi-natural ecosystems. A workshop on the review and revision of critical loads and dose response relationships was held from 23-25 June 2010 in Noordwijkerhout (The Netherlands). In this paper the approach and the outcome of the 2010-review and revision have been described.. At the end of the meeting, the workshop agreed on the revised list of empirical N critical loads for European natural and semi-natural ecosystems. In this paper the updated empirical N critical loads for (semi-) natural vegetation occurring in The Netherlands and Flanders is given, together with the changes compared to the previous update in 2002. In addition, some remarkable changes for important ecosystems have been discussed.

A synthesis of results of European N addition experiments in dry and wet grasslands, wetlands, (sub)Arctic and alpine vegetation showed a clear negative-exponential relationship between exceedance of empirical N critical loads and plant species richness. Hence, although there are limitations and uncertainties in the methods used to derive empirical critical loads, exceedance of these values is clearly linked to reduced plant species richness in a broad range of European ecosystems. In conclusion, the empirical critical N-loads approach is a sound approach to quantify the sensitivity of European ecosystems to the biodiversity impacts of N deposition, and is, thus, an useful tool to identify areas where control of N emissions are (highly) needed, such as in The Netherlands and Flanders.

How much for the Skylark’s song?

J.F.F.P. Bos, H. Sierdsema, H. Schekkerman & C.W.M. van Scharenburg

Birds of arable farmland are closely tied to agriculture, and their fate is therefore greatly influenced by the effects of the EU’s Common Agricultural Policy (CAP) on land use. Depending on the design of the CAP for 2014-2020, payments to farmers earmarked for specific purposes, including biodiversity, may become more important. Within the context of a changing CAP and biodiversity targets for birds of arable farmland, this paper examines conservation measures required in Dutch agriculture to meet these targets, and the costs of these measures. Given species-specific demographic bottlenecks, measures provide either safe nesting sites and cover, sufficient summer food or sufficient winter food. Our estimates of the intensity with which measures need to be implemented in the farmed landscape intend to stem further population declines. Estimates are made for two scenarios, i.e. one in which the entire population is enabled to benefit from measures (‘nationwide approach’) and one in which measures are concentrated in areas with the highest densities (‘core area approach’). The estimates are based on the literature and should be regarded as ‘best guesses’. Annual costs of an individual species-specific measure are calculated as the product of (1) the costs of the measure per ha, (2) the required intensity of the measure per 100 ha farmland and (3) the predicted size of the national distribution area or the predicted total size of all core areas of the species. Total costs of measures for Grey partridge, Skylark and Yellowhammer are € 88 – 176 million in the nationwide approach and € 12 – 20 million in the core area approach. Given some methodological limitations of our core area approach (e.g., based on three species only), we consider € 20 million per year an absolute minimum of what would be required to stop further declines of arable farmland bird populations, or 2% of total CAP subsidies received by The Netherlands in 2008. We estimate that currently € 10 million is spent annually on conservation measures for arable farmland birds. Whether forthcoming CAP reforms for 2014-2020 improve future prospects for farmland birds remains to be seen.