W. J. Ter Keurs

The impact of roads on the densities of four bird species in an open field habitat—evidence of a long-distance effect

Roads may effect animal communities in various ways. One such way is ‘di sturbance’, i.e. emission of stimuli to which animals may respond by avoiding the vicinity of the road. The extent, intensity and mechanism of this effect is almost entirely unknown. Veen (1973), studying the bird species lapwing Vanellus vanellus, black-tailed godwit Limosa limosa, oystercatcher Haematopus ostralegus, redshank Tringa totanus and ruff Philomachus pugnax in open grassland areas, found disturbance over surprisingly long distances, ranging from 500–600 m for a quiet rural road to 1600–1800m for a busy highway. However, his approach has met with serious methodological criticism. The validity of Veens conclusions was tested by critically reanalysing bird distribution in one of his study plots. It is inferred that his conclusions do hold for the lapwing, the godwit and possibly the redshank, though not for the oystercatcher. An additional field study in four areas yielded similar results, with comparable disturbance distances. The total population loss over this distance may amount to 60%. Rough indications were obtained that the distance-density graph is a logistic one, while the relation between traffic volume and total population loss is possibly logarithmic. In addition confirmation was obtained of the general impression that, apart from roads, disturbance may also be caused by farms, other buildings and plantations, suggesting that disturbance caused by a road is not easily eliminated by planting trees alongside. It is recommended that extra care be taken in planning new roads, while impact statements concerning roads which disregard disturbance and other long-distance effects on the fauna should be rejected.

A framework for the design of ecological monitoring programs as a tool for environmental and nature management

Environmental and nature management can not operate effectivelywithout reliable information on changes in the environment andon the causes of those changes. Ecological monitoring canrepresent an important source of information. However, manyoperational monitoring programs are not very effective, i.e., not very useful for decision-making. We present a conceptualframework for the development and maintenance of effectiveecological monitoring programs. In the decision-making process,two main functions for monitoring can be recognized: an earlywarning and an early control function. Both these functionsrequire a high diagnostic power. This is used as a guideline forthe design process. The design consists of choices concerningmonitoring objectives, objects and variables to be monitored,sampling strategy and design, data collection, data handling, maintenance and organization. Arguments commonly put forward inliterature and in practice to support the various choices aresubjected to a critical analysis. The framework will be helpfulin the design of effective monitoring systems as it avoidsimportant components to be overlooked, clarifies the relationbetween the different components, maximizes the exploitation ofexisting possibilities and opportunities and identifiesshortcomings in advance. This will result in monitoring programsthat should be able to live up to their expectations.

Declining plant species richness of grassland ditch banks—a problem of colonisation or extinction?

Small-scale landscape elements, such as ditch banks are an important remaining source of biodiversity in many agricultural landscapes, including the Western Peat District in the Netherlands. Unfortunately, plant species richness is declining even in these habitats. To understand the factors threatening biodiversity, we studied demographic traits (occupancy, trend, colonisation and extinction) for a large number of plant species, in a 25-year long data set. We developed a method to investigate the relative importance of colonisation and extinction for species increase and decrease in multi-species assemblages. We show that colonisation has been more important for determining species trends than extinction. Decreasing species were small and characterised by low nutrient tolerance and high light requirements, indicating that competitive ability influences species trends. The mechanism by which high nutrient levels reduce plant diversity appears to be closely related to colonisation (germination and seedling establishment). Local management should therefore continue to focus on nutrient reduction and the creation of regeneration sites. Yet, these measures will be insufficient for restoring species richness since isolation also hampers species increase. Therefore, to maximise the effects of local management, additional regional management solutions are required to improve seed dispersal for example, from nature reserves.

Sustainable development: looking for new strategies

Abstract Many strategies have been proposed to reach sustainable development. A great many of these strategies aim at one type of problem-preventing environmental deterioration-while ignoring the importance of economic or social goals. In addition, while political decisions are at the heart of the choices to be made, most researchers seem to consider sustainable development as a mere technical problem. In this paper we describe a more complete strategy for sustainable development. We use the outlines of this strategy to find out what knowledge and skills are still needed. The strategy is based on the idea that it is necessary to find consensus on the development of a socio-environmental system as a whole, and between all people involved. It leaves us with at least two main areas that need further study: the supply of information and the management of consensus building. A formal procedure for consensus building might be developed based on the literature and on experiences with Environmental Impact Assessments. Special attention is paid to the information needed. It can be summarized as information about: (1) delimiting a socio-environmental system; (2) the needs and wants to be satisfied via that system; and (3) the physical, ecological, economic, social and cultural constraints of satisfying those needs and wants.

Impact of Outdoor Recreation on the Density of a Number of Breeding Bird Species in Woods Adjacent to Urban Residential Areas

Abstract Outdoor recreation is often supposed to have an important impact on wildlife, although this assumption has not been tested very often. The resulting lack of knowledge becomes apparent in situations where parties with conflicting interests disagree on the number of visitors an area can sustain without major repercussions. In 1980 the possible effects of recreation intensity upon bird densities were studied in seven study plots adjacent to urban residential areas in The Netherlands. Of the 31 bird species found, only 13 could be studied in detail, being present in at least 20 territories. Significant negative correlations between recreation intensities and bird densities were found for 8 of these 13 species. The slopes of the regression lines enabled us to rank the 8 species in a sequence of decreasing susceptibility. The results indicate that the disturbance is caused rather by the recreation intensity during the week than by the recreation intensity at weekends.

Survival of black-tailed godwit chicks Limosa limosa in intensively exploited grassland areas in The Netherlands

Abstract The Netherlands is a stronghold for the breeding population of the black-tailed godwit Limosa limosa . Due to intensive mowing, survival of chicks is usually assumed to be very low. In a study in intensively exploited dairy farm grasslands the number of chicks fledged was about 0·3–0·6 per breeding pair, which is probably too low to maintain current population levels. Until the end of June, families with chicks stayed mainly in ‘herb-rich’ fields with either short or tall grass. Just-hatched chicks ran the greatest risk from mowing (38–95% killed), while most of the older chicks were able to escape (5–45% killed). The number of chicks present during mowing could be significantly reduced by putting plastic bag ‘flags’ in the fields one day before mowing. Areas where nests were marked with garden canes or the use of wire mesh guards in cattle-grazed fields had similar fledging success as those in nature reserves or so-called managed areas.

Effects of ditch management on caddisfly, dragonfly and amphibian larvae in intensively farmed peat areas

Conservation of natural values within farming practice is growing rapidly within the Netherlands. The focus is primarily on terrestrial flora and fauna such as the vegetation in ditch banks and meadow birds. Knowledge needed to enhance biodiversity in ditches is limited. Therefore, a field study was set up to determine the effects of dredging, ditch cleaning and nutrient supply in the adjacent fields on caddisfly, dragonfly and amphibian larvae in the ditches in a peat area.Two-hundred forty ditches spread over 84 dairy farms were selected to determine the individual effect of several management aspects. Generalised linear modelling was used as a tool to detect the most relevant aspects and to obtain quantitative relations with the chance of the larvae being present.Dredging had an impact on the presence of all larvae types. The type of dredging machine, the dredging period, the water depth and the frequency of dredging can influence the presence of the larvae. The presence of caddisfly larvae was also affected by the cleaning machine and period and by the P supply in the adjacent field. The presence of amphibian larvae was also affected by the cleaning period.Measures that will enhance the presence of the larvae are formulated. Options for water boards and other government authorities to stimulate farmers to take these measures are given.

Hatching dates of waders and mowing dates in intensively exploited grassland areas in different years

Abstract Intensification of grassland management threatens grassland breeding waders such as lapwing Vanellus vanellus, black-tailed godwit Limosa limosa and redshank Tringa totanus in several European countries. Temperature sums (a measure of spring warming) are shown to be associated with hatching dates of two of the three studied species and with mowing. Because birds nested earlier in years with early mowing, the negative effect of mowing on hatching success was limited. This is contrary to the general idea among conservationists that grassland breeding birds have a more or less fixed breeding season and that early mowing will therefore reduce their breeding success severely. By postponing the current median mowing dates by 1–2 weeks, the probability of the clutches surviving mowing may be increased to the level necessary for maintaining the current population levels. Farmers could contribute to the conservation of these waders by using these well-known temperature sums for predicting hatching dates.

Monitoring the biotic aspects of our environment as a policy instrument

As all environmental programs also programs monitoring the biotic aspects of our environment (dealt with in this article) should contribute to a more effective and efficient environmental policy. These programs have to function therefore (as no other type of environmental information does, according to the authors) as cheap and efficient ‘early warning’ and ‘early control systems’, providing decision makers with ‘important’ and reliable monitoring results.How these monitoring programs should function in the decision making process is illustrated in abstract in this article by a simple control system with feedback (as shown in Figures 1, 2 and 3).The monitoring programs dealt with in this article should enable us to detect and forecast changes in the most important biotic aspects of our environment and-by continuous monitoring-to control whether the use of policy instruments has been effective or not in averting or diminishing unwanted changes (‘problems’).Two options of decision makers with respect to monitoring results are shown (either to disregard unwanted changes as a problem or to accept these changes as a problem and to do something about them). To contribute to an effective and efficient environmental policy monitoring results therefore have to be ‘important’ and reliable enough to react upon.The question is raised which biotic aspects in our environment are (or have to be considered as) important (because of their own value, as indicators and/or as biotic ‘conditions’) and how reliable monitoring results can (have to) be obtained.It is discussed how environmentalists could try to make it more difficult for decision makers to duck the problems (by monitoring only important aspects and by using only perfectly clear targets and standards) and how they could try at the same time to make it easier for them to take action (by setting up integrated ‘environmental monitoring programs’ in order to find out how desired and undesired changes can be influenced). The role of active publicity is stressed in this connection.

Natal philopatry in the Black‐tailed Godwit Limosa limosa L. and its possible implications for conservation

A study was carried out on the basis of ringing data (period 1900–1991) to find out to what extent young Black‐tailed Godwits return to their birth place for breeding. We found that most birds in t...