De Levende Natuur nummer 3 van 2003 (English summary)

Climate change in The Netherlands

Baede, A.P.M.

The geographical distribution and composition of natural ecosystems are determined. to a large extent by climate. Therefore climate change, natural or human induced, may have a considerable impact on flora and fauna, in particular in combination with other environmental stresses. The Intergovernmental Panel on Climate Change (IPCC) has concluded that global climate is changing and will continue to change at an unprecedented rate due to human emissions of greenhouse gases. This article discusses global climate change during the 20th century and its relation with climate change in The Netherlands. The temperature increase in De Bilt, The Netherlands, of 1 °C parallels the global temperature increase suggesting a causal relation between human emissions of greenhouse gases and climate change in The Netherlands. The 1990´s were particularly warm and wet, especially in winter. This is caused partly by the exceptionally positive NAO-index in recent decades. Whether this phenomenon is related to human induced climate change is unclear as yet. On the basis of the IPCC climate scenarios for the 21st century and the relation between local and global climate, projections for the climate in The Netherlands are presented which may be used to study the potential impact of future climate change on flora and fauna.

Effects of climate change on vascular plants in The Netherlands

Tamis, W.L.M., M. van 't Zelfde & R. van der Meijden

In The Netherlands nation-wide databases are available with about 10 million records of occurrences of vascular plant species in the 20th century on a scale of approximately 1 square km. These data were analysed statistically with a view to identify relationships between changes in botanical biodiversity and climatic and other environmental characteristics. The records were devided into three periods: 1902-1949, 1975-1984 and 1985-1999. Between the periods 1902-1949 and 1975-1984 there were small but significant increases in the presence of both ‘warm’ and ‘cold’ species. However, in the final decades of the 20th century there was a marked increase in ‘warm’ species only, coinciding with the marked increase in ambient temperature observed during this period, evidence at least of a rapid response of Dutch flora to climate change. Urbanisation was also examined as an alternative explanation for the increase in ‘warm’ plant species and was found to explain only 50% of the increased presence of such species in the final decades of the 20th century. Besides temperature-related effects, the most important change during the 20th century was a strong decline in plant species of nutrient poor sites and a marked increase of plant species of nutrient rich sites.

Changes in lichen and moss flora in relation to climate change

Herk, C.M. van & H.N. Siebel

Recent changes in the Dutch lichen flora as well as changes in the moss flora appear to be attributable significantly to global warming. Particularly warm-temperate species with a (sub-)atlantic or mediteranean distribution pattern are increasing, while species with a boreo-montane distribution are decreasing. Dragonflies are flying earlier and expanding northwards: an effect of climate change? Drs. ing. R. Ketelaar . A balance of Dutch dragonflies in terms of changes in distribution shows that the number of increasing and decreasing species are approximately equal. However, it appears that species with a mainly southern distribution dominate the increasing group. The decreasing group consists mainly of more stenotopic species. Northern species generally decrease in The Netherlands. Not only changes in distribution are apparent, it is also shown that dragonflies have shifted their flight season. In an analysis for ten common species it is evidenced that for nine species the peak flight season is nowadays much earlier than in 1980, in some cases two weeks earlier. Climate change (especially warmer summers) is thought to be one of the driving factors behind these processes and this is shortly discussed.

Changes in the Dutch invertebrate fauna

Kleukers, R.M.J.C. & M. Reemer

Until now range changes in Dutch invertebrates were only documented for a few, large and conspicuous species, e.g. Argiope bruennichi, Volucella zonaria and Phaneroptera falcata. For the first time now a substantial part of the Dutch fauna was analysed, in a pilot study relying heavily on the expert judgement of the specialists of European Invertebrate Survey -The Netherlands. In total 1331 species of Apidae, Asilidae, Carabidae, Formicidae, Mollusca, Odonata, Orthoptera and Syrphidae were studied. In this paper we focus on the 339 species of which the northern border of the range runs through The Netherlands. No less than 101 species of this group have expanded their range to the north in the 20th century, especially in the groups Odonata, Syrphidae and Mollusca. In total 63 species were found to have retreated to the south, especially the Apidae. The expanding species of most groups are mainly eurytopic species, characteristic for disturbed, cultivated habitats. The declining species are mainly stenotopic species restricted to nature reserves. The Carabidae are an exception, as the expanding ground beetles seem to be mostly stenotopic.

Forest insects and global climate change

Moraal, L.G.

Pest insects on trees are being monitored in The Netherlands since 1946. In recent times we have observed invasions of foreign species such as Haematoloma dorsatum, Thaumetopoea processionea, Pulvinaria regalis and Cameraria ohridella. Furthermore shifts in indigenous species are noticed: Diprion pini and Coleophora laricella are not important anymore, while Agrilus biguttatus and Operophtera brumata have become more prominent. Relations between the shifts of the pests with global change and other factors are discussed.

Marine coastal organisms as indicators of climate change in the southern North Sea?

During the last two decades some remarkable observations on marine coastal organisms of Belgium (Southern Bight, North Sea) are presented, mostly from the (second half of the) nineties. Exemples are chosen from autochtonous crabs and shrimps (Crustacea: Decapoda) and aliens. Populations fluctuate following severe or mild weather conditions, disappearing after harsh winters and coming back more rapidly then in the past. Some offshore species are stranded or wrecked more often. Species new to the area, including aliens, turn up and establish. These observations are believed to be mainly triggered by changes in the oceanographic/climatic conditions, luring or forcing southern species into the southern North Sea and the coastal waters. The marine fauna and flora of the English Channel is acting as a waiting or retreating room, from which establishment or rapid recovery can take place. Aliens profit from the hydrological changes and from the intensive ships traffic (fouling, ballast) to settle in the warmer and sheltered marinas, harbours, sea-inlets and on buoys in nearshore waters. These artificial habitats can act as ‘stepping stones’ for a spread in the area.

Phenology of grassland species on the Bemelerberg (1979 and 2002)

In 1979 the phenology of (chalk)grassland species on the Bemelerberg (South-Limburg) was monitored for one summer season. In 2002 this research was repeated, to record possible changes in the phenology. Two aspects are important. On the one hand fluctuations that take place because of different weather-conditions in both years, and one the other hand real changes that have happened due to climate change. We visited the Bemelerberg 17 times during the growing season, and recorded the state of the phenology of the same group of species as in 1979 by monotoring all phenological stages. To be able to give an interpretation of the found data, data on the weather (sunshine, rainfall, temperature) were also collected from a nearby weather station. The results show two trends. One group of species shows an earlier growing season (all events). This corresponds with European reseach on this subject by Menzel & Fabian (1999; Menzel 2001) and to Dutch research on phenology by Van Vliet & De Groot (2001). The second group shows earlier spring events, like making flowering buds and flowering, and prolonged autumn events, like spreading of seeds. For the second group, only for three out of eight species an explanation could be found in the weather: when ripe seeds were expected, the weather was quite unfavorable (lots of rain, less sunshine), so it is possible that the species have posponed the ripening of the seeds. The study demonstrates the importance of monitoring all phenological stages of species in stead of registering a limited set of some obvious events (like first flowers, colouring of leaves).

Are climate changes the cause of the decline of the Black grouse?

Loneux, M.

Population data and meteorological records performed for several decades have allowed us to model the climates influence on Black grouse (Tetrao tetrix) population dynamics. Results obtained in several European protected areas where the species breeds still nowadays have shown the important role of some climatic parameters during the life cycle of the bird to explain the observed fluctuations. The common factors involved in the modelling for the different geographical sites studied in West-Europe suggest that global climate warming can explain the declining trend of the species. On one hand the winters are more and more rainy and less snowy due to the warming of the minimal temperature, while Black grouse is adapted to rough snowy conditions. On the other hand, rainfalls are more and more abundant during key-times of this species brooding period. However the new climatic trend can not fully explain the general decline of Black grouse, observed even in protected areas in Western Europe. The species is suffering from the global climate change in addition to attacks on its habitat and tranquillity. At short-term and local level, decisions and actions of managers to improve and maintain the quality and carrying capacity of the typical habitats used by the species during its whole life cycle will play major role for the short-term survival of this emblematic bird in the west positions of its distribution. On longer term, the future of the small isolated populations of the species will depend on its ability to face the changing environment.

Reaction of natural systems to changing climate is not linear

Heij, G.J.

Generally speaking, the reaction of natural systems to changing external conditions, such as climate change, is not linear. Therefor these systems are too complex. The health of the systems is determined by many factors and complicated interactions between them. Although the health of a system may be sub-optimal due to one single factor (for example, disease or plague or extreme drought), this is not usually the case; in general there is a situation of multi-stress. Consequently, studying a particular factor in isolation can lead to wrong conclusions. Change often occurs gradually, but there can also be threshold or hysteresis effects with sometimes drastic consequences. It is very important to understand these phenomena in order to take the correct measures to preserve or attain a situation as it should be.

Shifting links – climate change disrupts food chains.

Visser, M.E. & F. Rienks

Structurally warmer, earlier springs in Northwestern Europe can disrupt food chains dramatically. Winter moth caterpillars for example are too early for the fresh oak leaves and starve. Great tit chicks are born too late for the peak abundance of caterpillars and miss the optimal feeding conditions. The different species within a food chain use different ‘cues’ or ‘rules’ to assess the right moment of development or reproduction. Mistiming, asynchrony of the links in a foodchain, is the consequence when the (combination of) cues become(s) invalid. This will form a major problem for especially vulnerable and fragmented species that are not capable to adjust or to ‘hop’ along with the shifting climate zones. More general species with sufficient genetic variation might be able to adjust at least partly. Within songbirds like tits they may learn to lay earlier, start incubation earlier, and give up making second broods within a season. The whole life cycle has to be taken into account before any conclusions on whether a species - or an ecosystem - can overcome the effects of climate change can be drawn.

Modelling the effect of climate change on species ranges.

Nagelkerke, C.J. & J.R.M. Alkemade

Three main types of models can be used to understand and predict climate-related range shifts. Equilibrium models predict potential future distributions from the current climate envelope of a species, but do not take migration constraints into account. They show that future range changes can be large. Migration models investigate migration speeds on the front edge of a range after a stepped climate change, but are difficult to parameterize because past, current and future migration processes are not well understood. New, dynamic profile models focus on the influence a shifting climate has on processes on both the advancing and the retreating range edge. They reveal that the tracking delays developing at the two edges are very much influenced by the way climate actually affects (meta)population dynamics. Due to various uncertainties none of the models can be used to accurately predict future ranges. However, useful qualitative inferences are possible. For example, it appears that habitat destruction greatly increases the deleterious effects of climate change.

What can we learn from global climate models?

Leemans, R.

Many models are used to assess different aspects of climate change. The most advanced climate models show that a major factor to explain the observed climate change during the 20th century is the enhanced concentration of greenhouse gasses in the atmosphere. Impact models illustrate that with increasing mean global temperatures ecosystems become more vulnerable, because natural adaptation capacity rapidly becomes limited. Integrated models that simulate the whole causal chain (emissions, concentrations climate change and impacts) illustrate that emissions have to be reduced worldwide by at least 60% to halt climate change. CO2 sequestration in ecosystems can never reduce emission levels that much. Developing sustainable energy sources and increasing energy efficiency are more appropriate measures. When these mitigation measures are not implemented, ecosystem management and nature conservation must focus on increasing resilience and decreasing vulnerability by developing adaptation measures.

Respond of nature policy to climate change is urgent

Leeuwen, B.H. & P.F.M. Opdam

Climate change effects nature and Dutch nature policy has to respond to that. In addition to the preservation of habitats and species, the migration of species from the south to the north has to be accommodated. Also increased local extinction, as a result of extreme weather conditions causing enhanced fluctuations in population sizes, should be accounted for. The completion of the planned National Ecological Network with nature reserves and corridors is of vital importance, and adjustments in its design are necessary. Spatial planning on a European scale is urgent. Policy adjustments require research that links concepts from metapopulation ecology and biogeography. The visible effects of climate changes on flora and fauna offer useful material to enlarge public awareness. Policy changes take time and flora and fauna are already changing. Action is urgent.

Climatological changes can no longer be neglected.

Tooren, B.F. van & M.E. Visser

This issue of De Levende Natuur discusses the already detectable ecological consequences of the climate change in The Netherlands and also in Flanders. The effects are already impressive and, since more severe climate change can be expected, it can be assumed that the species composition of plants and animals in our area will change tremendously during this century. Several papers indicate changes in the distribution area of species: lichens, mosses, dragonflies and other insects. Also phanerogams with a southern distribution become more common. It is much more difficult to identify species which are decreasing due to climate change or by other factors who can explain an observed decrease. Changes in phenology can affect the life cycle of species and especially the interaction between species can be severely affected. Another phenomenon is the increasing number of introduced species in The Netherlands. More species than in the past can be expected to cause. problems for native species. Several ecosystems will be affected by increasing sea or river water levels. However, there is little direct evidence that these effects are already occurring. It is difficult to indicate the consequences for nature policy and nature management. It may be assumed the increasing temperature will be more important for species viability or species composition in nature reserves than eutrophication. Especially for the slowly migrating species an effective Ecological Infrastructure is important. However, it is doubted if nature policy will be effective in order to establish this Ecological Infrastructure. Protection of individual species, an important part of nature policy, is only effective if we can establish that the viability of the protected populations is not threated by climate change.