Albert Grootjans

Ecological restoration for future sustainability in a changing environment

Abstract Since its emergence in the past decades, restoration ecology has demonstrated an astounding growth as a new discipline of applied science. At the same time, this young discipline has been criticized for its retrospective goals largely based on the past, its fragmented approach, and its idealistic goals, which do not relate to the real world context. Restoration with past-focused, idealistic, and/or ad hoc goals may not work in the future because an ecosystem that is restored for the past environment is not likely to be sustainable in the changing environment of the future, simple recomposition of isolated and fragmented naturalistic patches is not likely to restore ecosystem functions, and unrealistic goals and work plans are not likely to gain public support. We advocate directing the principles and practice of ecological restoration to the future. Future- aimed restoration should acknowledge the changing and unpredictable environment of the future, assume the dynamic nature of ecological communities with multiple trajectories, and connect landscape elements for improving ecosystem functions and structures. In this paper, we discuss the predictability of restoration trajectories under changing environmental conditions, the application of ecological theories to restoration practice, the importance of interdisciplinary approaches and human interventions in ecosystem recovery, and the social context of ecological restoration.

Fens and floodplains of the temperate zone: Present status, threats, conservation and restoration

ABSTRACT This Special Feature focuses on lowland fens and flood plains. In this introduction we discuss the most important mire-related terms, present status, threats and conservation and restoration attempts. Floodplains and especially lowland fens are rare and vulnerable ecosystems. They are highly threatened all over the world because of direct conversion to agricultural land and especially the lack of appropriate management and altered catchment hydrology. Finally we present a framework for the conservation and restoration of these ecosystems. This consists of (1) optimising abiotic conditions; (2) safeguarding propagule availability of the target species; (3) creating and maintaining conditions for (re)establishment of these species, and (4) appropriate management to keep the conditions suitable.

Wetland restoration in Central Europe: aims and methods

Wetlands have always been of particular signifi- cance for mankind. While originally attractive as hunting grounds, they were later cultivated and modified from sinks into sources. Today, great efforts are being made to restore disturbed or destroyed wetland areas. Different models and goals for wetland restoration exist. From a global point of view, reduction of climatically relevant trace gas emissions is relevant, especially in the case of fens. Regionally and locally, the creation of retention basins for water and compounds or the establishment of characteristic fen species and communities may have high priority. In order to avoid goal conflicts, nature development plans are required which consider not just the wetland to be restored, but the entire catchment area. Such plans should include spatially and temporally differentiated recommendations for implementa- tion of restoration measures and a proper land use system. When it comes to defining concrete aims, the participation of local people should be encouraged. Rewetting and oligotrophication are the most common approaches to boost biodiversity in fen ecosystems in Central and Western Europe. Rewetting includes both quantitative and qualitative aspects, requiring quantitative hydrological models and chemical analyses of the groundwater in the region. In addition, re-introduction of species is often neces- sary, at least in heavily fragmented cultural landscapes. Trans- fer of hay from donor areas to severely damaged, seed-de- pleted peatland to restore fen meadows, was successful. How- ever, despite short-term successes, complete restoration of wetland areas requires a long period of time.

The effects of drainage on groundwater quality and plant species distribution in stream valley meadows

Conditions in fen meadows in Dutch stream valleys are influenced by both deep (Ca2+-rich) and shallow (Ca2+-poor) groundwater flows. The distribution patterns of phreatophytic (groundwater-influenced) plant species showed distinct relationships with the distribution of different groundwater types. Large fluctuations in the ionic composition of groundwater were observed in the upper peat layers of drained areas. Ca2+-rich groundwater was replaced by precipitation water to a considerable depth (1–1.5 m). These fluctuations in groundwater composition were less pronounced in undrained areas. It was observed that characteristic species of fen meadow communities and rare phreatophytic species were restricted to areas with high water tables, which were nourished by either Ca2+-poor or by Ca2+-rich groundwater. Few species showed a preference for drained areas, where replacement of groundwater types gave rise to the occurrence of an intermediate groundwater type, which was thought to be the result of an increased acidification of the top soil (increased influence of infiltration water). It was argued that the endangered species were best preserved in areas with an undisturbed discharge of natural groundwater flows.

Succession and fluctuation in a wet dune slack in relation to hydrological changes

Vegetation changes in a wet dune slack complex have been studied over a period of 23 yr. The vegetation was recorded in 40 permanent plots: all plots in 1964, 1977, 1983 and 1987 and some also in five other years. There were large fluctuations in annual precipitation during this period, including some extremely dry (1976) and wet (1985) years. Many species of wet calcareous and pioneer habitats declined in cover between 1964 and 1977, when there were prolonged dry summer periods, though few species were lost from the sampled quadrats. Practically all calciphilous and pioneer species disappeared between 1977 and 1983, when there were relatively many wet summers. It is suggested that extremely dry conditions temporarily obscure the impacts of hydrological changes in local hydrological system, by retarding the vegetation succession. After a period of excessive precipitation the (acidifying) effects of ground-water withdrawal rapidly became evident in the species composition of the dune slack.

European dune slacks: Strong interactions of biology, pedogenesis and hydrology

Dune slacks are a unique type of wetland ecosystem, highly ranked on the international conservation agenda because of the occurrence of many rare and endangered plant species and their associated fauna. Ecologically they present some of the few examples of primary succession seres with a high degree of facilitation between functionally distinct groups of plants and a strong impact of the interannual variation of the water table. Recent research has focussed on the biological and environmental processes counteracting the rapid loss of diversity owing to human impacts along most north-west European coasts.

Nutrient limitation and vegetation changes in a coastal dune slack

Basiphilous pioneer species are among the most endangered plant species in The Netherlands. They find most of their refuges in young coastal dune slacks, especially on the Wadden Sea islands. For the purpose of nature management it is important to know which processes control the presence of basiphilous pioneer communities, and to learn about the nature of slacks harbouring the concerning successional sequences. In a large dune slack on the Island of Terschelling, we assessed soil nutrient status and tested for nutrient limitation in four chronosequential stages: 2, 6, 37 and ca. 80 yr of age. Stage 2 harboured a basiphilous pioneer vegetation; in the stages 3 and 4 a dense vegetation of dwarf shrubs and grasses occurred. Soil organic matter and nutrient concentrations in each stage were measured in 1991. In 1992 and 1993 fertilizers were applied to all stages to detect nutrient limitation. Rates of accumulation of organic matter, nutrients and above-ground biomass were estimated. When interpreted as successional stages, the different stages represent a sequence as expected on the basis of general successional theory. There was a peak in yearly nutrient accumulation between the 6- and 37-yr old stage and a steady state after ca. 80 yr. Between the first two and the latter two stages a shift occurred from allogenic to autogenic succession which correlated with a shift in emphasis from available nutrients to light availability as limiting resources. Basiphilous pioneer species suffered only deficiency of nitrogen, probably because of their low phosphorus requirements. It is concluded that in dune slack habitats, in addition to a low nutrient availability in general, a very low phosphorus availability favours basiphilous pioneer species to species showing co-limitation of nitrogen and phosphorus as found in some grasses and dwarf shrubs. A comparison between the effects of lime addition and the effects of nitrogen and phosphorus additions suggests that, in the early stages, soil buffering increases the availability of nitrogen and inhibits the availability of phosphorus. Sod cutting is an effective technique for restoring basiphilous pioneer vegetation, when slacks are acidified only superficially and buffering-mechanisms can be reactivated. Yearly mowing and removing of standing crop may prolong the lifespan of basiphilous pioneer vegetation, when soil acidification has not yet dropped below pH 6.

Numerical assessment of plant species as indicators of the groundwater regime

The relation between the occurrence of plant species in environments varying in moisture status and groundwater regime was tested using numerical methods. The groundwater regime during the vegetation period was expressed by means of four parameters, the average (AVG), mean highest (HIGH), mean lowest (LOW) groundwater level and the maximum fluctuation (AMP). 67 records of five vegetation types were selected from hydrologically stable sites in brook valleys in the northern part of The Netherlands. Response curves were calculated for 30 representative species. Calculated optima for AVG, HIGH and LOW are strongly correlated to each other. The vegetation reacts independently from overall wetness to the amount of fluctuation of the groundwater level (AMP). Response curves of single species as well as combinations of both present and absent species were used to find the best set of indicators for each parameter. The use of combinations of species clearly improves the indicating Value of Vegetation records. The vegetation appears to be the most sensitive to the parameter HIGH, which can thus be considered to be a key factor in controlling vegetation composition. The four parameters can be predicted satisfactorily only in the middle part of the investigated gradient. This is not only due to arithmetic artifacts, inherent to the applied method, but also to the fact that at average groundwater levels below -60 cm or above 0 cm other factors become predominant.

The state of the art of aquatic and semi-aquatic ecological restoration projects in the Netherlands

The Netherlands are a small, low-lying delta in W. Europe (42000 km2; 50°–54° N; 3°–8° E), mainly consisting of alluvial deposits from the North Sea and from the large rivers Rhine and Meuse. The country was ‘created by man’. The conversion of natural aquatic and terrestrial ecosystems into drained agricultural land was a major cultural operation over the past 1000 years. Roughly 55% of the country’s surface area is still agricultural land. Some decades ago, The Netherlands’ landscape was characterised by an armoured coastline and bridled estuaries, a drastically reduced area of saline and freshwater marshes, fully regulated rivers and streams, and numerous artificial lakes. The aquatic ecosystems beyond the influence of the large rivers, the Pleistocene raised bogs and moor lands, have almost been completely annihilated in the past. Acidification and eutrophication led to the deterioration of the remaining softwater lake vegetation. Last but not least, an artificial drainage system was constructed, leading to an unnatural water table all over the country, high in summer, low in winter. Only very recently, some 25 years ago, the tide has been turned and ecological rehabilitation and restoration of disturbed ecosystems are in full swing now, enhanced by the European Union policy to set aside agricultural land in the Netherlands in favour of the development of ‘nature’. The state of the art of aquatic and semi-aquatic ecological restoration projects in the Netherlands is given. Starting from the conceptual basis of restoration ecology, the successes and failures of hundreds of restoration projects are given. Numerous successful projects are mentioned. In general, ecological restoration endeavours are greatly benefiting from progressive experience in the course of the years. Failures mainly occur by insufficient application of physical, chemical or ecological principles. The spontaneous colonisation by plants and animals, following habitat reconstruction, is preferred. But sometimes the re-introduction of keystone species (e.g. eelgrass; salmon; beaver) is necessary in case the potential habitats are isolated or fragmented, or when a seed bank is lacking, thus not allowing viable populations to develop. Re-introduction of traditional management techniques (e.g. mowing without fertilisation; low intensity grazing) is important to rehabilitate the semi-natural and cultural landscapes, so characteristic for the Netherlands. For aquatic ecosystems proper (estuaries, rivers, streams, larger lakes) the rule of thumb is that re-establishment of the abiotic habitat conditions is a pre-requisite for the return of the target species. This implies rehabilitation of former hydrological end geomorphological conditions, and an increase in spatial heterogeneity. The ‘bottom-up’ technique of lake restoration, viz. reduction in nutrient loadings, and removal of nutrient-rich organic sediment, is the preferred strategy. The ‘top-down’ approach of curing eutrophicated ecosystems, that is drastic reduction of fish stock, mainly bream, and introduction of carnivorous fish, may be considered as complementary. For semi-aquatic ecosystems (river-fed and rain-fed peat moors, brook valleys, coastal dune slacks) it also counts that the abiotic constraints should be lifted, but here the species-oriented conservation strategy, the enhancement of the recovery of characteristic plant and animal species, is mainly followed. An important pre-requisite for the rehabilitation of the original natural or semi-natural vegetation is the presence of viable seed bank. Restoration of salt-marsh vegetation has to deal with a short-lived persistent seed bank, which means that transport of seeds by water currents is important. Isolated softwater ecosystems may rely on the long-lived seeds of the aquatic macrophytes. The paper ends with some notes on the predictability of the outcome of ecological restoration measures and the societal position of restoration ecology as a science. Scientists hold different views on the predictability of restoration measures. A fact is that the predictability of ecosystem development increases, with increasing knowledge of the underlying environmental processes.

Nutrient limitations in an extant and drained poor fen : implications for restoration

In a species-rich poor fen (Caricetum nigrae) and a species-poor drained fen, the difference in nutrient limitation of the vegetation was assessed in a full-factorial fertilization experiment with N, P and K. The results were compared to the nutrient ratios of plant material and to chemical analysis of the topsoil. A rewetting experiment with intact sods was carried out in the glasshouse and the results are discussed in view of restoration prospects of drained and degraded peatlands. In the undrained poor fen the above-ground biomass yield was N-limited while the vegetation of the drained fen was K-limited. Experimental rewetting of intact turf samples, taken in the drained site, did not change the biomass yield or the type of nutrient limitation. It was concluded that mire systems which have been subjected to prolonged drainage are inclined to pronounced K-deficiency, probably due to washing out of potassium and harvesting the standing crop. This may hamper restoration projects in degraded peat areas where nature conservation tries to restore species-rich vegetation types with a high nature value.