Management Strategies on Duke Populations

Effect of Diffrent Management Strategies on Populations of Selected Plant species on the DUtch Wadden Sea Islands

Introduction

Coastal dune slacks is the wet, low-lying area between sand dunes which are flooded during winter and most of the spring. These ecosystems harbour many rare and endangered plant species (Grootjans et al. 1988; Lammerts 1999) and were gained a special attention regarding to their conservation status.

Generally, dune slacks in coastal area formed in two different ways. The primary dune slacks have arisen from sandy plains that have become isolated from the influence of the sea by the formation of new dune systems. The primary dune slacks are generally very large and, if the initial lime content of the soil is high, may sustain alkaline conditions for a long time. Secondary slack systems are formed further away from the coast by wind blowing, generally in dunes unfixed by vegetation. The secondary dune slacks are generally smaller and tend to have a short life span of several decades or less.

Dune slack soils can be calcerous or relatively acid, depending on the initial lime content of the dune complexes. In areas with precipitation surplus and initial lime content of more than 0.3%, young slacks are usually calcerous; old slacks may be acidic or alkaline. Dune slacks show an enormous variability with respect to species composition which closely reflects the characteristics of the groundwater regime. Hydrological conditions are important in maintaining calcium-rich dune slacks habitats.

The rate of organic matter accumulation, however, appears to be influenced by the hydrological regime in a dune slack. In dune slacks fed by a regular supply of groundwater, the accumulation of organic matter in soil and vegetation can be very slowly (Sival & Grootjans 1996), and pioneer stages can persist for many decades. Slacks predominantly fed by rainwater acidify rapidly in decalcified dune areas. The rate of accumulation of organic matter is rapid in such slacks and pioneer stages with many rare and endangered wetland species disappear within 10-15 years (Lammerts et al. 1995; Lammerts & Grootjans 1998). It was thought that the decline of this wet plant communities are because of natural process and also anthropogenic (Grootjans et al. 1991; van Dijk & Grootjans 1993).

Hydrological regime

The species-rich habitat of dune slacks are controlled largely by water chemistry and fluctuations in groundwater. The distribution of individual species is controlled by key hydrological parameters such as depth to the water table and seasonal variation in water table level (Lammerts et al., 2001). Groundwater chemistry is another factor controlling plant distributions (Lammerts et al., 1992; Stuyfzand, 1993; Grootjans et al., 1996) and this depends to a great extent on whether it is precipitation fed, as in an isolated dune system (Willis et al., 1959b), or externally derived, either from upwellings or from sub-surface flow from inland (Stuyfzand, 1993). Both the buffering capacity (Sival and Grootjans, 1996; Sival et al., 1997) and nutrient status are particularly important. Therefore, greater understanding of the sources of groundwater and the chemical composition of the groundwater is necessary when managing a dune slacks. Understanding these processes allows managers to accurately identify the causes of observed change, and to predict which parts of the system are most sensitive to future perturbations such as altered rainfall patterns.

Vegetation

Vegetation in wet dune slack is characterized by a high species diversity and low productivity (Bakker et al. 1979). The characteristic pioneer vegetation of wet dune slacks consists mainly of plant communities of the associations Parnassio-Juncetum atricapilli and Junco baltici-Schoenatum nigricantis (Westoff & Den Held 1969; Bakker et al. 1979).

Succession

Natural succession in dune slacks can be roughly divided into 4 phases: a pioneer phase (phase 1) in which small pioneer species establish on an almost bare soil, which is usually covered with a thin layer of green algae and laminatedmicrobial mats (van Gemerden, 1993; Grootjans et al., 1997), (phase 2) colonisation of phanerogams adapted to very low nutrient availability, (phase 3) development of a moss layer of pleurocarpic bryophytes and establishment of typical dune slack species, and on older phase (phase 4) in which rapid accumulation of organic matter and increase of tall grasses and shrubs appears, which leads to the decline of typical dune slack species.

The microbial mat in phase 1 stabilises the sandy substrate (Pluis & de Winder, 1990). The Cyanobacteria in the microbial mats can fix nitrogen (Stal et al., 1994) and may, therefore, assist in the colonisation by phanerogams. The dense layer of pleurocarpic bryophytes in phase 3 promotes the rapid built up of organicmaterial and the establishment of tall grass and willow species. These eventually form a dense vegetation cover which prevent light penetration through the dense canopy, leaving little space for small dune slack species. Red list species are most abundant in phase 2 and 3. Orchids only occur in these early successional stages, where they receive nutrients from soil mycorrhizas (Smith, 1966). Juvenile orchids in particular are almost totally dependent on nutrients from mycorrhizas. Juveniles are also probably more sensitive to changes in the environment.

Study species

This study will focus on Liparis loeselii (Orchidaceae), Pedicularis palustris (Scrophulariaceae) and Schoenus nigricans (Cyperaceae). All three species are dune slack species of pioneer stages. They live under low productivity environment and base-rich conditions. The occurrence of these three species at the dune slack was being monitored. The different life span and dispersal mechanism between these species makes them an interesting species to study.

Liparis loeselii is a small, inconspicuous, rare an endangered orchid occurring in Europe and north-east America. L. loeselii is a perennial, its fleshy green pseudobulb wintering over just beneath the substrate surface. Often the previous year's pseudobulb is still present in spring, fused to the current year's from which a new shoot emerges in late May or early June. Flowering occurs from late June to mid-July (McMaster 2001). The seed of L. loeselii are minute and because this species is often found in coastal environments, dispersal by wind is even more likely. Even though L. loeselii is known to be autogamous, but it shows a higher level of genetic variation than expected (Pillon et al. 2007). The species is listed in endangered in both the Habitat Directive and the Bern Convention, and therefore has the highest conservation priority. Earlier research done in Great Britain shows that the populations of L. loeselii are short-lived and rapidly expand or disappear as conditions change (Jones 1998; Wheeler et al. 1998).

Pedicularis palustris is limited to the northern hemisphere and occurs throughout Europe in natural fens and in moderately grazed or mown fen meadows. This hemiparasitic species has biennial life cycles, which reproduce exclusively by seed. Seeds are buoyant and can be dispersed by water (Kleinschmidt & Rosenthal 1995). Only a minor fraction of seeds germinate immediately after seed-shedding in summer. During the first growing season, a rosette develops, which forms a winter bud in autumn. Flowering takes place in June and July of the second growing season. Flowers are pollinated by bumble bees. The species is short-lived and has only a short-term persistent seed bank (Thompson et al. 1997) and thus make this population persistence depends on regular reproduction by seed.

Schoenus nigricans usually found on acid and alkaline peats, mineral soils rich in organic matter and calcareous marls. Generally, the habitats of Schoenus are waterlogged, with the water table slightly below the surface. The genus Schoenus has a large diffusion in Europe, growing from Scandinavian Peninsula (Mossberg et al. 1994; Hendrèn 1997) to southern Europe and Northern Africa (Zangheri 1976). S. nigricans is wind pollinated as a rule, but self pollination may occur. Seeds germinate within the inflorescence if the flowering stem is broken and the inflorescence is close to the ground. Seed is dispersed mainly by the wind. Some seed is held in the inflorescence for most of the winter, and is release in strong wind. Pollen is shed from early July onwards and the seed is set in August. The seed is held firmly in the spikelet, and may not be shed until December. Some seed can be found in the flowering heads in the following spring. This species is characterized by a high concentration of silicon (Ernst et al. 1998) and is considered a typical pioneer species, important in wet dune slacks (Ernts et al. 1988, 1966). The hybrid of S. nigricans x S. ferrugineus has been reported from Europe where both species occur and were confirmed by a molecular study (Scotti et al. 2002). Say something on population structure(Van de Ham & Ernst 1985?)

Metapopulation

Metapopulation theory is frequently used in conservation biology (Frank & Wissel 1998; Hanski 1999; Menges 2000; Akçakaya et al. 2000). The metapopulation concept was introduced into biology by ecologists wishing to take into account the fact that many species consist of an assemblage of ephemeral subpopulations or demes that persist over time in a dynamic balance between local extinction and recolonization (Levins 1968, 1969). Metapopulation models have been used numerous times to analyse species distribution and dynamics for the purpose of making management recommendations. For instance, models helped gain knowledge about the effectiveness of corridors (Westphal et al. 2003), reintroduction and/or translocations (Akçakaya et al. 1995; Bretagnolle & Inchausti 2005), dispersal capability of species (Lamberson et al. 1994; timing of management actions (Volis et al. 2005), and optimal fire-management regime (Brook & Griffits 2004; Regan & Auld 2004).

Key Ecological factors limiting populations of your species

What are the main environmental or ecological factors in dune slack

Organic matter accumulation

pH (why is that important) (E. Dijk) Dactylorhiza incarnate)

Water level (why is it important)

Which species is most sensitive to long time flooding

Hypothesis

These following questions will be addressed for this research:

(1) do different management strategies gives different impact on coastal plant community structure? and

(2) what is the colonization history of selected populations (at different spatial scales)?

Research goals

The objectives of this study are:

i) to predict the stability of the population according to different environmental conditions

ii) to determine on the conditions favoring the establishment and survival of endangered species

iii) to estimate origin and dispersion of selected population

Methodology

Sampling sites

The study will take place in three sites with different management policies and on different islands: a) natural and undisturbed, b) managed (sod-cut) of different ages and c) degrading sites. The study sites will be on Schiermonnikoog, Vlieland, Terschelling and Texel.

Species

The focus of the present project will be on Liparis loeselii, Pedicularis palustris and Schoenus nigricans. Assignment tests and the computer program STRUCTURE (Falush et al. 2007, Mol.Ecol Notes) will be used to investigate the colonization history of the populations.

Vegetation survey

In each of the differently managed sites, the vegetation composition and dynamics will be analyzed; the population structure of Liparis loeselii, Pedicularis palustris and Schoenus nigricans and measure key environmental factors governing the site conditions will be described. The total species composition will be assessed and will be compared with already existing long term monitoring data (25 years) on vegetation composition and succession. Special attention will be give to the habitat dynamics of the species and to the carrying capacity (nr of individuals per m2 in different successional stages and different hydrological conditions.

Measurement of environmental factors

Environmental factors that will be measured are: amount of organic matter in the top layer (correlated with nutrient contents), pH and wetness characteristics (water table). Small scale hydrological conditions with respect to salt/freshwater gradients will also be described, using analyses of ground and surface water. Other ecological factors (redox, oxygen and sulphide) will be measured in the soil profile using microelectrodes to illustrate the differences between sites. We will also note management or no management (mowing, sod cutting)

Molecular work

DNA of Liparis loeselii, Pedicularis palustris and Schoenus nigricans will be extracted and will be used for AFLP reaction. Asssignment tests (Cambell et al. 2003) will be used to identify the source populations. Explain about markers, because this facilitates your work and selection of species.

Reference

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