Patterns in Species Diversity during Succession of Coastal Dunes

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    Patterns in Species Diversity during Succession of Coastal DunesAuthor(s): Maike IsermannSource: Journal of Coastal Research, 27(4):661-671. 2011.Published By: Coastal Education and Research FoundationDOI: http://dx.doi.org/10.2112/JCOASTRES-D-09-00040.1URL: http://www.bioone.org/doi/full/10.2112/JCOASTRES-D-09-00040.1

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    Patterns in Species Diversity during Succession ofCoastal Dunes

    Maike Isermann

    Vegetation Ecology and Conservation BiologyBremen UniversityLeobener Strasse, 28359 Bremen, Germanymaike.isermann@uni-bremen.de

    ABSTRACT

    ISERMANN, M., 2011. Patterns in species diversity during succession of coastal dunes. Journal of Coastal Research,27(4), 661671. West Palm Beach (Florida), ISSN 0749-0208.

    The humped-back relationship in species diversity during succession was tested using vegetation in a coastal sand dunesystem of the German Wadden Sea island of Spiekeroog. Permanent plots were studied over 15 years along a spatialchronosequence from young grey dunes to old brown dunes. Species diversity, succession rate, and environmentalindicator value were used to evaluate multitemporal dynamics of the ecosystem. Long-term development of the dunevegetation was reflected along the chronosequence, whereas fluctuations of plant communities were analyzed by short-term changes of each permanent plot.

    The study confirmed the intermediate stress theory, whereas highest species diversity was reached at the transitionzone of the environmental gradients. Total species richness showed humped-back relations along the xerosere. Hotspotsin species diversity varied with the life form group. Highest richness of herbaceous plants was reached in semidynamicyoung grey dunes, whereas highest richness of bryophytes and lichens shifted due to competition effects to the driestparts of the dune gradient in older successional stages.

    Moreover, the study confirmed the biodiversity-stability theory, with highest ecosystem stability at highest diversity.More stable environments showed lower succession rates than dynamic, disturbed environments. Thus, duringsecondary succession with probably repeated disturbance, the succession rate was higher and no clear direction ofvegetation development was found in comparison to primary succession. The succession rate in a primary seriesrepresented a unimodal relation with total species richness. Thus, species-poor vegetation often dominated by onespecies, such as heathlands, as well as species-rich vegetation, showed lowest succession rates. These communitiesprobably are more stable due to a balanced species combination represented by higher evenness.

    ADDITIONAL INDEX WORDS: Chronosequence, fluctuation, permanent plot, succession rate, time series, vegetationdynamics.

    INTRODUCTION

    Coastal dunes are one of the most vulnerable landscapes in

    northwest Europe and include priority habitats, considering

    the European Union Habitats and Species Directive. For

    example, habitats with open, short, dry grasslands at the

    mainland are often threatened due to agricultural use.

    Furthermore, many coastal dune habitats contain rare species

    and are species rich (Doody, 2001). In general, species diversity

    depends on different ecological features like plant productivity

    (Rosenzweig, 1995), which is often correlated with environ-

    mental factors like soil pH (Isermann, 2005) and scale

    dependent (Auerbach and Shmida, 1987). Relationships among

    the changes of species diversity in the course of ecological

    succession are different. General models of ecological succes-

    sion predict an increase of species diversity with increasing age

    (Odum, 1971).

    Vegetation succession is affected by external and internal

    factors (Bakker et al., 1996). External effects, like atmo-

    spherically nutrient deposition, often give rise to various

    internal developments, such as soil acidification. Vegetation

    composition is also affected by various internal mechanisms,

    like altered competition interactions, and shows a feedback

    mechanism by the vegetation itself (Bakker et al., 1996).

    Vegetation development is controlled by processes, which often

    differ during primary and secondary succession (Austin, 1981).

    Most sand dunes are spatial sequences representing chron-

    ological series (Salisbury, 1952), because the spatial series of

    dune ridges from the sea inland developed one after another. In

    general, these chronosequences describe the formation and

    development of vegetation and environmental factors of the

    dunes (Cowles, 1899; Ranwell, 1960). Mechanisms of direc-

    tional changes in species composition are governed by abiotic

    factors; species interactions or spread of dominant plant

    species retrospectively affects abiotic conditions. Long-term

    vegetation changes in dunes are especially linked with the

    development of the soil (Salisbury, 1925). Strong relationships

    between plant communities and soil parameters, especially the

    C:N ratio and soil pH, were shown, e.g., along a dune zonation

    DOI: 10.2112/JCOASTRES-D-09-00040.1 received 12 April 2009;accepted in revision 2 December 2009.

    Coastal Education & Research Foundation 2011

    Journal of Coastal Research 27 4 661671 West Palm Beach, Florida July 2011

  • in Denmark (Frederiksen et al., 2006). Mechanisms determin-

    ing dune plant patterns appear at both the individual and the

    community level (Feagin et al., 2005), e.g., in changes of species

    abundance and species composition of the plant community.

    In view of their patterns of development, dunes are

    particularly suitable for the study of the relationship between

    succession and zonation (Johnson, 1997; Lichter, 1998).

    Successional dynamics in vegetation have mostly been eval-

    uated by using permanent plots and indirectly by using

    chronosequence studies of the vegetation zonation (Foster

    and Tilman, 2000). Investigations of chronosequences can

    expose regional-scale successional trends due to changes of

    vegetation and environment (Bakker et al., 1996); permanent

    plots, on the other hand, can reveal changes on a local scale.

    Nevertheless, directional vegetation change in dunes can be

    overlaid by seasonal fluctuations, which are determined, e.g.,

    by variation in precipitation and groundwater (Van Der

    Maarel, 1978, 1981), wind disturbance, and associated sand

    erosion and accumulation (Martnez, Vazquez, and Sanchez,

    2001). Therefore, it is a methodological challenge to distinguish

    between fluctuation and succession in dune vegetation using a

    multitemporal approach.

    The present study evaluates changes in plant diversity

    during the past 15 years in dune vegetation influenced by

    natural succession. The main scope of the study was to analyze

    species diversity in relation to succession. Questions addressed

    by this study are as follows: (1) Does species diversity of coastal

    dune vegetation change in relation to succession in a humped-

    back (>) manner? (2) Does the chronosequence approach reflect

    the time-related vegetation development? (3) Does a relation-

    ship exist between succession rate and species diversity, and

    are species-rich communities more stable? and (4) Do species of

    later successional stages change in cover abundance strength

    compared with those from earlier stages?

    METHODS

    Study Area

    The study area was located on the German Wadden Sea

    island of Spiekeroog (Figure 1). The area is protected as part of

    the Wadden Sea National Park (intermediate protection zone).

    The island can be divided in distinct areas of different age

    (Figure 1). The oldest part originates from around AD 1650,

    and the eastern part has developed since AD 1960 (Gerlach,

    Albers, and Broedlin, 1994). Foredunes on Spiekeroog are due

    to continuing sand dynamics up to 20 years old, the main yellow

    dune ridges are 45 to 70 years old, the grey dunes are 70 to

    170 years old, and the brown dunes are up to 270 years old

    (Gerlach, Albers, and Broedlin, 1994). The study area was

    composed of a dune chronosequence in the older, western part

    of the island, and plot ages were estimated according to

    Sindowski (1970).

    The dry dune chronosequence, the xeroseries, is character-

    ized by a typical vegetation zonation. On the beach driftline,

    vegetation such as the Salsolo-Cakiletum maritimae occurs.

    The xeroseries started with low embryonic dunes grown by the

    Figure 1. The island Spiekeroog, the location of the permanent plots (Niedersachsisches Landesamt Fur Okologie, 1993), and the development of the dune

    areas on the island (Gerlach, Albers, and Broedlin, 1994; according to Sindowski, 1970). A line represents the location of the chronosequence along which the

    permanent plots were located. Plains (white) in the south are saltmarhes, in the centre reflect the village, and in the eastern part the white plains reflect

    dunes in the north and salt marshes in the south. The geographic coordinates are for plot 1 (53u46933.80 N, 007u42948.40 E), plot 2 (53u46932.40 N, 007u42952.20E), plot 3 (53u46922.60 N, 007u42930.40 E), plot 4 (53u46927.20 N, 007u42934.90 E), plot 5 (53u46922.60 N; 007u42930.40 E), plot 6 (53u46920.40 N, 007u42948.70 E),plot 7 (53u46912.50 N, 007u43901.20 E), plot 8 (53u46918.70 N, 007u43901.80 E), plot 9 (53u46923.00 N, 007u42930.60 E), plot 10 (53u46907.00 N, 007u42957.50 E), andplot 11 (53u46906.60 N, 007u42956.70 E).

    662 Isermann

    Journal of Coastal Research, Vol. 27, No. 4, 2011

  • Honckenyo-Agropyretum juncei. In the case of sand accumula-

    tion, dunes rise to higher yellow dunes, typically covered by the

    Elymo-Ammophiletum and characterized by sparse vegetation

    and a raw soil more or less without organic matter. With lesser

    sand accumulation, shrublands like the Hippophao-Sambuce-

    tum establish on the landwards slopes. Increased sand

    stabilization, continued leaching out of nutrients by precipita-

    tion, and increased vegetation cover support the origin of soil

    organic matter, so that grey dunes develop. Grey dunes in

    relation to a decreasing gradient of sand accumulation and in

    relation to soil development, e.g., expressed as a decreasing soil

    pH, are covered by plant communities like the Phleo-Tortule-

    tum ruraliformis, the Festuco-Galietum veri, and the lichen-

    and bryophyte-rich Violo-Corynephoretum. These grey dune

    communities often contain many rare species and occur in less

    disturbed conditions more often on the islands than on the

    mainland, so they are highly valuable in the sense of nature

    conservation. The following brown dunes with low soil pH and

    high organic matter content are characterized, on the one

    hand, by short, dense grasslands like the Carex arenaria

    [Koelerio-Corynephoretea] community and, on the other hand,

    by heathlands, which on Spiekeroog are represented by the

    Carici arenariae-Empetretum. The oldest dune parts are

    grown by dune woodlands, including Betula pubescens, Pinus

    silvestris, Populus tremula, Quercus robur, and since about

    10 years ago, Fagus sylvatica.

    Dunes are in general characterized by sand dynamic, which

    supports small-scale vegetation mosaics and younger vegeta-

    tion stagesespecially in grey dunes. Therefore, natural and

    human-induced disturbance plays an important role. The

    dunes on Spiekeroog were grazed by cattle and sheep until

    about 1900; rabbits have been eradicated since 1880 (Meyer-

    Deepen and Meijering, 1970), only hares and pheasants with

    lower scrabbling activities occur. Many parts of the outer dunes

    are stabilized by planting of marram grass; thus, higher sand

    accumulation into the following dunes is more or less stopped.

    Only beach and foredunes show higher sand dynamic,

    particularly due to recreation activities. During the past

    15 years, disturbance in the inner dunes was low, including

    human impacts, e.g., due to recreation activities. Establish-

    ment of the national park and general enhanced public

    environmental awareness, combined with increased respon-

    siveness of global change, e.g., the importance of dunes in

    relation to sea-level rise, support the decline in human dune

    disturbance.

    During the last century, land use changed and in the

    following dunes developed to be more fixed and without an

    appreciable amount of open sandy areas (Meyer-Deepen and

    Meijering, 1970). Due to changes in land use, dunes in the

    North Sea area are, since the middle of the last century,

    characterized by an increase in various scrub vegetation, e.g.,

    native shrubs such as Crataegus monogyna, Hippophae

    rhamnoides, and Ligustrum vulgare and nonnative ones like

    Rosa rugosa (Isermann and Cordes, 1992; Van Der Laan,

    1985). The development towards older successional stages on

    Spiekeroog was already visible around 1950 (Wiemann and

    Domke, 1959). Further changes of the dune vegetation were

    analyzed in 1990 on the landscape scale using vegetation maps

    (Isermann and Cordes, 1992), and recent changes were studied

    on a smaller scale with permanent plots.

    Sampling

    Along a transect from (young) grey to (old) brown dunes, 11

    permanent plots (Figure 1), placed in typical plant commu-

    nities, were established in 1990. In comparison to strictly

    random sampling design (Frederiksen et al., 2006), the

    permanent plots were established in typical plant commu-

    nities, initially with plots containing only one plant community

    instead of a possible mixture of different communities in one

    plot. Moreover, this sampling design was used because a long-

    term development was of primary interest instead of a short-

    term competition approach between two plant species. Along

    the chronosequence, vegetation changes with indirect and

    direct methods were compared. Moreover, vegetation changes

    were compared on large and small spatial scales, as well as

    considered on different temporal scales, and time-intensive

    vegetation mapping (Isermann and Cordes, 1992) and perma-

    nent plots were combined.

    Permanent plots were recorded to detect long-time vegeta-

    tion changes. Because of sand mobility, it was not possible to set

    up plots in dunes more seawards. Plots, 1 m2 in size, were

    marked with a wooden peg at each corner. Lost plots were

    reestablished at the most probable same place in relation to

    global positioning system (GPS) data and photos of the plot

    location in the dune landscape. Changes in species composition

    were studied in most cases every fifth year from 1990 to 2005;

    in total, 34 releves were analyzed (Appendix). Fieldwork was

    carried out in late summer (July/August). This variation has no

    effects on the results of this study, especially not for short-lived

    species, because of the rather long period of the study.

    Vegetation releves were carried out, and the percentage of

    cover of each vegetation layer (shrubs and trees, herbs and

    grasses, and bryophytes and lichens) was estimated. Plant

    species cover was recorded using the Barkman-Doing-Segal

    scale (Barkman, Doing, and Segal, 1964). The data were

    converted into average percentages of the cover range.

    Ellenberg indicator values (Ellenberg et al., 1991) were used

    to compare environmental conditions in different vegetation

    groups.

    Statistical Analyses

    Statistical analyses were, if not otherwise mentioned, carried

    out with the program Minitab (Anonymous, 1998). To distin-

    guish different vegetation groups according to the zonation, all

    releves were classified using a two-way indicator species

    analysis (TWINSPAN), running PC-ORD software with cut

    levels 0, 2, 5, 10, and 20 (Mccune and Mefford, 1999).

    All raw data of the 34 observations were used to analyze

    changes in vegetation (cover and species diversity of different

    vegetation layers) and in environmental conditions (cover-

    weighted Ellenberg indicator values) along the chronose-

    quence. A choice of diversity indices was used to compare the

    resulting differences between the indices. The chronosequence

    of different plant communities was expressed as numbers of the

    vegetation groups mentioned in Appendix. Regression analysis

    Species Diversity Patterns during Coastal Dune Succession 663

    Journal of Coastal Research, Vol. 27, No. 4, 2011

  • was used, and the significance of the quadratic model in

    relation to the linear one was tested by forwards and

    backwards stepwise regression.

    The variation in species diversity was measured as number

    of species in total and for each vegetation layer separately.

    Differences in total species richness between the earliest and

    the latest observation were shown graphically in biplots.

    To estimate changes of vegetation and environment in

    relation to the development from one community to another,

    differences in environmental factors, vegetation cover, and

    species diversity between distinguished vegetation groups

    were assessed with one-way analysis of variance.

    The change in cover abundance values of different species in

    plots between the first and the last observation years was

    estimated (data not shown), and species with a clear response

    ($5% total cover change) are marked in bold (Appendix).

    General changes of the species composition in time were

    assessed by detrended correspondence analysis (DCA) running

    CANOCO software (Ter Braak and Smilauer, 2002) with its

    default options. Species with only one occurrence were omitted.

    Ordination analysis was chosen because the variation during

    time was expected to be continuous and because the method is

    useful to examine relationships over time in different stands

    (Austin, 1977). To analyze the direction of change in vegetation

    composition, a DCA ordination diagram was used. In the

    sample plot, subsequent years were connected by arrows to

    indicate the direction in changes of species composition.

    To analyze the direction of vegetation changes, Spearman

    rank correlation, running SPSS 12, between plot scores of the

    ordination axis and both environmental and vegetational factors

    were used. Environmental factors were represented by mean

    Ellenberg indicator values; vegetational factors were repre-

    sented by the number of species and cover of each vegetation

    layer, as well as species-diversity indices. Furthermore, dune

    ages were correlated with the DCA ordination scores.

    To measure the change of floristic composition between the

    survey dates, Euclidean distance was used (Myster and

    Pickett, 1994; Olff and Bakker, 1991). It was calculated for

    each plot based on the relative abundances of the species used

    in the DCA analysis described earlier. The overall rate of

    succession (net rate) was calculated as the Euclidean distance

    between the first and the last years of observation. The 5-year

    rate of succession was calculated as the average Euclidean

    distance between successive investigation years. To evaluate

    relations between succession rate and species diversity,

    relationships between Euclidian distance and number of

    species, as well as diversity indices, were analyzed.

    NOMENCLATURE: Wisskirchen and Haeupler (1998)

    for vascular plants, Koperski et al. (2000) for bryophytes, and

    Wirth (1995) for lichens; plant communities according to

    Schaminee, Stortelder, and Westhoff, (1995).

    RESULTS

    Plant Communities

    The TWINSPAN classification resulted in four main vegeta-

    tion groups, based on floristic similarities (Appendix). Group 1

    (G1) represented earlier succession stages of grey dunes (Phleo-

    Tortuletum ruraliformis, Festuco-Galietum veri), mostly char-

    acterized by higher sand dynamic. Group 2 corresponded to

    lichen- and bryophyte-rich plant communities of the old, fixed

    grey dunes (Violo-Corynephoretum). The Violo-Corynephore-

    tum group was divided into four subgroups: a typical one (G2a),

    a group rich in the neophyte Campylopus introflexus (G2b, C.

    introflexus [Koelerio-Corynephoretea] community), a lichen-

    rich one (G2c), and a group rich in Dicranum scoparium (G2d).

    Group 3 reflected later succession stages with communities

    dominated by sedges and grasses (C. arenaria [Koelerio-

    Corynephoretea] and Deschampsia flexuosa [Nardetea/Cal-

    luno-Ulicetea] communities). Group 4 (Carici arenariae-Empe-

    tretum) consisted of heathlands on brown dunes and repre-

    sented a dominance of dwarf shrubs with Calluna vulgaris

    (G4a) and with Empetrum nigrum (G4b).

    Zonation

    The classified vegetation groups revealed a strong zonation

    from young grey dunes (G1) to brown dunes (G3 and G4). A

    significant increase occurred in dune age (Table 1); thus, the

    zonation of the vegetation (Appendix) reflected the dune

    chronosequence.

    Along the chronosequence and the succession series, respec-

    tively, Ellenberg indicator values of pH and N declined linear

    Table 1. Relationships between classified vegetation groups and dune

    age, indicator values, vegetation cover, number of species, and diversity

    indices were estimated by regression analysis. Shown are best-fitting linear

    or quadratic regressions, tested stepwise backwards and forwards. Slope of

    the linear relation, form of quadratic relation (< or >), coefficient of

    determination (R2adj.), and probability (p) are given. Number of

    observations was n 5 34.

    Linear Regression Quadratic Regression

    Slope R2adj. p Form R2adj. p

    Dune age (years) +23.52 0.65 ,0.001Indicator value

    pH (R indicator) 20.30 0.45 ,0.001

    Light (L indicator) > 0.74 ,0.001

    Moisture (F indicator) < 0.53 ,0.001

    Temperature (T

    indicator) > 0.49 ,0.001

    Nitrogen (N indicator) 20.10 0.13 0.021

    Cover (%)

    Total 7.89 0.17 0.009

    Grasses > 0.15 0.033

    Bryophytes > 0.44 ,0.001

    Lichens > 0.12 0.057

    Species richness

    Total 22.33 0.63 ,0.001

    Shrubs and trees < 0.26 0.004

    Grasses 20.38 0.49 ,0.001

    Herbs 21.56 0.49 ,0.001

    Bryophytes > 0.18 0.018

    Lichens > 0.42 ,0.001

    Species diversity

    Jaccard index 20.01 0.51 ,0.001

    Shannon index 20.10 0.21 0.003

    Euclidean distance 1.81 0.13 0.021

    Srensen index 20.02 0.38 ,0.001

    664 Isermann

    Journal of Coastal Research, Vol. 27, No. 4, 2011

  • (Table 1). Indicator values of light and temperature showed

    humbed-back relations, and moisture showed U-shaped rela-

    tions. Moisture reached lowest and light and temperature

    highest values in the lichen-rich Corynephorus sward (G2c).

    Thus, the Corynephorus sward was characterized by the

    lightest, warmest, and driest conditions of the xerosere.

    The cover abundance of each vegetation layer differed along

    the xerosere. The total vegetation cover generally increased

    linearly from grey to brown dunes (Table 1), which is in line

    with a decrease in bar ground reflecting the decline in sand

    dynamic. No linear or quadratic relation occurred considering

    the cover of shrubs and trees, as well as the cover of herbs.

    Cover of shrubs and trees was only remarkable in the brown

    dunes, and cover of herbs was only remarkable in the younger

    succession stages, such as Phleo-Tortuletum ruraliformis,

    Festuco-Galietum veri, and typical Violo-Corynephoretum.

    The cover of grasses, bryophytes, and lichens (slightly) showed

    humped-back relations along the succession series, with high-

    est values in the Corynephorus swards (Table 1).

    Species diversity varied among species groups along the

    succession series. The number of trees and shrubs showed a U-

    shaped relation and was higher in the young grey dunes, e.g.,

    with communities of the Festuco-Galietum veri, as well as in

    the heathlands. Moreover, the number of grasses decreased.

    The number of bryophytes and especially of lichens showed

    similarly their cover abundance; humped-back relationships,

    with a higher number of species in the old grey dunes. Like the

    total number of species, diversity indices (Shannon, Jaccard,

    and Srensen) declined; Euclidean distance increased along

    the succession series (Table 1). The Jaccard and Srensen

    indices showed clearer results than the Shannon index and

    Euclidean distance.

    Succession

    During the 15 years of observation, succession was restricted

    to a relatively low community level, mainly from one subgroup

    to the next older subgroup (Appendix). Vegetation development

    was represented by changes from the Festuco-Galietum veri

    (G1) to the Violo-Corynephoretum (G2a), which reflects a

    significant decrease in the number of herbaceous species

    (Table 2). Moreover, soil moisture and pH conditions declined

    during succession. Mainly developments came from younger to

    older succession stages within the Violo-Corynephoretum

    (G2ab, bc, and cd), whereas between the typical subgroup

    (2a) and the lichen- and bryophyte-rich one (2b) a significant

    increase occurred in the cover of bryophytes, a decrease

    occurred in the Jaccard index, and in most cases a decrease

    occurred in soil pH (Table 2). Only in one case did stronger

    development occur from Violo-Corynephoretum (G2) to brown

    dune grasslands (G3). This development was connected with a

    decrease in light availability and an increase in N conditions.

    Remarkably, no clear successional change was found in the

    brown dunes with grassland and heathland communities

    (Appendix).

    According to the ordination diagram (Figure 2), the lines

    indicate that plots of different investigation years were mostly

    situated along the third ordination axis. The dune age was

    negative correlated with the first three axes (Table 3); there-

    fore, the oldest dunes were situated at the bottom of the

    diagram. The ordination axes were characterized by different

    environmental and vegetational changes (Table 3). Along the

    second and third axes the indicator values for light and pH

    increased and the value for moisture decreased, and along the

    third axis temperature showed a slightly increasing trend.

    Furthermore, along the second and third axes, the number of

    geophytes and hemicryptophytes increased and that of woody

    chamaephytes decreased. Moreover, an increase occurred

    along the first and second axes in the number of therophytes.

    Species diversity (Shannon index and evenness) increased

    and dominance (Simpson index) decreased along all axes.

    Hence, at the lower-left part of the diagram species-poor

    vegetation types are situated, and at the upper-right part of the

    diagram are species-richer plots.

    The number of species, as well as the cover of both grasses

    and lichens, increased, especially along axis 3 (Table 3). Hence,

    in dominant vegetation units, especially of the brown dunes (E.

    nigrum heath, plot 11), Hieracium pilosella dune (plot 2), C.

    arenaria grassland (plot 7), and C. introflexus turf (plot 5),

    grasses, sedges, and lichens increased; related to the plot

    position, these changed from lower parts to the top right of the

    diagram. The Deschampsia grassland (plot 8) tended slightly

    to a cyclic development (Figure 2). The grey dune (plot 3),

    affected by secondary succession due to slope erosion, showed

    various development directions and had a high Euclidean

    distance (Table 4). Plots of both Corynephorus swards (plots 4

    and 6) and the CallunaEmpetrum heath (plot 9) changed from

    upper parts to the bottom left of the ordination diagram

    Table 2. Differences of vegetation parameters and environmental factors

    between those plant communities that developed from one to another

    vegetation group. No detectable differences in the change were found

    between group 2b and group 2c. Presented are the mean (Mn) 6 standarddeviation (SD). Vegetation groups are G1 (Phleo-Tortuletum ruraliformis

    and Festuco-Galietum veri); G2 (Violo-Corynephoretum) with G2a

    (typicum), G2b (Campylopus introflexus rich), and G2d (Dicranum

    scoparium rich); and G3 (Carex arenaria [Koelerio-Corynephoretea] and

    Deschampsia flexuosa [Nardetea/Calluno-Ulicetea] communities).

    Mn SD Mn SD F p

    G12a

    Moisture

    (F indictor) 3.98 0.18 2.77 1.01 7.76 0.032

    pH (R indicator) 4.62 0.47 3.37 0.72 9.23 0.023

    Herbs (n) 14.40 2.61 5.00 6.93 8.07 0.030

    Dune age (years) 640.00 0 713.30 63.51 7.50 0.034

    G2ab

    Cover bryophytes

    (%) 15.00 22.54 85.70 17.53 22.10 0.005

    Jaccard index 0.95 0.05 0.88 0.01 8.21 0.035

    G2ad

    pH (R indicator) 3.40 0.72 2.20 0.29 9.41 0.028

    G2cd

    pH (R indicator) 2.60 0.18 2.20 0.29 6.24 0.047

    Cover total (%) 119.50 5.79 101.10 6.01 19.44 0.005

    G2d3

    Light (L indicator) 7.60 0.57 6.30 0.42 15.46 0.006

    Nitrogen (N

    indicator) 1.80 0.18 2.70 0.38 19.14 0.003

    Cover total (%) 110.10 6.01 142.58 18.61 17.92 0.004

    F 5 F-value of the ANOVA, ration of within- and between group variance,

    p 5 probability.

    Species Diversity Patterns during Coastal Dune Succession 665

    Journal of Coastal Research, Vol. 27, No. 4, 2011

  • (Figure 2); they developed to species-poorer and less diverse

    communities. The opposite development of the Calluna

    Empetrum heath (plot 9) was in line with a decrease in the

    indicator values of light, temperature, and pH and an increase

    in moisture, reflecting the increase in woody chamaephytes

    characterizing the heath.

    Species-specific Cover Changes

    Some general trends of several species showed marked

    (.5%) cover abundance changes between the first and the last

    observation years (Appendix). In the young grey dune vegeta-

    tion was a decrease in Tortula ruralis, a typical moss for

    pioneer vegetation and an increase in bryophytes of later

    succession stages like D. scoparium and Hypnum lacunosum,

    as well as an increase of Agrostis tenuis. Lichen-rich grey dune

    vegetation was often characterized by a decline in Coryne-

    phorus canescens, Rumex acetosella, and sometimes tube-

    shaped Cladonias (e.g., Cl. anomea and Cl. chlorophaea).

    Moreover, this lichen-rich vegetation showed an increase in C.

    arenaria but even more in the neophytic moss C. introflexus; in

    one case, an increase was found in the relatively foliose

    Cladonia foliacea that probably grew on the Campylopus turf.

    The grasslands of the old dunes, the C. arenaria and the D.

    flexuosadominated plots, showed a reverse development of C.

    arenaria and D. flexuosa, respectively. Furthermore, species of

    older succession stages (Hypnum ericetorum and Cladonia

    arbuscula) increased. The brown dune heathlands represented

    an increase in D. scoparium and both H. ericetorum and

    Pleurozium schreberi. Moreover, the CallunaEmpetrum heath-

    land showed an increase in cover of E. nigrum and C. vulgaris

    and hence a vegetation change towards older succession stages.

    Changes in Species Richness

    Changes in species richness varied in relation to succession.

    Comparison of the number of species in the first and the last

    observations, and additional regression analyses between

    species richness and observation year (data not shown because

    they are not significant), showed successional trends, as well as

    fluctuations (Appendix).

    The number of herbaceous species (Figure 3b) decreased in

    the Phleo-Tortuletum ruraliformis (plot 1), typical for the

    young grey dunes. In comparison, the number of bryophytes

    and lichens showed more variation. The number of bryophytes

    and lichens (Figure 3c) decreased between 1990 and 2005 in

    the Corynephorus grey dunes (plots 4 and 6). In contrast, the

    number of herbaceous species fluctuated, probably because of

    the occurrence of annual and other short-lived species.

    Bryophyte and lichen richness increased at both sites with

    secondary succession (plots 3 and 5), e.g., due to the increase of

    C. introflexus. However, at dominant Campylopus stands (plot

    5) strong fluctuations occurred, probably due to bryophytes

    and lichens growing temporarily in small gaps or on Campy-

    lopus turfs. This resulted in a decline (plots 4 and 6) and an

    increase (plot 3) in the total number of species (Figure 3a). The

    dense D. flexuosa grassland (plot 8) was characterized by a

    decrease in bryophytes and lichens, as well as strong

    fluctuations of herbaceous species richness, probably due to

    reduced space and changed environmental conditions between

    the Deschampsia tussocks in comparison to the open Coryne-

    phorus swards. The brown dunes showed a clear increase in

    bryophytes and lichens (plots 911), which are typical in

    heathlands with the enhanced moisture contents. The number

    of other herbaceous species fluctuated a little, probably

    because only few spaces between the heathlands allowed the

    establishment of further species.

    Succession Rate

    The succession rate of the species composition was repre-

    sented by the Euclidean distance (Table 4) between the first and

    the last years of observation. Plots dominated by one species,

    like the H. pilosella community (plot 2), the C. introflexus turf

    (plot 5), and the E. nigrum heath (plot 10), showed only few

    changes in their species composition and had a low overall rate

    of succession (Table 4). According to the mean rate of succes-

    sion, moreover, the D. flexuosa grassland (plot 8) and both plots

    of the lichen-rich C. canescens swards (plots 3 and 6) showed a

    lower 5-year rate of succession than species-richer communities.

    The Euclidean distance showed a slight but not significant

    trend to a humped-back relation with the total number of

    species (Figure 4a); low succession rates were observed in

    species-poor communities, as well as in species-rich ones.

    Furthermore, a slight and significant humped-back relation

    was found between the overall succession rate and the

    Figure 2. Ordination diagram using detrended correspondence analysis

    of all 34 releves, x 5 axis 1, y 5 axis 2 (eigenvalue: total 5.588, axis 1 5

    0.903, axis 2 5 0.636, axis 3 5 0.219, and axis 4 5 0.182; lengths of

    gradient: axis 1 5 6.709, axis 2 5 4.143, axis 3 5 2.748, and axis 4 5 3.397).

    The lines indicate the changes in species composition of the permanent

    plots (no. plot/year). Symbols reflect the vegetation groups (Table 1): black

    dots 5 G1 (young grey dunes); black diamond 5 G2 (bryophyte- and lichen-

    rich old grey dunes); grey dots 5 G3 (dune grasslands); and grey diamond

    5 G4 (brown dune heathlands).

    666 Isermann

    Journal of Coastal Research, Vol. 27, No. 4, 2011

  • evenness (Figure 4b). The overall succession rate at first

    increased with increasing evenness and then showed a

    reduction and a runout at the higher values of evenness.

    DISCUSSION

    Chronosequence Approach

    The dunes of the island of Spiekeroog are one example in

    which environmental conditions changed with the vegetation

    during succession. Nutrient content, expressed as indicator

    value N, and soil pH declined along the chronosequence. Thus,

    soils of young grey dunes were characterized by higher soil pH

    and higher nutrient content. Along the chronosequence, light

    and temperature showed a humped-back relation and moisture

    a U-shaped one. Therefore, the Corynephorus sward of the old

    grey dunes was composed of light, very dry, nutrient-poor

    stands with a low soil pH. Finally, the brown dunes with

    grasslands and heathlands included less dry soils with a very

    Table 3. Spearman rank correlation between Ellenberg indicator values (cover weighted); detrended correspondence analysis ordination axes 1, 2, and 3;

    correlation between percentages of life forms (cover weighted); and cover abundance and species richness of life form groups with each ordination axis.

    Moreover, the correlation between the ordination axes and some diversity indices and the correlation with the dune age are shown. Spearman rank coefficient

    (rS) and probability (p) are given.

    Axis 1 Axis 2 Axis 3

    rS p rS p rS p

    Ellenberg indicator value

    Light (L indicator) 0.444 0.008 0.654 0.001

    Temperature (T indicator) 0.309 0.071

    Moisture (F indicator) 20.568 0.001 20.838 0.001

    pH (R indicator) 0.503 0.002 0.425 0.011

    Dune age (years) 20.425 0.012 20.613 0.000 20.482 0.004

    Life form (%)

    Chamaephytes, woody 20.573 0.001 20.706 0.001

    Hemicryptophytes 0.433 0.009 0.681 0.001

    Geophytes 0.561 0.001 0.475 0.004

    Therophytes 0.309 0.071 0.508 0.002

    Cover abundance (%)

    Total cover 0.522 0.001

    Shrubs and trees 20.526 0.001 20.711 0.001

    Grasses 0.355 0.036 0.500 0.002 0.427 0.011

    Herbs 0.496 0.002

    Grasses and herbs 0.360 0.034 0.499 0.002

    Lichens 0.489 0.003 0.765 0.001

    Bryophytes and lichens 0.407 0.015

    Species (n)

    Total 0.511 0.002 0.831 0.001 0.669 0.001

    Shrubs and trees 20.400 0.017 20.623 0.001

    Grasses 0.414 0.014 0.695 0.001 0.466 0.005

    Herbs 0.547 0.001 0.310 0.070

    Grasses and herbs 0.288 0.094 0.677 0.001 0.454 0.006

    Bryophytes 0.456 0.006

    Lichens 0.494 0.003 0.791 0.001

    Bryophytes and lichens 0.287 0.095 0.453 0.006 0.665 0.001

    Species diversity

    Shannon index 0.808 0.001 0.762 0.001 0.526 0.001

    Simpson index 0.769 0.001 0.610 0.001 0.447 0.008

    Evenness 0.731 0.001 0.423 0.013 0.299 0.086

    Succession rate

    Euclidean distance 20.417 0.014 20.575 0.001

    Srensen index 20.362 0.036

    Jaccard index 0.407 0.017 0.460 0.006

    Table 4. Overall succession rate measured as total Euclidean distance between the first and the last years of observation, and 5-year succession rate

    measured as mean Euclidean distance of all observation years. Given are also the vegetation groups (Appendix) reflecting the youngest and the oldest

    successional stages of each plot.

    Plot number 1 2 3 4 5 6 7 8 9 10 11

    Successional stage 1 12a 2ab 2bc 2bd 2cd 2d3 3 4a 4ab 4b

    Euclidean distance (total) 40.1 25.0 70.1 96.7 15.5 53.8 51.2 44.9 58.3 4.1 53.3

    Euclidean distance (mean) 55.6 33.9 39.6 55.0 49.1 31.2 51.2 32.7 57.9 33.0 53.3

    Species Diversity Patterns during Coastal Dune Succession 667

    Journal of Coastal Research, Vol. 27, No. 4, 2011

  • low soil pH. These changes of environmental conditions along a

    dune zonation were typical for the dune xerosere and are

    known from various other regions, such as the Swina Gate

    Barrier in Poland (abuz and Grunewald, 2007). In general,

    the interplay of different processes like accumulating sand at

    the first dune ridges, leaching out of nutrients, increasing

    vegetation cover, and accumulating organic matter in the

    landwards following dunes resulted in different plant commu-

    nities along the chronosequence (Carter, 1993; Salisbury,

    1925). With ongoing succession in dunes, climatic aspects

    became increasingly important. The humped-shaped tempera-

    ture gradient along the studied chronosequence reflects the

    warmer conditions on southern slopes with lichen- and

    bryophyte-rich Corynephorus swards and the colder conditions

    on the northern slopes containing Empetrum heath. Dry

    valleys of the grey dunes were often grown by C. arenaria or

    D. flexuosadominated grasslands; moreover, south slopes or

    flat areas were grown by the dominant neophytic moss C.

    introflexus, especially on disturbed sites with following

    secondary succession.

    A typical change of the vegetation structure occurs along the

    xerosere: The young grey dunes are characterized by mostly

    short grasses and herbs; on the grey dunes, bryophytes and

    especially lichens play an important role; and on the brown

    dunes, trees and especially dwarf shrubs become important

    cover abundances. These pattern and processes of dune

    succession on Spiekeroog are comparable on a global scale

    because the vegetation structure is similar (Doing, 1985).

    In general, the chronosequence showed an initial increase in

    species richness from the species-poor yellow dunes to the

    young grey dunes after surface stabilization, followed by a

    Figure 3. Biplots of the number of species in the first and last years of

    observation, which indicate increase and decrease in species richness

    between both years. (a) Total number of species, (b) herbaceous species, (c)

    bryophytes and lichens. (Spearman rank rS correlation across all 5 years:

    bryophytes and lichens, as well as total number of species in plots 4 and 6,

    and herbaceous species in plot 1: rS 5 21.000, p , 0.001).

    Figure 4. (a) Relationships between overall succession rates measured as

    total Euclidian distance between the first and the last years of observation,

    and species richness shown as the mean total number of species of each

    plot over the years (R2adj. 5 0.10, p 5 0.266). (b) The relationship with the

    average evenness over the years (R2adj. 5 0.41, p 5 0.048). Numbers

    represent permanent plot numbers.

    668 Isermann

    Journal of Coastal Research, Vol. 27, No. 4, 2011

  • relatively constant level or a decrease during later parts of

    succession (Morrison and Yarranton, 1973). Average of total

    species richness increased in a humped-back manner, e.g., in

    dunes of the German Baltic Coast (Isermann, 2005). In this

    permanent plot study, only a linear decline was found in total

    species richness because the succession only started with the

    grey dunes, which had the highest number of species. The

    yellow dunes could not be taken into account in the permanent

    plot study due to sand mobility. Similar to other dune studies,

    highest values of species diversity occurred in young grey

    dunes, where disturbance in the sense of sand accumulation

    and erosion reached intermediate levels. Although yellow

    dunes are missing, the study confirmed the intermediate stress

    theory, whereas highest species richness is reached at inter-

    mediate levels of environmental and disturbance gradients.

    Similar to our results, much lower species richness than in

    the young grey dunes is known from other regions in pioneer

    communities, such as yellow dunes with Ammophila arenaria,

    as well as from old grey dunes with grasslands dominated by C.

    arenaria (Bogaert and Lemeur, 1995). On Spiekeroog, from the

    young grey dunes inland, total species richness declines with

    dune age, which was also shown for coastal Lake Michigan

    sand dunes in the United States (Lichter, 1998). In comparison

    to the assumed humped-back relation of total species richness,

    species diversity, as well as cover abundance of bryophytes and

    lichens, showed a humped-back relation along the chronose-

    quence. The highest species diversity of bryophytes and lichens

    in the old grey dunes reflects the enhanced competition of

    bryophytes and lichens in comparison to herbs and grasses on

    these dry and acid soils. Thus, species diversity of different life

    forms varies in relation to the dune type and along the

    chronosequence. The diversity within different functional

    types reflects the variation of environmental conditions

    (Garca-Mora, Gallego-Fernandez, and Garca-Novo, 2000).

    Succession

    The succession series of the dunes on Spiekeroog confirms

    differences in species diversity relationships regarding both

    primary and secondary succession. Regarding secondary suc-

    cession, species richness increased after slope erosion in the first

    5 years in the Corynephorus sward, but the increase was

    reduced in the following years and total species richness did not

    reach the original number of species. The vegetation changed to

    a C. introflexusdominated turf of bryophytes. Thus, the species

    composition changed and the primary succession was deflected,

    whereas the secondary succession was a progressive one in

    which the cover abundance of C. introflexus increased strongly.

    The increase of C. introflexus generally results in species poor

    communities, such as dry calcareous grasslands (Van Der Laan,

    1985). Thus, the presented dune study approves the general

    decline in species richness of secondary successions after an

    initial species increase. Similarly, these relationships were

    shown in secondary succession on exposed lake sediments

    (Odland and Del Moral, 2002), on coastal dunes in Canada

    (Morrison and Yarranton, 1973), and in eastern Denmark

    (Vestergaard, 2006).

    In dunes, sand dynamics (accumulation as well as erosion)

    creates periodic vegetation disturbances and is one of the most

    significant factors affecting vegetation and succession (Junger-

    ius et al., 1995). On Spiekeroog, the rate of successional change

    following disturbance, e.g., by erosion of dune slopes, is fast in

    comparison to the whole dune series, but this could explained

    by the primary character of these sites within a secondary

    succession series. Unstable environments are often character-

    ized by strong year-to-year variation in environmental and

    vegetation conditions (Vestergaard, 2006), as well as in a faster

    species turnover (Martnez, Vazquez, and Sanchez, 2001).

    The study also confirmed that the development of disturbed

    areas, in particular on small scales, require time-series data

    gathered from particular sites and cannot be estimated from a

    static survey using a chronosequence (Foster and Tilman,

    2000).

    During primary succession, cover abundance of pioneer and

    persistent species showed a reversed development; the coloniz-

    ing succession stage contains many pioneer and few persistent

    species. By the way, similar to the development on exposed lake

    sediments (Odland and Del Moral, 2002); not only bryophytes

    and lichens but also sedges and grasses with clonal growth, like

    C. arenaria or Festuca rubra, play an important role, especially

    in secondary dune succession (Isermann and Krisch, 1995).

    Moreover, during primary succession at earlier succession

    stages, like the young grey dunes, therophytes are more

    important than in older succession stages (Olff, Huisman,

    and Van Tooren, 1993). The intermediate stages of succession

    have medium numbers of pioneers and persistent ones; in the

    later stages, many persistent species occur and few pioneers

    remain (Morrison and Yarranton, 1974). Hence, in the old grey

    dunes hemicryptophytes and geophytes and in the old brown

    dunes woody chamaephytes and phanerophytes are more

    abundant (Olff, Huisman, and Van Tooren, 1993). Due to the

    changing spectrum of competition strategies, species richness

    of vegetation is highest in the transition period, represented,

    e.g., by young grey dunes. At the beginning of primary

    successions, environmental conditions are generally uniform

    over relatively large areas (Morrison and Yarranton, 1974),

    and the vegetation, e.g., yellow dunes dominated by A.

    arenaria, often is homogenous. In landscape types like coastal

    dune series with well-developed environmental gradients,

    species-rich vegetation will occur in the middle part of existing

    gradients (Van Der Maarel, 1978). In coastal dunes, e.g.,

    species richness was highest at intermediate levels of soil pH

    (Isermann, 2005). Moreover, species-rich vegetation is related

    to environmental heterogeneity (Morrison and Yarranton,

    1974); e.g., the transition succession period of the dunes with

    intermediate soil pH levels showed also the highest standard

    deviation of soil pH (Isermann, 2005).

    Species-poor communities of grey and brown dunes, domi-

    nated by only a few species, probably have low succession rates

    because they showed a metastable stage, resembling older

    dunes. Moreover, in the case of high numbers of species, the

    succession stages rate was low. These species-rich communities

    probably are due to their high diversity that is more or less

    stable. Both cases could be explained according to evenness:

    communities with a balanced distribution of species showed the

    lowest succession rates.

    Species-rich vegetation of the young grey dunes on Spieker-

    oog showed only few changes in species composition during the

    Species Diversity Patterns during Coastal Dune Succession 669

    Journal of Coastal Research, Vol. 27, No. 4, 2011

  • study period. In general, during primary succession, commu-

    nities with higher species richness showed less temporal total

    variation (Tilman and Downing, 1994). Thus, more diverse

    communities are more stable, because stability in ecosystems

    has to be considered as a dynamic process. Moreover, species-

    poor heathlands with E. nigrum showed only few changes in

    species composition, probably because heathlands are one of

    the old succession stages in the dune xerosere. Thus, the dune

    xerosere reflects that vegetation changes are lower in old

    succession stages than in earlier stages, because the rate of

    succession change in later stages generally declines over time

    (Foster and Tilman, 2000). Thus, the study is in line with the

    biodiversity-stability theory, with highest ecosystem stability

    at highest diversity.

    Similar relationships between vegetation zones and distinct

    successional trends are known from salt marshes, where

    succession trends were mostly restricted to a particular

    altitudinal zone of the salt marsh (Roozen and Westhoff,

    1985). Vegetation changes from one to another succession stage

    of the salt marsh are shown to be rare, because these processes

    need much longer times to develop (Roozen and Westhoff,

    1985).

    CONCLUSIONS

    In coastal dunes of Spiekeroog, changes in plant species

    composition, species diversity, and succession rate had clear

    differences during the development from younger to older

    succession stages, as well as during primary and secondary

    succession. Differences in plant communities were more visible

    along the chronosequence, reflecting long-term changes during

    succession. In addition, fluctuations and stepwise, short-term

    development of plant communities could be shown by the

    vegetation development of each permanent plot. Therefore, the

    study shows the need for multitemporal approaches to

    distinguish between short-term fluctuation and long-term

    vegetation succession.

    ACKNOWLEDGMENTS

    The author expresses sincere thanks to Laurence Boorman

    for the comprehensive linguistic revision of the manuscript, to

    one anonymous reviewer, and especially to Johannes Koll-

    mann for substantial comments supporting the manuscript.

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    APPENDIX

    Vegetation groups (14) are distinguished by two-way

    indicator species analysis (TWINSPAN) classification. Young

    grey dunes (group 2) are divided into four subgroups (2ad),

    and group 4 is split into subgroups 4a and 4b. Moreover, the

    corresponding plot numbers and their plant communities are

    represented. Species with a total change in percentage of

    cover abundance between 1990 and 2005 larger than at least

    5% of the total are in bold. Furthermore, the vegetation

    groups distinguished by TWINSPAN analyses were shown

    and differentiated by vertical lines.

    Moreover, following species occur in the given periods:

    Centaurium pulchellum (0.5), Eryngium maritimum (0.1),

    and Tortula ruralis (5.0) in plot 1 1990; Holcus lanatus (0.5),

    Taraxacum laevigatum (agg. 0.5), and Viola tricolour (0.1) in

    plot 1 2000; Cerastium semidecandrum (0.5) in plot 2 1990;

    Erigeron acris (0.1) and Peltigera canina (2.0) in plot 2 1995;

    Arabidopsis thaliana (0.3), Brachythecium albicans (4.0),

    Brachythecium rutabulum (1.0), Rosa rubiginosa (0.3), Rubus

    caesius (1.0), Trifolium arvense (0.3), Vicia lathyroides (0.3),

    and Rhytidiadelphus triquetrus (1.0) in plot 2 2000; Lepidocea

    reptans (0.3) in plot 4 1990; Cladonia rangiferina (0.1) in plot

    4 2004; Plantago coronopus (0.5) in plot 5 1990; Cladonia

    ciliata (0.5) and Hypogymnia physodes (0.5) in plot 5 2000;

    Cladonia mitis (1.0) in plot 8 2005; Quercus robur (0.1) and

    Sorbus aucuparia (0.1) in plot 9 1990; Scleropodium purum

    (1.0) in plot 9 2005; and R. caesius (1.0) in plot 11 2005.

    Species Diversity Patterns during Coastal Dune Succession 671

    Journal of Coastal Research, Vol. 27, No. 4, 2011

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