PhD Reza Erfanzadeh 2009 - Ghent Ecology - Universiteit Gent

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completely destroy the existing vegetation by covering it by storm-driven sediment, but in other cases it can grow through a thin layer of fresh sediment. Secondary succession can also start on a mature soil if plant propagules are left after the former vegetation has been virtually destroyed. In such succession most of the plant species are either present from the outset as buried seeds, bulbs and rhizomes or invade shortly afterwards (Packham & Willis 1997). 4 Of the three major mechanisms of succession outlined by Connell & Slatyer (1977), none by itself can account for the complete range of floristic replacements found in salt- marshes. 1.2.1 The facilitation mechanism In the facilitation mechanism, species replacement is assisted by environmental changes brought about by organisms in earlier stages in the succession (Packham & Willis 1997). In this mechanism, the early-succession species modify the environment so that it is more suitable for late successional species to invade and grow to maturity (Connell & Slatyer 1977). Whittaker (1975) stated that in the facilitation mechanism “one dominant species modified the soil and microclimate in ways that made the entry of a second species possible, which then became dominant and modified the environment in ways that suppressed the first and made the entry of a third dominant possible, which in turn altered its environment.” This sequence continues until the resident species no longer modifies the site in ways that facilitate the invasion and growth of a different species (Castellanos et al. 1994; Huckle et al. 2000). 1.2.2 The tolerance mechanism The tolerance mechanism does not depend on the initial presence of early successional species. Species, which occupy a site early, have little or no influence on the recruitment of other species, which grow to maturity despite their presence (Burrows 1990). Any species can start the succession but those which establish first are replaced by others that are more
tolerant (competitively superior) and usually longer-lived at the habitat. In this mechanism species that appear later are simply those that arrived either later or at the very beginning, but germinated and/or grew more slowly. The sequence of species is determined solely by their life-history characteristics. In contrast to the early species, the propagules of the later ones are dispersed more slowly and their juveniles grow more slowly to maturity. They are able to survive and grow despite the presence of early-succession species that are healthy and undamaged (MacArthur & Connell 1966; Farrell 1991). 1.2.3 The inhibition mechanism In contrast to the first mechanism, in inhibition mechanism, once earlier colonists colonize a habitat, they secure the space and/or other resources, and subsequently inhibit the invasion of new colonists or suppress the growth of those already present. The latter invade or grow only when the dominating residents are damaged or killed, thus releasing resources (Connel & Slatyer 1977). In this mechanism, invasion is prevented by the present occupants of the site, perhaps through heavy shading or allelopathic mechanisms; replacement will occur only when previous colonists are removed. The species, which colonize the site first, thus gain a major advantage (Packham & Willis 1997). In salt-marsh conditions, it is generally expected that vegetation changes in time are driven by the facilitation mechanism. Soil trapped by early colonizers, that themselves are able to endure the harsh pioneer stage environmental conditions, elevates the substrate, thus facilitating the colonization by mid- and late-successional species, which were not able to endure the early succession conditions of daily inundation with salt water. Beeftink (1965) and Hoffmann (1993) stated that Salicornia spp. or Spartina townsendii-dominant communities would eventually change to Elymus athericus (on levees) or Halimione portulacoides-dominant (on backlands) communities through the facilitation mechanism by sedimentation (Fig. 1.1). However, inhibition mechanism through spatial competition could 5
Page 1: Ghent University Faculty of Science
Page 5: Spatio-temporal aspects of early ve
Page 9 and 10: Acknowledgements The accomplishment
Page 11: List of Abbreviations ADF Acid Dete
Page 14 and 15: XII 3.5 DISCUSSION ................
Page 16 and 17: 1.1 What is succession? 2 Successio
Page 20 and 21: also occur in salt-marsh habitat, a
Page 22 and 23: seed production (Willson 1983; Pric
Page 24 and 25: 1.3.2 Inundation, vegetation and su
Page 26 and 27: affected plant species richness in
Page 28 and 29: 14 In chapter 4, the effects of she
Page 30 and 31: elationship between soil characteri
Page 32 and 33: areas which are re-colonized. They
Page 34 and 35: Fig. 1.4. The position of the newly
Page 36 and 37: 22 There are some photos available
Page 38 and 39: were collected systematically along
Page 40 and 41: Table 1.1. Materials and methods us
Page 42 and 43: with one or more reference sites (T
Page 44 and 45: pilot study performed in the area i
Page 46 and 47: Fig. 1.7. The conceptual framework
Page 48 and 49: 2.1 Abstract Restoration of salt-ma
Page 50 and 51: 2.2 Introduction The successful res
Page 52 and 53: physiological process depending on
Page 54 and 55: separated from it by a dike (with a
Page 56 and 57: scale (Londo 1976). According to th
Page 58 and 59: 2.4.2 Seed bank at the restoration
Page 60 and 61: Table 2.3. Average (± SE) species
Page 62 and 63: particular those species coming fro
Page 64 and 65: germinate, the seeds should have ap
Page 66 and 67: the restoration site along a strong
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3.1 Abstract 54 The effect of inund
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3.2 Introduction 56 Tidal marshes a
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more stable. Consequently, species
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3.3.2.2 Inundation frequency 60 The
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and 2007) for those variables that
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maritima) increased over time (Fig.
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perennial species between years, wi
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68 Perennial richness 1.4 1.2 1 0.8
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70 Species turnover 1.2 1 0.8 0.6 0
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Reznicek 1986). They therefore play
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Suaeda maritima. Spartina is well k
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4.1 Abstract 76 In this paper, the
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4.2 Introduction 78 Salt-marshes ar
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available on the influence of sheep
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consecutive months, sampling effort
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factor was applied. In case of sign
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Table 4.1. The result of repeated m
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88 Cover(%) 2.5 2 1.5 1 0.5 0 C a b
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90 2.5 2 1.5 1 0.5 0 a b a b Grazed
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succession leading to rapid vegetat
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(van Wijnen et al. 1997). In additi
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5.1 Abstract 96 It is generally acc
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5.2 Introduction 98 One of the main
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area started in 2002, when part of
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high and highly significant (see Ta
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104 Although the percentage of spec
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5.5 Discussion 106 Not surprisingly
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europaea zone as long as the elevat
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110
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6.1 Abstract 112 Seed bank density
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6.2 Introduction 114 The persistenc
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116 Our study area consists of thre
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were also placed randomly on the sh
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Seed density(m²) Seed density(m²)
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122 Plant species in the above-grou
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6.4.2 Seed bank properties and sali
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Seed density(m²) Seed density(m²)
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conclude that Suaeda seeds are most
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130 Both the similarity between sta
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marsh were found not to be fundamen
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134 Permanent plots in this study g
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(soil and elevation), and between v
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138 In literature it is generally a
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ecome extinct, some palatable and s
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production, but their massive produ
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144 Grazing in the entire year migh
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146
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Bakker, E.S. & Olff, H. 2003. The i
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Bertness, M.D., Wise C. & Ellison A
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Burrows, C.J. 1990. Processes of ve
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de Leeuw, J. 1992. Dynamics of salt
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Egler, F.E. 1954. Vegetation scienc
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Garbutt, A. & Wolters, M. 2008. The
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Harper, J.L. 1961. Approaches to th
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Hoffmann, M. 2006a. 5. De natuurher
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Janssen, J.A.M. & Schaminée, J.H.J
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Klotzli, F. & Grootjans, A.P. 2001.
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Levine, J.M., Brewer, J.S. & Bertne
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Myster, R.W. & Pickett, S.T.A. 1990
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Packham, J.R. & Willis, A.J. 1997.
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Poschlod, P., Tackenberg, O. & Bonn
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Rozema, J. & Blom B. 1977. Effects
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Smith, T.B., Kark, S., Schneider, C
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Thompson, K., Bakker, J.P. & Bekker
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van Leeuwen, C.G. 1966. A relation
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Wijnen, H.J.V. & Bakker, J.P. 1999.
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186
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of a continuous water bridge betwee
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Appendix F - Continued Samolus vala
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Appendix G - Continued Rubus caesio
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PhD Reza Erfanzadeh 2009 - Ghent Ecology - Universiteit Gent

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