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SER – Summer School 2009 – Münster University

Hamburg University. The (potential) role of seed ecology in restoration: Germination, seed banks and establishment Kai Jensen Applied Plant Ecology University of Hamburg kai.jensen@botanik.uni-hamburg.de. SER – Summer School 2009 – Münster University. Department Biology. Introduction.

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SER – Summer School 2009 – Münster University

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  1. Hamburg University The (potential) role of seed ecology in restoration: Germination, seed banks and establishment Kai Jensen Applied Plant Ecology University of Hamburg kai.jensen@botanik.uni-hamburg.de SER – Summer School 2009 – Münster University Department Biology

  2. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Outline • Introduction • Germination • Influence of abiotic factors • Persistence and Seed Banks • Primary and secondary dormancy • Seed bank types • Dispersal • Hydrochorous seed transport • Establishment • Seed- versus microsite-limitation • Summary and conclusions

  3. Introduction Germination Seed banks Dispersal Establishment Conclusions 1950 1985 1000 m Drainage, Eutrophication Abandonment 2002 Kai Jensen SER Summer School 2009 02.07.09 Changes of fen grassland area and distribution (1950 – 2002; Lake Vollstedt, Northern Germany Yacoub (2002)

  4. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Seed banks and succession in changing landscapes • You have only to dig a pond anywhere … and you will soon have … the usual waterplants (Thoreau 1860) • Early phase of farm abandonment in New England • Forest recovery • You have only to restore the site conditions including a proper hydroregime anywhere and you will soon have the usual wetland species • Application of fertilizers led to an eutrophication of the landscape • Widespread land use has greatly homogenized formerly dissimilar habitats • Human development and land-use changes are accompanied with habitat fragmentation

  5. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Questions • Are seed banks and seedling establishment important for the conservation and/or restoration of wetlands? • Which factors affect the longevity of seeds in the soil? • Germination requirements? • Dormancy pattern? • Seed morphology (weight, shape)? • Which factors affect hydrochorous dispersal? • Seed buyoancy? • Seed production? • Which factors limit the establishment of species in wetlands? • Seed availability (seed banks, seed dispersal)? • Microsite availability (gaps, disturbance)?

  6. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Germination Ecology • Germination is a complex process which includes the imbibition of water, an increase in respiration activity, the mobilization of nutrient reserves and the initiation of growth in the embryo. Finally, germination results in the bursting of the testa and the extrusion of the plumule or radicle. • How is germination of wetland species affected by abiotic factors? • Temperature and temperature fluctuations • Light quantity and light quality • Salinity • Do germination requirements of individual wetland species vary? • Within individuals? • Among populations? • Temporally?

  7. Introduction Germination Seed banks Dispersal Establishment Conclusions Silene flos-cuculi Germination [%] Senecio aquaticus Temperature [°C] Kai Jensen SER Summer School 2009 02.07.09 Temperature and germination Methods • Dry-stored seeds • Constant tempe-ratures (3 – 35°C) • Fluctuating tempe-ratures (5/15°C; 10/25°C) • Diurnal light regime Patzelt et al. (2001)

  8. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Temperature fluctuations and germination Carex elongata Methods • Dry-stored seeds • Daily fluctuating temperatures (amplitudes from 0 – 16°C) • Mean temperature 22°C Germination [%] Carex elata Schütz (1999) Amplitude [°C]

  9. Introduction Germination Seed banks Dispersal Establishment Conclusions Phytochrome-System R 660 PFR germi-nation FR 730 PR Kai Jensen SER Summer School 2009 02.07.09 Canopy effects on light quantity and quality • Above leaf-canopy • red : far-red = 1.2 • Below leaf-canopy • red : far-red = 0.18 Pons (19xy)

  10. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Light quality and germination Primula farinosa Tofieldia calyculata Maas (1989)

  11. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Seed mass and light-requirement for germination Jensen & Gutekunst (2003)

  12. Introduction Germination Seed banks Dispersal Establishment Conclusions N = 25 17 35 23 100 (2003) Kai Jensen SER Summer School 2009 02.07.09 Germination in light and in darkness

  13. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Variation of germination within single inflorescences 25°C Bidens frondosa Dispersal ability low high Number of germinated seeds 10/20°C Days Brändel (2004)

  14. Introduction Germination Seed banks Dispersal Establishment Conclusions primary dormancy Dormancy release Dormancy induction Germination [%] secondary dormancy 1991 1992 1993 Kai Jensen SER Summer School 2009 02.07.09 Temporal changes of germination requirements Silene flos-cuculi Milberg (1994)

  15. Introduction Germination Seed banks Dispersal Establishment Conclusions Elymus athericus 100 Spartina anglica 80 60 Germination percentage 40 20 0 0.0 0.7 1.4 2.1 2.8 3.5 Salinity [%] Kai Jensen SER Summer School 2009 02.07.09 Germination ecology and zonation in wetlands • Germination of both species is negatively affected by increased salinity • Interaction between species and salinity Spartina has a higher germination percentage than Elymus at high salinity Elymus has a higher germination than Spartina at low salinities

  16. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Summary: Germination • Most (temperate) wetland species germinate at a wide amplitude of temperatures, but have an optimum between 20 and 30°C • Germination of many wetland species is increased by alternating temperatures, which might restrict germination to the spring • Light requirement for germination is higher in small-seeded species than in large-seeded ones. The light requirement can be interpreted as an adaptation against fatal germination in the soil • Germination requirements vary spatially (within inflorescences, among individuals, among populations) and temporally (dormancy cycles)

  17. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Seed persisitence and seed banks • Circumstantial evidence for high longevity of seeds (e.g. Nelumbo nucifera: dried bed of a former lake in NE China; germinating seeds were radiocarbon-dated to be 1288 ± 250 years, Shen-Miller et al. 1995) • Seed densities in the soil vary greatly (1 – 100,000 seeds/m²) between ecosystems • In general, seed density of individual species exponentially declines after it disappeared in the vegetation

  18. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Seed bank types • transient • seed persistence in the soil for less than 1 year • short-term-persistent • seed persistence in the soil for at least 1 year, but less than 5 years • play a role in the maintenance of plant populations after a ‚bad year‘ (e.g. poor seed set in a dry year) • long-term persistent • seed persistence in the soil for at least 5 years • may contribute to the restoration of destroyed or degraded plant communities

  19. Introduction Germination Seed banks Dispersal Establishment Conclusions A SPECIES FOUNDx Present in the seed bank xxxxxxxxxxx x Absent from the seed bank xxxxxxxxxxx x xxxxxxxxxx TRANSIENT xxxxxx Present in vegetation or vegetation not described Soil layers not subdivided xxxxxxxxxxxxxxxx Soil layers subdivided by depth xxxxxxxx Present in vegetation or vegetation not described Present only in surface soil xxxxxxxxx xxxxxxx xxxxxxxxxx PRESENT xxxxxx xxxxxxxxxx TRANSIENT xxxxxx < 5 years since species last grew at site Species absent from the vegetation x More freq. in upper but present in lower soil layers AT LEAST SHORT-TERM PERSISTENT SHORT-TERM PERSISTENT xx > 4 years since species last grew at site At least as freq. in lower as in upper soil layers LONG-TERM PERSISTENT xx LONG-TERM PERSISTENT xx Species absent from the vegetation x < 5 years since species last grew at site > 4 years since species last grew at site LONG-TERM PERSISTENT xx Kai Jensen SER Summer School 2009 02.07.09 Classification rules for seed bank types Criteria Presence/absence in vegetation and seed bank Depth distribution in the soil Thompson et al. 1997

  20. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Main conclusions of Thompson et al. (1997) • Grassland species have in general a low seed persistence • Rare species have a lower persistence than common ones • Seed size and shape are good predictors of seed persistence Is that really true??

  21. Introduction Germination Seed banks Dispersal Establishment Conclusions 100 100 80 80 60 60 40 40 20 20 0 0 Sep Jan May Sep Feb Jun Nov Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov Mar Jul Nov Apr 1997 1996 1997 1998 1999 1998 Kai Jensen SER Summer School 2009 02.07.09 Dormancy and seed longevity:Burial experiment with seeds of wetland species Bromus racemosus Sanguisorba officinalis Darkness Light Mortality Germination [%] Mortality [%] Date Jensen (2004)

  22. Introduction Germination Seed banks Dispersal Establishment Conclusions 100 80 Darkness Light 60 Mortality 40 20 0 Nov Nov Jan Jan Mar Mar May May Jul Jul Nov Nov Sep Sep Mar Mar Jan Jan Jul Jul May May Sep Sep 1996 1996 1997 1997 1998 1998 Kai Jensen SER Summer School 2009 02.07.09 Dormancy and seed longevity:Burial experiment with seeds of wetland species Rhinanthus angustifolius Pedicularis palustris 100 80 60 Germination [%] Mortality [%] 40 20 0 Date Jensen (2004)

  23. Introduction Germination Seed banks Dispersal Establishment Conclusions Viola palustris Carex echinata 100 100 80 80 Darkness Light 60 60 Mortality Mortality [%] 40 40 20 20 0 0 Nov Nov Jan Jan Mar Mar May May Jul Jul Nov Nov Sep Sep Mar Mar Jan Jan Jul Jul May May Sep Sep 1996 1996 1997 1997 1998 1998 Date Kai Jensen SER Summer School 2009 02.07.09 Dormancy and seed longevity:Burial experiment with seeds of wetland species Germination [%] Jensen (2004)

  24. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Dormancy and seed longevity:Burial experiment with seeds of wetland species Jensen (2004)

  25. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Database on seed banks of wetland species • Seed bank analysis • 31 wet grasslands in Northern Germany • Meso- and eutrophic fen grasslands (Scheuchzerio-Caricetea, Calthion, Lolio-Potentillion) • Managed and abandoned sites • Burial experiments • 45 species of the regional fen flora • Carex (Schütz 1997, 1998, 1999) • Regional rare species (Jensen 2001, 2004) • Asteraceae and Lamiaceae (Brändel 2004) • Database and literature survey • ‚Thompson-Database‘ (Thompson et al. 1997) • 16 seed bank studies (‚wet grasslands‘, 143 sites in Europe)

  26. Introduction Germination Seed banks Dispersal Establishment Conclusions A SPECIES FOUNDx Present in the seed bank xxxxxxxxxxx x Absent from the seed bank xxxxxxxxxxx x xxxxxxxxxx TRANSIENT xxxxxx Present in vegetation or vegetation not described Soil layers not subdivided xxxxxxxxxxxxxxxx Soil layers subdivided by depth xxxxxxxx Present in vegetation or vegetation not described Present only in surface soil xxxxxxxxx xxxxxxx xxxxxxxxxx PRESENT xxxxxx xxxxxxxxxx TRANSIENT xxxxxx All COUNTS REAL SEEDBANK COUNTS < 5 years since species last grew at site Species absent from the vegetation x More freq. in upper but present in lower soil layers AT LEAST SHORT-TERM PERSISTENT SHORT-TERM PERSISTENT xx > 4 years since species last grew at site At least as freq. in lower as in upper soil layers LONG-TERM PERSISTENT xx LONG-TERM PERSISTENT xx Species absent from the vegetation x < 5 years since species last grew at site > 4 years since species last grew at site LONG-TERM PERSISTENT xx Kai Jensen SER Summer School 2009 02.07.09 Classification rules for seed bank types Criteria Presence/absence in vegetation and seed bank Depth distribution in the soil Thompson et al. 1997

  27. Introduction Germination Seed banks Dispersal Establishment Conclusions short-term + long-term persistent records LI = transient + short-term + long-term persistent records transient short-term long-term- LI persistent persistent All counts 34 52 30 0.7 Real seedbank counts 6 52 30 0.9 Burial experiments 0 2 2 1.0 Kai Jensen SER Summer School 2009 02.07.09 Methods: Seed bank research • Classification of species to seed bank types • Indirect procedure following Thompson et al. (1997): All counts, Real seedbank counts • Direct procedure (burial experiments) • Calculation of the Longevity-Index (LI, Bekker et al. 1998) • Silene flos-cuculi

  28. Introduction Germination Seed banks Dispersal Establishment Conclusions Low habitat specifity High habitat specifity All counts Real seedbank counts Burial experiments Forage grassland Forage grassland Forage grassland Others Others Others Ruderal Ruderal Ruderal Wet grassland Wet grassland Wet grassland Reed Reed Reed Fen Fen Fen Kai Jensen SER Summer School 2009 02.07.09 Seed persistence of species groups LI ns a ab 1.0 ab ab ab b 0.8 a 0.6 ab ab ab ab b 0.4 0.2 0.0 Kruskall-Wallis-Test

  29. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Habitat specifity, rarity and seed persistence Low habitat specifity High habitat specifity Common Rare 1.0 0.8 0.6 Longevity - Index *** ** 0.4 0.2 0.0 All counts Real seedbank counts Burial experi-ments All counts Real seedbank counts Burial experi-ments Mann-Whitney-U-Test

  30. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Summary: Persistence and seed banks • Seed banks of many wet grassland species are at least short-term persistent • Rare or endangered wet grassland species do not have a lower persistence than common species • Seed persistence in the soil has been underestimated by the methods applied by Thompson et al. (1997) • Seed banks can be an important factor for the conservation or restoration of species-rich wet grasslands

  31. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Methods: Seed dispersal research • Seed transport by running water • Seed trapping (Eider: 2 years; Soomaa: 1 summer) • Recapture experiment (Eider) • Dispersal of seed mimics (Elbe) • Modelling of hydrochorous seed transport (Elbe) • Seed sedimentation during flooding • Drift-line material (Eider, Soomaa, Elbe) • Astroturf mats (Eider and Elbe: 2002, 2004) • Dispersal by wind and animals • Community seed rain (Eider; Jensen 1998) • Seed shadow of wet grassland species • Seed content of cattle faeces

  32. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Establishment: Methods and questions • Factorial field experiments. Manipulation of … • Seed availability (e.g. sowing, removal of the seed bank, exclosure of seed dispersal, application of seed-containing drift-line material) • Microsite availabilty (e.g. creation of gaps, mowing) • Is seedling establishment of wetland species limited by seed or by microsite availability? • Is species richness of wetlands limited by seed or by microsite availability?

  33. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Sowing experiment (Pedicularis and Rhinanthus) • 10 blocks per species • 4 disturbance treatments (control, mowing, small gaps, large gaps) • 4 sowing densities (control, 250, 1250, 5000 seeds per m²) • Monitoring of recruitment, survival and reproduction Large gaps Control Small gaps Mowing

  34. Introduction Germination Seed banks Dispersal Establishment Conclusions Number of individuals Kai Jensen SER Summer School 2009 02.07.09 • bienniel • Seed weight: 1.1 mg • Limited by seed and by microsite availability • annual • Seed weight: 2.2 mg • Limited only by seed availabilty Rasran, Vogt & Jensen (2006)

  35. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Field experiment in floodplain grasslands (Soomaa NP, Estonia) Drift line yes no no small gaps Disturbance large gaps

  36. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Effects of seed banks and dispersal on wetlands Drift line Disturbance 16 c 12 b Species number of recruiting seedlings per 625cm² a 8 4 0 yes no no small gaps large gaps Wanner (2002)

  37. Introduction Germination Seed banks Dispersal Establishment Conclusions 50 45 40 35 30 25 20 15 10 5 0 Kai Jensen SER Summer School 2009 02.07.09 Effects of seed banks and dispersal on wetlands: Baltic coastal grasslands without vegetative regrowth with vegetative regrowth Number of seedlings per gap Yes No Yes No Ludewig (2009) Seed Bank

  38. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Summary: Establishment • Species not present in the vegetation are in general limited by seed availability (Pedicularis, Rhinanthus) • Species with high seed densities in the seed bank or with high potential of hydrochorous seed dispersal might establish after some kind of soil disturbance • Germination from seed banks might contribute to species richness in wetlands (floodplain grasslands, coastal grasslands)

  39. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Summary and conclusion • Many wetland species have persistent seed banks • Hydrochorous dispersal enables wetland species to move large distances and to reach new habitats • Seed banks and seed dispersal can significantly contribute to nature management and restoration of wetlands • Conservation of still existing wetland patches should obtain priority • Restoration success of wetlands depends on: site conditions, management, spatial and temporal aspects

  40. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 THM • You have only to dig a pond anywhere … and you will soon have … the usual waterplants (Thoreau 1860) • You have only to restore the site conditions and a proper hydrological management anywhere and you will soon have the usual wetland species

  41. Introduction Germination Seed banks Dispersal Establishment Conclusions Kai Jensen SER Summer School 2009 02.07.09 Vielen Dank Postdoc Markus Brändel Antonia Wanner Technische Mitarbeiter Claudia Mählmann Jutta Krüger Detlev Böhm Doktoranden und wiss. Mitarbeiter Kati Vogt Leonid Rasran Wiebke Schoenberg Sonja Heemann Sigrid Suchrow Gesine Engels Ebrahem Mohamed Kristin Ludewig Frauke Müller Sebastian Schmidt Katharina Schmidt Christian Butzeck Abschlussarbeiten Sandra Burmeier Anke Brandt Dirk Lübsen Jessica Hensel Jan Schwertdfeger Marie Hrach Nina Pohlmann Felix Heydel Jessica Ehrhardt Jessica Klepgen Christian Klaus Lotte Korrell Agathe Schaddach Jule Krause Katharina Kleiß Friederike Freiwald Sinaida Albrecht Frauke Brunckhorst Carolin Gallinat Jana Melanie Hanke Caroline Thiem Nina Moniac

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