Southern Africa

1. Southern Africa SER Summer School Restoration Ecology 2009 - Münster, Germany Soil seed banks in relation to degradation of aridgrazing lands in southern Namibia Niels DreberBiocentre Klein Flottbek & Botanical Garden, University of Hamburg

2. Southern Africa INTRODUCTION the study area NAMA-KAROO _670 240 km2 (23% of the southern African subregion) x Source: Cowling, R.M., Richardson, D.M., Pierce, S.M., 1997. Vegetation of Southern Africa, Cambridge University Press.

3. Southern Africa INTRODUCTION the study area NAMA-KAROO _670 240 km2 (23% of the southern African subregion) _open grassy dwarf shrubland

4. Southern Africa INTRODUCTION the study area NAMA-KAROO _670 240 km2 (23% of the southern African subregion) _open grassy dwarf shrubland _rainfall 100-200 mm coefficient of variation: 80% x study sites Source: MAWRD, mean annual rainfall

5. Southern Africa INTRODUCTION the study area NAMA-KAROO _670 240 km2 (23% of the southern African subregion) _open grassy dwarf shrubland _rainfall 100-200 mm coefficient of variation: 80% _carrying capacity: ~ 1 SSU / 5 ha small stock farming study sites x Source: MAWRD, mean above ground biomass estimate

6. Southern Africa INTRODUCTION the study area Land degradationis a widespread problem in the region,especially in communal areas! The main driving factors:(i) a lack in regimentations(ii) high population & stock densities(iii) the highly variable climate

7. Gellap-Ost: governmental rotational grazing karakul sheep low grazing pressure stable land tenure 70 years + Nabaos: communal open access pasture goats high grazing pressure 30 years + no seasonal restric- tions or stocking limitations Southern Africa INTRODUCTION the study area fenceline contrast – ‘a natural experiment‘

8. Above ground degradation on location increase in bare soilreduction in plant total coverloss of valuable plant speciesincreased topsoil crusting & erosionchanges in diversity & abundance of rodents & ground beetles Southern Africa INTRODUCTION degradation facts

9. Southern Africa INTRODUCTION degradation facts Such profound regime shifts in savannah rangelands might be attributable to to a loss of ecosystem resilience due to sustained grazing pressure

10. Southern Africa INTRODUCTION degradation facts Is the degraded state reversible? 40 years x

11. Southern Africa INTRODUCTION study questions „Assessment of seed banks is a constructive tool to assess rangeland condition and restoration potential,especially in combination with habitat appraisal.“ Jones & Esler 2004, Biodiversity and Conservation 13 Central study questions: 1 To what extent has the structure of the viable soil seed bank changed after long- term over-utilization of the communal rangeland? 2 What is the impact of different microhabitats on the seed bank patterning? 3 Are there microhabitats functioning as potential seed sources for the recovery of target plant species which are absent from the standing vegetation?

12. Southern Africa SOIL SEED BANKS & DEGRADATION methods THE SAMPLING DESIGN Stratification of the area: selection of comparabel habitats regarding bedrock soil type geomorphology woody character species homogeneous vegetation regarding species composition & structure

13. Southern Africa SOIL SEED BANKS & DEGRADATION methods THE SAMPLING DESIGN after seed shet, before any germination event Under shrub canopy seed bank (macro safe sites)

14. Southern Africa SOIL SEED BANKS & DEGRADATION methods THE SAMPLING DESIGN after seed shet, before any germination event Seed bank of the inter-shrub matrix

15. x x x x x x x x x x vegetated patch (n=45) x x x bare patch (n=45) x x x sampling point Southern Africa SOIL SEED BANKS & DEGRADATION methods THE SAMPLING DESIGN Inter-shrub matrix: vegetated patches (micro safe sites) & bare patches

16. Southern Africa SOIL SEED BANKS & DEGRADATION methods DIRECT SEEDLING EMERGENCE METHOD

17. Total number of Year germinants species 2007 5207 36 2008 6417 45 Overall 11880 49 Southern Africa SOIL SEED BANKS & DEGRADATION first results 2007: W1-62%, W3-85%2008: W1-62%, W3-81%

18. Southern Africa SOIL SEED BANKS & DEGRADATION first results Total species richness of the soil seed bank

19. Southern Africa SOIL SEED BANKS & DEGRADATION first results Total seed density of the soil seed bank

20. REF: 626.60±717.25 DEG: 1519.76±1332.12 REF: 1206.00±1050.13 DEG: 3383.83±3059.15 REF: 2083.89±1708.28 DEG: 4305.22 ±2199.34 Southern Africa SOIL SEED BANKS & DEGRADATION first results p < 0.05 Mean seed densities / m2 of the germinable soil seed bank

21. Southern Africa SOIL SEED BANKS & DEGRADATION first results Plant functional groups in the soil seed bank _species on REF and DEG are similar distributed within the plant functional groups _proportions of germinants within the single groups are highly different among the sites

22. Helichrysum candolleanum Microcharis disjuncta Stipagrostis uniplumis Dicoma capensis Southern Africa SOIL SEED BANKS & DEGRADATION first results Species Abundance DistributionsSAD-Curves for the soil seed bank of the inter-shrub matrix (MISs & BPs)

23. Indigastrum argyroidesTrianthema parvifolia>80% Aristida adscensionis Kohautia caespitosa Schmidtia kalahariensis Southern Africa SOIL SEED BANKS & DEGRADATION first results Species Abundance DistributionsSAD-Curves for the soil seed bank of the inter-shrub matrix (MISs & BPs)

24. Southern Africa SOIL SEED BANKS & DEGRADATION first results Species Abundance DistributionsSAD-Curves for the soil seed bank of the inter-shrub matrix (MISs & BPs) _dominance of small-seeded, annual plant species _antipodal species abundance pattern comparing REF and DEG species common under low grazing pressure are seldom on the heavily grazed site & vice versa

25. Helcan, Micdis, Lotpla Indarg, Tripar Stipagrostis uniplumis Limarg, Tepdre Aristida adscensionis Kohautia caespitosa Schmidtia kalahariensis Southern Africa SOIL SEED BANKS & DEGRADATION first results Species Abundance DistributionsSAD-Curves for the soil seed bank & vegetation of the inter-shrub matrix _species composition of the soil seed bank & standing herbage is similar _proportional composition of the vegetation mirrors the condition of the soil seed bank

26. Southern Africa SUMMARY Structural heterogeneity of the environment causes a horizontal patterning of the seed bank provides effective microsites for seed retention and accumulation contributes to the presence of species diverse seed pools of high seed numbers Long-term over-utilization of the communal rangeland has altered the size, species composition and plant functional composition of the soil seed bank has reduced (and partially depleted) ‘desirable’ seed banks

27. Southern Africa CONCLUSIONS in a restoration context Evaluation of the restoration potential the seed bank is dominated by single species of low grazing value which recruit in high numbers the seed bank contain a few ‘residual’ species of the previous vegetation, but in very low proportions safe sites (shrubs) contain high seed numbers (30.000/m2) & comprise species rich seed banks, but provide no material for restoration as target plant species are lacking the lack in valuable species – such as perennial grasses – is attributable to a failure in seed production & a reduction of adequate safe sites for establishment

28. Southern Africa CONCLUSIONS in a restoration context the natural regeneration capacity of the rangeland towards an improved postdisturbance vegetation with species common under sustainable management is limited an improvement of site coditions is unlikely to occur in appropriate time as the seed bank is ‘degraded’ passive restoration practices (e.g. resting) are not an option active accelerating interventions such as seeding + brush packing ploughing soil transfer creation of refuges implemented in a long-term strategical restoration framework have to be applied

29. Thank you