Presentation is loading. Please wait.

Presentation is loading. Please wait.

Soil seed banks in relation to degradation of arid grazing lands in southern Namibia Niels Dreber Biocentre Klein Flottbek & Botanical Garden, University.

Similar presentations


Presentation on theme: "Soil seed banks in relation to degradation of arid grazing lands in southern Namibia Niels Dreber Biocentre Klein Flottbek & Botanical Garden, University."— Presentation transcript:

1 Soil seed banks in relation to degradation of arid grazing lands in southern Namibia Niels Dreber Biocentre Klein Flottbek & Botanical Garden, University of Hamburg SER Summer School Restoration Ecology Münster, Germany

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

3 INTRODUCTION NAMA-KAROO _ km 2 (23% of the southern African subregion) _open grassy dwarf shrubland the study area

4 INTRODUCTION x Source: MAWRD, mean annual rainfall study sites NAMA-KAROO _ km 2 (23% of the southern African subregion) _open grassy dwarf shrubland _rainfall mm coefficient of variation: 80% the study area

5 INTRODUCTION NAMA-KAROO _ km 2 (23% of the southern African subregion) _open grassy dwarf shrubland _rainfall mm coefficient of variation: 80% _carrying capacity: ~ 1 SSU / 5 ha small stock farming x Source: MAWRD, mean above ground biomass estimate the study area study sites

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

7 INTRODUCTION 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 the study area fenceline contrast – ‘a natural experiment‘

8 INTRODUCTION Above ground degradation on location increase in bare soil reduction in plant total cover loss of valuable plant species increased topsoil crusting & erosion changes in diversity & abundance of rodents & ground beetles degradation facts

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

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

11 INTRODUCTIONstudy 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 SOIL SEED BANKS & DEGRADATIONmethods 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 SOIL SEED BANKS & DEGRADATIONmethods THE SAMPLING DESIGN Under shrub canopy seed bank (macro safe sites) after seed shet, before any germination event

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

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

16 SOIL SEED BANKS & DEGRADATIONmethods DIRECT SEEDLING EMERGENCE METHOD

17 SOIL SEED BANKS & DEGRADATIONfirst results Overall speciesgerminantsYear Total number of 2007: W1-62%, W3-85% 2008: W1-62%, W3-81%

18 SOIL SEED BANKS & DEGRADATIONfirst results Total species richness of the soil seed bank

19 SOIL SEED BANKS & DEGRADATIONfirst results Total seed density of the soil seed bank

20 SOIL SEED BANKS & DEGRADATIONfirst results Mean seed densities / m 2 of the germinable soil seed bank REF: ± DEG: ± REF: ± DEG: ± REF: ± DEG: ± p < 0.05

21 SOIL SEED BANKS & DEGRADATIONfirst 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 SOIL SEED BANKS & DEGRADATIONfirst results Species Abundance Distributions SAD-Curves for the soil seed bank of the inter-shrub matrix (MISs & BPs) Stipagrostis uniplumis Helichrysum candolleanum Microcharis disjuncta Dicoma capensis

23 SOIL SEED BANKS & DEGRADATIONfirst results Species Abundance Distributions SAD-Curves for the soil seed bank of the inter-shrub matrix (MISs & BPs) Indigastrum argyroides Trianthema parvifolia >80% Aristida adscensionis Schmidtia kalahariensis Kohautia caespitosa

24 SOIL SEED BANKS & DEGRADATIONfirst results Species Abundance Distributions SAD-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 SOIL SEED BANKS & DEGRADATIONfirst results Species Abundance Distributions SAD-Curves for the soil seed bank & vegetation of the inter-shrub matrix Helcan, Micdis, Lotpla Stipagrostis uniplumis Limarg, Tepdre Indarg, Tripar Aristida adscensionis Kohautia caespitosa Schmidtia kalahariensis _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 SUMMARY 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 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

27 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/m 2 ) & 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 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


Download ppt "Soil seed banks in relation to degradation of arid grazing lands in southern Namibia Niels Dreber Biocentre Klein Flottbek & Botanical Garden, University."

Similar presentations


Ads by Google