southern africa
DESCRIPTION
Southern Africa. SER Summer School Restoration Ecology 2009 - Münster, Germany. Soil seed banks in relation to degradation of arid grazing l ands in southern Namibia. Niels Dreber Biocentre Klein Flottbek & Botanical Garden, University of Hamburg. Southern Africa. INTRODUCTION. - PowerPoint PPT PresentationTRANSCRIPT
Soil seed banksin relation to degradation of aridgrazing lands in southern Namibia
Niels DreberBiocentre Klein Flottbek & Botanical Garden, University of Hamburg
SER Summer School Restoration Ecology 2009 - Münster, Germany
INTRODUCTION the study area
NAMA-KAROO
_670 240 km2
(23% of the southern African subregion)
Source: Cowling, R.M., Richardson, D.M., Pierce, S.M., 1997. Vegetation of Southern Africa, Cambridge University Press.
x
INTRODUCTION
NAMA-KAROO
_670 240 km2
(23% of the southern African subregion)
_open grassy dwarf shrubland
the study area
INTRODUCTION
x
Source: MAWRD, mean annual rainfall
study sites
NAMA-KAROO
_670 240 km2
(23% of the southern African subregion)
_open grassy dwarf shrubland
_rainfall 100-200 mm coefficient of variation: 80%
the study area
INTRODUCTION
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
x
Source: MAWRD, mean above ground biomass estimate
the study area
study sites
INTRODUCTION the study area
The main driving factors:(i) a lack in regimentations(ii) high population & stock densities(iii) the highly variable climate
Land degradationis a widespread problem in the region,especially in communal areas!
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‘
INTRODUCTION
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
degradation facts
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
INTRODUCTION
Is the degraded state reversible?
40 years x
degradation facts
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?
SOIL SEED BANKS & DEGRADATION methods
THE SAMPLING DESIGN
Stratification of the area:
selection of comparabel habitats regarding
bedrocksoil typegeomorphologywoody character species
homogeneous vegetation regarding species composition & structure
SOIL SEED BANKS & DEGRADATION methods
THE SAMPLING DESIGN
Under shrub canopy seed bank (macro safe sites)
after seed shet, before any germination event
SOIL SEED BANKS & DEGRADATION methods
THE SAMPLING DESIGN
Seed bank of the inter-shrub matrix
after seed shet, before any germination event
SOIL SEED BANKS & DEGRADATION methods
THE SAMPLING DESIGN
Inter-shrub matrix: vegetated patches (micro safe sites) & bare patches
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x x
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x xvegetated patch (n=45)
bare patch (n=45)
xsampling point
SOIL SEED BANKS & DEGRADATION methods
DIRECT SEEDLING EMERGENCE METHOD
SOIL SEED BANKS & DEGRADATION first results
4911880Overall
4564172008
3652072007
speciesgerminantsYear
Total number of
2007: W1-62%, W3-85%2008: W1-62%, W3-81%
SOIL SEED BANKS & DEGRADATION first results
Total species richness of the soil seed bank
SOIL SEED BANKS & DEGRADATION first results
Total seed density of the soil seed bank
SOIL SEED BANKS & DEGRADATION first results
Mean seed densities / m2 of the germinable soil seed bank
REF: 1206.00 ±1050.13
DEG: 3383.83 ±3059.15
REF: 626.60 ±717.25
DEG: 1519.76 ±1332.12
REF: 2083.89 ±1708.28
DEG: 4305.22 ±2199.34
p < 0.05
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
SOIL SEED BANKS & DEGRADATION first results
Species Abundance DistributionsSAD-Curves for the soil seed bank of the inter-shrub matrix (MISs & BPs)
Stipagrostis uniplumis
Helichrysum candolleanum
Microcharis disjuncta
Dicoma capensis
SOIL SEED BANKS & DEGRADATION first results
Species Abundance DistributionsSAD-Curves for the soil seed bank of the inter-shrub matrix (MISs & BPs)
Indigastrum argyroidesTrianthema parvifolia>80%
Aristida adscensionis
Schmidtia kalahariensis
Kohautia caespitosa
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
SOIL SEED BANKS & DEGRADATION first results
Species Abundance DistributionsSAD-Curves for the soil seed bank & vegetation of the inter-shrub matrix
Helcan, Micdis, Lotpla
Stipagrostis uniplumis
Limarg, Tepdre
Indarg, Tripar
Aristida adscensionisKohautia 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
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
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
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
Thank you