Transcript ppt.

Cerrado
South America- Brazil
Moist Savanna Site
Dr. Dulce Alves da Silva
(University of Brasilia)
Cerrado
• Covers 2 million Km2
• Approximately the size of Western
Europe
• Cerrado in Portuguese = closed, dense
Typical Vegetation
Landscape
• Savanna of very variable structure,
termed cerrado sensu lato :
– Well-drained soils,
– Avoiding valley bottoms
• Other vegetation:
– Patches of base-rich soils.
Ex: Mesophytic Forests
– Soil prone to water logging for
considerable periods
Ex. Gallery forest: vegetation following the
watercourses
Distribution of Cerrado Vegetation
• Seasonal precipitation
– Which cannot entirely explain the predominance of
Cerrado vegetation,
– Present climatic conditions would favor the
establishment of forest in most of the Cerrado Biome
region
Other explanations:
• Soil fertility
• Soil drainage
• Fire regime
Climate
• Variable: big area
• Mean Temperature: 18º to 28ºC
• Rainfall: 800 to 2,000 mm
– Intense dry season
(April – September)
Mosaic of Physiognomies
Encompasses a series of vegetation physiognomies from
open grasslands to dense woodlands
Gallery forest
Campo Sujo
Vereda
Cerrado sensu stricto
• Dominated by trees and shrubs often 3-8
m tall
• Provides more than 30% crown cover
• Still a fair amount of herbaceous
vegetation between them
Cerradão
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Almost closed sclerophyllous woodland
Crown cover 50 to 90%
Trees 8-12 m
Ground layer much reduced
Physiognomies
Savannic Physiognomies
• Ex. Campo limpo, Campo sujo,
cerrado sensu stricto, cerradão
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Predominate in the landscape
Well-drained Soil
Low-fertility soils
Sclerophylly is common
– Mixture of plants of two fairly distinct layers
with features of pyrophytic savanna
vegetation:
• Woody layer: trees and large shrubs
• Ground layer: subshrub and herbs
Savanna
Ground Layer
• Herbs, subshrubs and smaller
shrubs
• Much richer than trees and
large shrubs
• Castro et al. (1999): 6,836 spp
Woody layer
• Trees:
– with low contorted form
– with fire-resistant bark
– Leaf phenology: Deciduous, brevi-decidous and evergreen
species
• Hydraulic lift: passive movement of water from drier
to moister portions of the soil profile via root systems
(Jackson et al. 1999)
– Can contribute to the water balance of
neighboring plants
Woody Species
• 1,000-2,919 tree/shrubs species (Ratter & Ribeiro 1996, Castro
et al. 1999)
• High Local diversity of trees and large-shrubs:
– Alpha diversity = 100 - 150 species per hectare
(Ratter et al. 2003, Felfili et al. 2004)
• Aluminum is extremely toxic to most cultivated plants
• Most native species are aluminum-tolerant (Haridasan 1982,
Haridasan et al. 1986)
Woody Species
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Most important families in terms of species numbers:
– Leguminosae (153 spp, all 3 subfamilies)
– Malpighiaceae (46 spp.)
– Myrtaceae (43 spp.),
– Melastomataceae (32 spp.)
– Rubiaceae (30 spp.)
Many areas of vegetation dominated by Vochysiaceae (23 spp.).
Abundance of 3 species:
– Qualea grandiflora
– Qualea parviflora
– Qualea multiflora
Largest Genera:
– Byrsonima (Malpighiaceae, 22spp.)
– Myrcia (Myrtaceae, 18 spp.)
– Kielmeyera (Guttiferae, 16 spp.)
– Miconia (melastomataceae, 15 spp.)
– Annona (Annonaceae, 11 spp.)
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High regional diversity
315 sites
914 species (trees and shrubs)
300 species occur at 8 or more sites (i.e. ≥2.5%
of the total ), while the remaining 614 species,
including 309 unicates, are very rare.
Bioma Cerrado:
Main Regions according to the
composition
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C & SE: Central and south-eastern;
CW: Central-Western;
FWM: Far western mesotrophic sites
N & NE: North and North-eastern
S: Southern
Ratter et al. (2003)
Intense Human Pressure
• Conversion of mixture of trees and grasses to
predominantly herbaceous vegetation
– Expansion of agriculture
– Grazing lands
– Anthropogenic burning disturbance (igniting the
majority of present fires in tropical savannas)
• Climate change: indirectly influence through
changes in the frequency of fire due to
alterations in the fuel load
Brazilian Hotspots
• 2 hotspots: Atlantic Forest and “Cerrado”
– Among 25 global biodiversity “hotspots” of absolute
importance for conservation (Myers et al. 2000)
– Conservation efforts in the Cerrado have not
achieved international = standards 1.6 % (Amazon
~6%) (Cavalcanti & Joly 2002)
Fire
• Burning occurs at intervals of 1-3 years –
a rate that exceeds the precolonization fire
regime
• Frequently used management tool
(Pivelllo & Coutinho 1996)
• Most of the savannic flora are fire-adapted
species
• However, now subjected to frequencies in
excess of the environment in which they
evolved
• Gallery forest species are not fire adapted
• Recurrent fires tend to: result in soil
impoverishment
Fire
• Affects all aspects of the
demography of Cerrado plants,
reducing (Hoffmann 1996, 1998, 2000)
• Fire induce reversions of woody
species from larger to smaller size
classes
• Frequent fire damage favors the
ground layer = Producing more
open physiognomies
Seedling in Cerrado
• Main restriction:
– Frequent fire
– Low nutrient availability
– “Veranico”: unpredictable dry spells in the wet
season (Hoffmann 1996, Nardoto et al. 1998)
– Prolonged drought (dry season)
– Herbivory
• Vertebrates (Nardoto et al. 1998)
• Invertebrates (personal observation)
– Competition mainly with grasses
• Native species
• Exotic species (Hofmann et al. 2004)
Size vs Time
Species
Plant size (cm)
Plant age (years)
Bowdichia virgilioides
8.3 (0.5)
2
Dalbergia miscolobium
23 (2.7)
7
Kielmeyera coriacea
2.3
2.7
2.8
8.3 (1.8)
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2
3
5
Qualea grandiflora
5.3 (0.3)
1
• Seedling develop a tree canopy layer in the grass matrix through a slow
process
(Franco 2002, Nardoto et al. 1998)
Seedling vs Fire
• For 7 of 12 species establishment success
of experimentally placed seeds was found
to be:
– Lower in recently burned sites
– No enhanced establishment when burnt 1 or
more years previously
Seedlings in Cerrado
Ex. Kielmeyera coriacea
– Seeds: not dormant (<20 days), but with short
viability
– First year:
• Rainy season (after 3 months of
transplantation) “veranico” – negative impact
• First dry season: was not a major influence on
survival:
– Second year:
• 35% of surviving plants were removed by
armadillos (Dasypus spp) (Nardoto et al. 1998)
– When the interval between fires is not enough to
reach a fire-tolerant size, seedlings re-sprout and
form “seedling bank” (Oliveira & Silva 1993,
Nardoto et al. 1998).
Root system in Cerrado Seedling
Taproot
(Hoffmann & Franco 2003)
– Early growth (high root/shoot rate)
– Stores carbohydrate permit re-sprouting following fire,
drought or herbivory
– Root length to access water in deeper soil water:
Stryphnodendron adstringens and Qualea grandiflora
~55 cm (greenhouse experiment - 7 months) (Moreira &
Klink 2000)
– Water potential at 60 cm depth did not drop below
-1.6 MPa, indicating a permanent source of water within
reach of deep taproot (Franco et al. 1996)
Fire Re-sprout
• Species also are able to re-sprout after
fire:
– 8 out of 9 savanna species were able to
survive fire when less than 1 yr old (Hoffmann
2000).
– Survival of burned seedling was positively
correlated to seed mass
Light
– Grass vs Seedlings - Assimilation rate in
Kielmeyera coriacea:
• 5 cm high plants range between 26 to 40 % of photosynthetic
capacity
• 50 cm (not hide by grass layer): 80% of photosynthetic
capacity (Nardoto et al. 1998)
– Growth of many species did respond to light level,
with the effect being positive for some species and
negative for others (Hoffmann & Franco 2003)
Cotyledons
• Play an important role in seedlings
establishment:
1 to 6 months
(Nardoto et al. 1998, Sassaki & Felippe 1992)
Nutrient vs Seedlings
• There is an overall positive effect of nutrients on
RGR
• There is no light–nutrient interaction
(Hoffmann & Franco 2003)
Woody Density
• Cerrado seedlings less dependent on
woody cover than gallery forest species
(Hoffmann 2000).
– Soil under trees might:
• Have better nutrient status
• Higher moisture content during dry periods than
open grassland
• Reducing the density of the competing herbaceous
layer
Species choice
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Common species
Seed availability
Seed viability
None of the species belong exclusively to
a particular Cerrado community
Grass Species
Echinolaena inflexa:
• common species in different
communities
• C3
• rhizomatous or loosely tufted
short-lived
• perennial grass
• 20-50 cm high
Woody Species
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Dalbergia miscolobium
Dimorphandra mollis
Pterodon pubescens
Kielmeyera coriacea
Qualea grandiflora
Eugenia dysenterica
Need better characterization
• Effects of litter
• Effects of grass competition for nutrients
• The influence of mycorrhiza in seedlings
establishment
• The impact of herbivory in the seedling
establishment
• How environmental changes will have an impact
in grasses and seedlings competition:
– light, nutrients, fire
Thank You