Cerrado South America- Brazil Moist Savanna Site Dr. Dulce Alves da Silva (University of Brasilia)
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Transcript of Cerrado South America- Brazil Moist Savanna Site Dr. Dulce Alves da Silva (University of Brasilia)
CerradoSouth America- BrazilMoist 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 periodsEx. 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
Vereda
Gallery forest
Campo Sujo
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• Almost closed sclerophyllous woodland • Crown cover 50 to 90%• Trees 8-12 m • Ground layer much reduced
PhysiognomiesSavannic Physiognomies
• Ex. Campo limpo, Campo sujo, cerrado sensu stricto, cerradão– 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
• 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
Woody Species• 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.)
• 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
• 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 TimeSpecies 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)
1
2
3
5
Qualea grandiflora 5.3 (0.3) 1
(Franco 2002, Nardoto et al. 1998)
• Seedling develop a tree canopy layer in the grass matrix through a slow process
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– 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)
(Hoffmann & Franco 2003)
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
• 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
• 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