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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 • • • • 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 – – – – 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 • • • • 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 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) 1 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 • • • • 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