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Caatinga vegetation. E.V.S.B. Sampaio. General aspects - geography. Large area (1 million km 2 ) All intertropical (2 – 18 o S) Low altitudes (1500 mm y -1 ) High luminosity. Pioneira. Tensão Ecológica. Caatinga. Cerrado. - PowerPoint PPT Presentation
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Caatinga vegetation
E.V.S.B. Sampaio
General aspects - geography
• Large area (1 million km2)
• All intertropical (2 – 18 oS)
• Low altitudes (<1000m)– High temperatures– High evapotranspiration (>1500 mm y-1)– High luminosity
Floresta Ombrófila
Floresta Estacional
Tensão Ecológica
Caatinga
Cerrado
Pioneira
General aspects - soils
• Two main geological types– Sedimentary and crystalline
• Large soil variations– several orders– from shallow to deep– from sandy to clayey– from low to high fertility (mostly low N and P)
General aspects - water
• Low, concentrated, and erratic rainfall– Very complex climate pattern– 300 – 800 mm y-1 averages– Mostly in 3 months– Beginning and end varying 1 – 2 months– CV > 30%, 100 – 1500 mm
• Water is the most important variable
Uses and vegetation cover
• About 40 % of native vegetation (secondary)
• Cattle almost everywhere (also goats, sheep)
• Permanent agriculture in valleys (3% of area)
• Slash and burn in the slopes– 3-5 y crops and 10-15 y fallow
• Extractivism (fuelwood)
• Natural fires are rare– Low density of material
Vegetation
• Large diversity– >5000 phanerogamic species– >1500 species, excluding transitions– But low local diversity (<100 species)– Open fields to forests– Rock outcrops to water bodies
Vegetation
• Adaptation to water deficit– Deciduous shrubs and trees– A few evergreen– Succulents (Cactaceae, Bromeliaceae)– Few vines and epiphytes– Short lived herbs
Trees and shrubs
• Usually short– 8-10 m tall (maximum 20 m)
• Not very thick– <20 cm DBH (maximum 70 cm)
• Variable density– Commonly 1000 – 3000 plants ha-1
• High basal areas: 10 – 40 m2 ha-1
• Biomass: 10 -100 Mg ha-1
Trees and shrubs
• Low local diversity– 15-50 species ha-1 (maximum 80)
• Dominated by few species– 3 species = 50-80% density and biomass– Varying from site to site
• Aggregate distribution
• Many rare species– 1-2 plants in a ha
Trees and shrubs
• Main families (#species, biomass)– Leguminosae (Caesalpinoideae, Mimosoideae)– Euphorbiaceae– Cactaceae– Anacardiaceae (few species, large trees)– Burseraceae (1 species, large tree)– Bignoniaceae (vines)
Herbs and low plants
• Mostly annuals
• Few perennials– Bromeliaceae and Cactaceae
• Variable density– Depends on tree and shrub cover– 5 – 100 plants m-2
• Biomass: 0.2 – 3 Mg ha-1
• Variable diversity– 7- 100 species ha-1
Herbs and low plants
• Main families– Leguminosae– Convolvulaceae– Malpighiaceae– Poaceae– Cyperaceae– Asteraceae– Malvaceae (high densities)
Phenology
• Leaves, flower and fruits year round– Mostly during the rainy season
• Kew species in critical periods– Bromeliaceae and Cactaceae
• Variable flowering patterns– More than once a year– Once in several years
• No studies on herb phenology
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J F M A M J J A S O N D J F M A M J J A S O N D0
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Tree and shrub seedlings
• Several studies on germination– Mostly orthodox seeds– A few species with dormancy
• One study on seedling survival– 2 species with few seedlings and high survival– 2 species with many seedlings and low survival
• One study on seedling origin– A few species with ramets (root sprouting)
Tree and shrub seedlings
• Few greenhouse studies on seedling growth
• Observations of irregular establishment– Years without and years with many
• Colonization explained– Sprouting in clearcut areas (firewood, pasture)– A few species in old fields
• No studies on effect of herbs in seedlings
Criteria Climate
Semi-arid
Leguminose Mimosa tenuiflora(Mimosoideae)Caesalpinia pyramidalis(Caesalpinioideae)Mimosa caesalpiniifolia(Mimosoideae)Bauhinia cheilantha (shrub) (Caesalpinioideae)
Non-leguminose Aspidosperma pyrifolium(Apocinaceae)Combretum leprosum(Combretaceae)Commiphora leptophloeos(Burseraceae)Croton sonderianus (shrub)(Euphorbiaceae)
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