caatinga vegetation

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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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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