Forestry & Society

Tropical Forests

HORT/RGSC 302

J.G. Mexal

Fall 2005

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Tropical Forests:Outline

• Definition

• Diversity

• Environmental Factors

• Forest Gaps

• Carbon Budgeting

• Nutrient Cycling

• Deforestation

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Tropical Forests-World Distribution

Sharma 1992

Tropical Dry

Tropical Deciduous

Tropical Rain

Temperate Evergreen

Temperate Mixed

Boreal

Temperate Evergreen

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Tropical Forests: Definition– Location: 23o27’ North (Tropic of Cancer)

23o27’ South (Tropic of Capricorn)– 40% of land surface = tropics

– Precipitation: • Rain Forest: usually exceeds 2,000 mm/yr (79 in/yr)• Dry Forest: 800-1,500 mm/yr (31-60 in/yr)

– Temperature: mean annual T = 27oC (81oF)• relatively narrow diurnal range = 6-12 oC (11-22 oF)

– Soils: highly weathered, nutrient-poor– Photoperiod: 11-13 hr

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Species Diversity- butterflies/ Longman & Jenik 1987

0 30 60 90 0 30 60 90 0 30 60 90 120 150

Americas Africa/Europe Asia/Russia

706050403020101020304050

Species (no.)

Sou

thN

orth

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Species Diversity- Tree Species

• Canada >55oN Picea (4 species) • Canada >50oN Pinus (9 species)• USA 25-50oN Pinus (37 species)• Mexico 15-30oN Pinus (80 species)• Brazil 10oS 100’s species /ha• Tierra del Fuego 55oS Nothofagus (3

species)

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Tropical Forests-Important SpeciesLongman & Jenik 1987

• Mahogany (Swietenia macrophylla)• Teak (Tectona grandis)• Spanish cedar (Cedrela odorata)• Gmelina (Gmelina arborea)• Cacao (Theobroma cacao)• Casuarina (Casuarina equisetefolia)• Ceiba (Ceiba pentandra)• Balsa (Ochroma sp.)• Rubber tree (Hevea brasilensis)• Rosewood (Dalbergia sp)

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Tropical Forests of Honduras, CA

Swietenia humiliscaoba

Enterolobium cyclocarpumguanacaste

Pinus oocarpaocote

Huertea cubensiscedrillo

Juglans olanchanusnogal

Symphonia globuliferabarillo

Cordia alliodoralaurel

Pterocarpus indicusrosewood-rosita

Magnolia yoroconteredondo-canelon

44 mm

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Tropical Forests Species

Rosewood Eucalyptus

Madagascar Ebony Koa

Paduk

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Tropical Forests Species-Chile

Prosopis chilensisAlgarrobo

Donoso Z. 1995

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Tropical Forests-Height = F(rainfall)/ Longman & Jenik 1987

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Tropical Forests-Canopy Layering/ Longman & Jenik 1987

0

1000

2000

3000

4000

5000

6000

7000

<1 2 5 12 20 30

Trees/haPalms/haBA (m2/ha)

15

10

5

0

Basal AreaStems (no/ha)

Tree Height (m)

Amazon forest

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Tropical Forests-Height = F(altitude)/ Longman & Jenik 1987

0

10

20

30

40

50

150 800 1500 1800

Altitude (m)

Height (m)

W. Malaysia

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Tropical Forests- Forest Gaps/ Longman & Jenik 1987

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Tropical Forests- Forest Gaps/ Longman & Jenik 1987

0

0.5

1

1.5

2

2.5

3

0 1 2 3 4 5 6

PrimarySecondaryAll

Time after Gap Formation (years)

Trees (no/m2)

Ghana Species

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Tropical Forests- Forest Gaps-Light/ Longman & Jenik 1987

Center of Gap

Edge of Gap

Inside Forest

Cecropia obtusifoliaMexico

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Tropical Forests-Canopy Layers-Ps/ Longman & Jenik 1987

Photosynthesis(mgCO2/dm2/h)

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Tropical Forests- Temperate Forests/ Longman & Jenik 1987

Annual Carbon Capture

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Forest Productivity Comparison

Forest Biomass (t/ha)

Net Primary Productivity (t/ha)

Tropical 450 20 Temperate-broadleaf

338

Temperate-conifer

240 10

Boreal 225 5 Woodland 100 6 Ag land 35 7

Tropical Forest Biomass/ Dezzo & Chacon ForEcolMgt 2004

0

50

100

150

200

250

300

350

400

450

Tall forest Medium forest Low forest Savanna

<2.5

<5

palms

Leaves>5

Branches>5

Stem>5

5

15

10

Biomass (kg/ha)

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Forest Comparisons/Forestry Hndbk 1984

Forest Biomass (t/ha)

Nitrogen (kg/ha)

Phosphorus (kg/ha)

Potassium (kg/ha)

Calcium (kg/ha)

Magnesium (kg/ha)

Tropical 378 7260 241 2157 4005 437

Temperate broadleaf

338

1085

73

463

1142

115

Temperate Conifer

291

664

47

263

717

Northern hardwoods

111

278

22

368

Boreal 129 447 50 291 488 108

Biomass & Nutrient Content of Standing Mature Forest

C Sequestration via Reforestation/ Restor. Ecol. 2000

y = -0.81x - 56.3

R2 = 0.27

y = 43.74Ln(x) - 21.88

R2 = 0.69

-150

-100

-50

0

50

100

150

200

0 10 20 30 40 50 60 70 80

AbovegroundSoil C

Biomass (Mg/ha)

Forest Age (yrs)

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Tropical Forests- Temperate Forests/ Longman & Jenik 1987

Litter7%

Wood40%

Soil50%

Leaves3%

Litter1%

Leaves2%

Soil17%

Wood80%

Temperate Coniferous ForestTropical Rain Forest

Organic Matter

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Tropical Forests-Temperate Forests/ Longman & Jenik 1987

Forest Location Biomass (t/ha)

Respiration (t/ha/yr)

Maintenance (t/t/yr)

wood leaves wood leaves wood leaves

Temperate (Fagus)

Denmark 129 2.7 4.5 4.6 0.035 1.7

Tropical (dipterocarp)

Malaysia 414 7.6 18.8 29.1 0.045 3.8

Carbon Fixation vs Respiration

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Tropical Forests- Nutrients Cycling/ Longman & Jenik 1987

Boxes = kg/ha

Arrows = kg/ha/yr

N = 6.5 K = 7.3P = 0.5 Ca = 3.6Mg = 1.3

Dry Wgt = 310,000 kgN = 683 K = 668P = 37 Ca 1,270Mg = 187

Dry Wgt = 7,550 kgN = 91 K = 28P = 5.1 Ca = 95Mg = 19

N = 30P = 2.5K = 71Ca - 19Mg = 11

Litter layerDry Wgt = 6,460 kgN = 91 K = 11.5P = 4.8 Ca = 96Mg = 14.5

SoilO M = 515,000 kgN = 19,200 K = 403P = 2,560 Ca = 3,750Mg = 682

RootsDry Wgt = 40,000 kgN = 137 K = 186P = 6.4 Ca =33Mg = 61

Forestry & SocietyForests of the World/ Litter & nutrient residence time (yrs)/Kozlowski & Pallardy 1999

Forest OM N P K Ca Mg

Tropical 0.7 0.6 0.6 0.2 0.3 --

Temperate deciduous 4 6 6 1 3 3

Temperate coniferous 17 18 15 2 6 13

Boreal deciduous 26 27 15 10 14 14

Boreal coniferous 350 230 324 94 150 455

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Tropical Forests- Nutrients (kg/ha)/ Longman & Jenik 1987

Component Nitrogen (N)

Phosphorus (P)

Potassium (K)

Calcium (Ca)

Magnesium (Mg)

Soil 1,830 (29%)

125 (90%)

820 (56%)

2,520 (49%)

345 (48%)

Trees 4,580 12 650 2,580 370

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Tropical Forests- Nutrients (kg/ha)/ Longman & Jenik 1987

0

200

400

600

800

1000

Nitrogen Phosphorus Potassium Calcium Dry Weight

Leaves Stems

Roots Litter

Soil (0-40 cm)

Kg/ha

Nutrient

t/ha

Venezuela

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Tropical Forest- -Review Questions

• What is a tropical forest? Where does it occur? What is the climate?

• What are some of the major species in a tropical forest?• How does species diversity vary with latitude? Give

examples. Why does this occur?• What is the ecological significance of a ‘forest gap’?• Describe how environmental factors such as rainfall,

elevation, light and temperature affect tree growth and establishment.

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Tropical Forest- -Review Questions

• Describe ‘canopy layering’ in a tropical forest, including the differences in tree number and size with increasing height in the canopy.

• Compare and contrast the carbon budgets of a tropical, temperate, and boreal forest. Don’t memorize numbers, just give concepts and relative differences.