Why Preserve Tropical Forests 1 Tropical forests produce

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Why Preserve Tropical Forests? (1) Tropical forests produce a lot of oxygen by photosynthesis,

Why Preserve Tropical Forests? (1) Tropical forests produce a lot of oxygen by photosynthesis, and if we cut down all tropical forests, we would lose that oxygen production and we (as oxygen consuming organisms) would be in trouble. (2) If we burn all the tropical forests, we not only lose the oxygen they produce each year, but we consume lots of oxygen from the atmosphere in the burning process, really putting us in trouble. Homework Questions: - Can you defend the above statements using principles of residence time and mass balance? - What is the residence time of O 2 in the atmosphere, and how much would be consumed by burning tropical forests?

Homework Problem – Answer these Questions: - Can you defend these statements using principles

Homework Problem – Answer these Questions: - Can you defend these statements using principles of residence time and mass balance? - What is the residence time of O 2 in the atmosphere, and how much would be consumed by burning tropical forests? DATA: • Total mass of oxygen in the atmosphere = 1. 2 x 10 21 g O 2 • Total “net” ecosystem production from global land photosynthesis = 1. 1 x 1015 g O 2/yr (tropical forests are ~20% of this total). • Amount of C in all tropical forests = 206 x 1015 g C • Amount of C in all land plants = 610 x 1015 g C Photosynthesis (Reduction) Respiration (Oxidation, Combustion) • Because of molecular weight differences for C and O 2, you need to know that 2. 67 g of O 2 are used to respire or burn 1 g of C. • The highest permanent human settlements are found in mountains where the oxygen is only 45% of that at sea level

The Tropical Rain Forest The tropical rain forest is the most productive and species-rich

The Tropical Rain Forest The tropical rain forest is the most productive and species-rich terrestrial ecosystem on earth What we wish to learn: • How can such productive forests grow on soils of extremely low fertility? • Why is biological diversity so high in the tropics? • What are the consequences of the expected, almost-total loss of humid tropical forests?

Several different types of forests exist in the tropics

Several different types of forests exist in the tropics

Timber production is a major cause of deforestation

Timber production is a major cause of deforestation

Tropical Land Use Change in 1990 -1997 Annual Deforested Area (km 2) Southeast Asia

Tropical Land Use Change in 1990 -1997 Annual Deforested Area (km 2) Southeast Asia (Indonesia) Latin America (Brazil) Africa Global 25, 000 ± 800 25, 000 ± 14, 000 800 ± 300 58, 000 ± 14, 000

Photo gmagazine. com Deforestation of Tropical Rainforests is proceeding rapidly! (see them while you

Photo gmagazine. com Deforestation of Tropical Rainforests is proceeding rapidly! (see them while you can…)

Tropical forests are highly productive, and so it is natural to assume that the

Tropical forests are highly productive, and so it is natural to assume that the soils are fertile (many nutrients). But, that would be wrong…

Soil Fertility & Nutrient Cycling 1. Rapid weathering and time have led to depleted

Soil Fertility & Nutrient Cycling 1. Rapid weathering and time have led to depleted soil nutrients 2. Waters draining tropical landscapes are nutrient poor 3. Nutrients are found mainly in the plant biomass 4. Experiments show the effectiveness of roots at capturing nutrients 5. Comparisons of 7 tropical forests and their biomass and nutrient stocks

Compare the amounts of Phosphorus in different locations – most P is in the

Compare the amounts of Phosphorus in different locations – most P is in the canopy, not the soils By comparison, in temperatezone forests there can be 10 x as much N and P in the soils as in the canopy. (kg/m 2)

Data on Tropical Forests Amazon, Venezuela Oxisol forest, Venezuela Montane rainforest, Puerto Rico Evergreen

Data on Tropical Forests Amazon, Venezuela Oxisol forest, Venezuela Montane rainforest, Puerto Rico Evergreen forest, Ivory Coast Dipterocarp forest, Malaysia Lowland rainforest, Costa Rica Moist forest, Panama Aboveground Biomass (tons/ha) 268 264 228 513 475 382 326 Root Biomass (tons/ha) 132 56 72 49 20 14 11 Total Soil Nitrogen (kg/ha) 785 1697 - 6500 6752 20, 000 - Total Soil Phosphorus (kg/ha) 36 243 - 600 44 7000 23 Turnover time of leaves (years) 2. 2 1. 7 2. 0 - 1. 3 - 0. 9 Modified from J. Terborgh, 1992, Scientific American Library * No relationship between aboveground biomass and soil nitrogen * Inverse relationship between root biomass and soil nitrogen * Rich soils have faster turnover time of leaves

BIODIVERSITY (of vertebrates only) From the Millennium Ecosystem Assessment, 2005, World Resources Institute

BIODIVERSITY (of vertebrates only) From the Millennium Ecosystem Assessment, 2005, World Resources Institute

Example of increasing biodiversity toward the tropics – # of bird species

Example of increasing biodiversity toward the tropics – # of bird species

BIODIVERSITY Tropical forests contain ~50% of the 5 -30 million species on earth. Why

BIODIVERSITY Tropical forests contain ~50% of the 5 -30 million species on earth. Why are tropical forests so diverse? (1) Ecological specialization Multi-layered forests (2) Evolutionary history Geographic isolation Episodes of climate change (3) Other factors High year-round productivity

Up to 5 Layers of vegetation exist in the tropical forest, compared to only

Up to 5 Layers of vegetation exist in the tropical forest, compared to only 2 -3 layers in a temperatezone forest.

“Guilds”

“Guilds”

There are more bird “guilds” in the tropics (light bars) than in the temperate

There are more bird “guilds” in the tropics (light bars) than in the temperate zone (dark bars) # of species

Species have specific “ranges”, and geographic isolation can lead to the evolution of new

Species have specific “ranges”, and geographic isolation can lead to the evolution of new species.

Repeated climate change in the tropics may have led to frequent geographic isolation, and

Repeated climate change in the tropics may have led to frequent geographic isolation, and thus more species. Annual precipitation, mm Area receiving <1500 mm (tan)

Species loss is studied in deliberately created forest fragments, here shown in Brazil

Species loss is studied in deliberately created forest fragments, here shown in Brazil

Deforestation is due both to slash and burn for agriculture and to cutting for

Deforestation is due both to slash and burn for agriculture and to cutting for timber and firewood – How does this affect the nutrients?

Crop yield drops quickly after slash and burn agricultural

Crop yield drops quickly after slash and burn agricultural

Deforestation causes massive erosion and disrupts the water cycle, which may alter the regional

Deforestation causes massive erosion and disrupts the water cycle, which may alter the regional climate

Summary • High productivity, but low nutrients in soils • Most nutrients in biomass,

Summary • High productivity, but low nutrients in soils • Most nutrients in biomass, Efficient nutrient cycling • 50% of world’s species - why? • Specialization in a complex, stable environment • Evolutionary history - climate change and forest fragmentation • Human impacts - loss of area (20% originally to 7% now, to <1% when? -- soon…) • Interplay of people, ecosystem function (agriculture, logging, ranching, mining), and politics influence the rainforest

Take Home Message “ Sometimes knowing the science just isn’t enough…”

Take Home Message “ Sometimes knowing the science just isn’t enough…”