(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? Why Preserve Tropical Forests?

DATA: Total mass of oxygen in the atmosphere = 1.2 x g O 2 Total “net” ecosystem production from global land photosynthesis = 1.1 x g O 2 /yr (tropical forests are ~20% of this total). Amount of C in all tropical forests = 206 x g C Amount of C in all land plants = 610 x 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 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?

The Tropical Rain Forest 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? The tropical rain forest is the most productive and species-rich terrestrial ecosystem on earth What we wish to learn:

Several different types of forests exist in the tropics

Timber production is a major cause of deforestation

Tropical Land Use Change in Annual Deforested Area (km 2 ) Southeast Asia (Indonesia)25,000 ± 800 Latin America (Brazil)25,000 ± 14,000 Africa 800 ± 300 Global58,000 ± 14,000

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

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 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 canopy, not the soils By comparison, in temperate- zone forests there can be 10x as much N and P in the soils as in the canopy. (kg/m 2 )

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) Root Biomass (tons/ha) Total Soil Nitrogen (kg/ha) ,000- Total Soil Phosphorus (kg/ha) Turnover time of leaves (years) Modified from J. Terborgh, 1992, Scientific American Library Data on Tropical Forests * No relationship between aboveground biomass and soil nitrogen * Inverse relationship between root biomass and soil nitrogen * Rich soils have faster turnover time of leaves

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

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

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

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

“Guilds”

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.

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

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

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, 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…”