(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 Why Preserve Tropical Forests?
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(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.
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(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 O2 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 1021 g O2
• Total “net” ecosystem production from global land
photosynthesis
= 1.1 x 1015 g O2/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)
CO2 + H2O CH2O + O2 Respiration (Oxidation, Combustion)
• Because of molecular weight differences for C and O2, you need to know that 2.67 g of O2 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 O2 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 1990-1997
Annual Deforested Area (km2)
Southeast Asia (Indonesia) 25,000 ± 800Latin America (Brazil) 25,000 ± 14,000Africa 800 ± 300 Global 58,000 ± 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).
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 soilsBy comparison, in temperate-zone forests there can be 10x as much N and P in the soils as in the canopy.
(kg/m2)
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
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