-Tropical forests are characterized by high temperature and moderate to high levels of precipitation
-There are tropical dry forests
-precipitation can vary
Forest Canopy Structure
Tropical forests have well-developed canopy structure
-The overstory includes trees that emerge above the thick, closed canopy
-It gets pretty dark on the forest floor
The dynamic nature of forests
-A variety of random disturbances, ex trees falling over
-Many tropical forest trees require gaps in the canopy to start growing-light levels are too low in the absence of gaps
-Gaps are formed when old or diseased trees fall over, clearing patches of vegetation.
Latitude and diversity
-As you travel north or south from the equator, the number of species in most taxonomic groups declines
-due to a combination of the greater age, high rainfall, and high solar inputs of tropical regions
-High species richness in the tropics is associated with high solar inputs and plenty of rainfall
NPP and Carbon Storage
tropical forests store carbon
-DONT CUT DOWN TREEs
Why are forests good at carbon sequestration?
Many woody plants have lifespans well overa century
-woody material is recalcitrant to decomposition
-long-term carbon storage in both standing biomass and ofest soils
-however, in TROPICAL forests, not much carbon is stored in litter and soil
Rates of Nutrient Cycling
-The rate of nutrient cyclin in terrestrial ecosystems is someimes limited by temperature and moisture
-high temp and recip generally favor rapid recycling of nutrients because they favor microbial growth (fungi, bacteria) and microbes are ofter major decomposers
-nutrient cycling is much faster in tropical rainforests than it is in either the desert or the tundra
decomposition of detrits limits the rate at which nutrients move through an ecosystem. Decomposition rate is influenced by abiotic condition and the quality of the detritus as a nutrient source.
influenced by abiotic conditions. in tropical wet forests, highly diverse decomposer communities quickly break down litter; abundant rain leaches remaining nutrients out.
So where's the carbon
-in trop forests...in the LIVING PLANT BIOMASS
-when the biomass is cut down and removed or burned, the carbon and nutrients are transferred out of the forest ecosystem-not stored in teh soil
-Tropical soils therefore LOSE FERTILITY quite quickly when they are cleared and used for agriculture
-And because of the heavy rains in the tropics, soil erosion is a huge problem following clearing-soil ends up in sreams and rivers
-agricultural system in which plots of land are cleared and farmed until soils lose fertility
-natural succession is then permitted for a number of seasons of regrowth during which time crops are grown nearby
-after some years under succession, the land may be re-cleared for further cropping
-At any given time, most of the land under shifting cultivation may be unused and in the process of succession
-cultivation and fallowing are cyclical processes and the landscape isa mosaic
Recap on Succession and Disturbance
-The frequency and magnitude of disturbance are prime determinants of successional processes
-likewise, the sustainability of shifting cultivation practices depend upon the frequency and magnitude of disturbance.
-short fallow periods represent a high frequency of disturbance
-some clearing practices are high magnitude disturbances
-Long cropping periods are high magnitude disturbance
When disturbance is too high
-net nutrient loss over time
-in tropical forests, substantial nutrient levels are stored in lving plant tissue
-If woody plants are repeatedly removed, soil will become exhausted and succession will stop
-There is also loss of organic matter over time
-Erosion of soils and loss of fertility
-Loss of seed bank
When is Disturbance too high?
slash and burn.
Slash and Burn
-Vegetation is cut and allowed to dry
-Some timber may be removed
-The rest is burned in situ
-Plots are cultivated for a few seasons (usually one to five years0 and then abandoned as fertility declines and weeds invade.
Severe disturbance=long regeneration
Burning and subsequent crop production are severe disturbances
-Forests do not recover (succeed) quickly, and if erosion is severe, may not recover over many human life spans.
-Most of the Madagascar central highlands plateau is "permanently" rendered infertile and unproductive, due to large scale erosion that resulted form the adverse surface runoff following slash-and-burn agriculture
The war on drugs?
-drug use and slash and burn agriculture are related
-Since the 1990s a rise in the use of slash and burn agriculture to plant coca, marijuana and opium poppy for the illegal drug trade has contributed to yearly deforestation of more than 100000 acres in Colombia alone.
Troical Deforestation Rate Are about asldfkjas % Per year
in chunks, animals can't migrate...
Tropical Forests Are Reservoirs of Biodiversity
High rate of primary productivity are associated with high levels of biological diversity
Discovery of 3 New Lemur Species Announced November 24, 2006.
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