Youtube: http://www.youtube.com/watch?v=Y3OWgb0Bv-A

1. English Transcript :
Which Came First - The Rain or the Rainforest?
Youtube: http://www.youtube.com/watch?v=Y3OWgb0Bv-A
A tropical rainforest without rain wouldn't be much of a rainforest. I mean, all
plants need water to grow, and without it, they shrivel up and die. So what about the
ancient Hawai'ian proverb,"Hahai no kauaikaulula`au", which means "the rain follows
after the forest"?
How could that be?
Well, all land plants lose water when the pores on their leaves open up during
photosynthesis, and this evaporation draws more water up through their stems. With
so much rain soaking the soil in rainforests, water is nearly unlimited, and accordingly,
rain forest trees can afford to move and lose more water than other plants. All that
water vapor rising from the forest feeds moisture-ladenclouds while causing
convection - together, these effects accelerate the formation of rain - which falls to the
soil and gets taken up all over again.
This cycle--absorption, evaporation, rain-- happens everywhere there are plants.
However, super-wet soil, fast-pumping trees and hot tropical sun make the cycle so
fast in the rainforest that - unlike other biomes where clouds might form in one place
and rain in another - all that water stays in the same region.

2. So without the forest pumping so much water into the air, rainforests wouldn't be as
rainy.
And without so much rain, the forest couldn't pump so much water into the air. So
which came first, the rain, or the rainforest?
Well, before rain forests, ancestors of trees like cypress, pine and spruce dominated
the land - but they were conservative when it came to using (and losing) water - so
the air tended to be dry, meaning less rain.
However, around 130 million years ago, a new kind of plant developed that took the
risk of losing more water in return for souped-up photosynthesis - these were the
flowering plants, and their risk paid off: their faster growth enabled them to
out-compete the ancestral pines and take over the tropical regions of the globe.
Angiosperms lost so much water into the air that as they spread, they brought their
own rain with them. And today, tropical rainforests receive more rain than if they
were replaced by pine forests- in some places as much as a meter more rain each year.
That's equivalent to an extra two and a half hours of heavy rain every week. Not
surprisingly, all that water cools off the forest, too, which is why the Amazon isn't
nearly as hot as the Sahara or even an east Texas pine forest in summer.
But the hot, dry tropics of the past may soon be a part of our future. In parts of the
Amazon where vast swaths of rainforest have been logged or cleared for agriculture,
weather stations are already observing decreased rainfall, and forest fires have
become more frequent.
Scientists worry that these changes will lead to ever hotter, drier and more flammable
tropics in the coming decades, making things tougher both for the remaining forest
and for the people who live there. So, when in drought, plant a tree. Seriously - Hahai
no kauai kaulula`au (the rain follows after the forest).