Hey everybody, got a special video for you today. I, you may not know this, love
trees they're tall and they're skinny just like me and they do so much for us
from making oxygen so we can breathe to cooling urban environments with their
shade the literally holding the ground together to prevent erosion so when we
here at scishow heard that Mr Beast and Mark Rober were assembling a team of
tree lovers to help them plant 20 million trees by the end of 2019
we were all in everybody on the scishow team agreed we are #TeamTrees
and we want you to join us. For every dollar you donate at teamtrees.org the
Arbor Day Foundation will plant a tree the goal is to get to 20 million by
December 31st and we've put together this compilation of our favorite tree
episodes to inspire you to donate. So kick back enjoy the show and be sure to
head to teamtrees.org afterwards to help us plant trees.
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First up we're going to talk about what is arguably the most delicious tree out
there: avocado trees. Don't eat the tree part, though, but who doesn't love their
tasty green fruit mashed and spread on a piece of toast? But it turns out it is a
bit of a miracle that avocados are still around we very nearly lived in a world
without them. Here's Michael to explain their almost tragic fate.
whether it's sliced on top of a salad
tucked into California sushi roll or mashes guacamole in a burrito people
seem to love avocados in fact people in the United States munched through 4
billion of them in 2014 alone they taste great they're good for you but one of
the most amazing things about avocados is that they still exist see they had a
special relationship with huge beasts that lumbered around Central America
tens of thousands of years ago and when these animals went extinct avocados
could easily have gone down with them but luckily for us they were saved by
some prehistoric farmers the word avocado comes from the Aztecs
specifically the Nahuatl word avocado which means testicle I mean you can kind
of see where they got the name it probably has something to do with the
you know the shape and texture of avocados the way they hang from trees
anyway before they became popular in the rest of the world they were cultivated
in Mesoamerica for thousands of years avocados are a fruit basically swollen
plant ovaries but nutritionally they're very different from other fruits you'd
find in the supermarket first like apples and oranges are composed mostly
of water and sugar and in general fruit is probably better for you than say a
bag of sweets or a sugary drink because it contains fiber which slows down the
sugar absorption and makes you feel fuller faster by comparison avocados
have much less sugar but more protein in fat that gives them that smooth creamy
texture but it also puts them on the calorific side for a fruit anyway they
also contain high levels of potassium and folate nutrients as well as vitamins
c e and k and technically avocados are berries like grapes and blueberries
rather than holding lots of little seeds the avocado goes all-in on one big seed
that massive ball at the core of each fruit and avocados with their huge seeds
evolved alongside equally huge guts tens of thousands of years ago during the
Pleistocene epoch a menagerie of mega fauna or giant animals roamed the
Americas while woolly mammoths chilled out in the North ground sloths weighing
three tonnes and armadillos the size of cars lived in the warm equatorial forest
sneeze giant sloths and armadillos a lot of avocados their digestive systems
would break down the tough skin and absorb the high-energy pulp then the
indigestible seed which contains bitter toxins that kept the animal from chewing
it up passed right out the other end the animals got a tasty meal and the avocado
trees got to scatter their offspring throughout the Mesoamerican forests plus
the seeds got some nice warm fertilizer to give them a
nutritious boost and with these mega fauna around to eat the fruit avocado
trees could keep growing berries with increasingly massive seeds a bigger the
seed the more nutrients could be stored inside as a starter kit for the baby
tree this is especially useful in dense tropical forests where canopies of older
trees block out much of the light for the saplings below so instead of
depending entirely on sunlight for energy the avocado seedlings could
supplement photosynthesis with the nutrients in their seed to survive this
happy evolutionary match didn't last though eventually the megafauna suffered
a mass extinction around ten to thirteen thousand years ago we don't know exactly
why but scientists think the warming climate at the end of the last ice age
was partly responsible though it was also suspiciously close to the time
humans began spreading across the Americas no doubt enjoying lots of giant
mammal meat along the way this meadow vacarro's were in trouble without their
large gutted evolutionary partners the trees stopped thriving the fruit fell to
the ground and the seeds mostly just became food for mold but more hungry
creatures were nearby the new human arrivals love the avocados flesh as much
as the ground sloths did they also had the tools to eat them and the brains to
figure out how to grow them avocados were all set for domestication the
avocados we eat today are probably a little different than the ones that grew
tens of thousands of years ago for example thanks to artificial
selection they probably have more pulp than their ancestors but they've kept
their huge seeds ready and waiting for the guts of long-dead beasts
so we're lucky that thousands of years ago some farmers decided to plant a
bunch of avocado trees and hey I bet that thousands of years from now our
descendants will be pretty happy if we plant a whole bunch of trees too so
don't forget to go to team trees org after this episode to help us plant 20
million trees and speaking of planting trees avocados aren't the only tree
whose fate is in our hands the American chestnut is also struggling to survive
our modern world though that's because of a deadly fungus not the lack of seed
spreaders time for Olivia to explain
picture a forest full of gigantic trees soaring 30 meters into the sky with 5
meter wide trunks you probably envisioned something like the giant
sequoias and redwoods that grow on the western coast of the United States but a
little over a century ago the east coast of America was also home to giant trees
so somewhat smaller than their Western counterparts American chestnuts were
huge and they were all over the eastern US at the dawn of the 20th century then
within a few decades they were almost extinct the culprit a
fungus that strangled the trees from within brought by accident from Asia
since their demise scientists have been trying to figure out if there's a way to
bring the American chestnut back and thanks to technological advances they
may finally have a solution if they can convince the government to let them
plant genetically modified trees to understand what happened to the American
chestnut we have to go back in time to the end of the 19th century back then
American chestnut trees were known as the Sequoias of the east because they
had huge trunks and were tall like the West Coast Giants and they were all over
in 1900 around 1/4 of the hardwood trees east of the Mississippi were American
chestnuts in some places they made up as much as 40% of the forests but by the
1940s they were all but gone the first signs of trouble were seen in the Bronx
Zoo in 1904 when Soares called cankers were discovered on a stand of dying
trees scientists soon realized that the disease was widespread and by 1912
botanists had managed to identify both the fungus responsible and it's point of
origin the chestnut blight fungus gets under the trees bark by hitching a ride
on insects the fungus then attacks and feeds off of the trees water
transmitting cambium tissues essentially choking the tree the blight fungus
probably arrived in New England in the 1870s when Japanese chestnut trees
became popular ornamental plants the imports are resistant to the blade so
it's likely they carried it to America where the chestnut trees were totally
susceptible and by the 1940s it's estimated that nearly 4 billion trees
had died but they didn't go extinct entirely a few scattered populations
still exist mostly trees that people planted outside of their original range
there are also smaller specimens along the east coast that were isolated enough
from their kin to avoid infection and it turns out that like the Dread Pirate
Roberts even the dead trees are only most we did while the blade destroyed
their trunks their root systems remained and even decades later these living
stumps occasionally eke out a chute of new growth but it's usually in vain
because the blight is still around although it isn't doing much damage to
them it's still lurking in oaks that took over after the chestnuts were wiped
out so before any chestnut shoots can reach a reproductive maturity they catch
the blight but where there's growth there's hope so scientists have been
trying to figure out a way to bring American chestnuts back to their former
glory since the 1980s forestry specialists and geneticists have tried
all sorts of things to make blight resistant trees they attempted a
technique called back crossing for example we're surviving specimens and
their offspring were carefully bred together to select for natural
resistance genes but while this method seems to work for European chestnuts it
hasn't worked as well with the American ones probably because the European ones
were more resistant to begin with researchers have also tried hybridizing
American chestnuts with blight resistant Chinese chestnuts but so far they
haven't been able to get the resistance traits to reliably pass down from
generation to generation but one method that does seem to work is genetically
modifying the trees it turns out that we trust a fungal disease of wheat has a
similar mechanism of infection to chestnut blight both use a compound
called oxalic acid to soften up important structural tissues while also
attacking their host cambium by stimulating the growth of calcium
oxalate crystals blocking the flow of nutrients resistant forms of wheat
produce an enzyme called oxalate oxidase which breaks down the acid thereby
blocking the dispersal of the disease and preventing the growth of those
crystals scientists have introduced this wheat gene into American chestnuts and
in 2014 they revealed that they produced a 100% resistant tree that passed that
trait onto its offspring success but the trees haven't been planted yet the
researchers have conducted some preliminary studies to show the trees
don't cause any unexpected harm to the organisms that live in the environments
that they once inhabited and then they requested permission from the US
Department of Agriculture to release the transgenic trees into the wild but
they're still waiting for the green light and that could take a while if
it's ever granted at all aside from the general anxiety that accompanies the
development of any GM some ecologists worry that a return of
the American chestnut would disrupt a century-old
ecosystem that's developed without it on the other hand if successfully put in
action this method could also work for restoring other wild tree populations
beleaguered by fungal invasives like elm trees I guess only time will tell if the
Sequoia of the east will once again stand tall
it's really sad that billions of chestnuts just died so suddenly even
today we're losing trees at an alarming rate which is why it's more important
than ever to plant more and you can help us do that if you go to team trees org
after this episode it would be a shame if we didn't have all the wonderful
weird trees we have today like for example the ones in Europe's dancing
forests oh look it's a younger version of me here with the deets on those
the dancing forest of Kaliningrad is exactly the kind of place where you'd
expect to find a werewolf creeping through the mist located in a place
called the caronian spit off the Baltic Sea on the border of Russia and
Lithuania the strange forest is known to locals by a jollier name the drunken
forest because well the stand of pine trees looks more than a little
schnockered as they twist and curves stretching upward and contorted loops to
find their way to the sky and here's the thing no one knows why these trees look
like they're grinding to Marvin Gaye of course theories abound some suggesting
unstable soils the cause or beetle damage or even nuclear radiation local
legends say that crawling through one of these tree loops in the right direction
will earn you an extra year of life a more popular non-magical theory suggests
spousal winds were the original shaping force and there is a precedent for that
if you've ever hiked into an Alpine zone forests you've probably seen patches of
stunted twisted supercooled mini trees called Krumholtz they get so thoroughly
clobbered by a harsh cold winds that they end up growing more horizontal than
vertical but some people think that the trees in the dancing forest have been
trained to grow that way humans have long been manipulating trees for
commercial or aesthetic purposes in mr. Miyagi and his bonsais he was all about
tree shaping humans can train a young tree to grow in unconventional ways by
laying a heavy object on its skinny trunk sometimes for years the tree just
like the house plant in your windowsill wants to grow toward the Sun really bad
and no weight is going to stop it from reaching the light a process called
phototropism and whether plants are made to bend intentionally or not the effects
of phototropism can change the character of its tissues in trees the wood that
forms under the pressure of weight is called reaction wood or in conifers
compression wood it's created when the layer of tissue beneath the bark called
the cambium thickens below the source of the pressure to support the horizontal
weight of the tree in time the funny shape of the bend becomes permanent and
it leaves behind a record of oval or oblong instead of more circular rings in
the case of the dancing of forests local historians have no recollection of any
human manipulation to create this effect but there is another forest in Northwest
Poland called the crooked forest made of about 400 pine trees that all have
uniform 90-degree bends at base of their trunks the trees are all
the same age and they all bend north because of this uniformity many people
believe that this forest was manipulated by humans perhaps to grow uniquely
shaped wood for oxen yokes ship hulls or for furniture making that particular
theory maintains that the trees were shaped before 1930 but were abandoned
before they could be harvested with the outbreak of World War two but ultimately
even the cause of the crooked forests odd tree shapes remains a mystery and
they could also be attributed to some powerful force like strong winds heavy
snow and ice pack or even the result of one of my favourite theories being run
over by Nazi tanks as young trees during the war you know all this reminds us
that while scientific explanations of natural phenomena are usually pretty
cool and often necessary sometimes it's maybe a little bit cooler for it just to
be a mystery oh those twisty trees are very cool you
know what else would be cool if team trees successfully plants 20 million
trees in the next two months you know you want to be a part of that and you
can be if you go to team trees org to donate and speaking of cool things it's
fall here in the northern hemisphere which means the temperature is falling
and leafy trees are painting the landscape with beautiful yellows oranges
and reds if you've ever wondered why that happens we'll wonder no more
Michaels got the skinny on autumn leaves the changing leaves of autumn are really
awesome to look at but they're also a really striking example of nature taking
extreme measures to protect itself you're probably familiar with
photosynthesis it's the process plants use to turn carbon dioxide water and
light energy into sugars and oxygen and you probably also know that
photosynthesis depends on a pigment a colored compound called chlorophyll but
you may not realize that plants contain lots of other pigments as well some of
the most important are the carotenoids yellow orange and brown pigments they
give color to things like corn carrots pumpkins and sweet potatoes and the
anthocyanins which give red and purple color to cherries berries pomegranates
and red apples to name a few all of these pigments play an important role in
the plant's functions but there's usually far more chlorophyll in a plant
than anything else because photosynthesis is a plant's number-one
job however many trees are less active in the winter because they grow at
northern and southern latitudes that get less sunlight during those months these
trees are called deciduous from the Latin word that means
to fall off since deciduous trees don't do much photosynthesis in the winter it
doesn't really make sense to spend of energy maintaining big green leaves
so when the days get shorter and the temperature gets cooler they send less
of their limited resources to the leaves and start using what water and nutrients
they have to keep the rest of the tree alive the chlorophyll in the leaves
breaks down and the green color gradually goes away and when that
happens the other pigments which were there all the time are better able to
show off their colors before the leaves die entirely and fall off the tree so
the leaves aren't actually changing pigments they're just losing their
strong green pigment to reveal the other colors in the tissue after the tree
stops supply of food and water to the leaves all that's left is for the tree
to cut them off the tree forms a special layer of weakly bound cells near the
base of the Leafs stock then another layer of cells at the very bottom of the
stalk expands to push the leaf away eventually the leaf can be knocked off
easily even by a light wind and then it's your job to rake them up it's
pretty weird when you think about it that deciduous trees just discard huge
chunks of themselves every year to make it through to spring it's just like oh I
don't need these hands anymore I'll grow new ones in a few months so here's a
really young me to talk about the oldest trees in the world well when you started
talking about the oldest or biggest or almost any other superlative in nature
you're unlikely to find a cut and dry answer there are in fact two contenders
for oldest tree and it depends on how you define the term the oldest known
individual tree was discovered in 2012 in the white mountains of east central
California a great northern Bristlecone pine that's 5060 three years old that's
older than the pyramids here's a photo of a similar Bristlecone pine now it
doesn't look exactly alive and that may be part of its secret to success the
high cold arid climate of the White Mountains turns out to be the perfect
environment for fostering these ancient trees strangely the higher you go in
those mountains the older the trees get and several studies have suggested that
the longevity of pines there is directly related to how bad the growing
conditions are not only is the average rainfall in the White Mountains less
than 30 centimeters per year but most of the trees are growing on dolomite a type
of limestone in highly alkaline soil with very few nutrients but over time
bristlecones have adapted to this alkalinity unlike other trees which has
left them to grow without much if any competition
whistle guns also don't expend a lot of energy on their growth in a good year
the trees girth will increase by about 0.25 millimeters so instead they can
make the most of their meager resources as a result bristlecones tend to have a
pretty high proportion of dead to live wood but this has its advantages to
reducing respiration and water loss and it also helps that there aren't many
other trees around which makes it less likely that they'll fall victim to a
forest fire over the millennia researchers are able to determine these
trees precise age thanks to a process called cross dating which involves
taking core samples from both living and dead trees and then matching up the
patterns of their rings to come back with a timeline that goes back thousands
of years for our second contender we're going to Fish Lake National Forest in
south-central Utah here it lives a clonal colony of quaking aspen that may
very well be the oldest living thing on earth it's been named Pando and every
tree or stem as they're called in the half square kilometer colony is
genetically identical although no individual tree in the colony is older
than 200 years they're all connected by a single root system that's at least 80
thousand years old and possibly much older at over 6,000 metric tonnes it
also holds the distinction of being the heaviest known living organism on earth
so how did bando get so old clonal colonies like panda can reproduce either
by flowering and producing seeds or by producing a clone of themselves in this
case cloning just means extending the enormous network of roots enforcing a
new stem up through the ground because the heart of Pando is so far beneath the
ground it can't be killed by a forest fire recent studies have found that
Pando hasn't reproduced sexually in more than 10,000 years that's quite a dry
spell and not that surprising given its age that just means that it's up to the
root system to continue producing clones and letting the forest fires burn to
keep invading conifers at bay so thanks for the evolutionary tips world's oldest
trees I'll be sure to keep them in mind when I turned 5000 years old and want to
go for another five thousand 80,000 years just imagine what Pando has
witnessed in its lifetime it must feel like every new clone tree grows into a
totally different world and it's not just Pando of course lots of trees can
live for centuries if not millennia trees planted today could last long
after you and I are gone they'll be witness to the future we're creating
with the choices we make so let's make good choices for them and for us by
planting trees we can make the world a better place in all sorts of ways so I
hope you'll join us you can be part of team trees by donating at team trees org
every dollar donated plants a tree thanks to the Arbor Day Foundation
you