why do leaves fall during autumn?
922462
Because they have died from the main tree, and during autumn there are strong winds that usually blow them off. Normally into our garden!!
884021
I like Katie's answer...very thorough...sounds like one of my lectures in my college Botany class...also.....due to chemical changes in the leaves and the slowing of the nutrient flow in the tree/leaves fall off due to the formation of an abscission layer of corky material  at the base of the leaf stem or petiole where it attaches to the tree twig. Cutting off water/food and it drys and weakens the attachment, then with a gust of wind shaking it loose to give us some work to rake them up.....oak trees hold tenaciously to their leaves and are often seen with some of their dry browned leaves on them throughout the winter......
867650
The fall colors are the "natural" color of the leaves.  The same leaves look green during the spring and summer, because they are filled with chlorophyll, which is itself green.  When the tree stops growing in the cooler months, it stops producing chorophyll, which dies off, leaving the reds, oranges and yellows that we see.\n\nHope this helps.  Good luck!!
167159
In Spring there is happiness all over around,Flowers r just blossoming everywhere ,Birds r chattering,Every1 is happy this atmosphere also makes u to be remain happy.Hey Thoughtful may i ask u a question whats ur opinion about Autumn?
789781
they are dead.\n\njust like dead tree limbs, they fall off in time.\nit's called gravity.\n\nthe tree goes dormant, the leaves are not needed any longer for this year.\n\nthe leaves are dead and gravity will pull them to the ground
864820
Depends on the plant species.  Some trees shed their leaves in fall and don't grow them back until the next spring.  Anyway you're thinking wayyyyyyyyy too much about plants at a lunar base.  Anything brought there would most likely be stuck under some kind lamp to simulate light conditions on the earth, so your problem is moot.
534312
In the spring and summer months when the weather patterns are unstable.  The second answer would be at night.
986566
Hello friend.. \nHope you have heard of chlorophyll and other colouring (pigments) agents naturally present in plant leaves.Chlorophyll is the chief chemical helping reactions that finally end up in production of starchy food in plants. \nThese chlorophylls themselves break down and  are being continually used up in the food-manufacturing process. \nBut while the plant grows the plant resynthesizes this pigment and  leaves seem green.\nBy the end of  summer, cells called cork cells, which are degenerate products, get accumulated in the base of the leaf-stump. This results in blockage of water transport to leaves through their "veins".  Chlorophyll from then on degenerates and breaks down. \n    In the fall (autumn as we call it here), seasonal changes slow down the rate of  chlorophyll-synthesis.\nCarotenoids which are another group of pigments present in leaves become clearly visible through these leaves devoid of Chlorophyll. Light is not needed in order for a plant to produce carotenoids, therefore these pigments are always present in a living plant. Aspen, Black Cherry, Sycamore,  Maple and  Poplar are some of the trees famous for their pictureque beauty in Autumn. Carotenoids appear in colours ranging from Brown or red to yellow depending on its concentration in these leaves.  Examples of carotenoids found in leaves include lycopene, which is red, and xanthophyll, which is yellow.  When found naturally, carotenoids give colour to carrots, beetroot, and a number of plant and animal produces like mango, banana egg yolks etc.\nBesides these natural Carotenoids, there are a group of pigments called Flavanoids that appear in the leaves only during autumn. Examples of flavonoids include flavone and flavol, which are yellow, and the anthocyanins, which may be red, blue, or purple, depending on pH (strawberry, apple,  cherry etc..)Anthocyanins are the chief agents among these flavanoids. They are a result of degeneration of sugar moieties in leaves. In autumn, as a plan to prevent losing precious minerals, ions and vitamin-enzymes through falling leaves, these chemicals are transported into the trunk/stem of the plant. But Carbohydrates, being complex molecules aren't transpoted to the main stem/trunk. The transport of ions back into stem causes a  fall in the phosphate concentration in the leaves,which in turn triggers production of Anthocyanins. This process is dependent on physical influences like soil-acidity and brightness of Sun light. Brighter, the days, brighter the colour of autumn leaves and vice versa.\nLeaves containing primarily anthocyanins will appear red. Leaves with good amounts of both anthocyanins and carotenoids will appear orange. Leaves with carotenoids but little or no anthocyanins will appear yellow. In the absence of these pigments, other plant chemicals also can affect leaf color. An example includes tannins, which are responsible for the brownish color of some Oak leaves. \nHope that clears your doubt.\nbye..
144172
Fall starts with the Autumnal (fall) Equinox. This is the time when the sun is directly over the equator and headed toward being above the hemisphere that we are judging seasons by. For the Northern Hemisphere, the Autumnal Equinox begins anytime between the 22nd and the 24th of September, the exact day depending on the year. For the Southern Hemisphere, the Autumnal Equinox begins anytime between the 19th and the 21st of March, again depending on the year.
129451
Monsoon season cause it was always raining!!\nSeriously.. I would guess late fall early winter.
973799
well..start with describing it..colors smells.. sensations (wind ) sounds..\n\nthen just write what fall rminds you of.....\nwhere i live.. it's minus 30 celsius withou wind.. so for me my fall is over its kind of hard to imagine when the tree is up and windows are frosted right over..
887479
since plants are mainly composed of chlorophyll and chlorophyll is green then the plants tend to be green. but they also have other colors such as red or yellow. thats why when trees shed their leaves in the fall what they are really doing is killing off the chlorophyll allowing the other colors to come out and be noticed.
385744
I'm guessing....\n\nIf I remember my high school biology, guard cells sit around the stomata on the underside of most plant leaves.  Plants open up their stomata to improve gas exchange (they want to take in CO2 and get rid of O2).  They typically only do this at night because they want to limit their water loss through the stomata.  If the chloroplasts in guard cells have a purpose other than photosynthesis, it might be that they are acting as sensors so that the guard cells will be able to tell when it is nighttime (time to open up the stomata!).
709391
Many animals mate in the fall to reproduce in the spring when temperatures are moderate and food is abundant.  This is triggered by day-length.  This increases the likely-hood that the offspring will survive.
522653
It could get confused, but only for one season.\n\nTrees drop there leaves based on declining day length, and it takes many weeks of exposure for them to be able to 'read' the time correctly. If you took a tree across the equator it could well suffer from the seasonal change.\n\nHowever if it survived then the following year it would have no problem at all. It would drop its leaves when the days started drawing in in Autumn just like it did back home.\n\n\nTrees don't have some mystic link with the place where they germinated. They just read the signals from the place where they are growing.
336425
The autumnal equinox (or fall equinox) marks the beginning of astronomical autumn. It occurs during the month of September in the Northern Hemisphere, and during March in the Southern Hemisphere. In Chinese culture it marks the middle of autumn. At the same moment that the autumnal equinox occurs in one hemisphere, it is the time of the vernal equinox in the other hemisphere.\n\nIn 2006, the autumnal equinox of the Northern Hemisphere falls on September 23 at 04:03 UTC[1][2]. In the Southern Hemisphere the equinox occurs at 18:26 UTC on 20 March.
851355
Spring & Fall - Spring because it shows the 'rebirth' of all the trees and flowers, gives us something to look forward to in the summer.  Fall because of the beautiful colours God paints on the trees, gives us the knowledge that after winter is over, there will be another 'rebirth'.