WEBVTT - Why Don't Evergreen Trees Lose Their Needles? 0:00:01.920 --> 0:00:06.840 Welcome to brain Stuff production of iHeart Radio, Hey brain 0:00:06.880 --> 0:00:10.920 Stuff Lauren vogebam here. Evergreen trees seem to thrive during 0:00:10.960 --> 0:00:14.560 the colder months, steadfastly holding onto their brightly colored, needle 0:00:14.600 --> 0:00:18.200 like leaves as temperatures plummet, bringing welcome color and contrast 0:00:18.320 --> 0:00:21.959 to snowy landscapes. On the other hand, the wide and 0:00:22.079 --> 0:00:26.000 flat leaves of their deciduous counterparts transformed into brilliant shades 0:00:26.040 --> 0:00:28.360 of red, orange and gold during the chili and dry 0:00:28.440 --> 0:00:31.320 days of fall and early winter, only to eventually shed 0:00:31.720 --> 0:00:36.680 Their branches will remain barren until spring. So why are evergreens, 0:00:36.720 --> 0:00:41.120 which include many, but not all, conniferous trees such as pines, furs, junipers, 0:00:41.159 --> 0:00:45.000 and spruces immune to seasonal leaf changes in shedding, while 0:00:45.120 --> 0:00:48.519 species of deciduous trees like aspens, birch, cherry, oak, and 0:00:48.600 --> 0:00:52.440 maple aren't. It mostly comes down to a little thing 0:00:52.560 --> 0:00:56.040 you might have learned about in biology class called photosynthesis. 0:00:57.160 --> 0:01:00.320 Both deciduous and evergreen trees use energy from the sun 0:01:00.360 --> 0:01:03.120 and water from the ground to turn carbon dioxide in 0:01:03.160 --> 0:01:06.960 the air into food. The difference is that shorter days 0:01:07.040 --> 0:01:09.840 brings less sun during the fall and winter, and that 0:01:09.880 --> 0:01:14.480 translates into less energy, so deciduous trees bearing broad flat 0:01:14.560 --> 0:01:17.400 leaves go dormant or into a sort of hibernation mode, 0:01:17.600 --> 0:01:19.880 and shed their leaves to help them conserve water and 0:01:19.920 --> 0:01:22.680 stay alive until spring arrives and new leaves grow from 0:01:22.720 --> 0:01:27.640 new buds. Evergreens, meanwhile, boast needles that are actually tightly 0:01:27.760 --> 0:01:31.039 rolled leaves, and the low surface area of this shape 0:01:31.080 --> 0:01:34.679 helps the needles conserve water throughout the fallen winter. A 0:01:34.720 --> 0:01:37.200 waxy coating on the needles also helps keep water from 0:01:37.200 --> 0:01:41.800 evaporating compared with broad, delicate leaves. These dense, waxy needles 0:01:41.840 --> 0:01:44.839 resist cold and stay moist, which keeps them green throughout 0:01:44.840 --> 0:01:49.240 the winter. But evergreens actually do shed their needles, just 0:01:49.360 --> 0:01:52.520 not all at once. As needles age, they turn yellow 0:01:52.520 --> 0:01:55.040 brown or a reddish tan and will fall from the tree, 0:01:55.280 --> 0:01:58.040 but usually only a handful at a time. The trees 0:01:58.040 --> 0:02:00.640 are constantly growing new needles, so they can stay green 0:02:00.760 --> 0:02:05.200 year round. Evergreens greater leaf longevity means they can survive 0:02:05.240 --> 0:02:08.520 in environments that don't work for their deciduous cousins. In fact, 0:02:08.639 --> 0:02:12.640 evergreens can be found on every continent except Antarctica. The 0:02:12.639 --> 0:02:15.640 bottom line is that Although those colorful deciduous trees attract 0:02:15.720 --> 0:02:18.840 their share of seasonal leaf peepers, trees that stay green 0:02:18.919 --> 0:02:21.480 year round add character to people's yards during the fall 0:02:21.520 --> 0:02:24.280 and winter, offer shelter to birds and small animals when 0:02:24.320 --> 0:02:27.120 the winter is cold, and many species are dense enough 0:02:27.160 --> 0:02:35.280 to serve as wind breaks and privacy screens. Today's episode 0:02:35.320 --> 0:02:37.639 was written by Windy Bowman and produced by Tyler Clang. 0:02:37.960 --> 0:02:40.560 The brain Stuff is production of iHeart Radious How Stuff Works. 0:02:40.880 --> 0:02:42.920 For more in this and lots of other evergreen topics, 0:02:43.000 --> 0:02:45.679 visit our home planet, how stuff Works dot com. And 0:02:45.760 --> 0:02:47.760 for more podcasts from my heart Radio, you can visit 0:02:47.800 --> 0:02:50.400 the iHeart Radio app, Apple Podcasts, or wherever you listen 0:02:50.440 --> 0:02:51.360 to your favorite shows.