How did deciduous trees evolve?

Question

How could this happen if evolution takes millions of years? Any genuine scientific explanation would be appreciated.

Answer 1

Trees growing in habitats that lack marked seasons still show characters usually considered as adaptations to temperate climates. The trees will grow in flushes forming resting buds between successive flushes but this has no correlation to external factors. These growth rhythms are timed internal progressions but are not based on an annual or seasonal fluctuation.
http://links.jstor.org/sici?sici=0002-9122%28196910%2956%3A9%3C1033%3AUSGPIA%3E2.0.CO%3B2-F&size=LARGE&origin=JSTOR-enlargePage
Given a base of growth cycles the next step was adapting the canopy loss to external factors of seasonal variation. Plants already responded to light in reversible ways. Stomata are co-regulated with light and water stress to allow gas exchanges for photosynthesis.
Abscisic acid (ABA) stimulates the closure of stomata (water stress brings about an increase in ABA synthesis). Mutation in the expression of a factor like ABA may have been one of many steps that shifted the internal regulation of growth rhythms to external regulation. Now ABA is known to inhibit shoot growth but does not have as much affect on roots or may even promote growth of roots even in dormancy. Also ABA is known to play a role in the induction and maintenance of dormancy.
Plants, faced with ever chillier seasonal variations, suffered slowed growth but those with high rates of photosynthesis able to produce an excess had more to live on for the, initially brief, slack periods. Selection favored those high photosynthetic plants. Next a mutation in regulation appeared that tied the canopy regeneration to a seasonal trigger. Once the plants rhythms were seasonally regulated further mutations just refined the responses.
Now temperate trees enter dormancy when the whole tree carbon balance shifts. For growth to continue there must be more photosynthate (carbohydrate) made than is used to support both the tree's basic functions including below ground and in the trees woody parts plus reserves for spring bud break. With less light and a decrease in temperature to between 5 & 10 C the tree struggles to support foliage. So there is a break-even point between available light energy and temperature that predicts actual canopy loss trigger point but the plant continues to live and basal respiration continues to support this minimal function.
Several factors may have further positive and negative selection impacts on leaf form & timing. Dropped leaves shed insect infestations to the leaf litter for soil invertebrates to consume.
Shedding leaves avoids the weight of ice & snow that might build up on the broad leaves adding incredible weight that could lead to limbs breaking and other damage to the tree.

Later bud break may be selected by herbivorous larvae and late freezes. Very early bud break will be damaged by heavy larvae populations before their predators also hatch as well as rare late freezes. If the larvae hatch first the tree suffers less because the larvae can't chew the bud scales to get the tender leaves inside. The larvae in turn are prey so can't delay their hatch to coincide with late opening leaves or they become easy prey.
Some trees, like oak and beech, do not shed their dead leaves until spring. This may protect low branches from foraging deer. The withered, non-nutritious leaves may deter deer from feeding on the tasty live twigs and buds under the dry leaf layer. Another thought is the leaves are frost protection in winter.

Answer 2

Just like all living things. With the sharing of genetic material. DNA. Granted since trees life span is longer then animals they evolve slower but plants were on land before animals this giving them more time to adapted to the various environments that are found on the surface of the earth. So how did deciduous trees evolve? Thru adaptations to their environment.

Answer 3

Deciduous trees evolved much as most of living things have on Earth. Yes, long time spans are required. Science has a genuine explanation.

"Life on Earth continued to evolve, and in the late Paleozoic, gymnosperms appeared. By the Triassic Period (245-208 mya), gymnosperms dominated the Earth's forests. In the Cretaceous Period (144-65m mya), the first flowering plants (angiosperms) appeared."
http://www.ucmp.berkeley.edu/exhibits/biomes/forests.php

Ecosystem Evolution
http://www.encyclopedia.chicagohistory.org/pages/410.html

Genome duplication in angiosperm evolution
http://darwin.eeb.uconn.edu/uncommon-ground/archives/2007/09/genome-duplicat.html

GLAZE ICE, CAUSE OF DECIDUOUS FORESTS
http://charles_w.tripod.com/glaze.html

Answer 4

Animals evolved into two groups: vertebrates and invertebrates. Vertebrates evolved into two groups: those that lay land eggs and those that don't. Mammals evolved into two groups: egg-layers and non-egg layers. Non-egg layers evolved into two groups: marsupials and placentals. Monkeys evolved into two groups: new world monkeys and old-world monkeys. Other plants evolved into two groups: vascular plants and non-vascular plants. Vascular plants evolved into two groups: seed plants and those that don't have seeds. Seed plants evolved into two groups: naked seeds and covered seeds. Flowers evolved into two groups: monocots and dicots. Most anything can be divided into two groups, so your question has more to do with why people like to divide things into two groups. (Even when there is a range of intermediates.) Another way to look at it is, any time a new feature evolves, there will be those with it and those without it, so there are always two groups. So trees either lose their leaves or not, so (surprise) you have two groups. But not all trees would fit neatly into your two groups--what about larch and bald cypress, which are deciduous conifers? But deciduous and conifer are not what we call "natural" groups (grouped by evolutionary relationships). Some divisions into two groups have more significance than others, and we can easily classify things into any number of groups. One could argue that trees evolved into three main groups: Ginkgo, gymnosperms and angiosperms. So the short answer is, trees didn't evolve differently than anything else.

Answer 5

Deciduous plants, including trees, shrubs and herbaceous perennials are those that lose all of their leaves for part of the year. This process is called abscission.
Forests with a majority of tree species that lose their foliage at the end of the typical growing season are called deciduous forests. These forests have distinctive ecosystems, understory growth, and soil dynamics.
1. Temperate deciduous forest biomes - have formed under climatic conditions which have great seasonable temperature variability with growth occurring during warm summers and leaf drop in fall and dormancy during cold winters.They are impacted greatly by the seasonality of their climate, mainly temperature and precipitation rates
2.Tropical and semi tropical deciduous forest biomes have developed in response not to seasonal temperature variations but to seasonal rainfall patterns. During prolonged dry periods the foliage is dropped to conserve water and prevent death from drought.

Answer 6

From chapter Ecosystem development of this site:
http://www.encyclopedia.chicagohistory.org/pages/410.html:
"The spruce forest lasted for about 1,000 years, until about 15,000 years ago, when climate warmed and deciduous trees became more abundant, including balsam poplar (Populus balsamifera), black ash (Fraxinus nigra), and ironwood (Ostrya virginiana or Carpinus caroliniana). Balsam fir (Abies balsamea) also was present, as was spruce, although not as abundantly as before.
About 13,000 years ago climate apparently cooled again, and spruce became more abundant and black ash less common. During this time birch (Betula) and alder (Alnus) were also important components of the vegetation."

So the changing of climate initialized the adaption to cold winters and warm summers. In winter there is not enough light for effective photosynthesis like in summer and the large surface of all those leaves usefull in summer for better photosynthesis provides storms and snow with a target. Therefore leaf shedding developed.

here some more info:
http://www.gardenbanter.co.uk/archive/index.php/t-36486.html