Hi All, I’ll try to make this as clear as I can. I understand that temperate trees require a period of “rest†over the winter in order to remain healthy. For deciduas trees this involves dropping of leaves and for evergreen it’s “chilling out†for a few months (sorry for the pun). Now, I understand the need to shed leaves as a form of waste disposal, but what, from a metabolic stand point, is meant by “resting� Plants don’t strain muscles and organs in the same way as animals. Nor do they use their rest period to regenerate as animals do. So, what essential process is it that takes place during the “winter rest†period of temperate trees? Thanks M.
Interesting question, and I don't know the exact answer, but I would assume the main reason plants need to rest is that there is very little energy available for active growth in the short days of winter. I guess some plants respond to the shortening daylength and cooler temperature and that this triggers them to manufacture chemicals that affect their future growth in the next season. I have read of studies where apples and other temperate fruit trees that require winter chill have been tricked into dormancy in tropical areas, simply by picking all the leaves off the plants and that this resulted in successful fruiting. That seems odd to me.
Well, I can to this question through bonsai. It relates to how one has a hard time growing temperate plants in the tropics and how you can't keep temperate plants indoors. This seems a little suspect to me. "Leaf Pruning" as it called in bonsai is a technique used to increase "twigginess" and reduce leaf size. It is very draining on a tree, quite the opposite of a rest. M.
I believe the rest period for deciduous trees was more to do with the ground getting frozen and there not being any water available, a drought responce more than anything else.
No it's not about the ground freezing - many places that get cold enough to induce dormancy in plants or trees don't have frozen ground and lots of water is available. It's about the light (intensity and number of hours) along with cooling temps.
I'd suspect it is mainly about ensuring the plant does not produce tender new growth during the period when frosts might be expected to occur.
I agree with you Michael, however how do you explain, new growth in spring and late spring frosts....actually thinking about it most of our natives are late to leaf its mostly imports that are hit by late frosts..so i guess i just answered my own question. wow Rima you say that with such conviction... this would be the trigger mechanism letting the plant know the winter is coming with the potential for frozen ground....all the evergreens from very cold climates i can think of, have an adaptation to drought...so i say your wrong, and i stand by what i said its a drought defence.
from the department of energy USA first site i found from the second in the list. http://www.alongtheway.org/teachers/teachers.html from MSN encarta
Yep - non-native plants adapted to different climates will not have evolved to "know" what can be expected in the climate where it has been planted. Also, like all living things, a plant will always "push its luck" to maximise its competitive edge - there is a balance in that waiting until after the very last spring frost means missing out on a lot of good growing weather, resulting in slower growth and a reduced ability to compete with other plants. However, a plant that takes the risk of leafing out earlier gets the benefit of early good weather, so can grow faster in most years, except those few when it gets hit by an unusual late frost (which may only do temporary damage, not kill it). Up to a point, this plant will win over competing plants.
There is indeed a whole host of reasons/advantages for a tree entering into winter dormancy. My initial question, however, related more to what is happening during that dormancy. As said earlier, there is much talk in bonsai about people wanting to keep temperate trees indoors or in warm climates, and aside from light (which can, at some $$$, be dealt with artificially) the lack of a significantly cold period poses a serious danger to the tree. So much so that some people, in Florida for example, give a false winter to their temperate trees by means of an old refrigerator. The claim is that if temperate trees are denied a rest they become exhausted and loose their vigor. Death is the unavoidable consequence. Now, rather than anthropomorphizing trees by giving them exhaustion and the need to rest, I agree whole heatedly with the more scientific explanations given here. Which is why I asked the question here and not on a bonsai forum. But the question remains, should a tree be denied dormancy in a warm climate free from frost/frozen ground, what kills the tree? This is of coarse assuming that all Ive read about it is not just myth/folk wisdom, which it may be but I strongly doubt it. M.
If a tree is in a climate where the ground doesn't 'freeze', it still doesn't mean it's a 'warm' climate, just something that more often doesn't go below freezing much (except for a few hours on a few days in late Jan.) if at all, but still cools off (e.g. to around 40 Fahr.) compared to what it's like in summer, and the shorter daylight hours plus the cooler temps give it the dormancy it needs, though it may well just go d. by itself as some indoor plants will do (take a break for a few wks during which they need much less water, stop growing, possibly lose leaves, etc.) because they're genetically programmed to do it - which is why there's huge arguments in bonsai forums about keeping certain trees (Chinese elms, for instance) indoors vs out, and the pros and cons of it if they're kept indoors for years, but it's interesting as they may still lose leaves, need less water, etc. over those times - in relatively warm places under supplementary lighting 14 hrs/day.
