treeline in NE,hey this is beginners forum.

7:05 a.m. on November 5, 2011 (EDT)
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quick question,why is treeline at ~4500-5000' in NE? and so much higher everywhere else that i know of,what atmospheric conditions determine treeline?

8:14 a.m. on November 5, 2011 (EDT)
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That is an extremely complex answer to question ;)

The short version is that treeline is determined by a combination of factors, and results when those factors create environmental conditions that are to harsh for trees to grow. 

In the Whites of NH for example, the treeline can be quite low because the atmospheric conditions and seasonal flow patterns drop the Jet Stream right on top of the mountains there. This produces some of the nastiest weather on earth, and keeps the treeline low. 

9:46 a.m. on November 5, 2011 (EDT)
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thanx gonzan,i know at the s. end of at same alt. there's plenty of trees,gotta be temp.,oxygen is same i think its based solely on elevation/gravity,gas weight.summits in smokys' grow almost year round at same elevation.there must be some tough trees out west,what's treeline out west?

8:34 p.m. on November 5, 2011 (EDT)
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Growth season partially determine what trees grow where.  Growth season is a combination of factors, some described by others.  Without getting too technical, trees have two basic modes of existence: actve growth periods, and periods where they produce insufficient nutrients to sustain life over a long period of time.  When the right conditions exist trees flourish and grow, producing more nutrients than required just to get by.  But when conditions fall below a threshold required to sustain tree life, and those conditions last a long enough duration, trees are unable to exist in such environs.  Thus length of growth season is one reason why tree line varies from region to region.

Actually there are many tree lines on any tall mountain.  Each specie of tree requires a different set of conditions to flourish.  Some of these conditions, for example temperature, and the mix and concentration of gases in the air are affected by altitude.  Thus the astute observer will notice certain species of trees do not grow at higher elevations, such as aspens and cottonwoods.  These tree lines are less apparent because other species better adapted to higher elevations are mixed in this zone and provide greenery beyond these lower tree lines.  To our perceptions these lower level divides in growth do not represent tree lines as such, but that is what the tree line is; the upper level which trees can flourish.  It just happens to be that  higher up only a few species can flourish under those conditions, so when their limit is reach, nothing is left to extend the green belt.

You ask why the tree line is so low in the north east.  It is not the lowest tree line by any means; for example no trees grow in most of Death Valley, so the tree line in many parts of the monument are at or below sea level.  The point is the tree line fluctuates by region, based on the growth needs of trees, and a particular geography's combined factors to support life.  My guess the poor soils of the mountains in the North East, coupled by prolonged winters and a short growth season make for too harsh an environment for trees to grow and reproduce.

Ed

1:29 a.m. on November 6, 2011 (EST)
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In Colorado the tree line is between 11,500 and 12,300 feet depending upon where you are in the state.  Tree line seems to get lower and lower the closer you get to the coast(s) depending upon many factors as Ed & gonzan explains above.

2:29 a.m. on November 6, 2011 (EST)
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Here in central Norway it is somewhere in the 600-700 m range (2000-2300 feet), but very variable and influenced by a long history of sheep grazing. Birch, not a conifer, is the treeline species. I am a plant ecophysiologist but in this case I'm less inclined to provide a hard answer, because the jury is still out (and has been for a century or so) on this one -- the causes of treelines and mechanisms that limit tree growth and reproduction there are perennial topics in plant ecology and physiology, and still not completely settled. I think the main factors are  a short, cold growing season that limits productivity, combined with the effects of pruning by wind-blown snow and ice. Both of these depend not only on altitude and latitude but regional and local climate, for example proximity to the ocean, the jet stream, storm tracks. Locally other factors, such as grazing (here), soil development, or for another example reproductive dynamics (silver beech treelines in NZ) may come into play. 

6:56 p.m. on November 6, 2011 (EST)
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The tree line is the edge of the habitat at which trees are capable of growing. Beyond the tree line, they are unable to grow because of inappropriate environmental conditions (usually cold temperatures or lack of moisture).

7:38 a.m. on November 11, 2011 (EST)
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Combine Ed and Gonzan's answer.  

it is true that a variety of factors influence where trees can grow on mountains.  latitude, for example, has some influence, which explains why high mountains in Mexico have a higher treeline than the rockies or the tetons.  but, the tetons and New Hampshire's white mountains are on roughly the same latitude.  wind also has some influence, but the rockies and tetons have pretty nasty, snowy weather too.   

the controlling factor in this case is the type of weather that mountains experience during the summer, what Ed was driving at.  the mountain ranges in the middle of the country (rockies, tetons) are larger than those on the east coast and experience warmer, drier summer weather than the east coast.  the cooler, cloudier summer weather in the white mountains shortens the period of time that trees have to emerge, grow, and spread seeds to reproduce the cycle.  

6:20 p.m. on November 15, 2011 (EST)
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