Why West Coast trees are much taller

Discussion of general forest ecology concepts and of forest management practices.

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Re: Why West Coast trees are much taller

Post by edfrank » Wed May 09, 2012 5:03 pm


One consideration here should be that some species of tree needs to be the tallest. The other consideration is that the two tallest tree areas are in the pacific northwest and in the New Zealand/Australia, both temperate rainforest. So comparing eastern and western NA species is not comparing like species to like species, but different species that evolved from different root species in different climates. Both Eucalypts and sequoia grow tall in other climates than their native home. This seems to suggest an evolutionary/genetic factor is responsible for their height rather than purely climatic or historical factors. Since they both have their origin in similar climates there must be some evolutionary factor that caused them to evolve as a taller species in their native areas that was not present for trees growing in areas with different climates. It could simply be the parent species genetic characteristics that accounts for the difference, but discounting that for now, lets consider climate. So the question should not be why the climate allows them to grow so tall presently, because they don't need need that climate to grow tall, but why they evolved that characteristic and why climate played a role in that evolution.

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Re: Why West Coast trees are much taller

Post by Rand » Thu May 10, 2012 12:13 pm

Some of the ideas I've heard bandied about (It might have been this group, I forget) are that the humid summers in the east promote more decay than the dry summers that prevail out west, making it structurally difficult to grow tall and/or shortening the life of the trees. Same thing with intense winds from derechos/intense thunderstorms.

Also a recent news item reports that the Smokey Mountains region gets 50-60% of its precipitation in the form of mist/fog/light rain:
Most people don't realize, Barros says, the southern Appalachians have the highest annual rainfall of the southeastern United States, as much as humid Florida. It rains on average 54 inches per year in the Everglades, about 50 inches in North Carolina, and about 58 to 60 inches a year in the Appalachians. The Mountains contribute to the enhanced weather: moist air bumps into them as it moves over the land, and when it rises, it cools and can't hold on to its water vapor which condensates and forms clouds. This leads to as much rain falling in the Appalachians as is delivered to the coast by hurricanes like Francis or Ivan. And in years without a hurricane or tropical storm to factor in, it rains nearly the same amount, on average, every month in the southern Appalachians. Forty percent in summer and up to 60 to 70 percent in winter of all that rainfall is very light rainfall.

That's why the Smokies are called the Smokies, Dr. Barros explains. "There's always a little bit of fog and low level clouds and there's always a little bit of rain going on in the air." Until her team measured it, scientists didn't know how important light rain is to the region. At all times of the day, light rainfall is the dominant type of precipitation. And because light rainfall is the most reliable and most frequent form of rainfall in the region, Barros says, contributing 50 to 60 percent of total precipitation over a year, it governs the regional water cycle. Light rain is no less than the lifeline of freshwater resources for the landscape's ecosystems. This is probably also true in mountainous regions everywhere, Barros' finds, which carries big implications for communities worldwide.
http://pmm.nasa.gov/featured-articles/l ... in-smokies

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Re: Why West Coast trees are much taller

Post by Don » Fri May 11, 2012 2:34 am

All very interesting speculation, which is all that I can add too...geographically, California is mostly one long valley running 400-500 miles in north/south orientation. That places to mountain ranges in the way of weather from the Pacific Ocean. The Coast ranges get exceptional (well, relative to California) amounts of rain (up to 220 inches per year) precipitation, but do so up to a maximum elevation somewhere around 5000' (off the top of my head). The next mountain range is the Sierra Nevadas, which has interesting vegetation banding running it's entire length. While the elevation range of each of the half dozen forest types/communities varies with latitude (higher at lower latitudes), the patterning is unmistakable.

With the average Central Valley elevation around 1000' (again a guess), and the Sierras ranging from more than 14,000 in the South, and up to 7,000 in the North, the opportunity for topographic niches for each and every species might be the basis for optimized growth (vertical/horizontal). The western slope of the Sierras rather gradually increase from 1,000' to well over 10,000' in about 50 miles, before decreasing to 3,000-4,000' feet in less than 5 miles.

Further north, Oregon and Washington have a much different geography, other than having a coastal range that runs across much of the two states before dropping into Great Basin country. Where California has pieces of temperate rain forests, Oregon and Washington have significantly more temperate rainforest ecosystems, and provided for some of the tallest trees, historically known.

All I know is, it's not just one thing that makes one area have taller trees...it's many things, and it's also chronologically determined too, in the sense that the timing of climate regime changes and forest condition classes have in places created "perfect storms", where all the conditions were right, and in the right sequence, all the disturbances synergistically supporting optimum growth potentials.

For god's sake, let's keep those that we've still got!
Don Bertolette - President/Moderator, WNTS BBS
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