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Related question I've always had: does anyone know why trees on the west coast of the US and Canada grow so tall? You'll find the tallest species of fir (dougla

Related question I've always had: does anyone know why trees on the west coast of the US and Canada grow so tall? You'll find the tallest species of fir (douglas fir or if you're being pedantic the grand fir), pine (sugar pine), hemlock (western hemlock) and cedar (western red cedar) as well as the redwood species. Other places with similar climate grow tall trees but nearly so high. Is it something about the climate or are forests here just full of highly evolved specimens involved in an arms race?

OkayPhysicist 3y ago
There's a couple factors. A big one is that the North American Pacific coast was just one the last places to get significant settlement, so we didn't cut down all the big trees like we did elsewhere. Appalachia, for instance, used to have its share of giant trees. But those trees are still dwarfed by the sequoias. The West Coast's wet-dry spells lead to more forest fires, presenting another evolutionary pressure on tree height. Tall trees put their canopies far enough away from the flames that fires can sweep through the undergrowth without ever reaching them. There's also the fact that we have one of the most mild climates in the world: wild temperature fluctuations cause difficulties in getting water up tall trunks. Finally, there's the fog that keeps the canopies moist.
- asadotzler 3y ago
  Re: fog We've got two recent studies from around here (Santa Cruz mountains) showing that some of our coast redwoods get as much as 30% of their total water from fog. Perhaps relevant to these baby forests in the UK, I suspect that permanently depriving a younger coast redwood of the consistent fog would primarily compromise its photosynthesizing power limiting food production and stunting its growth. One other thing I've been thinking about but have no data for is a 30% reduction in water would likely also compromise the secondary metabolism that produces tannin and certain resins that can act as a sort of adhesive among fibrous cells and serve to reinforce the tree's wood from fracturing under wind stress or hits from falling neighbors. One of the redwood's keys to longevity is the wood's structure and makeup, both of which are influenced by those that secondary metabolism. Depriving an established tree of 30% of its total water consumption would likely lead to immediate crown thinning and might cause enough hydraulic system failure to result in something like apical tip die-back. That would not only lead to a serious loss in growth capability for all but those already near the height limits because they can pack on more total mass adding height and girth than girth alone. Loss of the terminal bud would also open the tip to rot which could eventually hollow out much of the tree. This is not uncommon among mature coast redwoods and the numbers of these hollow giants we find belie the true frequency as the hollowing weakens some of them enough so that wind or fire can more easily take them out. (Note: if you're not familiar with trees, don't worry. they are not made unhappy by the the hollowing. they live on their outsides and the insides are long dead.) We're seeing the die back here on the east side of the range where the trees redwoods that survived along valleys and creeks down into the foothills and even some into the flats have all lost the top 10% or so most likely from the droughts of the last 50 years. The upper parts of the eastern side and most of the west get the coastal fog to water them and the ones down lower on the east side do not in times of drought and we've had 20 of the last 50 years in moderate or severe drought.

OkayPhysicist 3y ago

There's a couple factors. A big one is that the North American Pacific coast was just one the last places to get significant settlement, so we didn't cut down all the big trees like we did elsewhere. Appalachia, for instance, used to have its share of giant trees. But those trees are still dwarfed by the sequoias. The West Coast's wet-dry spells lead to more forest fires, presenting another evolutionary pressure on tree height. Tall trees put their canopies far enough away from the flames that fires can sweep through the undergrowth without ever reaching them. There's also the fact that we have one of the most mild climates in the world: wild temperature fluctuations cause difficulties in getting water up tall trunks. Finally, there's the fog that keeps the canopies moist.

asadotzler 3y ago
Re: fog We've got two recent studies from around here (Santa Cruz mountains) showing that some of our coast redwoods get as much as 30% of their total water from fog. Perhaps relevant to these baby forests in the UK, I suspect that permanently depriving a younger coast redwood of the consistent fog would primarily compromise its photosynthesizing power limiting food production and stunting its growth. One other thing I've been thinking about but have no data for is a 30% reduction in water would likely also compromise the secondary metabolism that produces tannin and certain resins that can act as a sort of adhesive among fibrous cells and serve to reinforce the tree's wood from fracturing under wind stress or hits from falling neighbors. One of the redwood's keys to longevity is the wood's structure and makeup, both of which are influenced by those that secondary metabolism. Depriving an established tree of 30% of its total water consumption would likely lead to immediate crown thinning and might cause enough hydraulic system failure to result in something like apical tip die-back. That would not only lead to a serious loss in growth capability for all but those already near the height limits because they can pack on more total mass adding height and girth than girth alone. Loss of the terminal bud would also open the tip to rot which could eventually hollow out much of the tree. This is not uncommon among mature coast redwoods and the numbers of these hollow giants we find belie the true frequency as the hollowing weakens some of them enough so that wind or fire can more easily take them out. (Note: if you're not familiar with trees, don't worry. they are not made unhappy by the the hollowing. they live on their outsides and the insides are long dead.) We're seeing the die back here on the east side of the range where the trees redwoods that survived along valleys and creeks down into the foothills and even some into the flats have all lost the top 10% or so most likely from the droughts of the last 50 years. The upper parts of the eastern side and most of the west get the coastal fog to water them and the ones down lower on the east side do not in times of drought and we've had 20 of the last 50 years in moderate or severe drought.