Tall trees

I am a notorious fan of them after they die, but here consider the living ones.

Global forest exceeds 40 million km^2 which is a lot. May have been almost double that Before Agriculture, but y'know, priorities. Even so, it seems that living trees still exceed 3 trillion in number.

Too many topics here, but one has nagged me, related to height. With earth gravity and water capillary tension being as they are, maximum tree height is below 120 meters. Can't get water up any higher, and without water, forget about photosynthesis. Widely across earth forests, you find lots of trees between 40 to 70 meters tall. But here's the odd thing: only two species grow 100 meters tall. That is 2 among 60,000 species. They are outliers by any definition.

Those two, a Sequoia and a Eucalyptus, could not be more different. One conifer and one broad-leaved. One slow growing and the other very fast. They are in very different climates and 'fire regimes'. This really nags. The subject has been reviewed by Ng (I can't pronounce his name either) who went through many possible explanations and finally said "I do not know".

Neither grows in tropical forests, having very high species diversity. This could be a clue. After all, trees don't grow in 'the world' they grow in one place surrounded by near neighbors. Let's say you are a tree. If your neighborhood is of many different species (each with their own growth plan), you can grow a little bit taller and get the 'light advantage'. Grow much taller instead and the next big wind storm will punish your adventure (you live long, so there will be a wind storm). Or, suppose that you are surrounded by neighbors of your own species with the same growth plan. If you 'break ranks' and grow just a bit taller, you get the light advantage. You produce more seeds and next generation of trees is more like you. Lather, rinse, repeat over evolutionary time.

Difficult to test this idea, because trees live longer than scientists (much longer than research projects). It's a hard paper to write. But perhaps a new ecology/evolutionary idea lurks here. Evolution, fundamentally, is about how much the next generation differs from the current (and can they 'get away' with it?). Ecology is concerned with how well you perform, compared to your neighbors. Tropics (including forests) obviously have highest species diversity with niches narrowly sliced and filled. It is heretical to suggest that lower-diversity systems could 'breed' higher structural diversity. Yet that is what nags.

Trees don't lie. But what are they 'saying'?

 

Sequoia sempervirens and Eucalyptus regnans are those two exceptional species. Both magnetically attract chain$aw$, and inhabit small fractions of their former ranges. You are in the one; maybe others from Victoria (AUS) or Tasmania would post their ideas as well?

 

Yeah, OK, a lot of forests get cut. My latest calculations on global fates of wood:

Harvest (bioenergy, paper, construction) - 1 petagram carbon per year
Wildfire - 2.5 Pg C y-1
Decomposition in situ - 10 Pg C y-1

This is not a call for more chainsawing; just putting the numbers in perspective. Other than in a manuscript in review they have not been assembled before.

Harvest is probably an underestimate because not all gets reported. But nothing above 1.5 seems realistic. Wildfire estimates fully range from 1.9 to 4, but as they are now done by look-down satellites heat signature, there is no under reporting (lying) going on. Decomposition in based on lots of publications and some simple modeling.

For now I just want to talk about three interesting post-wildfire aspects. Some tasty morel (mushrooms) only grow in that environment. Alaskan forests have been Burny McBurnface recently and the morel hunters there are really busy.

Can't recall if I mentioned jewel beetles here before. Some of them only lay eggs in charred wood, and they can locate this resource from >100 km away. Apparently they are detecting longwave infrared just as those satellites do.

Surely you have heard of conifer trees whose seeds only germinate after fires.

Even burned forests can be interesting. I appreciate fine woods as much as the next fella. And decomposition in situ, well don't get me started...

Point is that while living trees are perfectly fascinating, it does not end when they finally surrender to gravity.

 

We can see that any amount taller accomplishes the 'goal' (solar pre emption). Too much height in your neighborhood quickly increases wind damage potential. All guesswork is constrained because we don't know whether tree height is under genetic control, or simply physics (engineering) pruning pieces that extend into energetic environments above the local canopy.

The vast knowledge recently obtained about plant metabolic genetic pathways comes from a plant that is 'big' at 25 cm. It does not teach much about 'how to be a tree'.

Darwinian evolution had a major flaw, and it wasn't related to creation + 6000 years. It was thus: every cell in your body has the same genome, but they develop into very different things. Skin, bone, liver, why make a long list? This is epigenetics, new cells develop to conform with what is going on in their neighborhood. We 'get that' now, and evolutionary theory has been revised.

For all Darwin's genius, it is fascinating that he missed this thing staring him in the face.

Trees are amazing things; they can make completely different leaves near the ground and way up high. Their immune systems are as different from ours as it may be possible to imagine. Sad to say, how they 'negotiate' canopy tops is far down any list of fundable research questions.

 

Students come with ideas about what is 'the niche' of some tree species. Find a window and throw that idea out! Tree seeds germinate widely on forest floors, where the few surviving 'do something'. Those grow into the subcanopy where the fewer surviving do something else. Those grow into the canopy where the still fewer surviving do something else entirely different. Trees have no niche. Those final few survivors persisted through a series of very different environmental challenges. Surviving adult trees producing seeds are somewhere, and we map those spots in forest plots across the world. It is not their niche; it is at most the places where not all have previously died.

A lot we don't know about trees, especially in tropics where very many species persist. I am making my peace with the idea that we might never know.

 

I think Sitka spruce and Giant Sequoia are the next two shorter species, in the 90 to 95 meter range. No cedar sp. that I know approaches such heights.

Best reason to add Sitka to the discussion is that it reaches much more poleward than the others. This means lower sun angles, which matter a lot for the 'geometry of shade'.

 

One concept clarifies thinking about annual expansion of wood (tree rings). It is the economics of carbon. All here know where that carbon comes from. Small concentrations of CO2 enter leaves through improbably small holes, while a thousand (or thousands of) H2Os are whooshing out in the opposite direction. Inside, carbon becomes fixed into usable compounds by photosynthesis.

So, a tree obtains a steady flow of carbon compounds whenever leaves are illuminated, and enough water is available for whooshing. Initial carbon compounds become something else and go somewhere else. No good at all to remain in leaves as those will be discarded in a year or so. In this, trees behave as if possessing a set of priorities. First must be enough material to construct next year’s leaves. Root-system growth and function must also be financed. All tissues (from top to toe) are susceptible to damage, and repairs all require carbon.

Flowering and seeding can be just as variable through years as stem growth. ‘Stories are told’ that varying these manipulates herbivores, pollinators and dispersers. I can’t defend those in general, but it would be an ill-adapted tree that blew its carbon budget on growth during what would have been a good year for reproduction.

In last place is expanding the stem itself, and the radial (not height) growth is what we see as tree rings. This low priority can be justified in at least two ways. First, current year’s stem was adequate to support leaves doing photosynthesis. That it will be adequate next year as well is not a bad gamble. Second, ring widths among years vary all the way down to zero - a ‘missing ring’, with the last being not uncommon. If you were to compare ‘leaf displays’ from year to year (only a few do this…), the variation is much less.

Root growth variation is very hard to measure. It’s dark down there and almost any sampling you can think of disrupts the enterprise. Carbon ‘on hand’ for repair is also difficult to quantify. You can get a handle on that by damaging a bunch of trees to different extents and see which ones can recover. Not my kind of experiment (philosophically), but doable.

What results is a system with annual radial stem growth affected by everything affecting that tree. Neighbors, high winds, fungi, herbivores, water supply, plus other factors that slip my mind. By no means are rings widths solely thermometers. This me hearties, is what makes dendroclimatology hard. There are many techniques employed, on different spatial scales, to extract temperature signals from everything else that is going on. Y’all could read about them, but probably will not. Perhaps it is fair to say that dendroclimatology signals are only meaningful when they line up with independent techniques like carbonate in caves and chemicals in sediments.

Trees don’t lie but their testimony is complicated. Let that be the message.

It has been long known that some trees grow as clones and they pass carbon among their connected root systems. More recently we learn that unrelated trees can do the same, with mycorrhizal fungi making the web. In those I would expect ring widths to be better thermometers, with other factors affecting carbon supply smoothed out across tree space. Dendroclimatologists appear not to have looked at that yet.

 

The news @12 is helpful (as usual) and leads us to consider charcoal at depth in local soils. They found 14C AMS ages of local fires to match. This is a big deal because elsewhere soil charcoal ages are used for fire paleohistory without 'local controls'. So we have the best there is and not surprising that Thomas Swetnam is doing it.

However, that this one site, excellently examined, overturns global paleoclimates derived from many proxies & places, is another unfortunate example of motivated reasoning. I urge readers here to not devalue Swetman's research because of such a weakness.

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An irony of all this is that dendroclimatology began by one fellow's search for 11-year solar cycle. There it was, but so many other things were there as well...

 

Sequoia and oaks present a few species that grow very wide, but only into the 50 to 80 meter height range. They are hard to fit into my carbon economy framework @13, but there they are. The data/understanding ratio remains uncomfortably wide.

 

Lindenmayer and Laurance have helpfully just published an article illustrating tree tallness

 

These 5 tall species are distinctly either 'slim' or 'wide'. Have to check how many of those rosewoods survive. I think they may have mostly been furniturized.

 

Wazgonna mention musical instruments. If TV expose is to be believed, some manufacturers are a bit sleazy in their sourcing.