Forests of the World

We are asked here first if we hug trees. If you do, you may be interested in general patterns of the world's forests. Inspired here by a 'treehugger' link that eaglesight333 posted in his ongoing series:

8 of the oldest forests in the world : TreeHugger

These are pleasant to look at, even though they draw attention to the fact that many 'old' forests have been re purposed since humans started to use wood and do agriculture in big ways.

Most forests are not like that - they have been trimmed in many ways and have smaller carbon stores both alive and dead. It is difficult to reconstruct what global forests looked like before Mr. Axe arrived but they have probably been reduced in extent by about one third. Pollen in lake sediments provide evidence. Harder still to determine how much dead wood there used to be, but it could be twice of what we see now, or even higher. Untouched forests (as in link above) provide evidence for that, but we really don't know if such survivors are representative of the whole thing in that distant past. But for global patterns:

Live tree weights are most closely linked with temperature. This makes sense because it can be too cold to grow. Obvious secondary factor is water - hot doesn't help if you can't get water up to the leaves for photosynthesis. Fun fact is that about 1000 water molecules exit stomates for each CO2 molecule that comes in. Talk about swimming upstream! The most water-thrifty plants are not trees at all, so we won't consider that here.

Dead wood and soil organic matter both show the opposite pattern. They both tend to hang around better at lower temperatures. Again this makes sense because decomposition is temperature dependent.

So, globally, live trees and dead stuff from them show opposite patterns. Dead wood is affected by both - supply and decomposition - and these process tend to balance out. So distributions of dead wood across all forest biomes are very similar.

You many have heard of Tunguska 1908, when a big chunk of Siberian forest got knocked down. A lot of that dead wood is still on the ground 100+ years later. Such could never occur in tropics because of much faster decomposition there.

When old forests are replaced by young ones, live growth can be much more rapid. But the dead stuff 'bleeds out' over time and would not recover unless the replacement forest is left to grow for a very long time.

Forests, especially at mid-to-high latitudes, are susceptible to fire. This puts upper limits on how much stuff can accumulate there, alive or dead. However, essentially everywhere that people have looked for charcoal in soils, they have found it. This leads to a new understanding that all forests burn, some just have much longer 'fire return cycles' than others.

Tropical forests have the most tree species. We don't even know how many. In contrast go to Finland and see only 4 tree species. Such patterns do influence carbon storage but even more how diversity of everything else in forests plays out.

By a restrictive definition of plantation forests (all trees there are planted and harvested on short rotations), they represent less than 7% of global forest. I an still surprised by that because it seems otherwise to a forest walker. Key there is probably accessibility - persistent forests just don't have roads.

==
That's my opening salvo. If there is interest in this topic we can explore details.

 

That is a lovely oak, Trollbait. I speculate that stem damage caused proliferation of stem wannabees, some of which were overtaken by gravity.

Among shortest trees are shinnery oak of Chihuahuan Desert, often shorter than a meter. Tallest trees, of two disjunct species, are substantially taller than next group down. It is a mystery, for which I have an hypothesis, which appears impossible to test over human timescales.

 

To be a shrub (or bush) and not a tree is somewhat vague. Multiple stems at or near ground level, and not too tall.

 

Walnut trees have plant-unfriendly chemicals in their leaves that dissolve into throughfall. So you get a zone of death under their canopy. Trees inspire poetry and soaring thoughts, but they can be pretty sneaky.

 

Pressure-treated lumber is worse, but yeah.

 

Well that's a head scratcher...

My thinking was that human exposure to PTL was much more than Juglans.

 

Global forest area about 41 million km2. Or approaching 60 is you include areas with about 10% tree cover. Savannahs and woodlands. Knowing this helps if one is interested in afforestation plans:

These drones plant trees by firing seed pods at the ground | Popular Science

Which if done in full would increase forest area by 4%. Readers were wondering I am sure

 

blackjack oak@3. This species ramifies like crazy:



An obscure relationship has been proposed about the sum of cross-sectional areas at any tree height or their cube roots. It is so obscure that I can't find it now, which is, well, obscure.

But I look at that blackjack and imagine grad student with a ladder measuring every little piece and cramming into a spreadsheet.

 

Forests of the world may have had an unusually large burn-down 12800 years ago. I am awaiting delivery of articles about it.

Seems strange that it would not have been noticed before because people have been digging up charcoal and measuring its 14C age for quite a while.

But the overall picture is (may be) that continental glaciers retreated, forests said "oh yeah" and then BAM.

Don't hug 'em until they stop smoldering.