Our lives are entangled with trees much more directly and intimately than we usually have occasion to notice, yet we treat them as cavalierly as we do rocks. With few exceptions, trees are merely backdrop to our concerns, entirely utilitarian, a resource for firewood, construction material and paper making, to be cut down when they are in the way of what we see as progress. We may be entirely ignorant of their names and unique characteristics and personalities.

Trees have been a vital element of terrestrial life for nearly 400 million years, since the Devonian, though the pines (Gymnosperms) and hardwood species (Angiosperms) appeared in the Jurassic and Cretaceous. Forest systems are primarily responsible for the creation of soils that sustain plant life, for biogeochemical cycles, and for vast proportions of photosynthetic activity and thus the oxygen production that underwrites animal life. Our lives are entangled with trees much more directly and intimately than we usually have occasion to notice, yet we treat them as cavalierly as we do rocks. With few exceptions, trees are merely backdrop to our concerns, entirely utilitarian, a resource for firewood, construction material and paper making, to be cut down when they are in the way of what we see as progress. We may be entirely ignorant of their needs, their names, and their unique characteristics and personalities. 

Lignin, an organic polymer, is the key to structural rigidity of woody plants, and represents about 1/3 of the total biomass produced in the biosphere. 

/Lignin provides the hydrophobic surface that allows plants to transport water to heights greater than 100 m (Carder, 1995; Koch et al., 2004) and contributes to the mechanical strength that can support trees weighing more than 2,000 metric tons (Fry and White, 1938)
http://www.plantphysiol.org/content/plantphysiol/154/2/555.full.pdf


/Lignin bestowed the early tracheophytes with the physical rigidity to stand upright, strengthened the water‐conducting cells for long‐distance water transport, and allowed plants to expand significantly in body size... Because lignin degrades only slowly, large amounts of atmospheric carbon were fixed by early tracheophytes, resulting in the significant drop in atmospheric CO2 levels and a corresponding increase in O2 levels during the late Paleozoic era... The lignin‐rich biomass buried in swamps and peat bogs during the Carboniferous period fossilized over hundreds of millions of years to become coal, the most widely distributed fossil fuel reserve, and one that has greatly propelled human industrialization
The origin and evolution of lignin biosynthesis
Jing‐Ke Weng  Clint Chapple  in New Phytologist (2010)


/Wood is composed of a number of complex organic biopolymers that give it its strength, lightness, and flexibility. The most abundant of these, cellulose, is completely digestible by fungi, bacteria and protozoa. Higher organisms like insects and ruminants that get their food from plants rich in cellulose rely on symbiotic relationships with microorganisms in order to digest it. More interesting, though, is the fact that wood’s second most abundant biopolymer, lignin, cannot serve as an energy source for any organism... It is estimated that 30% of the earth’s non-fossil organic carbon is in the form of lignin...  /Terrestrial animal life is crucially dependent on terrestrial plant life, which is crucially dependent on soil, which is crucially dependent on the gradual photo- and biodegradation of lignin. Fungi accomplish the biodegradation, and the surprising fact that it costs them energy to do so keeps the process gradual. The peculiar properties of lignin therefore make perfect sense when seen as part of a coherent design for the entire ecosystem.(https://evolutionnews.org/2012/07/the_lignin_enig/)


/Fungi are the only major organism that can break down or significantly modify lignin. They're also much better at breaking down cellulose than most other organisms. In fact, fungi are even better at it than people and the machines we've developed. The bioenergy industry can't yet efficiently and affordably break down lignin, which is needed to transform non-food plants such as poplar trees into biofuels. Most current industrial processes burn the lignin or treat it with expensive and inefficient chemicals. Learning how fungi break down lignin and cellulose could make these processes more affordable and sustainable.
...the group of fungi known as white rot was the first type to break down lignin. That group is still a major player, leaving wood flaky and bleached-looking in the forest.
https://phys.org/news/2018-02-fungi-nutrients-world.html