What would the appearance and structure of trees be like if they used chitin, instead of lignin, for cell walls? This is assuming that all other properties are basically unchanged.
These trees would be in a tropical environment with nutrient rich soil and plenty of water and sunlight available. They utilize photosynthesis and have efficient vascular systems.
Would chitin effect how hard or soft they can get? Or how tall they can grow?
Credit to Philip Newsom
Whilst not plants as you specify in your answer, you may very well be able to draw inspiration from this. From an answer i received on my own question i learned that prototaxites were large fungal structures that existed long before trees dominated the earth. These structures could grow up to seven meters tall.
As you can see, these structures had rings similar to that of trees. However, unlike trees, they were composed of chitin. The image you see here has been edited to enhance the ability to distinguish the outlines of each ring. The pressence of rings shows that these prototaxites were able to withstand changing environments and endure for a long time, no small feat for a structure of that size.
Willk compares this to the modern bracket fungus which produces spores and is hard as wood, it is also called the shelf fungus as it is used to make actual shelving.
Applying this to your question, your trees would likely have a very similar internal structure to these prototaxites, still consisting of rings but their shape and colour may be different than those you find in wood.
Note: This answers refers to the original version of the question, which was about replacing cellulose with chitin.
The structural material in tree mechanics is not cellulose, but lignin.
Lignin is a class of complex organic polymers that form key structural materials in the support tissues of vascular plants and some algae. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily. Chemically, lignins are cross-linked phenolic polymers.
The chemical structures of chitin (left) and cellulose (right). See how similar they are. Pictures from Wikipedia.
Chemically, cellulose and chitin are very similar; they are both simple polymers, derived from glucose. Lignin (from Latin lignum, "wood") is entirely different:
A possible chemical structure of lignin. Note the aromatic rings, utterly absent from chitin and cellulose, and the numerous and irregular cross-links between units. Picture by Karol Głąb, available on Wikimedia under multiple licenses including a public domain dedication.
As a biopolymer, lignin is unusual because of its heterogeneity and lack of a defined primary structure. Its most commonly noted function is the support through strengthening of wood (mainly composed of xylem cells and lignified sclerenchyma fibres) in vascular plants. (Wikipedia, s.v. Lignin)
The conclusion is that replacing cellulose with chitin is immaterial; the strength of the mechanical structure is given by another material entirely.
