One of the main reasons to digitize the large summary tables used within the Jungle Rhythms project was to save a digital copy of the physical original. The original copy as stored in the Yangambi herbarium was in a dire state, and preservation was a primary concern. Certain paper, when not stored properly, has the tendency to yellow and slowly become brittle and decay as time passes.
Mainly, newsprint and some other papers are made from ground wood or straw contain more non-cellulose compounds (lignin) compared to cellulose in European paper (pure cellulose) or grass fibers in Asian style paper. These non-cellulose compounds and lignin in particular are subject to oxidation, which alters their molecular structure by turning them into amongst others phenolic acids, and changing the colors we perceive to yellow and brown.
These phenolic acids not only make the paper yellow, they also make it brittle. These days paper will have either all lignin removed, or will contain an alkaline substance (calcium bicarbonate) to neutralize any lignin left, this kind of paper is called acid-free paper.
Luckily the paper used for the summary tables was sufficiently thick to keep it from falling apart due to oxidation. However, even so it was not safe from water damage or the occasional rodent looking for nesting material. The current state of the paper is therefor a mix of internal paper chemistry, adsorption of dust and dirt, water damage and mechanical damage / stress (rodents, manipulation,…).