What are the sources of paper pulp?

Here is a promising new source.

Here are some numbers:

“Today, over half of the material used to make paper is recovered waste.[29] Paper products are the largest component of municipal solid waste, making up more than 40% of the composition of landfills.[30][31] In 2006, a record 53.4% of the paper used in the US (or 53.5 million tons) was recovered for recycling.[32] This is up from a 1990 recovery rate of 33.5%.”

Source

No such thing as a natural forest anymore unless you go to a wilderness area and even then. I guess that depends on what the definition of natural is.
With my long ago utilized forest mgt degree, the desire is for old growth trees because they are the most profitable to log and profit-that’s been stopped for the most part. Big trees like that are primarily for the building industry. My limited knowledge, and what I have seen through a good portion of the northern latitudes of the US is companies rip up swatches of medium aged regen trees from 20–40 year ago clear cuts. The technology is so good now they can lath these trees for plywood or chew em up for pulp quite much more efficiently and in a shorter growth cycle.
The thing is the forest harvest practices or aftermath is often looks like a war zone, yielding a intended monoculture, or very aesthetically unpleasing forest, despite what they say.
In my part of the country that is the case, sickly spruce forests are chewed up for pulp. The sad thing a 100 years ago, the same area would likely be a grandiose mixed-climax community of large diameter white and red pine, and now just commercial aspen and spruce for the paper you read. In the case of spruce monoculture they are solely for pulp. Whatever you do, don’t ever hike in a previously harvested forest area that is currently being grown for pulp, the forest equilibrium is completely out of whack.

Want to know about old growth forests and pulp mills? have a look at the situation in Tasmania, Australia.

@marinelife Interesting. I hadn’t given a thought about the proportion of paper in landfills. That’s mostly the answer I was looking for.

@Garebo What is your definition of a natural forest? I’ve seen a few clear cuts, but they’ve never angered me or anything.