Muddy that article is partially right in a pine needle doesn't give off carbonic acid.
All I can tell you is get a ph meter and check the soil under the trees here you will get 5.5 to 6.0
I taught college level organic chemistry to incoming engineers.
All decaying plant and animal life gives off ammonia, nitrogen, hydrogen sulfide and carbon dioxide "most"
has reached its peak release rate from 14 to 21 days.
The county I live in is the most forested county in the state with 96% of the county being forest.
Carbonic acid has always been a problem just not as bad as the last 40 years.
Most of East Texas was deciduous forest with the leaves falling late Oct. to early Nov typically our driest time of year.
The deciduous forest has been replaced with over two million acres of pine plantation.
The continuous release of the needles in a constant state of decay along with 60+ inches of rainfall makes for acidic runoff.
Water plus Carbon dioxide make carbonic acid, this is not Acid Rain.
Most rainfall is generally slightly acidic due to the carbonic acid from carbon dioxide in atmosphere. Acid rain is caused when sulfur dioxides mainly come in contact with water making sulfuric acid. That is simplified as sulfur dioxides get oxidized further
to sulfur trioxdes causing sulfuric acid.
With all that said a lot of variables come into play the amount of decaying matter the stage of decay along with
water comes into play. Coupled with sandy soil that leaches out the lime .
Here is a pretty simple explanation
http://www.ausetute.com.au/acidrain.html
I happen to live where conditions are perfect.