Alarm as study reveals world’s tropical forests are huge carbon emission source

This was a little vague... does anybody know how exactly degradation and disturbance cause carbon emission at such high levels? Is it just decomposition of dead organisms? If that's the case, this doesn't seem much different than other forms of carbon release due to human activity in rainforests, like burning the forests down.

This article seems to explain things a little better:

https://www.sciencenews.org/article/tropical-forests-have-fl...

Also actual study, Guardian's link is/was broken:

http://science.sciencemag.org/content/early/2017/09/27/scien...