Complex sentence: China's forest scientists argue that monoculture tree plantations are more effective at absorbing the greenhouse gas carbon dioxide than slow-growth forests, so while diversity may be lower, the trees purportedly help to offset China's carbon emissions.
Split into simpler sentences: China's forest scientists argue that monoculture tree plantations are more effective at absorbing the greenhouse gas carbon dioxide than slow-growth forests. So while diversity may be lower, the trees purportedly help to offset China's carbon emissions.